Superwedge Issues & Modifications

MAPUG-Astronomy Topical Archive     AstroDesigns    MAPUG-Astronomy.net

 

Also see: Other Wedge Designs,  Permanent Piers  and  Observatory Designs

rule

Subject: Superwedge Strength & Use of the Central Bolt    Top

From: Doc G

From: Rick Woods
> I understand that the Milburn and a few other wedges are more precisely
> engineered than the Superwedge. This, though, seems like it would only
> make a difference when adjusting the wedge. Am I right in thinking that
> once the wedge is permanently mounted and precisely aligned, however
> long that takes, the Superwedge is just as good a performer as the
> others? Just as rigid and solid? Or are there differences there, too?

Your assumption about the strength of the Meade wedge is absolutely correct. The wedge is hard to adjust because it is made of castings that are not machined as well as some others. But the castings are very strong and very rigid. The Meade wedge is totally suitable for any of the LX scopes.

That said, I have owned several other wedges. They are machined out of flat stock in general and have finished rolled rods and bearings that are more precision and easier to adjust. I would strongly recommend the Mitty wedge as the best among them and the Milburn wedge a very close second. I would be more sanguine about the rest, and there are a few that are too complex in my opinion and a few that are flimsy.

A would also recommend one of the more precision wedges for portable use because of its adjustability. A few modifications to the Meade wedge will make it more adjustable as well. These modifications are described in the mapug archives in some detail. For a permanent installation, and if you have the patience to set it up carefully, the Meade wedge is fine.

Any bobbling and flexing of the scope on the wedge is totally due to the design of the RA shaft and the bearings in the base of the LX scope and not the wedge.

I have never understood why the wedge does not have a hole for a fourth bolt that penetrates into the core of the bearing cone. On the tripod, you generally have the central bolt and also positions for the three additional bolts. I know it takes some time to put them in, but one should always bolt the thing as well as possible.

The structure of the base for the "classic" can be seen here:

You can clearly see that the bearing cone is the thing that holds the whole scope RA axis in place.

It is true that the center bolt is a major part of the base which holds the central bearing cone in all of the LX scopes. I would recommend using a bolt in this location. I do not understand why Meade never recommended using a bolt in this location. It will surely strengthen the whole RA assembly. In alt/azm mode, this bolt holds the entire scope in place.

This also goes for the bolting and firming up of the sides of the wedge. There is room for two bolts on each side of the wedge to hold the declination plate. In fact if you have four bolts and tighten them up little by little you will reduce the shift that you can get when doing the final tightening. With four bolts to tighten you just go around to each and tighten it a bit. it is just like clamping a head to an IC engine, for those of you who have ever worked on automobile engine. All these bolts are standard English thread and easy to get at a local hardware store.

rule

Subject: Superwedge Problems & Cures     Top

From: Michael Hart

Shannon Gomes wrote:
> Things with the Super Wedge I've found since last-frustrating-night:
> 1) There was some play in my tripod. If I twisted the tripod head
> around it would twist. I tightened the hinge bolts at the top.
 
> 2) The azimuth peg holder I believe is too long. This is the part that
> attaches to the threaded rod used for adjustment of azimuth and contains
> the peg that fits in the slotted bracket. It appears to be actually
> touching the slotted bracket and possibly holding up the entire end of
> the wedge!

I found the slotted bracket to be the culprit. When I laid a steel rule across the bottom of the Superwedge, the peg holder you describe was fine. The slotted bracket that is attached to the tripod was not. It angled up a bit, so I took round file and removed some metal from the lower end to allow the entire slotted bracket to be flat with the top of the tripod.

> 3) There is considerable lateral slop with the interface between the super
> wedge and the tripod. If I loosen the three bolts and the center main
> bolt just a little bit, I notice I can laterally move the whole wedge
> side to side or front to back quite a bit. This is not good since the
> azimuth adjustment should just be a rotational adjustment and not
> include any side to side or front to back movement. (Side to side isn't
> as much of a problem as front to back since this will show up in the
> eyepiece as a latitude movement.)

I added nylon bushings (found in hardware stores) with a fairly close fit to the bolts but larger than the slotted Superwedge mounting holes. I sanded flats on them with an 80 grit belt sander ending with 240 grit to just fit the slots and lubed the top of the tripod with lithium grease. Finally, I added brass washers under the bolt heads to allow the bolts to be snug to tight, but allow azimuth movement, even when tight due to the leverage produced by the azimuth screw. This allows tweaking polar alignment on my permanent mount without loosening the bolts and slightly throwing the altitude adjustment off. for the altitude bolts, I just lubed everything and added brass washers under the bolt heads.


> 4) The super wedge as designed is missing a critical component. There is no
> cross bracing anywhere. Solely orthagonal members will not make a
> stable configuration. Flexure of the wedge sides will cause a coupling
> between azimuth and latitude adjustments. I'm planning on attaching a
> piece of sheet metal across the entire back of the wedge. This will
> provide a great deal of strength and not add very much weight.

Shannon, you may have a point here, especially when the altitude bolts are not fully tight. Please keep us informed as to what improvements you obtain with your bracing. I don't recall the backs of any commercial wedges with cross bracing, including an Ultima 8 wedge at our observatory. Still, your bracing could allow the altitude bolts be less tight and still allow good alignment.

rule

Subject: SuperWedge Modifications     Top

From: Chris Heapy <Chrisha_teasynet.co.uk>

The problems with the Meade Superwedge concern making fine adjustments rather than a lack of stability. There are many modifications listed mentioned here on this page, and these are aimed at improving fine adjustment and ease of placing the OTA onto the Superwedge.

I was less than impressed by the engineering on the eample of Superwedge I received. I replaced all the bearings with Phbronze bushings and nylon washers, all the hex socket screws were replaced with T-bolts, the azimuth threaded dog was replaced (that thing that locates in the slot and pushes the wedge side-to-side) with a longer one with closer fitting thread so it doesn't 'twist' (a fault causing backlash), and I added a large(ish) alloy plate about 10" x 3-1/2" x 1/2" just above and forward of the central lock knob (this both stiffens the wedge and has six 1-1/4" holes for holding eyepieces). I also planed the bottom of the wedge base flat. I'm not saying all this was essential to get the thing to work, but the modifications have made a significant improvement and make accurate setting up much easier. The Milburn has decent bearings to start with (apparently) so fine adjustments are easier out of the box.

On my Superwedge I can now turn either the alt or azimuth knob half a turn and get smooth precise movement of the star; I can turn the knobs backwards half a turn and get the star back where it started from. There is no backlash and it's not necessary to adjust the tension of the locking T-bolts to make adjustments. This is how the factory version *should* work, but doesn't.

For my 10" LX200 I added a 1/2" square bar - bolted to the wedge plate to act as a locating ledge. The LX200's weight is taken by this ledge--not the top bolt, and it has the advantage of lining up the bolt holes automatically. Only requires 2 holes - threaded 6mm for 2 hex socket screws. Set your scope base up first, you'll be using the bottom edge to locate the position for the bar. Drill the ledge bar first (tapping size - 5mm)

Then clamp it in place and drill through the wedge plate. Tap the holes in the plate and then open out the holes in the bar to 6mm - counterbore the holes in the bar to sink the screw heads. There will be enough play to fine adjust the position if necessary. For the bar, round off the top corner which faces the scope base with a file. This will prevent scratches as you drop (!) the scope into position on the wedge.

Update: May, 1998

Subject: Super Wedge Modifications URL    Top

From: Chris Heapy <Chrisha_teasynet.co.uk>

A commentary on the Super Wedge, problems and fixes at the link below. Would be interested in feedback, corrections etc., or whatever your opinion. Really aimed at those who just heard rumours of problems with the SW, or are considering buying one.

<http://easyweb.easynet.co.uk/~chrish/lx_swmod.htm>  Note: should open a new browser window over this one.

rule

Subject: More SuperWedge Mods     Top

From: Dave Schanz <dave23scha_tvalleytranscription.com>

There are those folks who are using the Superwedge wedge successfully, as manufactured, without any mods. I figure they either have unusually good wedges, or have a very high threshold of frustration and live with the idiosyncracies. I have (had) a crappy one based on my experience with it, and I have been taking advantage of the near constant cloud cover to rework it.

