Hi dubbie,
Wow, you are my hero, an d a hero in the Euro zone as well, lucky me !
I will try and make as accurate and comprehensive a drawing as I can...
I can also send you the knob and the two bits of the broken collet (and nut) to help you out... since these are of no use to me anyway, as it is...
Indeed I am too equipped for mechanical stuff, other than fixing my car... not the same scale
I don't think we have to worry too much about the thread since we can just make a metric pitch, and I would just go buy a metric nut to go with it ! At least this part should be easy and cheap, I would think...
Problem is that what remains of the thread is soooo short (as you can see on the previous pictures), that it's hard to get a reliable/Accurate measurement. Normally to measure a thread pitch (since I don't have gauges, I measure 10 "turns" with my calipers, and divide by 10... this is usually accurate enough.
So here I could only measure only one turn, so precision is catastrophic. My best attempt would indicate it's about 0.8mm. Way more than 0.5 and less than 1.0mm, at any rate.
OD of the thread looks to be 4,8mm.... rings a bell, this must 3/16" , since everything in this collet appears to be imperial size...
The flat nut that goes on it, requires a 1/4" socket, at least this bit is for sure..
Will try and do as accurate a drawing as I can, today maybe, and post it here.
If you can give me your address via a private message, I would send you the knob and all the bits and nut from the old collet, in a padded envelope.
No worries about the delay... I have plenty other stuff in the lab (and else where) to keep me busy...
For once I really ought to resume work on the restoration of my old Tektronix 317 scope... it too, requires me to order a bunch of imperial size spanners and wrenches for me to be able to remove all the parts that need to be removed
Aluminium or brass... I think brass is the best. Less prone to cracking than aluminium I think.
I have an old Nixie tube Frequency counter, 10 years older than this Tek scope... all the knobs have brass collets and they didn't break when I took them on and off.. it just inspired more confidence, somehow...
I guess ideally a collet would be "hybrid" : have a brass "cone" to grab the shaft, but a steel thread to that it's strong despite being extremely thin because of it being hollow. Obviously that would be too much trouble/cost, so it gets made from a soft metal all the way... and the user just has to be really, reaaaally careful not to over tighten it... which is sooo easy to do unfortunately ! Maybe these collets should come with a tiny torque wrench like high-end RF connectors do.. so that you don't over tighten them...