How to unstick correction collar on objective?

[Dubious]

Two new (to me) Olympus LWD CD Plan objectives (20x and 40x) have correction collars that won't turn at all. I understand they have been unused for years. Is there any easy method that might unstick them with reasonable safety, such as heat or penetrating oil? This is my first experience with an inverted microscope and I haven't encountered this problem before.

[Phill Brown]

Good luck.
I'd say anything but WD40.
Penetrating oil is intended to migrate across any surface.
It's unlikely to stop migrating at the point the collar frees up.
Clock oil intended to stay where it is put.
Interesting experiment is put a drop of chosen oil on a polished metal surface.

[Wes]

Try acetone or isopropanol. But use extremely tiny amounts (like less than 0.5 microliters at a time).

[apochronaut]

Having repaired more than 10 such objectives successfully and failing on a few, my rule of thumb is to remove the rotating ring, skirt or collar first, in order to get an idea of the way the mechanism works. Most of them are very similar but the way the collar comes off is different. The collar needs to slip freely in order to drive the mechanism and in most cases due to the large surface area that the collar slides over( a couple of square inches in some cases), the issue is more often than not the collar, rather than the worm, or the collar contributes a sufficiently high amount of drag in the system that it is unusable. Also, the collar is more exposed to the atmosphere, so there could be differential lubricant drying based on atmospheric exposure ; any of light, heat, air or other gases. Usually, just cleaning up and relubricating the collar is all that is needed and once it is off, a single drop of a light grade non gassing high quality oil such as one of the Nye oils won't hurt. Seldom does the mechanism need to be broken down.

If you want to avoid removing the collar, targeting an upper and lower entry point for the above type oil and then working the collar back and forth can often get the system working close to it's factory spec. and saves a lot of work. If you don't get a major improvement after 2 drops upper and 2 drops lower, then take the collar off.

[Dubious]

Thanks for the info and tips. Using them, I was able to get the 40x working. The 20x, though, remains stuck tight, so it looks like I'll have to attempt disassembly.

[PeteM]

One thing that has worked for me (sometimes) is to apply a little bit of heat using a hot air pencil (sort of like a tiny blow dryer) and gently work the iris back and forth a bit. This will often soften any hardened lube enough to free the iris -- and allow a drop of oil subsequently applied to penetrate free things up. You want the area warm to the touch, don't overdo it.

[apochronaut]

It can't be stressed too much that no oil is better than just a drop too much. There is a very old thread very similar to this one and the poster got it in mind that just another drop and then just another drop would make the ring rotate easier. Oil ended up in the lenses, because it was being fed in too fast and in too great a volume. It takes time for a drop of oil to migrate and disperse evenly through the lubricant mass.I usually wait a day before I make a determination of how well things are going and try to use gravity as a shop assistant.

[Crater Eddie]

I had good luck on a LOMO objective with frozen collar by applying gentle heat.
Good luck.
CE

[Dubious]

I tried heat, but no movement. I won't use more oil--thanks for the warning. So, looks like I'll be disassembling...