Got a late start today so not much done.
You might remember that I messed up the escapement gear. The sharp tips of the teeth were very fragile and I broke a few out on the tip and back edges. I made a replacement today and found a good cutting technique that preserves the tips of the teeth and I also used a close to zero blade clearance auxiliary table for my scroll saw which maybe helped too.
Improved Cutting Technique
Instead of cutting fragile tooth tips close to the pattern line I angled the entrance and exit cuts away from the tooth tips as shown in the photo below A good reason to leave some extra wood outside the pattern. This worked very well and no teeth were damaged this time.
After the completing the replacement escapement gear I wanted to sand it to perfect round and thereby also get rid of the excess tip material. When cutting gears it is a good idea to leave the pattern lines on the very tip to leave a sanding target.
To get accurate sanding, A sanding circle jig was made for my disc sander. If I didn’t have a disk sander I would have used it on my lathe disk sander. The jig is simply a couple of pieces of plywood with the top two pieces cut at an angle of 15deg. on one edge and then glued to the ply base to form a dovetail slot.
A sliding piece was cut at the same angle on each side to fit the dovetail slot and holes are drilled in the slider the same diameter as the holes drilled in the gear center. The drill bit is used as an axel to keep the gear running accurately. It took about 15 minutes to make.
It’s just to mount the gear, shove it into the sanding disk until you just sand away the pattern line on one tooth, then the slider is clamped as shown and the gear is revolved by hand until all the teeth are sanded. Very simple and effective. photo below
A test to Confirm Smooth Running
After sanding the idler and minute gears I mounted them temporarily to a board to see if they would run smoothly. This was a worthwhile test. I could feel a little drag in a couple of places so I marked with a pencil where it was binding and then filed down those areas.Very little filing was necessary to eliminate the drag. I don’t know if this is normal practice, but I thought it was a good idea Photo below
That’s it for today. Have a nice weekend and thanks for reading.
-- Mike, an American living in Norway.