With our first major exam behind us it was time to move on to the next unit. With winding stems we learned to cut stems on the lathe. Mostly right angles and flat surfaces. Our next task would introduce large tapers. We were to make a balance tack. The balance tack had a large flat base with a hole drilled in it and a long tapered cone, which had to be straight of course.
Next, we made a barrel closer out of acrylic. They key here was to have extremely fine turning lines so it would appear transparent. – This would be key for the next major project which was pivot gauges. With pivot gauges the key is to hit exact dimensions with burnished pivot shapes. The pivot gauges are cut from hardened and tempered spring steel (blue). Overall tolerances for dimensions on the pivot gauge were mostly +/- 0.03mm, but the pivot (the most important part) was always +/- 0.005mm. The pivot had to be burnished hard and with a blemish free mirror finish. This exercise simulates manufacturing a pivot on an axle that would run in a watch. The burnishing was carried out on a Jacot Tool. The pivot diameters started at 0.30mm and got smaller each time until 0.10mm for a total of 21 pivot gauges, not including exams and mistakes.
During this time I was also working on a screw head polisher. This tool is essentially a vise with three legs in which you can insert a pin vise with a screw to polish the head. It was constructed of brass jaws, steel runners and a steel thread with which to open and close down the vise.
Next, Watches I