> I'm still planning to:
> (1) install needle thrust bearings on each side for the AZ
> adjuster (outboard of the wedge side plates);

I put thrust bearings on both the inboard and outboard sides. I found only one on the outboard side didn't help much.

> (2) replace the three 5/16" screws that go into the tripod
> head with shoulder screws (3/4" long x 3/8" dia. shoulder
> with 1/2" long 5/16"-18 threaded end), using nylon washers
> under the heads;

Yes, do that for sure, but try to find ones with some sort of hand knobs so you don't need tools to adjust. That's just one more thing to keep track of in the dark. Use some nylon washers under the knobs to help them move more smoothly.

> (3) install needle thrust bearings on the alt adjuster (I
> plan to have two pieces milled to provide flat surfaces for
> the bearings to bear on);

I drilled out the holes in the side plates and pressed in brass bushings. That takes up the slop in the holes and provides flat surfaces for the bearings to mate to.

> (4) add Teflon washers to the screws which go into the tilt
> plate to (a) take up the excess clearance between the tilt
> plate and the side plates and (b) allow for tilt plate
> adjustment with the screws fairly tight;

I did that to mine and it works great. I couldn't find thin enough washers, but, I do have a dog that had one of those white cone type collars once (to prevent scratching her ears) and I cut some "washers" out of that. I have heard of others using washers made out of a margarine tub - thin, slippery and practically indestructible too.

> (5) add a sheet of Teflon between the wedge and the tripod head

I did that too. Also works great. I tried using one of the zillion AOL CDs I have laying around and it eventually gouged up pretty bad and snapped in two in the cold.

> Questions: (1) Is it is worth it to replace the tilt angle adjustment
> screws with knobs? (These are the screws in the curved slots.)

Yes. The previous owner of my wedge used SST socket head cap screws and I have to hunt around in the dark for the Allen wrench. I will be replacing them soon with either hand knobs, or, with a piece of SST threaded rod that passes through the wedge from side to side with wing nuts and Teflon washers on both ends.

> (2) I'm considering getting a bigger AZ thrust bar made. I
> don't have any excess play on the threaded rod, but the bar
> still wants to rock some (fore and aft, not side to side.)
> What about having a threaded hole in the bottom end of the
> bar, instead of a pin, and screwing the thrust bar tight to
> the tangent arm on the tripod once the wedge is mounted?
> Seems like that would sure eliminate the rocking of the
> thrust bar! A new thrust bar could also be made a tad
> longer to compensate for the thickness of the Teflon between
> the wedge and the tripod head.

I especially like your idea of removing the pin and replacing it with a screw. That will undoubtedly remove the backlash there and is a cleaner fix than what I did

> (3) Will I need to shim the holes where the AZ threaded rod
> passes through the sides of the wedge? There's excess
> clearance there, but I'm not sure if that will be a factor
> once the bearings are installed everything is tightened.

As mentioned above, I found a couple of 1/2" ID x 11/16" OD x 1" long oilite bushings at my local hardware store and drilled out the holes in the side plate castings. Now, the threaded rod is snug and there is no play to speak of. Oh, my original holes were way oversize too.

> (4) The bottom surface of my wedge is not all that flat. I
> was considering using a flat piece of something (glass?
> ceramic tile?) and lapping compound to smooth it off. Think
> that will work? (I don't have metal working equipment.)

I am not so sure that trying to lap the bottom of the base will get you very far. It seems like it would be rather tedious at best. I would hold off on that until you have some field time in and find you actually need to do that mod.

> Any other suggestions or good links?

I found another problem - the round bar that the tilt plate knob goes through (the non-threaded bar) was the source of significant backlash because it flexed badly when the tilt plate was tightened up snugly and the knob was turned to raise or lower the plate. That flexure, on top of the slop where the bar fits into the holes in the casting drove me nuts. I fixed that problem by replacing the round bar with a 1-1/2" square piece of cold roll steel bar that a buddy turned the ends down to fit into the holes and taking up the slop with shims as you did. It's a mod better seen than described. So, for what it's worth, here's a link to my mods:
   <http://www.valleytranscription.com/astro/>

Enter the site and click on the "wedge mods" link on the left hand side of the page with lots of pictures and a full description of what I've done. So far, I've got my mods done and I'm just waiting for the clouds to clear so I can give it a final test run. I am pretty sure I have all the problems licked once and for all - and I did 'em all for just over 50 bucks.

rule

Subject: SuperWedge Mods Article     Top

From: Daniel Cobb <DECOBBa_tsouthernco.com> Got my Superwedge modification article as a pdf file here.

rule

Subject: Cheap Mods to Meade Superwedge   Top

From: Ray Scott <ScottXRAya_taol.com>

This MAPUG page has much information about the Meade wedge and the mods necessary to improve it. Being on a limited budget drove me to find ways to achieve the result of the mods without having to go to the extremes of machine shops and custom parts. As Doc G suggests, nylon washers used in judicious places will go a long way to improve the results. Replacing the two elevation pivot bolts with 2 &1/2" shoulder bolts cuts the wear in this area. I also cut about 6" long strips of negative (old x-ray film is what I used) from some old film, and after taking the wedge apart, wrapping these strips around the two 1" tubular bars for the elevation adjustment (flush with their ends) makes a world of difference in the wedges performance in elevation. You can find a length that is just right to take the slop out of these bars. Secure them with electrical tape, after reassembling the wedge.

I found some Teflon (or UHMW) tape at a local plastic supplier, which has replaced the nylon washers on my wedge now. I used it on the top of the tripod, and the sides of the wedge elevation plate. Make sure you put a small piece in the recess for the elevation rods too. My wedge now moves very easily in both directions and reverses direction with less than a 1/4 turn on the knobs. Total cost for these mods was about $15, and results are very satisfactory.

rule

Subject: SuperWedge Thrust Bar Mod --part 1 of 4    Top

From: Danny Cobb <dndcobba_tbellsouth.net> or <DECOBBa_tsouthernco.com>

I've just completed my initial attempt at modifying my Superwedge. No first light for it yet, but it's obviously a tremendous improvement over the factory condition. The last mod was replacing the stock azimuth thrust bar. I had a 1-1/2" diameter brass bar made, 1/8" longer to account for the 1/8" thick teflon disk I added between the tripod and the wedge. Instead of having a pin on the bottom of the bar, mine has a 1/4"-20 hole. This receives a knob with a 1-3/4" long 1/4"-20 stud which has a spacer (1/2" O.D., 3/4" long) over the stud. This allows the thrust bar to be pulled down snugly against the tangent arm so it can't move. Additionally, the azimuth threaded rod is slightly loaded by the downward pull of the thrust bar, taking up any slop in the threaded connection. Fortunately, the new bar has very little play on the threaded rod in the first place. I'm hoping that this mod, along with the others, will eliminate enough backlash to eliminate polar alignment frustration. See a full article at:

  <http://www.bas-astro.com/pdf/wedge_mods.pdf>

---------------------------------------------------

Subject: SuperWedge Thrust Bar Mod --part 2     Top

From: Clark Williams <S.I.G.Ha_tix.netcom.com>

I've been looking at the Superwedge and what would make it more usable (especially in the asimuth adjustment) for several years. I've tried a few experiments with my local partner in crime Terry Koken. I have always believed that the round "thrust" bar needed to spread the load by being replaced with a "T" arrangement. But I believe now that Terry is correct. After several attempts at changing things Terry (a machinist by trade) and I have come to the conclusion that the threaded rod is turned (or at least the LX200 threaded rods we've seen so far have been turned) on a lathe. If you remove the threaded rod and pass a standard tap over the rod to clean it up, you may find that all your problems are solved. A standard tap won't cost anymore than cutting a new "T" bar and the Superwedge should be much smoother and far easier to adjust when you have finished.

It took two, very determined hands to move my LX200 Superwedge on my 12" before the tapping mod and following just running the tap down the rod and replacing the existing hardware back on the LX200, I can easily turn the azimuth wheels with either hand, alone, in both cold or warm weather.

