More delicate work on the escapement's detent blade. This time, I'll make a mounting for the detent jewel, which fastens the jewel to the detent blade.

The jewel is a pallet jewel intended for Brocot escapement clocks. These jewels are sized by the equivalent size of numbered drills, and this one is a #51, or .067" in diameter. The bottom part is a cylinder, with the rest of it a half-cylinder. Ideal, actually, for a detent jewel for a clock-sized detent escapment.

The mounting for the jewel is a cup made of brass. I began it by putting a piece of 1/8" brass in a WW collet in the Taig lathe. I drilled a number 53 hole in it, which is 2 sizes under the size of the jewel -- the hole should be no deeper than the cylindrical part of the jewel is long, or about a tenth of an inch. Then I re-drilled it with a #52 drill, which is one size under jewel size. At this point, I tried the jewel in the hole, and found it to be a perfect fit. The #52 drill drills a little oversize, so it worked out beautifully.

Then I removed the brass from the lathe, and sawed the cup from the mother material, leaving a little which will form the tang of the cup. I then reversed the cup in the lathe, with the hole just drilled inside the WW collet, and cut the tang.

This tang is made to the size of the hole in the fold on the detent blade -- only about .044". Care must be taken not to cut the tang too close to the bottom of the jewel hole, or one can break through and spoil the part. Since the tang will be riveted in place, it must be cut to a close fit to the hole in the fold on the detent blade.

When the tang is cut, I reversed the cup once again, chucking the tang in a WW collet. Then I thinned the 1/8" brass cylinder until the cylinder wall is only about .012" thick around the jewel hole. This is tiny work, and one must use a sharp tool and make small cuts.

Then I shortened the tang so that it is only slightly longer than the fold on the detent blade is thick -- about .012" thick. I riveted it in place by setting the top of the cup on a bench block, then making small taps on the tang with a small hammer. The result is a very solid connection.

The jewel can be rotated so that the plane on it can be properly oriented to the escape wheel tooth, when the escapement is set up. It will fixed in place with watchmakers shellac.

Today's links:

Machining cup mounting
Jewel and cup mounting
Jewel and cup mounting 2
Riveted tang on cup bottom
Mounting complete