So, after a few days of fooling around & doing a few home improvement projects (my wife has given me a long list!) I finally had another go at making the winding shaft. I forgot to mention that I have got only hunter cased versions of the Molnija pocket watch.
The winding shaft in this one also allows for the lid release mechanism. This prevents the use of the pocket watch stem in my wristwatch. I had to measure the existing winding shaft & modify the dimensions to correct this.
Anyway, this is how the stem was finally made:
First I made cones at the end of 3mm silver steel & turned it down till it was true. I also turned the end down to 1.35mm dia.
This along with a die 1.2mm X 0.25mm cuts the required thread for my crown. It took me two days of trial & error to find this out :-)
Here is how the threads look.
Next, I turned the entire shaft down to 1.2mm (the largest sectional dia.). This is where I went wrong last time. I cut the slot for the pull out piece first. When I tried turning the shaft down it snapped at this weakest point.
Next, I measured all the features, turned the dia of the square section area that will go through the castle wheel & Cut the slots. Only the pivot is left now.
The pivot area is too far away from the centres & the shaft is too weak by this point. So, it flexes when you try to turn the pivot down. This is why I trim the shaft, turn a new cone & then turn the pivot. here is the trimmed shaft.
This way, the pivot area is near the centre & with a little bit of care can be turned down to 0.4mm dia.
Finally, I made a parting cut & adjusted the length of the pivot in the claw runner.
This is what the finished shaft looks like.
Now all that remains to be done is to file the square section for the castle wheel. The shaft will be trimmed for a particular movement-movement ring-case assembly & only then hardened & tempered. Hope you enjoyed reading this. Aditya