primary mirror fabrication underway

Well, it's been a while since I've last posted, but in the interrim, fabrication of the key part of the scope has been undertaken! I commissioned Portland's Steve Swayze to make the primary mirror and he's well underway. His mirrors have an excellent reputation in online forums and people I've talked to. His prices are very competitive relative to other mirror makers. I won't say exactly what I paid but the index number of the check that I wrote him for a 50% deposit was the same as the amount of the check. Steve has been great about keeping me in the loop about progress on the mirror. It will be 16" diameter, f/4.5, 1.6" thick, and made from pyrex that was slabbed from a previous thicker mirror. Here are some pictures of the work in progress, copyright Steve.



These are the two slabbed pieces of pyrex. I don't know the provenance of the original glass, but it looks like it must have been from a 2.5-3" thick mirror or so. Slabbing it to 1.6" reduces the weight (it will be 26 lbs total), lets it cool quicker, and is generally not felt to cause the mirror to bend to any noticeable degree given the right flotation system supporting it.



This is the glass on the grinder. The grinding tool itself seems deceptively simple to me, it's just made of store-bought square tiles arranged in a circular pattern underneath the plywood disc. The gray material is "pitch", made of various different grades of abrasives dissolved in water. Using several grinding patterns and finer and finer pitch material, the glass is first ground to a spherical shape, then refined to a parabolic shape. There are a lot more details of this process that I haven't learned, so it's great that there are mirror makers like Steve who have!



The rough surface of the mirror status post some degree of grinding. At this point the shape still needs to be confirmed to be parabolic, and of course it needs to be coated with a reflective material.

Okay, I'll post more on the primary mirror as it progresses!