Ad Astra Observatory

It was another couple of weeks before I could get back to the project.

I thought about doing circular holes for the vents, but decided to stick with the design, and laid out Reuleaux triangle-shaped holes for the vents.

All of the router templates that I’d done so far had been on external edges, so cutting the vent holes was a bit of a head-scratcher. I eventually figured out how to use a piece of scrap for a template, though.

I cut the holes out with a jigsaw,

then routed them even with the template.

Once the vents were cut, I started to lay out the mount points for the primary mirror cell. The vents serve both to allow air circulation around the back of the mirror, and also give access to the collimation bolts.

The mirror cell was designed to bolt through the sides of a tube, so I constructed some cleats that bolt the cell down to the bottom ring. The cleats are cut out of solid red oak, which makes a nice contrast against the birch, and also matches the red oak in the rest of the structure.

I cut the hole in the focuser board blank. The focuser board is red oak ply.

I had marked the top ring for a 4-point spider, but I realized (belatedly) that I’d made the marks 45° off from where I needed them (it’s about whether there’s a spider vane in line with the focuser or not) so I had to reconstruct the center of the ring. This involved digital calipers, string, and binder clips.

Once I found the center, I mounted the spider onto the top ring.

I mounted the spider with L brackets above the top ring, which allows the focuser board to be low-profile.

That ended up being all I could get done this weekend; a final test fit of the hardware and optics comes next.