We switched from using the lathe headstock and motor to turning between centres using the hand lathe so that the whole winding stem remained concentric. The problem with using the motor entirely is that when you need to turn down the section of bar being held in the collet, you have to remove the bar from the collet. When its put back in, it doesn’t turn from the same central point.
Concentricity is important with a winding stem as there are a number components that interact with the stem to enable winding the watch and setting the hands/date. Turning between centres eliminates this problem as the bar is held by a point at each end, this allows it to be removed as often as necessary without loosing concentricity.
Turning by hand also provides a better turned finish, you have a much greater control of the turning speed using the hand wheel compared to the motors preset speeds. However, the headstock and collet still need to be used to initially create the points at each end of the bar and also to hold the stem when using a die to thread the end.
So on to the blanks, this time we made something even closer to a functioning stem with a small pivot at the front and a screw thread atthe opposite end. The diameters were much smaller this time and all we were missing was a square, a slot and a burnished pivot. The screw thread was created using a die that was twisted onto the bar which was being held in a collet. Plenty of oil and regularly turning the die backwards to clear the cutting teeth is vital to getting a nicely formed thread.
I made two of these blanks and we introduced a new process with the second one, hardening the steel which will make the stem harder wearing. This process involves wrapping the bar in wire and heating it until it glows cherry red. The still red hot bar is then plunged into salt water (brine), this process is called quenching. The hardening process hardens the steel but also leaves the steel very brittle. Another process called tempering needs to be carried out to toughen it up again, I will talk about this more in my next instalment.
With these last two blanks completed the next exercise would be to make a complete functioning stem. I was really looking forward to putting the skills I had learnt over the past couple of weeks to the test, all in one finished piece of work.
The course was definitely getting more challenging by the day with every new challenge getting smaller. I could see my skills rapidly developing though and anything was beginning to seem possible.