Ad Astra Observatory

I have been playing around with the numbers on a Dob base for Tirixie. My design requirement was to try to keep the conversion down to stuff that could be cut out of quarter-sheets of plywood, preferably able to be cut on the CNC machine (which, although it has a 2’x4′ table, loses about 4″ off of each axis because of the width of the gantries).

After much gnashing of teeth and tearing of hair, I came up with a design that “could possibly” work, and only required 2 quarter-sheets. The two most limiting measurements were the width of the rocker bottom (which needed to clear the sides of the telescope (plus the width of the sides), and the diameter of the altitude bearings, which have a “the bigger, the better” kind of thing going for them, but, being 2 half-circles, have an obvious limit of 24″ from a quarter-sheet of ply.

I had to get the mounting plates installed before I could get to work on the Dob base, so I spent the morning installing them. They look OK, very sturdy. I hold out some hope that I can get the scope to balance.

With the plates on, I had my final width measurements, and I started laying out the cuts.

I drilled the center hole for the bearings using the CNC machine, as it was too far in the center for a drill press.
I cut the rocker bottom from the ground board. They still need to be center-drilled, but that’s for later.

Then I started in on getting the bearings cut out. I needed to use my ancient circle-cutting jig and the hand router, because the 24″ circle was too big for the CNC machine. After a rough start of figuring out how to set up the jig again, I got the circular bearing (it will be cut into semicircular bearings) cut out. By design, the rocker sides are cut at the same time.

And, suddenly, I had all the primals cut for my Dob base!

The base consists of 2 sides, a bottom, and a ground board. There are also short front and back sides, but I can cut those from scrap.

The pointy tips of the sides are going to be cut down quite a bit; the whole side is only about 14″ high (12″ in the center).

Another evening or two, and this thing should come together!