Foolproof removal of brass lens flanges!
I don't claim this solution is original, but it beats all the other methods I have attempted.
The big difference with loosening the stuck flange/lens thread is that there is difficulty in holding the flange. The barrel/sleeve/tangential drive provides quite a good grip. I have tried different methods in the past including heating and impregnating fluid.
The fastest and most protective of the brass finish is as follows:
Remove the lens cells. Treat the barrel with great care as the threads/roundness of the barrel threads for cells are easily damaged with no chance of a perfect repair.
Find a length of scrap plywood which has about double the width of the barrel and 50cm in length. Cut a hole at one end which allows it function as an oversize lens board. Attach the lens flange/lens barrel to the plywood. Two screws at opposite sides of the flange are enough.
It may loosen now if you can wedge the end of the plywood on something solid (door frame). My experience is that this doesn't work! So you hold the barrel/flange in your left hand and, taking up a hammer, you give the other end of the plywood (the edge of course) some solid hammer blows. ANTI-CLOCKWISE!
Do not be worried about this treatment. As long as you hold onto the barrel, nothing nasty will happen. The torque which is applied by hammer blows is many times greater than you apply with ypur hands.
Obviously, you cease hammer blows as soon as there is movement and revert to unscrewing.
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