My perfectly serviceable but ~12 year old birding telescope (good quality with ED glass) has a female Imperial threaded socket for the eyepiece, ~28.42mm OD measured on a mating eyepiece male thread. I've just bought a newer, more powerful eyepiece with a slightly larger metric thread, 28.95mm male OD (+0.5mm), and having emailed several likely places without even a reply, I am wondering how best to get my new eyepiece to fit my older telescope. The pitch of both of the threads is very close to 32tpi. (Sorry about the mixed dimensions!) I think the material of the metric eyepiece thread is aluminium, as also I suspect is the Imperial threaded socket on the telescope. (Doesn't react to a magnet.)
(The importers of the telescope and eyepieces have offered to change the telescope thread to metric, but then my older Imperial eyepieces will need changing.)
I don't have a lathe, and haven't been able to find suitable tpi dies large enough; but do have time, a machine vice, small files etc. and am looking for practical advice on how best to reduce the larger thread. (As far as I'm aware I can't remove the optical cell, so any cutting would best be done without oily lubricant.)
Thanks for any ideas