---------------------------------------------------

Subject: SuperWedge Thrust Bar Mod --part 3     Top

From: Gregory Pyros <grega_tgregpyros.com>

It seems that you were in the lucky position of having your SuperWedge azimuth dog too tight on the threads, hence your need to use both hands to rotate it. I had replaced my threaded rod with an all-thread piece of stainless steel with no difference before this.

I think that most of us have had the opposite problem, the azimuth dog was too loose, leading to a rotation of the dog before it started moving the wedge, leading to the backlash.

By replacing the dog with the "T", all the backlash problems went away, and it was no more difficult to turn - and if you add a few thrust bearings when you are putting it back together, much easier.

I have a machinist's drawing on my website for anyone that wants to make (or have a machinist make) a "T", just go to the 'customizations' page and click on the thumbnail, it is the one in the second row down and second from the left. <http://www.gregpyros.com/> or direct at:
<http://65.211.227.74/greg/html/superwedge_azimuth_adjuster.html>

---------------------------------------------------

Subject: Superwedge Azimuth Adjuster Assembly Mod --part 4 of 4    Top

From: Scott Miller <ScottXRAya_taol.com>

While using nylon washers and Teflon tape, etc. and thumb screws make great improvements to the Superwedge, the biggest remaining problem seems to be the azimuth adjuster assembly. The Meade design is too weak due to the narrow adjustment pin on the azimuth screw. Many people recommend having a new part machined to replace the original, or welding additional bolts to it, etc, etc.

This weekend after perusing the MAPUG site and others, I came up with a solution that is just as effective as a machined part, requires NO special tools, ( ok...maybe 1), no drilling, tapping etc. and costs under $15.

I used a T-junction of 3/4" copper water pipe, and routine hardware and nuts and JB Weldbond epoxy to make the new azimuth part. It has removed all of the slop in the azimuth adjuster due to the poor pin design.

The total parts lists (all from Home Depot) is this:
Pipe cutter (rotates around pipe to cut it ...this is the tool)
1 ea 3/4" T junction copper pipe
1 ea 3/4" straight junction copper pipe (without rib)
6 ea 1/2" - 13 zinc nuts
1 ea 1/4" - 20 x 7/8" long rod coupling nut (7/8" thick 1/4"-20 nut) (three pack)
1 ea 1/4" - 20 x 1 1/2" stainless steel bolt
1 ea 3" X 1/2" - 13 bolt. Note...threaded continuously! (carriage bolts usually has these threads)
1 pack of JB weld bond epoxy
Some Scotch tape, toothpicks to mix and apply the JB weld, latex gloves to
keep yourself clean (maybe) (recommended), an Exacto knife or sharp pair of
scissors, a ruler or tape measure, and some sandpaper or a scotch bright pad.
A few paper towels to wipe your hands.

You will need a work area (half of kitchen table) to be covered with newspaper at least two layers thick. (the JB Weld can make a mess!)

First the general idea of the assembly:

Altitude Adjuster

If you check you will see that the 1/2" nuts almost fill the 3/4" pipe completely. There is, however, some slop but we're going to let the JB Weld take care of that. Also note that the inside of the tee will NOT let the nuts pass all the way though the junction to the other side. This is good, because the pipe is reinforced at the TEE, but will make our job a little more time consuming and difficult if we assemble the two sides separately. I did do mine all at once and it got very messy. However, by doing it all at once it ensures that the bolt aligns properly to the nuts and will be level in the TEE.

Also check, and note that the 1/4 -20 coupler fits in the center bore of the 1/2" nuts exactly. The 1/4 -20 bolt is going to be the bottom pin for the azimuth assembly and the two nuts that fit in the vertical shaft are going to hold the extender the bolt thread into.

To begin thread 2 of the 1/2" nuts on to the bolt. Thread them all the way to the end of the bolt. We need these bolts not to act as jam nuts for each other, and to allow the bolt to turn easily through them. At the same time we don't want the JB weld to penetrate between the two nuts and ruin the whole project by welding the bolt in place. Get the nuts aligned with each other as close as possible, without actually touching. The easiest method is to align the flat sides of the nuts to each other, with the smallest gap possible between the nuts. Cut a piece of scotch tape about 3" long and then cut it into a strip about 1/4" wide. Don't make it wider. Tape the two nuts together on the bolt, keeping the tape centered on the junction. Thread another two nuts on the opposite end of the bolt, and repeat the taping process. Then unscrew the second set together and set them aside. They should keep their spacing. Repeat for the final two nuts, and remove them also.

Insert the bolt into the Tee and practice threading a second set of nuts on the opposite end. Get a good feel for how the assembly will go together. Then remove the second pair of nuts and set everything aside.

Thread the 1/4 -20 bolt into the spacer, but don't tighten it too much, just till it bottoms, and insert the spacer into the final set of nuts. It should center well.

Time to start actual work!

Take the 3/4 pipe junction. Were going to cut this piece using the pipe cutter. We need an addition to the bottom of the tee that will be equal to the length of the current azimuth adjuster. For my tee it was an even 9/16". Since, I don't know if the tee's will all be machined to exactly the same length on the single axis yours MIGHT be slightly different. You can make a good estimate by removing your azimuth adjuster and measuring. However, I think 9/16" is going to be the average. Mark the measurement on the pipe and use the cutter to cut the pipe at that length, by rotating and tightening the cutter blade. Try to keep the cutter as even as possible so the pipe is cut off square. Once cut take the 9/16" piece and mate it to the bottom of the tee. Make sure it mates well and evenly to the tee and then tape it on using scotch tape, by wrapping it completely around the seam 1-2 times.

Using the sandpaper or Scotch Bright pad clean the copper tubing inside and out. This will roughen the copper enough to form a good bond.

Now for the messy parts.

Read the instructions for the JB Weld, and following them, mix up a batch (about 5" long strips of both types). Using the toothpicks or whatever you have decided to use to mix, apply the JB weld to the outside of the two nuts on the bolt. DO NOT GET THE JB ON THE BOLT THREADS OR HEAD or inside the nuts! Try to keep it only on the outside flats of the nuts, but apply it liberally. Insert the bolt into the tee and then rotate it to spread the epoxy inside the tee. Don't worry about the JB Weld setting up too fast. It will take about 30 minutes to even start setting up, and you can work it for about an hour.

If you want to do both ends at once, apply the JB Weld to the second set of nuts, again making sure that only the outside of the nuts is coated, and that none of the epoxy gets onto the bolt threads, and carefully thread them onto the bolt and into the tee also. The latex gloves are recommended if you do this as it will get messy trying to handle the nuts and bolt. When both sets are screwed on the bolt fully you can leave about 1/16" of the nuts extending from the tee on either side. Rotate the nuts to evenly coat the inside of the tee with the epoxy and spread it onto the nuts. Set the piece aside resting on the single part of the tee.

If you decide to only do a single side, then screw the second set of the nuts onto the bolt end and into the tee. Set aside, again resting the part on the single part of the tee. This position will allow the bolt and nuts to 'sink' to the bottom of the channel of the tee, and align the bolt and nuts to the axis of the tee. I used the all at once method, to ensure proper alignment through the tee.

Take the 1/4 -20 extender and bolt, and coat the outer part of the extender, again avoiding the bolt and threads of the extender. Place the 3rd set of nuts on the newspaper with the opening vertical, and insert the extender into the nuts with a twisting motion. Make sure the threads of the nuts are well coated with the epoxy. The end of extender will sink about 1/16" into the nuts. This is OK. Don't worry about the epoxy settling, but don't move the parts after seating the extender or you will get epoxy in the end of the extender.

Leave all pieces to set up for an hour or two.

When you return the epoxy should be set enough to allow you to remove the bolts, without the nuts turning. If the nuts do turn, stop and wait longer. If you didn't get the epoxy on the threads the bolts will come out freely. If you did, you can try to remove them, but may have just made an interesting but useless paperweight, and will need to start over.

If the bolts remove properly mix another batch of the JB Weld.

If you didn't do both ends at once, thread the second set of nuts all the way onto the bolt again. Repeat the process of applying the epoxy to the flats of the nuts and inserting the assembly into the tee, and threading it though the nuts in the other end. This will spread the epoxy in the tee again.

