Introducing the

Ulti-Wedge

from

Pad 55 Products

pad55@san.rr.com

The Ulti-Wedge is a new concept in wedges for fork-mounted SCT's. The Ulti-Wedge uses industrial bearings and bushings at all load-bearing pivots to virtually eliminate backlash. The novel design of the altitude mechanism provides a factor of five finer adjustment than is available with other commercially available wedge designs. It also provides a large mechanical advantage that significantly reduces the force needed to make an adjustment, so your alignments are smoother and more accurate. And the pair of linear bearings and rails convert the torque of the adjustment screw into a smooth linear motion that does not cause flexure in the tilt-plate. Note the large ball bearing pillow blocks on which the 5/8 inch diameter solid stainless-steel tilt-plate axle rotates. Most wedges give you two screws for this crucial pivot, often without a bearing to minimize wear. The azimuth adjustment mechanism is also unique in its ease of adjustment with nearly complete elimination of backlash - a major problem in most wedge designs. Also included is a UHMW polyethylene bearing that goes between the Ulti-Wedge and the top of your support (UHMW = Ultra High Molecular Weight). This slippery plastic layer greatly reduces the torque required to make the azimuth adjustment. Just in case you own or buy one of the 'M' wedges, this bearing is available separately in the options below. The end result for you is precise polar alignment without the difficulties often associated with wedges for SCT's. More on why the Ulti-Wedge was designed. 

 

 Yes, it looks a lot different than the other wedges! And I think it works better than the other wedges.

The standard model, pictured here and above, uses 3/4 inch aluminum plate for the base and tilt-plate and has a single altitude lever arm. This model gives excellent results with SCT's up to 12 inch aperture. If you have an even larger scope or are just a true fanatic, the EMHD Ulti-Wedge is also available at additional cost (EMHD = Even More Heavy Duty). The EMHD uses 1 inch aluminum plate and has two altitude lever arms.

To keep the price reasonable, the Ulti-Wedge is not polished to a high gloss and you will still find machining marks on some of the parts. Pretty finishes add cost! I prefer to put the money into the heavy duty parts where it pays off in performance for you. The prototype pictured above was built with slightly less expensive cast plate, which does have a somewhat polished finish but is not as strong as 6061 alloy, which will used in the future models. If you want a shiny wedge, I can build it with cast plate for you - same cost for you but not quite as strong and less corrosion resistant.

If you would rather spend your valuable dark time observing or imaging instead of fighting with your wedge, then contact me at Pad 55 Products at pad55@san.rr.com to order your Ulti-Wedge today.  Of course, you could also buy one just to impress your fellow astronomers at the next star party. It also makes an interesting coffee table decoration and is a dandy paperweight.

 

Pricing:

Standard Ulti-Wedge - $685 plus shipping & insurance

Shipping weight is approximately 45 lbs from zip code 92129.

EMHD Ulti-Wedge     - $785 plus shipping & insurance

Shipping weight is approximately 60 lbs from zip code 92129.

Standard accessories included with both wedges:

Three socket head cap screws for attaching your scope to the Ulti-Wedge. These are 3/8-16 thread: if your scope uses a different thread, let me know when you place the order. If you do not already own a set of hex keys, you can buy a set at your local tool store or order a set from the list of options below.

UHMW bearing to go between the Ulti-Wedge and your mount.

Threaded knob to clamp the Ulti-Wedge to the top of the tripod. This is a 1/2-13 thread (Meade® standard). If the center threaded rod on your tripod is not 1/2-13 specify what thread it is when you place your order.

Instruction sheets on installing, using , and maintaining your Ulti-Wedge.

 

Custom Design - email a detailed description of your telescope, tripod or pier, location, and requirements for a quotation.

 

Note: specify the make and model (include the diameter) of your SCT when ordering. Also specify the latitude at which you plan to use the wedge - this determines the length of the altitude lever arm and the position of the central bolt hole. The range of adjustment is approximately plus or minus four degrees on either side of this latitude. If you want to observe from a latitude outside of this range, then you can order additional lever arms for different latitudes - see the optional equipment list below.

