Telescope Making Diary Day 25: Things Go Right

With the final modifications completed, the scope is at last finished. At least for now...

The balance issue detailed on Day 23 was eating away at me, so I broke down and decided to make the necessary modifications after all. I’m glad I did. The work wasn’t as bad as I feared, and the results turned out better than I expected.

One of the old side bearings lies atop one of the new. They are different by only 3/4-inch in radius.

The rocker box is attached to a jig to ensure that the arcs routed into both sides are identical.

To eliminate the need for a counterweight, I decided to move the scope’s balance point forward by making new, larger side bearings and modifying the rocker box to accommodate them. I glued together two ½-inch thick scraps of MDF (medium-density fiberboard) to yield a 1-inch thick piece, from which I cut the new side bearings with my trusty router. (Actually, the bearings came out thicker than 1-inch because wood thicknesses are never what they’re stated to be for some reason.) I had to move the balance point 3/4 inch forwards, so the radius of the new bearings needed to be 3/4-inch larger than the original ones.

The new bearings, of course, no longer matched the mating curves in the rocker box sides. Modifying the rocker box wasn’t something I was eager to do since ensuring that the curves on both sides of the rocker would match exactly was bound to be a challenge. Not only did the radii of the curves have to match (which is pretty easy to do), but the position of the curves and their depth also needed to be the same. To accomplish this, I set up a jig to hold the rocker box in place and to precisely position the router.

Happily, everything went smoothly. The curves came out nice and neat, and after some painting and sanding, the scope was reassembled for a test drive under the stars. And that, I have to say, was a pure joy. The scope moves wonderfully. With a modest push, I can slew from target to target and track objects at high power without any jumpiness to the motions. That might sound like a minor accomplishment, but since it really was the point of this whole exercise, it is a big deal. And after all, a Dobsonian telescope is all about how smooth and controllable the motions are.

So now, the rebuild project is finally done. Of course, there’ll be the inevitable tweaks and modifications – no telescope is truly ever finished. But at least I now have the no-compromise observing machine I wanted. I expect that this will be my main scope for many, many years. Or at least until I decide to build something bigger and/or better.

(Previous Telescope Making Diary entries are compiled here).

The dog and the Dob. Sam inspects my newly completed telescope while we await sunset.