Now take the extender / nut assembly for the bottom pin. It will probably be stuck to the paper. This is OK but trim the paper around the nuts. The extender nut should have settled to the paper and formed a nice flat surface with the nuts and epoxy. Punch a hole through the paper and thread the bolt into that end of the extender loosely. Coat the outside of the nuts with the JB, avoiding the threads and the extender bolt. Insert the coated nuts into the bottom of the tee with a rotating motion, until they are nearly flush with the end of the tee. Remove the bolt, and set the tee aside on the newspaper, with the single axis down. The nuts should rise up into the tube when you do this.

Leave everything to set until dry (16-24 hours). You should be able to remove the bolt easily, and thread it through the tee completely. The tape around the bottom junction can be removed safely (the epoxy is much stronger). The bottom will have stuck to the paper, and the epoxy will have formed a nice flat. trim to the pipe. The 1/4 -20 bolt should also thread into the bottom easily. If so congratulations|you now have an azimuth tee that will have very little movement. Remove the old azimuth adjuster part and replace it with the new one. If it is too short a thin washer can be placed under it. Mine was a perfect fit and by placing a washer under the bolt head locks the pin vertical. The azimuth adjuster reverses direction immediately with the knobs now. I painted mine black, but the copper color has a nice sheen to it also.

rule

No More SuperWedge Backlash!    Top

From: Dick Green <Dick.Greena_tvalley.net>

At long last, after weeks of research, experimentation, advice from MAPUG posts and countless trips to browse at the local hardware stores, I've succeeded in eliminating all of the backlash in both the altitude and azimuth adjustment controls of the infamous SuperWedge. This was done with readily available parts and no exotic machining (I am neither an engineer nor a machinist.) Most of the ideas came from Mark <MRWmsa_taol.com> and the now-defunct LX200 newsletter edited by Jim Leonard (copies generously provided to me by Jack Russell, <DuaneJRussa_taol.com>) In the following description, there is both new information and repetition of previously posted material. Please forgive the repetition and the lengthy text. I thought it would be useful to have a complete description of these modifications in one place.

The first time I used my SuperWedge, I was able to confirm the symptoms reported by several members of this group. In spite of the massive knobs and screw rods, it was very difficult to make fine adjustments in altitude and azimuth. For one thing, the whole mechanism squealed like a pig when adjusting after tightening the altitude and azimuth lock bolts even slightly. Worse, there was considerable backlash in both adjustment controls, especially the azimuth control. Backlash means that you turn in one direction, then when you reverse direction, nothing happens until some sort of slack is taken up -- then you can continue adjusting. Depending on how tight the lock bolts are, the backlash can last from a fraction of a turn to several turns. The backlash made fine adjustment particularly difficult and annoying. It was darned near impossible to make a fine adjustment after the lock bolts were tight enough to hold the mechanism in place. Sometime the correct adjustment turned out to be somewhere in the backlash range, meaning that the adjustment control would be floating (i.e., not pressing firmly against the wedge.)

The SuperWedge adjustment problems appear to be the result of 1) the uneven mating surface between the bottom of the wedge and the tripod head, 2) excessive adjustment friction and deformation of the wedge when the altitude and azimuth locking bolts are tightened, 3) inadequate performance from the spring washer used as a "bearing" on the altitude adjuster, and 4) tilting of the Azimuth Thrust Bar when the direction of adjustment is changed. These problems were corrected as follows:

1.) Thumbscrews to Eliminate Overtightening

All seven locking bolts were replaced with thumbscrews (three 5/16" thumbscrews for the wedge/tripod and four 3/8" thumbscrews for the altitude plate). This eliminates the two different Allen wrenches needed to tighten the original bolts and ensures that the screws will not be tightened too much and deform the wedge (hand tight is plenty.)

2.) Brass and Nylon Washers to Reduce Friction

Two brass washers were used on each of the three thumbscrews that lock the wedge to the tripod head. For each thumbscrew, one washer goes between the wedge and tripod head and the other washer goes between the top of the thumbscrew and the wedge. The three bottom washers have to be placed on the tripod head before mounting the wedge, making it a delicate operation to mount the wedge without knocking the washers off. The washers don't have to line up exactly with the corresponding screw holes because they can be wiggled into place after the wedge is lightly secured with the large central knob.

The washers between the wedge and tripod serve two important functions: 1) they compensate for level variations on the bottom of the wedge and 2) they greatly reduce friction between the wedge and tripod. The wedge sort of floats on the three washers. The washers on the top side of the wedge keep the thumbscrews from digging into the wedge and spread the force of the screw heads more evenly.

Four nylon washers were inserted between the wedge and the steel washers on the altitude lock bolts (which, as mentioned above, were replaced with thumbscrews.) This greatly reduces friction when adjusting altitude and keeps the steel washers from gouging the sides of the wedge. Most of the backlash in the altitude adjustment comes from tightening these screws too much, which causes excessive friction and deformation of the wedge. The thumbscrews and nylon washers eliminate this problem.

3.) Thrust Bearing in Altitude Adjustment Control

In the original altitude adjuster configuration, the weight of the scope presses against a spring washer that is held by two nuts against a fixed bar at the rear of the wedge. This spring washer causes a lot of squealing and unevenness when turning the adjustment knob.

The fix is to replace the spring washer with a "thrust bearing". A thrust bearing puts the load of the scope's weight on a ball-bearing race that makes for quiet and smooth adjustments. Several members of this group have successfully installed thrust bearings, and each has used a different type of bearing. I used a common, inexpensive bearing that is probably intended for a lawn mower wheel. The outer race is a "pan" into which the inner race is dropped. The other side of the inner race is held in place by a steel plate. The inner race is flush on one side and sticks out a bit on the other side. The side that sticks out is seated against the bar at the rear of the wedge. The spring washer is placed on the other side of the bearing. Since it is curved, the spring washer holds the outer portion of the outer race, and does not press against the inner race. The two lock nuts hold the spring washer against the bearing.

Other bearing types will require different mounting strategies. The whole idea is to have the weight of the scope (communicated by the screw rod) resting against one race and to have the other race fixed in place.

4.) Replace the Azimuth Thrust Bar

By far, the most difficult problem to solve was the backlash in the azimuth adjustment control. This is caused by the Azimuth Thrust Bar tilting when the adjustment direction is changed. As you change direction, the Bar tilts away from the perpendicular. After a couple of turns, the screw rod catches the threads in the Bar, and the Bar tilts back to perpendicular. The wedge only moves when the Bar is perpendicular -- while the Bar is tilting back and forth, the wedge does not move. This backlash gets worse as the wedge/tripod bolts are tightened. The problem seems to have three causes: 1) The run of threads in the bar is short and the thread tolerance is loose, 2) The pin in the Bar does not fit tightly into the slot in the Tangent Arm, and 3) the Tangent Arm does not press tightly enough against the Thrust Bar (any gap between the two makes the tilt even worse.)

My first approach to the problem was to try to get the pin to fit more tightly into the Tangent Arm. I tried slipping a compression fitting over it in order to wedge it into the slot, but that didn't work (the compression fitting couldn't hold the pin.) Next, I tried tapping screw threads onto the pin. The idea was to tap identical threads into a cylinder and screw the cylinder onto the pin, pulling the pin and Bar tightly against the Tangent Arm. The problem is that the pin is not a standard size. It is slightly larger then 1/4", too big for a 1/4" thread die. I couldn't find a die that was large enough and would cut deep enough threads (neither 5/16" nor 7mm worked.)