 

Delivery: I purchase the large linear and roller bearings from surplus dealers. The parts are unused and getting them from these dealers keeps the cost reasonable. Usually, I can get these in about two weeks, making delivery of a an Ulti-Wedge three to four weeks after receipt of an order. I will keep this page updated to show the number of wedges for which I already have these major components in stock. If I have parts in stock, I will try to deliver in two to three weeks.

Currently I have enough parts to build 4 more wedges.

 

Options:

The Ulti-Wedge is already drilled and tapped for this level. Any accurate level can be used; in case you do not already own one, I have included this in the options. Because it is an expensive item on its own, I did not include it as a standard accessory. If you order this with the Ulti-Wedge, then I will mount it for you before the Ulti-Wedge ships. More on why precise leveling makes polar alignment easier.

 

If you observe at another location outside of the +/- 4 degree range around your latitude when you ordered the Ulti-Wedge, then you can swap out the arm to use the wedge at a different latitude. All that you need to do is remove two shoulder screws, put in the new arm, and reinstall the shoulder screws. 

6.5 inch diameter for Meade Standard Tripod (7,8,10 inch LX-series) - $15 plus shipping

8 inch diameter for Meade Giant Field Tripod (12 inch LX-200) - $20 plus shipping

Other tripods or piers - email a description of your tripod or pier base for a quote. 

 

All prices are in U.S. dollars.

 

Why I designed the Ulti-Wedge

I do CCD and film imaging and started out with a Meade™ Standard Wedge. It wasn't long before I was ready to upgrade, so I did research on the web and talked to other members of the local astronomy club. I read and heard many horror stories about money spent and time lost in the effort to make their wedges work they way they expected. Many felt that they had never actually achieved satisfactory polar alignment or had only gotten there after much frustration. So, I decided to design and build my own wedge. Studying the other wedge designs, I came to several conclusions:

  1. Trying to cover a wide range of latitudes with a simple, mass produced, mechanism results in compromises that result in backlash, lack of rigidity, flexure, coarse adjustment, and worst of all - loss of the alignment when the screws are tightened after spending an hour getting precisely aligned.
  2. Attempting to provide a wide range of azimuth adjustment leads to the same difficulties.
  3. Mass produced wedges use loose tolerances that allow the altitude and azimuth adjustments to contaminate each other.
  4. Castings or thin plates allows more flexure in the wedge.
  5. The more it gets used, it seems the worse the problems become.
  6. Another entire wedge could have been bought with the money spent to make some wedges work as they should.
  7. An entirely new wedge design is needed.
  8. All of these problems could be solved.

For the Ulti-Wedge, the design goals are:

  1. Use heavy plate for the large surfaces to reduce flexure. It costs more but it is worth it!
  2. Limit the total range of motion for either axis to 10 degrees or less if necessary. This allows precision mechanisms with low backlash: these are impossible or impractical if a wider range of motion is required. You know you latitude from maps and you can use a compass to align to within a few degrees of the pole, so a wide range of adjustment is usually not needed by an individual user..
  3. As far as possible, minimize backlash in all joints and pivots by using industrial grade bearings and bushings along with precision screws and a solid and strong main altitude axle - this bears the majority of the load. On every rotating or sliding joint use an industrial grade bearing or bronze bushing. The exception is the mating surface between the bottom of the wedge and the platform (tripod, pier, etc.); this bearing is utra-high molecular weight polyethylene sheet. All of the screws in the rotating joints are precision stainless steel shoulder screws to maintain tight tolerances everywhere.
  4. Increase the resolution of adjustment - give fewer degrees of motion per turn of the knob. The wedge shown in the photo requires 96 turns on the knob to move through the whole 9 degree range of altitude adjustment - 0.09 degrees per turn. Other wedges have adjustment resolution five to fifteen times more coarse.
  5. Make the knobs easy to turn to allow fine, precise motion. The large mechanical advantage and smooth bearings do this on the altitude axis. A bearing of high density polyethylene sheet that goes between the wedge and your tripod or pier does it for the azimuth axis.
  6. Eliminate cross-contamination of the altitude and azimuth adjustments. In many wedges this is caused by the altitude adjustment axis moving during the adjustment process because the screws that form the axis have to be loosened to allow the adjustment to be made. When they are tightened, torque is applied that shifts the axis slightly or torques the plate, spoiling the accuracy of the alignment.
  7. Make sure any locking mechanism does not change the alignment or eliminate them completely. The only locking mechanism is the central bolt handle. Since the hole for this bolt is drilled individually for each wedge, so that it is directly below the center of gravity of the wedge-plus-telescope, then tightening this does not create and altitude shift as often happens with some other wedges.
  8. Don't worry about the looks, worry about how it works. It takes a extra time to polish aluminum plate to a high gloss or to machine it to a fine finish. And without anodization, that gloss is temporary. I choose to put the time and money into the mechanisms. You can't see the finish in the dark but you will notice poor polar alignment in your photos or CCD images for years to come.
  9. To reduce wear, mate all rotating threaded rods with steel threaded inserts instead of tapping threads into aluminum. This gives a tighter thread fit, reducing backlash, and it reduces wear on the threads a factor of ten or more compared to threads tapped directly into aluminum. The inserts or threaded rod can be replaced without replacing other major parts.

