I posted about my mount on the astronomy site Cloudy Nights and a member by the name of DavidG suggested some changes to my pipe mount that he’d come up with. He calls it the Delmarva mount system and wrote an article on it in the Nov. 2012 Sky and Telescope magazine. He specifically “developed the system to offer a simple to make upgrade to the standard pipe mount that ATM’s or school groups could easily make without the need for machining.” It utilizes some PVC reducers and Teflon to provide better bearings. It looked like a good idea so I decided to give it a try. Below, I cover how I made his mount system, but it could be made with much simpler tools.
The first step is to modify the PVC 1-1/4″ to 3/4″ bushings. The 3/4″ side needs to be bored out using a 1-1/8″ Forstner bit so that a 3/4″ galvanized pipe can pass through it.
Next, the 1-1/4″ end needs to be bored out to large enough so that the 3/4″ pipe with Teflon wrapped around it can fit. I used 1/8″ thick Teflon which required me to bore bushing out to 1-3/8″. I did this on the lathe as it is easier to find the center of bushing. When boring the bushing you want to bore down only as far as needed so that a shoulder is left in the bushing to keep the teflon from sliding out.
The thread on most plumbing pipe is tapered. This can be used to our advantage to increase or decrease the friction on the bearings. If the bushing is slotted as shown below, as it is tightened it will bend in pushing harder on the Teflon and pipe. The bushing on the right has the Teflon bearing material installed.
To use the new bushings I had to redesign the mount. Some of the parts are still there but I’ve added a few new pieces. Instead of pipe threads acting as bearings on each other, 3/4″ galvanized pipe is held by the PVC and Teflon bushings. The 3/4″ pipe is threaded into a 1-1/4″to 3/4″ galvanized reducer and the whole piece spins.
Previously to get the scope rings apart I had to remove four 1/4″ nuts. To speed this process up I put small hinges on one side of the rings.
On the other side, I put some well nuts. I stumbled upon them at Lowe’s and they work well for this purpose. They’re made out of rubber with a 1/4″ nut set into the bottom. They’re easier to get a grip on than the hex nuts.
Viewing with the scope is much improved over the previous design. The scope now turns smoothly and stiction is pretty much nonexistent. On the downside, the mount gained another 2.6 lbs bringing the total weight up to 41 lbs with scope and counterweight. This was definitely a worthy modification though.