How to straighten bunged-up threads on an old lens?

[Marco Milazzo]

I have an large, old lens with rear threads damaged in one small spot -- as though they were hit by something like a screwdriver. Only two or three threads are affected, and these in a small spot, but now it won't screw completely into a metal ring.

Does anyone know a simple way to straighten out the threads -- a file of some sort or a knife-like device, perhaps?

TIA

[Vick Vickery]

I'd use a triangular file with two safe sides, leaving only one side to do the cutting. Don't remove any metal other than that needed to remove the burr/obstruction that is stopping the retaining ring. These can be purchased from any gunsmith supply company or you can easily grind one yourself if you have a belt sander and alot of patience!

[Jim Noel]

You need a lens vise. It will straighten and correct the threads.

[lenser]

If it is brass, it may be soft enough to use a small screwdriver like a jeweler's screwdriver to place in the thread groove on the distorted side and pull across the groove while putting gentle sideways pressure against the bend ridge. Do this several times in each groove that has a problem and you may be able to pull the damage back into position enough to thread onto the ring. At that point, the thread of the ring will help to align the damaged threads.

Be sure and use some sort of light lubricant like Vaselene so the lens and ring don't lock completely and rack it back and forth several times. Once you get to this point, then pack the lens out, lightly file the damaged ridges to remove any burrs, completely clean both sets of threads and re-lube with a good dry lube in very small quantity to avoid any build up that could lock things up.

[jim kitchen]

Dear Marko,

The best device happens to be a dye thread, set to the correct diameter, where you back the dye on and off the thread with the proper lubricating oil. A really good pipe-fitter or plumber will be able to assist you, quickly.

jim k

[Wayne Aho]

There are files specifically for repairing threads. If you can't find one, then a file for making screw slots can work. They are very fine and with a thin taper. Check auto parts stores. Most small files (like camera repair files) are too big.

Wayne

[Gordon Coale]

The best, and safest way, is to send it to S.K. Grimes.

[domaz]

The best, and safest way, is to send it to S.K. Grimes.

Mine as well give it a try first yourself. SK Grimes would probably sand down the threads and put new ones one anyways so no harm done if he messes them up more.

[Benjamin Lewando]

Assuming that your lens, like most large, old lenses, has fairly coarse mounting flange threads, this should be easy to do using a small (1/4") triangle file, the kind used for sharpening a handsaw. Best to wear reading glasses, even if you don't need them, to give you a more accurate view of what metal you are removing. With the file in the groove of one thread, note that the V of the thread is wider than the V of the file, meaning that it will cut the bottom of the thread more than the damaged top of the thread. In order to ensure that you cut the damaged thread top, lean or rotate the file a bit to the right for the first pass, and then a bit to the left for the second pass. Then check (with a loupe) before repeating the cuts. It should not take many cuts for each thread to do the job. The special file Vic suggested would be somewhat safer, but I've done this type of repair this way many times, and my personal experience is what I have to offer. That said, if the lens is worth a huge amount of money, or you are uncomfortable with the task, do seek the help of a professional.

[Bernard Kaye]

A sturdy lens wrench and a sturdy wrench used to open filter retaining rings may not work on older, heavy brass filter rings such as by Zeiss for 25cm. f 6.3 Tessar; the brass is too heavy and risk is forcing which will crack the front glass which also could happen using a lens vise if you lack experience: they are correct, approach with caution and do it slowly with a thin file or a strong knife or screw driver blade; watch your hands.
Bernie

[Liam:]

Dear Marko,

The best device happens to be a dye thread, set to the correct diameter, where you back the dye on and off the thread with the proper lubricating oil. A really good pipe-fitter or plumber will be able to assist you, quickly.

jim k

I agree, not sure why people are advising using a file...

[Marco Milazzo]

Thanks to all for many good suggestions -- you guys have smart brains.

Yes, using a thread-die would be the best solution. I'll search for a machine shop that has the right tools, but if not, I've found a small file (flat on one side), at a jewelers supply place that may work. If I use a magnifying glass, proceed cautiously, and don't drink too many beers beforehand, I may be able to fix the problem, myself.

I'll let you know.

Marco