very stubborn helicoid

[kiddo]

I've got this 1.4 DX yashinon very cheap because the lens was totally locked , I could open it all the way to the helicoid but this one it won't move at all. I've soaked it in acetone to see if it will release hopefully, but I do see lots of residue releasing, could it be some kind of glue? Just checked it out and it is some kind of very very sticky glue

.

[RokkorDoctor]

Well, if it releases and you can remove it all I think there's no need to worry about what it was.

Glue is unlikely but maybe a poor quality grease of which some of the components have polymerised/cross-linked due to long exposure to oxygen? Maybe one of our resident chemists can jump in here? (I am not a chemist but I have seen base oils separated out of helicoid grease turn into a sort of thin "plastic" film in old ROKKOR lenses, a film that even acetone has trouble removing)

EDIT: another (albeit unlikely) possibility is that the original grease had lithium stearate as a thickener (very common), and someone decided to "refresh" the grease by adding some polyurea-thickener-based grease. In general those two don't like each other very much and tend to harden when mixed, although there are exceptions.

[kiddo]

[Lloydy]

Boil it, the temperature won't hurt either metal and the different coefficient of thermal expansion at the same temperature should dislodge it.

[kiddo]

well , this very stubborn helicoid won´t realese after resting inside of gasoline, neither after heating it up , so ...i have to come out with new ideas

[visualopsins]

Tap tap tap...to free the jammed metal surfaces. slap it onto a hard flat surface. try sharp taps around the perimeter. use a tool to tap in direction of thread separation. drill some holes for more grip. But before all that have you tried using two strap wrenches?

[kiddo]

I guess , I've used all the options available with no result, unfortunately.

[Vercingetorix]

I would try an ultrasonic cleaner.

[DConvert]

[kiddo]

[visualopsins]

"on a hiding to nothing" I had to llok that up! LOL

https://www.phrases.org.uk/meanings/on-a-hiding-to-nothing.html

[kiddo]

no dents, neither deformation , so ´´hiding to nothing´´ still applying lol

[Lloydy]

I spent many years as a Maintainence Fitter in the sewage treatment industry and seized pipe threads were an everyday problem. One of the tricks I used was to use a big heavy duty clamp and move it around the pipe joint and use enough pressure to distort the pipe joint slightly oval, and keep moving the clamp radially around the joint. The trick is to not permanently distort the pipe joint, just ovalize it enough that it springs back to round.
I would try a small woodworkers F clamp with plastic covered jaw faces, and just 'massage' the helicoid oval and let it spring back, and keep rotating it.

Start VERY LIGHTLY, it should move the two parts. I was using a bloody big clamp and forcing it tight with a length of pipe on the handle, it was brutal - but it worked in places I couldn't use a welding torch or a a BFH ( Big f*****g Hammer ) to achieve the same results. The method works, it's introducing movement into the seized thread.