WATCH CASE THREAD CUTTING

   The need to chase threads on a watch case or any other item can be a challenging proposition. Most instrument lathes have little or no thread cutting appliances, and if they do, the limitations become apparent immediatly. I needed a simple and accurate piece of tooling to achieve this and my attention was drawn to a memory of a sort of thread-follower set-up I had seen in an old engraving. I set to work developing this attachment to fit the Derbyshire 10mm Elect. This tool took roughly fifteen hours to complete.

   A brief description of the tool is as follows. A bushed carrier is mounted to the lathe bed behind the headstock. In the carrier, a ground rod is able to slide with great ease and precision. On the far end of the rod is mounted a slide with a tool post, in the tool post, a hardened and ground thread follower is mounted. This follower rides against a threaded die that has been mounted on the headstock spindle. On the other end of the rod is the cutter arm. As the whole assembly is rocked forward, the follower picks up the threaded die and carries the rod with the cutter towards the headstock, creating an identical pitch thread on the work. As the follower slide is withdrawn, a deeper cut is made, this is the tool in-feed.

   The beauty of this attachment is in the threading dies, any pitch can be made, and the die is made very quickly on a good toolroom lathe. The other advantage is the speed of set-up for any given piece of work. I have made dies with 80tpi that will reproduce very nice threads such as those found on camera lenses.
   The piece being made is a giant 22 size wristwatch case. I will be posting more on this watch again.