I came up with a design, built the prototype, and tried it out. After carefully leveling the system (tripod, scope, wedge) I did a normal two-star polar alignment. Then I mounted my CCD camera, adjusted the azimuth, and then adjusted the altitude. I came back to do the next iteration of altitude adjustment and found it needed no further adjustment. I had always been told that I would need to go back and forth three or four times to get to a reasonable alignment. My criteria for the first test was less than five arc-seconds of declination displacement in five minutes. I achieved this in less than thirty minutes on the first try. The Ulti-Wedge worked! I tried this several more nights with similar results. Now, when the seeing is good, declination errors are typically ten times smaller than the RA errors. Since I can now achieve much more reproducible and accurate polar alignment, I do not need to retrain the PPEC on my LX-200 on each outing. The stars in my CCD images are more round and I can use longer times between guiding corrections which allows me to use fainter stars for guiding. Actually, the Ulti-Wedge works better than I expected it would.

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Leveling

I believe that many polar wedge users have problems achieving polar alignment quickly because they do not first accurately level the entire system. If the plane on which the wedge rotates is not extremely level, then any azimuth adjustment will also result in a change in the elevation angle of the polar axis. This will lead to making several rounds of adjustment -altitude, azimuth, altitude, azimuth, …. Eventually the desired result is achieved but only after a much longer time than should be necessary.

Consider an extreme scenario: the top of the tripod (or pier) is tilted low by ten degrees on the east side. Let's say that the actual polar axis is exactly 35 degrees above the horizon and let's also say that the wedge is set to exactly 35 degrees altitude. If you rotate the wedge from 0 to 90 degrees, then the RA axis moves from an elevation of 35 degrees to only 25 degrees when it is pointed due east. If the wedge were perfectly level at the start, no altitude error would occur when an azimuth adjustment is made. If you are in a location where you cannot see Polaris to do a two-star polar alignment as a quick start or even to get a rough alignment of the wedge before doing drift alignment, then this scenario is not so unrealistic, except that I doubt if you will have a tripod out of level by 10 degrees. But 1 degree is easy to miss unless you are using a reasonably precise level to set up before doing drift alignment. That is why I offer one for your convenience in the options above. Any high quality level will work. I prefer a circular level because the position of the bubble makes it easy to decide which leg(s) to adjust. And with experience, you quickly learn by how much to adjust the leg.

When working from my Meade Standard Field Tripod, I level it roughly, then add the wedge and adjust again if necessary. Next I add a twenty-five pound barbell weight laid on the three thin arms at the base of the tripod. This puts tension on the tripod legs and helps to reduce and damp tripod vibration and flexing. I have placed as much as fifty pounds there but I could see no additional improvement over twenty-five pounds. I check the level again and then add the scope and do a final leveling. Doing it in stages makes it easier since I don't have to do the coarse adjustments with the full weight of everything at once.

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