gc111

 

Technical Note gc111

Arthur Rosenfelder Roseoptics.com

Disassembling the focus shaft on a black Leitz Dialux 1.

If you notice when you remove the screw from the fine focus knob, there are hidden threads behind it (screw). I don't recall the thread size right now, but I think it is 6 mm. Yes, those threads are there to use as a jack screw. Unfortunately, without some preparation being done to the screw that you are using, you will probably "bugger" up the focus shaft and you won't be able to get that knob back on and also the threads for the cover screw will be damaged.  I build those jack screws by using a quality hex head screw about an inch long with a divot counter drilled into the tip using a lathe to keep everything centered, then a ball bearing silver soldered into that divot. That way the (lubricated) ball bearing rides and pushes against the shaft and hopefully, does not cause damage while the knob is being jacked outward. Another way uses the depth of the hole in the focus shaft. I use progressively longer lengths of piano wire and use an Allen screw, again this time with a hole drilled into the tip to accept the other end of the wire. If the length is too long, you won't be able to start the threads with the screw. In this manner, the wire pushes against the inside of the threaded hole at the bottom of the threads and pushes the knob off. With either type of puller, there is always a chance of causing damage. Make sure the ball and threads are lubricated so that you don't strip the threads if the knobs are very tight. Many of those older Leitz scopes have never had those knobs removed for maintenance and may be quite tight. Let me know if you really need a set of those tools and I could make a set.