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Hmm. Not getting the avalanche of keen and excited replies that I'd hoped!
To help trigger some replies, here's what I did: The female thread on the BinTel eyepiece has a (mean) minor diameter of 47.33 mm, although it is somewhat out of round. So I bored my brass tube to 47.33 mm. If the thread really is ISO, either metric or imperial, and close to 0.75 mm pitch, the depth of thread should be 0.406 mm by definition, with a "radius" of 0.108 mm in the valleys. If I'm using a non-radiused 60 deg carbide tool, I should use a thread depth of (0.406+0.108) = 0.554 mm because a 60 deg triangle sticks out one radius further than the enclosed circle. Therefore, I should bore to 47.33 mm, and then move the cross-slide a further 0.554 mm. Since the cross-slide is calibrated in diameter, not radius, I should change the reading by 1.108 mm. Did all of that. For what it's worth, the minor diameter is still 47.33, so I didn't overdo the threading step. The filter screws in (somewhat reluctantly, wanting to cross-thread), but only engages by 0.5 turns, whereas in the BinTel it engages by a full turn. What am I doing wrong?
Suspect I'm gonna have to cheat, find a dud filter from somewhere, scrap the filter itself, keep the frame, and superglue it in. Then screw the "real" filter into the female thread on the dud. Blecch!
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