I returned to the MAPUG posts and Jim Leonard's newsletter, where I had read notes on four modifications that fixed the problem. One, posted to this list a long time ago, referred to replacing the Thrust Bar with a "T", custom-made out of aluminum. Without details, I had a hard time visualizing what had been done (I kept thinking that the horizontal part of the "T" must fit in the slot of the Tangent Arm.) Jim Leonard, in his newsletter, showed a diagram of a custom "T" that would solve the problem -- this cleared up my confusion. The horizontal part of the "T" threads on to the screw rod, and the vertical part of the T hangs down from it just like the original Thrust Bar (presumably a pin would be fitted into this part of the "T" to mate with the Tangent Arm.) The idea is that the horizontal part of the "T" lengthens the run of threads enough to prevent tilting. Jim didn't have a lathe to make a "T" (neither do I), so he solved the problem by screwing two oversized 1/2" nuts against the Thrust Bar and welding two metal plates on either side of them. I didn't like this because I'm not a welder. A reader of the newsletter implemented a variation on this idea by turning the plates 90 degrees and putting holes in them just big enough to fit over the top and bottom of the Thrust Bar. The plates were held against the nuts by four bolt/nut sets at the corners of the plates. This configuration eliminated the welding, but required punching big holes into two metal plates. I tried it, but the hole made by my 1" chassis punch wasn't quite big enough to fit the Thrust Bar (another non-standard sized part?) Another reader wrote to describe an elaborate setup using nuts welded to iron straps -- I couldn't figure out what he did (no diagrams) and there was the welding again.

Finally, I got the idea that a standard "T"-shaped pipe coupler used for plumbing might do the trick. After some exploration at the hardware store, I came up with a rectangular "T" coupler with the following dimensions: Horizontal part: 1 9/16" W x 11/16" H x 11/16" D; Vertical part: 11/16" W x 7/16" H x 11/16" D. The part number on the side was 162-1262. There were screw threads in all three ends, but they did not go all the way through the horizontal part. Also, they were pipe threads, which I gather are not the same as bolt threads (a 1/2" bolt screwed in about 1/8" and stopped.) Using a 1/2-13 tap, I tapped a set of bolt threads all the way through the horizontal portion of the "T" coupler. Surprisingly, this worked rather well. The new set of threads went over the old set cleanly enough so that the 1/2" azimuth adjustment screw rod threaded through smoothly without binding. The vertical part of the "T" was not long enough to reach the Tangent Arm, so I threaded a 1/2"-13 x 1" steel hex head bolt into it. I didn't re-tap this set of threads because I wanted the bolt to wedge tightly into the hole (which it did.) The bolt forms the vertical part of the assembly, taking up the remaining distance between the screw rod and the Tangent Arm. Then, using a no. 7 bit, I drilled a 1/2" deep hole in the center of the bolt head. I threaded the hole with a 1/4-20 tap, and screwed in a 1/4" x 1" hex head bolt. Here's a crude diagram (view in a fixed-spaced font):

 ______________________
 | |
 Screw Rod -> | "T" coupler | <- Screw Rod
 |______________________|
 | |
 | |
 |________|
 | |
 |____| <- 1/2" x 1" bolt
 |______|
 Washer goes here -> | |
 |__| <- 1/4" x 1" bolt
 |____| 

The resulting "T" matches the vertical dimensions of the original Bar pretty well. I ended up placing a thick steel washer (about 1/16") between the head of the 1/2" bolt and the Tangent Arm to keep them snugly pressed against each other. The new "T" provides about twice the thread length as the old Thrust Bar. As long as the 1/2" bolt is pressed tightly against the Tangent Arm, there is no tilt at all.

5) Lubricate Both Controls

I used a Teflon-based spray lubricant on both the altitude and azimuth screw rods and the threads with which they mate. I wiped off the excess so it wouldn't get on any scope optics or electrical connections.

RESULTS

With the central knob and seven thumbscrews moderately tight, the movement in altitude and azimuth is as smooth as glass and there is absolutely no backlash. The time it takes to make the adjustments to center Polaris on each alignment pass is a fraction of what it used to be. On the last pass, as I tighten the knob and thumbscrews as tightly as I can by hand, there is very little movement of Polaris away from the center. The controls are stiff, but can still be used to make the final adjustment smoothly and without backlash.

I tried it out tonight and, while it may have been just one of those rare nights where all mechanical things worked well, a star centered in the 9mm reticle stayed in the box for a full 30 minutes. This time, I completed alignment in about 1/4 the time it has previously taken.

While my solution is kind of kludgy, it's easy to do and the parts are readily available. I'll probably refine it a bit -- maybe find an appropriate end-cap to use instead of the 1/2" bolt and press-fit a steel pin into it instead of using a 1/4" bolt. I imagine that those who are handy with metal cutting tools and have access to aluminum stock can fabricate a nice replacement for the Thrust Bar. But for now I feel like a long quest has finally ended in success (and it only cost me $395 to have all this fun...

rule

Notes on Two-Plate Pier Adapter for the Meade SuperWedge     Top

by Dick Green <Dick.Greena_tvalley.net>

This document describes a two-plate adapter system for mounting the Meade SuperWedge to a permanent pier. For more information and specific measurements, please refer to the three diagrams that accompany this document: Top Plate, Bottom Plate, and Side View.

A number of people have designed two-plate adapter systems. My design borrows from theirs, and was strongly influenced by Brandon Jones, who generously consulted with me on the MAPUG mail list. I learned about some important design issues from Brandon, and without his advice, I might have made several serious errors in this design.

THE DIAGRAMS

1. My original adapter was fabricated from plans drawn manually on paper. For ease of distribution and modification by others, the plans were converted to computer-readable form using CorelDRAW! version 3.0. While an effort has been made to ensure that the computer image dimensions match the original drawings, some small errors may have occurred during transposition. Also, it cannot be guaranteed that your printer will produce hard copies of the drawings exactly to scale. Therefore, it is crucial to check the diagrams against all verbal descriptions and measurements both here and on the diagrams themselves. Using a ruler, make sure that the dimensions of the plates and holes match the numbers shown on the diagrams (e.g., the Top Plate thread rods should measure 1 inch in diameter, while their mating holes on the bottom plate should measure 1-1/8 inch in diameter.) Also, lay the Top Plate diagram on the Bottom Plate diagram, hold them up to the light, and make sure the thread rods and holes line up exactly.

Since the drawings have been made to scale, they just barely fit on a piece of standard 8 1/2" x 11" printer paper. In fact, on my HP IIIP LaserJet printer, the default margins cut 1/16" off one edge of the top and bottom plate diagrams. This is not a big problem because all that is lost is one side line on each plate. Note that CorelDRAW can print the diagrams either as-is, or "Fit to Page" (an option in the print dialog box.) The "Fit" option allows you to see the entire picture, but will not be to scale. The drawings and a copy of this text file are available for download as a .zip file by clicking here.

2. The bitmap (.BMP) versions of the files also cannot be guaranteed for accuracy. I found that Paint Shop Pro scales the drawing to fit on the page in such a way that the result is slightly distorted and cannot be used for fabrication. Your results will probably depend on the specific software you are using and your printer.

3. If necessary, I can supply the drawings in several other export formats supported by CorelDRAW, including WMF, DXE, GIF, CGM, GEM, HPGL, PLT, PCT, PIF, SCD, TGA, TIF, and EPS. If all else fails, I will mail copies of the diagrams to anyone who supplies me with an SASE (Stamped Self Addressed Envelope.)

4. GIVEN THE FOREGOING, IT IS CRUCIAL TO VERIFY THAT THE FIVE SuperWedge MOUNTING HOLES IN THE TOP PLATE LINE UP EXACTLY WITH THE HOLES IN YOUR SuperWedge. YOU CAN VERIFY THIS BY LAYING THE SuperWedge ON A PRINTOUT OF THE TOP PLATE AND MAKING SURE THAT ALL THE HOLES LINE UP. YOU CAN ALSO CHECK THE DRAWING AGAINST THE TOP OF THE FIELD TRIPOD. A MEADE CUSTOMER SERVICE REPRESENTATIVE ONCE TOLD ME THAT HE COULD SEND ME A DIAGRAM OF THE BOLT HOLE PATTERN ON THE BOTTOM OF THE SCOPE. IF THIS IS TRUE, YOU MIGHT WANT TO OBTAIN THAT DIAGRAM TO MATCH AGAINST MINE. IN ANY CASE, IT IS ADVISABLE TO GIVE THE WEDGE TO THE PERSON FABRICATING THE PLATE ASSEMBLY AND REQUIRE THAT THE MOUNTING HOLES MATCH.

5. A good fabricator should be able to work from the printouts, even if they are not to scale. The important thing is to explain how the device works and supply your SuperWedge so that measurements can be checked.

