'Converting' a thread

I have some 1970's Russian microscope objective lenses that I want to use in my 1940s English-made microscope. I feel the quality of the Russian optics is a little better and the lenses are much larger diameter and let more light through.

The threads on the two tubes have the same outside diameter but unfortunately the English one is a 0.7mm pitch whereas the Russian one is a 1.0mm.

I ' think' there are two ways I could modify the Russian tube to make it fit.

(a) I could fill the thread with a hard solder and re-cut the new thread straight into the old one.

(b) Another way could be to machine back the Russian thread, glue/solder on a sleeve and recut that with the required 0.7 pitch.

I 'think' (b) sounds more sensible. Would you agree, or do you have any better suggestions ?

Since there is no real loading or stress on these thread why not 'overcut' the Russian thread with the 0.7 (32tpi?) you want?

I know this will offend many people here but is a practical and simple solution. Yes not all parst of all threads will be in engagement but there will be more than enough to ensure alignment of the optics

Ian P

The heat required to undertake the soldering process will cause distortion. You could consider removing the existing thread and fitting a sleeve to take the new thread, or possibly with the thread already cut/produced. The main body could be placed in a domestic freezer to cause it to shrink and the sleeve heated in a domestic oven to cause it to expand. The two part are then assembled producing a shrink fit. I appreciate that this still uses heat but the heating is far more uniform than with soldering and the temperature required is far less.

I would be inclined to use Loctite for any 'glueing' duties.

Tony

Assuming the top is the English one, and the other the Russian, are the focal planes the same? The threads seem to be in different positions along the tube as well as being of different pitch, or is there something I am missing?

As it stands, can't you simply machine off the Russian thread and cut a new English thread in the correct place for the English microscope, which seems to correspond to some solid material on the Russian tube.

Thanks all.

Ian, yes I wondered about trying this after seeing multiple threads on one bolt on a Youtube vid some time ago. My "feeling" is it wont go too well on a smaller scale with burrs etc.... BUT ....I have nothing to loose as I can skim back later if needed. I might even learn something in the process. If it fails, I'll glue on a sleeve as Tony suggests.

Peter, I did wonder about the actual positioning of the lenses relative to the thread. But I played about and it didn't seem to make a difference, as least as far as the focusing was concerned. Perhaps field of view or fringes might be worse. I'll admit to not really understanding optics. Let me get the thing properly screwed in and see how it works and re-thread in a different position as required.

Gerry

There is some useful information at

Understanding Microscopes and Objectives | Edmund Optics

It implies that the distance from the object to the real image plane of the microscope is very standardised. May not be true of prewar Russian units, but looking at your two samples I would suggest that they are designed (optically) to be very similar. The only difference being the mechanical design of the focus mechanism.

I suspect that you will end up repositioning the thread in order to get the objective to focus.

Edited By Peter Cook 6 on 20/02/2021 14:22:44

DEFINITELY NO heating!

Some of the lenses may be compounds and the heat will destroy /discolour the balsam between the elements..

IF the Russian objective is the lower one, could ,you machine off the thread (to clear the female thread in the microscope ) and then machine and cut the 32 tpi thread in the same position as the upper English one?

This assumes that there is sufficient metal wall thickness to do this.

Howard

On Howard’s theme, are you sure the thread is not imperial 36tpi?

Edited By not done it yet on 20/02/2021 18:33:15