Converting to a Dob Mount
A few years ago I (re) built an 8-in f/4 reflector to be used as a richest field scope and occasionally for imaging. It needed a set of rings so the tube could be rotated on an equatorial mount. I ordered a set of cast aluminum tube rings from Orion. Each of the rings has a 1/4x20 drilled and tapped hole on the bottom to attach to a mount head. There is another 1/4x20 hole on the opposite half of the ring to attach a camera or a mounting plate for a guide scope. The rings are built pretty good and they have worked great for their intended purpose.
I observed several nights in a row, usually with the 8-in on the Super Polaris equatorial mount. It got to be a pain to drag out the tripod/mount, battery pack and optical tube assembly and put it all together in the yard. Then after observing the process was reversed. How convenient if this scope was on a dob mount I thought one night. No problem, I'll just build one.
The next day I remembered how I attached the club's 6-in Meade apo to a dob-style head by using the drilled and tapped holes in the tube rings on the scope. That same approach should work with the dob mount for my 8-in f/6 StarHopper. After a few measurements I was pleased to realize that not only could this be done but it would be even simpler than I had thought.
There was a scrap piece of 3/4-in thick MDF (Medium Density Fiberboard) in my shop wood bin that was just right for this project. I cut it into two 6x12-inch pieces. As luck would have it 4-in thick wall PVC pipe has almost exactly outer diameter as the aluminum trunnion bearings on the Celestron scope. Using a chop saw I sliced two 1-in thick rings off of a piece of scrap PVC pipe I saved when the house was built a few years ago. Each ring was edge drilled in four places and the holes were countersunk to allow wood screws to fit flush against the outer edge of the PVC rings.
Two coats of black paint were applied to the MDF. Before attaching the PVC trunnions I sanded the outer surface of them with 80 grit sandpaper. I thought that they might be too slick and move too freely against the teflon pads. The assembly was soon completed and the “new' mount was tried out. It worked pretty darn good although the altitude motion was a tiny bit too stiff for my liking. Looks like I should have not been so aggressive with the sand paper. Maybe I will apply some car wax to the PVC to slick them up a little.
Now I have two 8-in scopes to use with one dob mount. The f/4 will be there until I want to do some high power planetary viewing. Then the f/6 will be mounted.
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About the Author:
Terry Alford has been an avid amateur astronomer since 1979. He is currently a member of two astro clubs: Bays Mountain Astronomy Club (founding member) and Bristol Astronomy Club. Since 2001 Terry has taught Astronomy Labs at East TN State University. His first ATM project was in 1979 and was an equatorial pipe mount for an 8-in reflector. His woodworking shop also turns out toys for grandkids.