THE DESIGN

1. The adapter plates were designed to fit my specific pier, so it might be helpful to describe it here. My pier consists of a 3' x 3' x 4' deep block of concrete with a 7' steel tube embedded in the center (4' of tube in the concrete and 3' sticking up above the concrete.) The tube is 4.5" OD and 4.0" ID with 1/4" walls. When the block was poured, the tube was filled with cement up to about 18" above the concrete, leaving the top 18" empty. I had the block poured when footings were being poured for an addition to our house. The excavation contractor dug the hole, and the building contractor made a wooden form for me. He used steel straps to hold it together. The straps were cut after the concrete hardened, allowing the form to be removed.

I also had a right-angle section of PVC pipe embedded in the cement block. The top of the pipe is set about 1' from the steel tube and sticks up about 1' from the top of the concrete block. The pipe runs down almost to the bottom of the block, where it makes a right angle, exits the side of the block, and connects to about 30' of PVC conduit running in a 4' deep trench to the house (also dug by the excavator.) The conduit is used to carry AC power and computer control cables for the scope, CCD camera, and dew heater. The computer cables run a total of about 100' to the computer in my home office.

One advantage of this design is that if I want to damp every last bit of vibration out of the steel tube, or beef it up for a much bigger scope, all I have to do it put an 8" diameter Sonotube around it and fill with cement! The resulting cement jacket will make the mount a full 8" in diameter!

Originally, the contractor estimated about $450 to fabricate the pier (it's impossible now to tell how much it really cost because the details were buried in the cost of a major renovation.)

2. I left the top 18" of the steel tube empty until I determined how I would attach the Bottom Plate to the tube. In the end, I decided to use three 17" lengths of 3/4" thread rod, arranged in an equilateral triangle pattern. The rods are cemented into the top section of the tube and stick up about 2" from the open end. More details on this part of the construction later.

3. While the central three holes in the Bottom Plate were designed for my bolt attachment system, you should be able to adapt it to just about any pier tube or shaft that has one or more mounting bolts protruding from the top. Note that I used 1" diameter holes to mount 3/4" thread rods. The extra clearance is very important -- it allows for some shifting of the rods when they are set (if you make the tolerance too close, you might not be able to slip the Bottom Plate over the bolts after the cement hardens!) The extra clearance also allows some minor azimuth adjustment on the Bottom Plate in case the bolts were not exactly lined up with true North. Note that my system does not allow for much adjustment in azimuth once the rods are cemented in. A single rod would allow for any amount of azimuth adjustment, but I felt that multiple rods would eliminate the possibility of any side slippage. However, you do have to be much more careful in construction to align the bolts with true North.

4. The Top Plate attaches to the Bottom Plate with three 6" lengths of 1" diameter thread rod. The large diameter was used to make sure there would be no flexure, even with the plates 5" apart. Two nuts are used on each leveling rod to sandwich the Bottom Plate. When the nuts are slightly loosened, it takes just seconds to perfectly level the Top Plate. Note that the 1" diameter rods mate with 1 1/8" holes in the Bottom Plate. Once again, this extra clearance is crucial to compensate for inaccuracies in welding the three rods. It also makes leveling much smoother.

5. Like the pier, the adapter design is heavy duty. Both the Top and Bottom Plates are made of 1/2" thick steel plate, and are kept to the absolute minimum dimensions (8" x 8"). Along with the 1" diameter leveling thread rods and closely spaced 3/4" pier attachment thread rods, flexure is reduced to a minimum (in fact, it's all in the SuperWedge and scope forks now).

6. The familiar four-hole pattern for attaching the SuperWedge is drilled into the Top Plate. It consists of a central 1/2" bolt hole surrounded by three holes tapped for 5/16-18 bolts. Note that the latter three holes are the only holes in the whole assembly that are tapped with threads. The three stock 5/16" wedge mounting bolts can be used. Any 1/2" bolt longer than about 1-1/2" can be used to mate with the big wedge knob. The central hole is slightly off-center front-to-back. This was done to keep the plate dimensions to a minimum. Also note that the central hole is centered directly above the center of the triangle formed by the three pier mounting bolts in the Bottom Plate. This also happens to be the center of the steel tube. Thus the nominal center of gravity of the SuperWedge is positioned directly over the center of the pier tube (I don't know if this ends up as the center of gravity with all the Meade scopes, but this is where the center of the tripod head ends up, too.)

7. This particular design includes a metal tab with a 1/2" diameter hole for a bolt that threads into my modified version of the Azimuth Thrust Bar on the SuperWedge. Both the modified Azimuth Thrust Bar and my method for securing it to the Top Plate were designed to overcome excessive azimuth adjustment backlash on the stock SuperWedge. The backlash, which makes it very difficult to do fine adjustments, is caused by wobble in the Azimuth Thrust Bar. The Bar wobbles because it has too small a run of threads and the coupling between the Azimuth Thrust Bar Pin and the Tangent Arm is loose.

I replaced the stock Azimuth Thrust Bar with a brass "T"-shaped pipe coupler I found at a hardware store. Using a standard thread tap, I tapped new 1/2" threads through the horizontal portion of the T and part way into the vertical section (from the bottom, of course). There are two advantages: 1) the top of the T has a much longer set of threads, and 2) a 1/2" bolt can be used to firmly secure the vertical portion of the T to the Top Plate. If you want more information about this, check the MAPUG archives for my postings on the subject in the autumn of 1995. I believe my last posting contains details about this modification and several others that make adjusting the SuperWedge much easier. I'll be happy to e-mail a copy of that posting to anyone who wants it.

The upshot is that the adapter plate design will not work with the stock SuperWedge. However, the fix is easy. Instead of drilling a 1/2" diameter hole in the tab, drill one to match the Azimuth Thrust Bar Pin. It won't work as well as designs that secure the Azimuth Thrust Bar, but will be no worse than the stock version. I believe that Brandon Jones simply made his plate large enough so that the edge butts up against the Azimuth Thrust Bar Pin, and he has some way of clamping the Pin to the edge.

8. Depending on how much extra thread is left on the pier mounting rods, the two plates can be positioned within about 2" of each other, and up to about 5" apart. When wide apart, there's a nice extra shelf for eyepieces, etc. I like to keep them close enough so the central 1/2" bolt won't fall out of the hole when I remove the wedge knob (it hits the 3/4" nuts first.)

9. One nice aspect of this design is that it also allows the scope to be mounted in ALT-AZ configuration. Since I'm primarily interested in CCD imaging, I doubt that I'll remove my precisely-aligned SuperWedge to do this very often, but it's still a nice option.

THE FABRICATION

I took my drawings to a local welding shop, along with the SuperWedge. I explained how the adapter worked and how I wanted it built. They looked at me a little funny at first, but then when they figured it out, were confident that they could do the job. I was very pleased with the result. They even coated all the exposed surfaced with some sort of rust-proof paint (in black to match the wedge). They did misread the diagram and drilled the leveling rod holes in the Bottom Plate to only 1" diameter. As expected, this made it almost impossible to get the Bottom Plate on and off the rods, and leveling was not smooth at all. At that close a tolerance, the welding is just not precise enough. It was a simple matter to take the Bottom Plate back and get the holes drilled out to 1 1/8". Total cost, including six 1" nuts for the leveling rods: $161.25.

THE CONSTRUCTION

1. I spent a lot of time sweating about how exactly I was going to cement those three rods into the steel tube. I've never worked with cement before, and, frankly, the stuff scares me. The bags are big and heavy, it takes a lot of bags to generate very little cement, you have to mix the stuff a long time, it's hard to pour down a narrow tube, and it takes a long time to set and dry. I considered several brands of quick-hardening hydraulic cement, but they hardened in only 5 minutes not a lot of time to mix, pour, and align the rods on true North. Finally, I found some material specially designed for setting anchor bolts. It mixes up like hydraulic cement, but takes 10 minutes to set and one hour to harden. Best of all, it mixes up to an easy-pouring batter-like consistency. It's also advertised to be harder than cement (and judging from the results, it is.)

