Focus tension on old Zeiss microscope.

[pe...@easthope.ca]

Hello,

The focus adjustment knob from a Zeiss surgical microscope is in the
photos here. I'd guess the scope was built in the 1950s or '60s.
http://easthope.ca/ZeissKnob1.jpg
http://easthope.ca/ZeissKnob2.jpg

The shorter setscrew here was in the knob when I began work on it. The
longer screw is one I made.
http://easthope.ca/ZeissSetscrew.jpg

The knob threads onto the focus adjustment spindle. The female thread
in the knob is visible in the photos.

Tightening the knob on the spindle increases tension on a clutch to
prevent the head of the scope from sliding out of focus.

Tightening the setscrew in the knob should lock it on the spindle to hold
the tension setting but the setscrew has no effect.

Obviously the setscrew would spoil the spindle thread by landing
directly on it. The setscrew must push on an intermediate part with a
thread matching the spindle. I don't understand why it doesn't work.
The longer setscrew is still too short?

Not an electronic problem but similar knobs were used on some vintage
high end electronic equipment.

Ideas?

Thanks, ... Peter E.

[Arie de Muijnck]

I have fixed items like that by inserting a small plastic plug between
screw and main thread. The plastic deforms without damaging the main
spindle thread, and securely clamps the spindle.

Arie

[pe...@easthope.ca]

In article <nnd$0893e6ee$093e5716@a5b2805ea737c182>, Arie de Muijnck <nor...@ademu.com> wrote:

> I have fixed items like that by inserting a small plastic plug between
> screw and main thread. The plastic deforms without damaging the main
> spindle thread, and securely clamps the spindle.

Thanks Arie. If I have to drill out whatever is blocking the setscrew
from having effect, a plastic plug is a good idea to avoid damaging
the thread on the spindle.

... P.