Tuesday, March 4, 2014

Fabricating A Pier Plate Adapter For A Celestron Nexstar 8 Telescope - Part Uno

This past weekend, I finally got my astrophotography observatory in Chiefland, Florida (above) up and running so I would have a place to image deep sky objects in a somewhat permanent setup. After having a chance to use my Takahashi TSA 102 refractor telescope on a pier (left) a whole new world opened up for me. I could slew the scope from one celestial target to another and then view the objects with absolutely no vibration or shaking in the telescope, even at high magnification. What a difference. The pier in the observatory is a 6 inch square steel tube that is set 3 feet into the ground with a surrounding 24 inch square concrete pad, built to support a heavy telescope/telescope mount. That was my first experience using a pier as the base for a telescope instead of a tripod and it caused me to give some serious thought to using a pier on the telescope I will be using at home for observing, an 8 inch Celestron Nexstar 8 (right). The problem is that despite a concerted effort to find a pier adapter to mount the Nexstar 8 on a pier, I couldn't find anyone who manufactured one. Not to be deterred, I decided to fabricate my own.

In order to fabricate a pier plate adapter, I needed a template to guide me with the design for bolt holes that would be used to secure the telescope to the pier plate. Unbolting the Nexstar 8 from the tripod exposed the base of the tripod plate (left). Removing the tripod plate was simply a matter of unbolting it from the tripod. Voila - the perfect template. Next I had to obtain the materials for the pier plate adapter. Since the tripod plate was fashioned from 1/2" thick aluminum I decided to follow suit with the same material for the pier plate adapter. The Nexstar and its one arm mount are very light making aluminum a plausible, solid material choice. A quick search on the web yielded a metal fabricating business a short distance from home and after a telephone call I was good to go. They had 1/2" aluminum in stock and it could be cut to any size. I settled on an 8" square piece for the bottom and a 10" square piece for the top. The bottom will be bolted onto a pier (more on that later) and the top will be the base for the telescope.

In addition to the two square pieces of aluminum, I had the metal shop cut four pieces of 1 1/2" aluminum bar stock into 4" lengths to serve as spacers between the top and bottom plates . By having 4 inches of clearance between the top late and the bottom plate I gave myself enough space to bolt the adapter to the pier. Equally important, the space between the plates would make it easy to attach and  remove the telescope from the pier by using socket cap screws through the underside of the top plate into the threads on the Nexstar's mounting plate. The plates and aluminum bar stock cost was less than $50. I picked up the necessary hardware at a local Ace Hardware - eight 1 1/2" long, 3/8" stainless beveled screws to attach the aluminum rods to the two bases and the three 1" long, 3/8" stainless socket cap screws - to build the pier adapter at a cost of $15. Now came the fun part.

Step one was drilling four 3/8" holes into the bottom plate (above, L). Although the image doesn't show it, I then used a countersink bit to create a "V" shaped bevel in each hole on the bottom of the plate so the beveled screws would be flush with the plate when inserted through the holes. Step two was drilling 5/16" holes through the center of each aluminum rod (left) and then threading the holes with a 3/8 NC tap (right) to accept the 3/8" screws. This is where the choice of aluminum stock was a blessing. Drilling and tapping thick aluminum is much easier than comparable steel stock.

Step three involved attaching the aluminum spacer bars to the bottom plate so I could make another template that would give me the location of bolt holes on the top plate (above).

I've used the template for the holes to mark their location on the top plate. After these holes are drilled and countersunk, all that is left to do is to mark/drill the holes to bolt the telescope to the top plate in order to finish the rough construction of the pier adapter. Because it was getting late, I decided to call it a night before drilling any more holes and stopped working on the project. I couldn't resist placing the top plate on the spacer rods to see how the finished adapter will look as shown in the image above which also depicts the telescope base on the top plate. I hope to finish the rough construction tonight and then prime/paint the entire pier adapter black.

After I finish the adapter I will be building a pier in the back yard and attaching the adapter to the pier. I'll probably use an 8" Sonotube filled with Sacrete and rebar rods for support. Threaded "L" rods inserted into the wet concrete will serve as the attachment method for the adapter to the pier. Stay tuned.


mike said...

I read your post and i appreciate your efforts. The information that you share in the above article is very nice and useful .All the things that you share with people, are very nice. Thanks for this article

Howard said...

As I have repeatedly stated, I know you are really an engineer at heart - the attorney, photographer things are just a clever cover. Now I see - a mechanical engineer, no less. Great blog, please post all blueprints at the completion.

Anonymous said...

Great design. I like it so much, I am copying it. Do you do any AP in equatorial orientation? I noticed your C8 is in alt-az on the pier.

Steve Slater

Pawan Yadav said...

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