2. When the steel tube was originally cut to size, the top edge was nice and level, but the cutting tool left a raised ridge of steel on the inner diameter. I ground this down with a grinding wheel on a hand drill, then filed the top edge completely flat. I used the Bottom Plate and a level to get it as close as possible. I smeared a bit of charcoal on the Bottom Plate so that when it was pressed against the top of the steel tube, the high spots were marked. A standard 12" flat mill bastard file removed the excess material very quickly.

3. To complete installation, I used three 24" lengths of 3/4" thread rod, twelve 3/4" nuts, three standard 3/4" flat washers, three SAE 3/4" flat washers (see below), three 3/4" split ring washers, and three flanged brass bushings 3/4" ID, 1" OD.

4. First, I used my original drawings to locate the center of the triangle formed by the thread rod holes in the Bottom Plate and used a drafting compass to outline a 4" circle and a 4.5" circle centered on this point. I filled in the ring between the two circles with liquid white-out. The idea was to outline where the top of the steel tube would contact the Bottom Plate.

5. Next, I attached each of the three thread rods to the bottom plate with one brass bushing, one SAE flat washer, and two 3/4" nuts. The bushings, which I found at a hardware store, fit exactly inside the 1" holes in the Bottom Plate and kept the thread rods centered in the holes while cementing. They have a flat flange at one end, which keeps the bushing from falling out of the hole and acts like a washer. I did have to cut about 1/8" off each bushing with a hacksaw because they were a bit too deep. The SAE washers have a smaller diameter than standard washers, which is required due to the close spacing of the three 3/4" thread rods.

6. I also placed a pair of nuts with one standard flat washer between them about halfway down each thread rod. This widened the diameter of the thread rod assembly, keeping it centered in the steel tube during cementing, and providing more surface for the cement to grab onto (I'm not an engineer, but I thought this might keep the rods from ever loosening and turning in the cement.)

7. I adjusted the length of the rods going down into the tube to be about 15" each, which put them about 1" above the peak of the existing cement in the steel tube. Then, using a hacksaw, I cut off the excess thread rod above the nuts on the top side of the Bottom Plate (I left about 1" above the nuts.)

8. I spent a lot of time orienting the whole Bottom Plate and thread rod assembly in the steel tube so that the front edge faced as close as possible to true North. This was complicated a bit by the fact that the compass was affected by all that steel. I used a real orienteering compass, not the one from Meade. This step really wasn't all that crucial, because the SuperWedge has plenty of azimuth adjustment room, but I wanted to get it as close as possible anyway. Once I got the Bottom Plate oriented, I painted small white alignment marks on the steel tube and underside of the Bottom Plate so I could find that spot again.

9. Finally, the moment of truth had arrived (i.e., I couldn't put off pouring the cement any longer.) I had to allow for volume displacement by the thread rod assembly, so I decided to do the pour in two steps. I mixed up a 9 lb. package of the cement and poured it to within about 6" of the top of the tube, then pushed the thread rod assembly down into the goop until the Bottom Plate came to rest on the top of the steel tube. I made sure the white ring I painted on the bottom of the Bottom Plate was centered on the steel tube, aligned the plate to true North by the little white marks I made earlier, and crossed my fingers. After about 1 = hours, I removed the Bottom Plate, bushings and nuts. The cement had hardened and the rods were in there to stay. I mixed up another 3 lb. batch of cement and slowly poured up to within 1/16" of the top rim of the tube. After another 1 = hours, the cement was hard as a rock and I was able to mount the completed two-plate assembly and SuperWedge.

10. When Polaris came out, I found that I was slightly off from true North. I could easily compensate with the SuperWedge, or I could remove the brass bushings and swivel the Bottom Plate enough so that the SuperWedge faces true North when its azimuth adjustment is centered. I elected to do the latter, and mounted the Bottom Plate with SAE flat washers and split ring washers (to keep the nuts from turning.)

11. Remember that 3/4" and 1" nuts are not everyday hardware items. Be sure that you have wrenches large enough to handle them.

Well, that's it. If you have any questions, send e-mail to <Dick.Greena_t valley.net>

rule

Subject: Homemade SuperWedge Knob Wrench     Top

From: Matt Considine <matta_tconsidine.net>

I don't know if anyone else has had a problem turning their SuperWedge azimuth knobs on a cold night but I have -- my wedge is pretty snugly attached to a permanent pier.

A solution I came up with is posted at:  <http://www.considine.net/mac/swkw.zip> (84k)

Made from a scrap piece of 2x4, this "knob wrench" provides a bit of leverage for loosening or tightening. The zip file contains a JPEG image, along with DXF, DWG, and TurboCAD workspace versions of the dimensions. The dimensions should be pretty close (they work for mine) but you'll probably still need to file and sandpaper to get a decent fit. I used a small bandsaw to make the cuts, but it could also be done with hand tools and some patience.

rule

Subject: Mettler Wedge--Alternative to Meade & Milburn       Top

From: Pat Lanclos

Before you decide on the Meade Superwedge or the Milburn Wedge for use with your Meade LX Series scope, I suggest you check out an alternative wedge design ..... the Mettler Wedge:
   <http://www.greatnorthern.net/~jam/links/Manuf/mettler.htm>
    Contact: Jeff Mobley, <jama_tgreatnorthern.net>

I have just completed a product review on a relatively new design in astronomical wedges. This is a "must read" for any and all Meade LX Series owners who are contemplating the purchase of a heavy-duty wedge. Though the Superwedge and the Milburn are the more popular designs, I feel that it is only because most folks don't know about the existence of the Mettler Wedge.

I did the review to try and get the word out that there is a third alternative design for folks to consider. It can be reviewed at the following URLs:

<http://members.aol.com/planclos/index/mettler.htm>
<http://www.solar-system.com/Hints/Wedge/mettler.htm>
Note: should open a new window over this one.

There are several new wedges being made by members of the Mapug list, see
   Ulti-Wedge by Randy Marsden
   Superior Wedge by Mitty Observatory

rule

Subject: Meade Superwedge vs. Milburn Wedge --part 1 of 3    Top

From: Don Tabbutt <dona_ttabbutt.com> Date: Mar 2002

In the following dialog, there is one assumption: alignment must be achieved with loaded jackscrews, both in RA and DEC.

Both wedges have backlash. The Milburn Wedge has much less backlash than the Meade Superwedge. Is this an issue?

I say no. Backlash is a bad thing. The amount of backlash, in my experience, is irrelevant.

Polar alignment is achieved by going from a starting point to the alignment point, while always keeping the jackscrews loaded. If a mount has any backlash at all, going beyond the alignment point is a fatal error. One must then reverse to the original starting point, or continue to a new starting point, then reverse and start over in order to achieve a loaded jackscrew at the alignment point.

Reversing back to the starting point is when backlash is encountered. Who cares whether it takes a 16th turn or a quarter turn (or more) to get through the backlash at this point? It means nothing at all to me. I bought the Milburn wedge thinking I could make hair-breadth adjustments back and forth to touch up the alignment. This is not the case. It has backlash, as does the Superwedge, but not as much. So what? I still have to go to a starting point and start over. How many cranks it takes to get to a starting point is completely irrelevant.

In addition, Chris Heapy and others in the past have stated that the castings of the Meade Superwedge are more rigid than the aluminum plate of the Milburn wedge. This allows for a more stable alignment, once achieved, with less deviation with differing telescope load conditions.

Furthermore, I've found the Superwedge compass and level to be entirely adequate for achieving rough alignment prior to drift alignment.

------------------------------------

Subject: Meade Superwedge vs. Milburn Wedge --part 2   Top

From: Dave Graham <hardwarea_tdatasolaz.com>

Very much on point, Don. Full agreement here! Some side notes from my experience:

When I first got my Superwedge, I found it very difficult to adjust, especially in DEC, and tightening the lock bolts resulted in HUGE axis shifts. Upon examination, I found that if the hinge and locking bolts on one side were snug while the other side was loose, there was a gap of over .140" between the side plate on the loose side and the scope mounting plate! I couldn't believe these mfg. tolerances, but the baseplate to side castings connection didn't allow for adjustment, so the tolerances had to be real.

