Pocket Watch Winding Stem

The first stem attempt for the pocket watch was handmade and it wasn't easy to do. It also didn't work very well. So I decided to use the CNC machine to make the next stem. Starting with 2.5mm silver steel rod (2.5mm is the largest dimension of the spindle) the machine gradually turns the profile of the spindle using a 0.2mm D bit.

The setup is able to machine to less than 0.1mm, but the initial attempt failed to give a good profile due to flex of the rod when the tool lowered in for a cut. After adding a wooden block under the rod and running the machine again, a good profile was machined.

The broken stem is on the left, the new one on the right.

The dimensions aren't absolutely correct, but it did work, after the sloping edge was added by hand. The square profile was also added by hand but was filed too small and eventually the corners were rounded off and the stem stopped being able to wind the spring.

I'm going to do a third attempt, with better dimensions and the second slope machined rather than done by hand.

The G code for the machining was done using a custom Tcl script that reads a DXF profile and outputs X-A axis G code to machine the same profile around a cylinder. This can't do the square end, but I'm going to create a new program for square pegs. That will be run as a second stage of machining after the main profile. Creating these scripts as separate tools should hopefully make them more reusable in the future.