So, I stayed up late last night looking though my local Home Hardware superstore's on-line catalog, as I sometimes do, and had one of my ideas. So I went there today, bought some stuff, and before the sun went down I managed to make this.
It's a telescope mount, built from galvanized iron pipe, brass fittings, threaded rod, and some roller-skate bearings. The action is so smooth, I can start it spinning and come back a minute later.
Australians will recognize this as another example of Hills-Hoist based technology.
You can just see one of the bearings on the lower swivel. I've seen a lot of iron pipe used in the construction of amateur 'scope stands and mounts (and even the optical tube assembly) but I've taken it a step further and used matching brass fittings to create bearing blocks that accept standard ABEC 608s.
The bearings can be quickly removed, and disassembled, as I did just then. Those brass parts cost $4 each new, the skate bearings cost me about a buck each back in the day (and have been sitting on a shelf for years) and I had the nuts and 8mm threaded rod lying around from previous projects.
The real secret (and most expensive item) was the special "self-centering step drill" bit that I used to ream out the ends of the fittings, to create a 22mm 'seat' for the bearing to sit within. I chucked this bit into my drill press, and manually turned the bit, (as if I were tapping a hole) instead of powering up the press.
I have a lathe, but really didn't want to use it for this. Partly this was to find a method that works for people who don't have access to a small machine shop, and partly because I don't like them because they're so insanely dangerous. "Experiment" and "Lathe" are two words that do not go together well.
Each only took a minute or two to carefully ream out to a depth of a couple of millimeters, even by hand. Brass is a lovely material to work... you can feel the chips coming off. (Brass was cheaper and more accurately machined than the equivalent galvanised steel, which was clearly die-cast, and had terrible dimensional accuracy. Don't substitute iron or steel, or use cast parts, you will regret it.)
Actually, the 22mm drill step left the fit a little too snug. The bearings would go in, but getting them out again took a small impact hammer. So I put a small grinding bit in my Dremel, and 'dusted' off a few more thou (just enough to smooth away the drill tooling marks, really) and now the bearings drop in and fall out perfectly. A file, or some sandpaper and time would have worked too.
Total cost for the two bearing assemblies? $20 in parts, and $25 in tooling.
Given that I've see people using four 'pillow block' bearings that cost $15 each on eBay (if you're lucky) I consider this a win. Especially since mine are a fraction of the size, inline, and require no extra mounting hardware to attach to the pipe.
I not only have a new telescope mount, I have a technique for making them at will.
Also, those facing inline threads will come in very useful when I start attaching motors and gearing and torqe plates. I have some designs already, but obtaining Arduinos and servo motors will take a little time. (Assuming I don't reallocate my CNC steppers.)