hijacking this post for build updates.
8/1
I decided to go a bit further than 5/8” so I started this phase by opening the ends more with a 3/4” step drill bit and then spent several hours using up most of a sheet of 150 sandpaper and a few feet of 2” masking tape to ream the narrow part between the ends. iballing with my iPhone. Here with a 3/4” OD brass tube. I started out with a 3/8” carriage bolt(head removed to fit smooth end in chuck), one layer of tape, and just enough sandpaper to wrap the bolt plus 1” under the tape. Spin it until it’s no longer snug then add another piece of tape under the sandpaper. When the paper gets dull(wood heats up with very little removed) turn the paper end for end to bring the fresh grit out and repeat ad nauseum. At times the wood got too hot to hold but the epoxy sealer stayed stable and never became gummy.
Later that same day… I took the other piece of wood out to the garage and cut out the center with a 1” hole saw. Then I popped the piece out with a chisel keeping some of the plywood attached for stability and switched to a 7/8” hole saw with tape and 150 grit to clean up the inside. Back to the 1” hole saw with enough tape to make it snug and clamped my hack saw blade to the table and oh so carefully nudged the table and blade into range as I pulled the handle on the spinning piece. That’s enough for now on this piece, it’s still ~1 mm bigger than the flat to flat dimension of the brass bezel nut but I need to re saturate it with epoxy sealer before making it closer to final dimension. As the wood gets thinner it tends to swell when saturated. This is the sealer I use.
8/2
Things started out well enough. To make the female threads I need to reduce the ID of 3/4” copper pipe to somewhere close to 19 mm, preferably a but less since the threaded ID of a P60 reflector which has the same 20 x 1mm pitch is ~18.8 mm. I cut a short length of pipe and removed a 5.5 or so mm strip. Then I annealed it on the stove and after a little filing and rolling it slipped right in.
Brazing on that went fine. It needs a small lip on one end and a means to clamp it in a vise on the other that allows the tap to feed through. Seems to be going well. As you can see the tap went skewed even with about 15 mm of extra length on the outer layer to act as a guide. Oh well, I’ll have to start over.
I’ve already remade the tube and liner but using slightly thicker copper sheet instead and a bit more length on the outer tube as well, The first try was a bit large at 19.2 mm. In addition, I’ve cut two strips from an aluminum can that take up the remaining slack between the outer tube and the tap which will hopefully get it started more on axis. I still need to cut the brass nut free from the original one so I can reuse it.
One good piece of news is that my lens arrived today and fits the now squared lip perfectly( lip was sloped before to accommodate the compression sleeve).
Link to more threading