Ad Astra Observatory

As with any other Beta test, taking Trixie out under the stars revealed a few things that still need a little tweaking.

In particular, the altitude movement is garbage.

So, I spent a little time troubleshooting today. I carefully measured the rocker box and the bearings, and I found:

– the rocker box is about 1/8″ out of square. I am letting it go. That should be insignificant across 3/4″ plywood.
– The focuser-side bearing is non-vertical,
– The bearings are not angled the same amount (one bearing is rotated “clockwise” relative to the other)
– the bearings are “toe-out” (closer at the back than at the front), and
– the bearings, when parallel (I know, I’m skipping ahead, work with me), are 1/2″ wider than the rocker.

First things first.

If the bearings are off in rotation, no other measurements are really valid, so I fixed that first. The ring-side bearing looked like it was the worse offender as far as being attached incorrectly, so I moved that one.

Once I’d fixed that, I noticed that the ring-side bearing was touching a truss pole, so I filed away some wood from the bearing until it doesn’t touch the truss anymore, and voila! all of a sudden the bearings are parallel to each other, and the focuser-side bearing is vertical! w00t!

This was when I noticed the 1/2″ discrepancy (see, skipping ahead). Turns out I just simply cut the rocker box the wrong dimension. So, I had several choices on how to fix it:
1) move the rocker sides out by 1/4″ each. This would exacerbate already-bad balance problems between the rocker and ground board, and would look funny, and would be weaker than the current build. No thanks.
2) buy more wood and cut out a new rocker bottom. While this would work, it is really a gnarly and “done”-killing method. I may do this later, but not yet.
3) trim the bearing spacers. I can’t trim the non-focuser-side bearing spacer at all, as it’s barely doing the job of keeping the scope from scraping the side of the rocker. Trimming the focuser-side bearing spacer is doable, but I would have to do more modification of the bearing (as in, cut a huge chunk out of it). This was the second best idea.
4) add another layer of ply to the outside of the focuser side of the rocker box. That would give the focuser-side bearing somewhere to ride, and neatly solve the problem. Not to mention I already had chunks of wood with more or less the right arc cut into them sitting around. This is the method I chose. I looks ghetto as hell, but it works. At least enough to move on. 🙂

A little sawing, a little sanding, and now both bearings are riding in a section of wood more than large enough to handle them. Sweet!

I didn’t get a lot of chance to test tonight; I had other stuff going on. But it feels like the Dob base is nearly complete.

I still have to put in the furniture slides on the altitude axis, and I am still thinking that I will probably put in “bearing keepers”, little chunks of wood that keep the scope from sliding left and right out of the altitude bearing seats in the rocker box. I have dozens of little chunks of wood lying around waiting for just such an occasion.

And I think, barring any unforeseen, that will be that. Once I get the whole scope up and running, it’s time to take everything apart and varnish.

Well, maybe I’ll wait for warmer weather… 🙂