4.5″ Mini Dob Project

I have a 4.5″ Newtonian reflector telescope that I got for $10 at a local thrift store. The views are OK, but the dovetail mount to the tripod is super wobbly, and the thing will shake if you even breathe on it, so I decided to build a Dobsonian mount for it.

I designed some telescope rings in Tinkercad, and 3D printed them in PLA. I used JB Weld to anchor some 1/4-20 all-thread in them, which was in turn used to attach the rings to a scrap of plywood and a 4″ PVC cap, which will serve as the altitude bearing.

I made the mistake of deciding to leave the dovetail mount attached to the telescope, which meant the rings needed to straddle it, causing them to be attached outside the bearing surface rather than inside as I had intended. This would cause issues later (The PVC bearings ride on some small felt furniture glides, and there is enough slop that some times the bolts will hit the glide as the scope is raised or lowered. This would have been totally avoided if the ring bolts were inside the bearing. I may just 3D print some guides to keep it from slopping and mount them on the outside edge of the rocker box. Depends on how often the bolts actually hit with the scope in use).

With rings and bearings attached, I could now measure for and construct the rocker box and ground board, which were both made from some left over plywood I had sitting around.

Couple coats of Flat Black paint, and it’s starting to look like something.

For the azimuth turntable, I mounted an old LP to the ground board, and felt furniture feet to the bottom of the rocker box. Fittingly, since I was doing this over the Christmas holiday, the sacrificial LP was “Ira Ironstrings Plays Santa Claus.” Sorry, Ira, but you were pretty scratched up. Many amateur telescope makers use Teflon here, but felt just, uh, felt right (no pun intended).

On the inside of the rocker box, I secured the ground board to the rocker box with a fender washer and a wingnut, so the amount of friction on the azimuth turntable is adjustable. The felt furniture feet are also adjustable, but that’s not a design feature, it just happened because the feet I had on hand had threaded inserts and I doubt I will ever adjust them.

I added a carrying handle to the front of the rocker box, and a 3D-printed eyepiece holder to the back.

Rubber feet on the bottom of the ground board completes the project. Now just need some clear skies.