Ad Astra Observatory

I’ve moved into the CNC part of the program on the Dob base.

I started with an easy one. The rocker bottom just needed a countersunk hole for the pivot bolt. It needed to be dead center. The countersink needed to be the correct size to hold a 7/8″ washer, which will end up being sort of a metal-on-metal bearing. I measured the center of the part out by hand, and ran the shortest CNC program ever.

The washer fits very snugly, and looks really cool.

Then I tried to do the ground board, but ran into a complication: the height of the piece is 20.6″, but my CNC machine will only do 19.5″. So I tried adjusting the part a little to make it fit, and decided to table it for the moment, and move on to the altitude bearings.

The bearings provided their own complication; the bearings are 23.5″ wide, so I needed to figure out how to carefully set up the workpiece to fit both parts. This led to an interesting “discovery”, that the CNC can easily run off of one end of the table, but can only come within maybe 12″ of the other end. This obviated part of the cut, but it still took some setup.

I was most of the way through cutting the first bearing when disaster struck. An aside, I like the word ‘disaster’, ever since I learned that it means “bad star”. Makes a great astronomy adjective. Anyway, back to the show.

The router jumped into the bearing, and the router and computer both shut down. The power strip that I’m using has an irritatingly easy-to-trip breaker in it. When I looked at the position of the end mill, I realized what had happened. OK, another aside about the way my CNC machine works. I have to tell it to go to a particular depth, and that depth is based on a “zero point” that I set by touching the mill to the work surface. Also, 3/4″ plywood is only “nominally” 3/4″; it’s actually a bit short of that. Often, the plywood isn’t all that flat, either. So to make sure you go through all the layers of the ply, you often end up gouging the CNC table a bit on the final pass…

And this time, I hit one of the mounting bolts that’s holding the CNC table together. It chewed up quite a bit of the bolt head, and crunched the end mill a bit, too.

I reset everything as well as I could, but that bearing is going to take a little more sanding than I normally have to. oh well.

The second bearing went very smoothly.

Here’s the finished pair.

The end mill is pretty trashed now. I need to get it sharpened (and I’ve got a new one on order). I am almost done; I just need to cut out the ground board, and I can start constructing.

I am actually of two minds about the ground board at this point. I could use the current (and nearly trashed) end mill, I could go buy a 1/4″ router bit at a local store, I could use the 3D bit to complete the job (although it would look a little weird), or…

I could just decide to leave the ground board rectangular. There’s something to be said for simplicity.

That’s a decision for tomorrow. I’m tired now.

Good work today. Nearly there!