To remedy the solution, I added 1/16" nylon washers (1" O.D.) between the side castings and scope mounting plate in all three positions on each side (I use all three bolts), and the same washers backed by brass washers on the outside. I also replaced the Meade bolts with slightly longer hex-socket cap screws to fully engage the threads. I had to trim the latitude indicator plate slightly to give clearance for the washers on one rear locking bolt here at 32 deg. North. I made a disk from high density polyethylene cut from an ordinary 5 gallon plastic bucket and flattened with the heat from an ordinary household iron and inserted it between the tripod and baseplate of the superwedge. I also gave the three locking bolts on the baseplate the same nylon/brass washer and longer cap screw treatment (slightly smaller dia. washers corresponding to the smaller bolts).

The end result is that the Superwedge is silky smooth in both planes, with only the typical Meade backlash slop, which is now no more than a slight annoyance. The alignment now stays put when I tighten down the locking bolts. I do all adjustments with significant pre load on the locking bolts, as the nylon and HDPE allows much easier slippage.

One thing I do after achieving final alignment is to release the load on the jackscrews after tightening the locking bolts to keep temperature changes which could change the length of the jackscrews from having any effect. I have experienced no further problems with alignment.

------------------------------------

Subject: Meade Superwedge vs. Milburn Wedge --part 3 of 3   Top

From: Ken Milburn <ken.milburna_tverizon.net>

I thought it might be helpful if I joined this thread and offered some information relative to some assumptions floating around on comparisons of the Meade Superwedge (MSW) with the Milburn Wedge (MW).

Casting vs. Plate: Which is stiffer?

It has been suggested that the MSW is stiffer that the MW. This assertion is based on an assumption that an aluminum casting (MSW) is inherently stiffer than a similarly sized construction using machined aluminum plate. Such an assumption is generally incorrect and at the very least an over-simplification. To be meaningful, any such comparison must consider the alloys being employed, and the material cross sections & geometry of the two configurations.

There are some differences in the modulus of elasticity (stiffness) between different aluminum alloys. Unless we're getting into exotic alloys, which is not the case here, these differences are minor... a few % at most. Castings, extrusions and plates of the same alloy can also exhibit some minor differences in elasticity. However, to draw a conclusion as to which chunk of aluminum is stiffer based solely on the fact that one is cast and the other is plate neglects too many other far more influential variables. Not the least of which is cross section and geometry.

The MSW employs a ribbed casting approach in its structural design while the MW uses solid machined plates. I consulted with a 20-yr structural engineer friend here at Boeing to get his thoughts on comparing the stiffness of two pieces of aluminum with similar outer dimensions: one a ribbed casting and the other a solid plate. He said it was no contest (well he actually said something else but this is a G-rated forum <g>). The solid plate wins hands down. The relationship between stiffness and cross sectional area is not necessarily linear. I won't pretend to be fluent in the equations (I'm just an EE) but for example: One can hog out (or leave out) 50% of the material from a given chunk of material and still preserve more than 50% of the original solid's stiffness if enough material is left in all the right places. However, a webbed casting with outer dimensions X, Y, and Z cannot be stiffer than a solid plate of the same dimensions if the materials are comparable. Any minor differences between the stiffness of cast aluminum and plate are easily swamped out by the effect of the maximized cross section and distribution of mechanical stress a pure solid provides.

With the above said, I do not believe the MSW suffers from a stiffness deficiency. However, I do believe that it is incorrect to conclude that the MW is not as stiff as the MSW, especially without detailed structural analysis or measurement data to back the conclusion. IMHO, given the similar overall dimensions of the two wedges, it is more likely that the opposite is true.

Be that as it may, the point is minor as both products are quite sturdy and certainly not the weakest link in the chain of variables that determines the rigidity of the LX200 set-up. Other considerations like ease of use, smooth motion, personal preference, etc. should be much bigger swingers than stiffness when deciding between these two products.

Wedge Adjustment Mechanism Backlash:

This probably is not news to many but for those that have not thought about it, here is some hopefully useful explanation of the backlash (or lack thereof) present in both the MSW and MW latitude-azimuth adjuster mechanisms.

That latitude adjuster of the MW does not exhibit backlash when changing directions to lift/lower the tilt plate. This is because the threads of the mechanism is always loaded in the same direction regardless of whether the scope is being lifted or lowered. I think the MSW is pretty much the same in this regard.

The Azimuth adjuster of both wedges will exhibit some backlash. The amount is somewhat variable depending on mechanical tolerances. It would be nice if there were no backlash but some has to be expected for this case because the load on the threads of this mechanism does change direction when switching motion between left-right. A little BACKLASH is unavoidable in a mechanism like this. Tighter mechanical tolerances can reduce the BACKLASH in the AZ adjuster but if things are too tight, a worse side effect can crop up...binding and stiff motion. Most would probably agree that for this particular device, a little BACKLASH is a good trade for smooth motion.

rule

Subject: Best Wedge for LX200?    Top

From: Chris Frye <cfryea_tix.netcom.com>

>I'm thinking about buying an equatorial wedge for my 10" LX200, but I'm
>not sure which one to get. I've read some of the MAPUG Topical Archives, and they
>tend to suggest that the Milburn wedge is best, but I've had difficulty
>putting all the facts together. Which wedge to you think is best? If you
>think the Milburn wedge is best, then where can I buy one? James Brasure

For your 10" LX200 there are many wedges available. The two most popular are the Meade SuperWedge and the Milburn Wedge.

Milburn Wedge:
  PLUS --- A really beautifull piece of precision engineering.
  PLUS --- Only cost about $400.
  Minus --- Multiple piece construction, adds to flexure.
  Minus --- Not anodized, will corrode if left out in high humidity conditions over time.

Meade SuperWedge:
  PLUS --- One piece cast-aluminum construction for added rigity.
  PLUS --- Chris Heapy's upgrade available to make this a precision wedge.
  Minus --- Really sloppy construction, precision polar alignment might take you the rest of your natural life.
  Minus --- With Chris Heapy's upgrade this wedge could easily cost you a total of over $700.

When I ordered my 10" LX200, I also ordered the Meade SuperWedge at the same time. I have now invested a few more bucks for Chris's upgrade. If I could do it over I think I would have gone with the Milburn, although I like the idea of the rigid one-piece construction of the Meade for long exposure (1 hour +) astrophotography. When Chris Heapy sends me my upgrade I will be happy to review his efforts and pass them on to this group. I am hoping that a solid cast aluminum wedge with Chris' upgrade will produce a superior, albeit expensive, wedge.

Editor's note: several new wedges are available as of 9/2002, see these Mapugger designs:
   
Ulti-Wedge by Randy Marsden
   Superior Wedge by Mitty Observatory

rule

Subject: Using Giant Tripod with 10" & Superwedge      Top

From: Brian Bond <brian.bonda_tblueyonder.co.uk> Date: Nov 2002

----- Original Message -----
From: Ralph Megna <ralpha_tdigi-empire.com>
> This weekend I had an opportunity to put my 10" LX200 (classic with
> Superwedge) on the giant field tripod that is normally sold with 12" scopes.
> The difference in stability was amazing... make that humongous. In
> combination with vibration pads (Celestron), no knock to the telescope
> assembly -- no matter the location or intensity -- took more than a second
> to dampen. Even manual focusing seemed to generate fewer, shorter-lived
> jitters. The assembly also appeared to hold polar alignment better than the
> standard tripod over a two-night star party that included over 40 degrees of
> temperature changes.
>
> Maybe this is a case of having a keen sense of the obvious, but I would
> strongly recommend this combo to anyone who loads their 10" LX200 with
> cameras and accessories.

That is the combo I use, but I found the weight of the assembly was too much for the vibration pads so had to go without those. I modified my tripod as it was a little too high for me to lift the scope into the Superwedge, but even so the vibrations are very well damped with extra weight added to the strut spider assemble.

rule

MAPUG-Astronomy Topical Archive   AstroDesigns   Top   MAPUG-Astronomy.net


Astronomy Answers Astronomy Answers is a new, free Question and Answer site dedicated to astronomy technology, equipment and software.
TiGra Networks MAPUG is hosted by TiGra Networks