I patterned the escapement for this clock after the detent escapement found in a Hamilton chronometer of WWII vintage. An interesting feature of this escapement is the micrometer adjustment which permits delicate adjustment of the detent blade. Moving the blade equalizes the clearances between the two proximate teeth of the escape wheel and the roller by moving the detent jewel a bit. I made a similar adjustment for this clock.
The pivoted detent is mounted on a moveable block. It has an elongated hole which permits sliding the block forward and back, a pin which holds it steady during adjustments, and a locking screw which locks it in place when adjustments are finished. The micrometer adjustment screw screws into a fixed block, and it has a collar which fits into a vertical slot on the movable block, so that the movable block moves when the screw is turned.
The fixed block is mounted to the escapement plate by a vertical screw and another steady pin. It has a hole for the other steady pin which fits in the elongated hole on the movable block, a threaded hole for the locking screw and another hole for the micrometer adjustment screw.
Both blocks are made from the same piece of 1/8" brass. I began by using a long piece of brass which I dressed to make its sides parallel. I clamped this in the vice on the big Enco milling machine and machined a 1/16" slot about a half inch long using a 1/16" end mill. Then, I used the same end mill to make a 1/16" hole a couple inches away in the same piece of brass; I did this by moving only the long axis of the mill. This makes the simple hole on the same line as the elongated hole, and they are also parallel to the jaws of the mill vice.
Then I removed the brass from the mill vice, inserted two 1/16" pins in the two 1/6" holes (both simple and elongated holes) and remounted the brass in the vice. This time, I clamped the brass at a right angle to its previous position, by resting the two 1/16" pins on the vice jaws. This aligns the piece to the top of the vice.
Next I used an end mill (a fly cutter would have worked as well) to shave a bit off the top of this mother block. Then I flipped it over and repeated the operation on the bottom of the piece. The result is a brass block whose sides are parallel to each other and to the sides of the elongated hole, with the simple hole exactly in line with the elongated one.
Then I re-clamped the brass block, but extended the block so that the end of the block with the elongated hole hangs exposed from one end of the mill vise. This permits milling an indentation on that end. The bottom of this indentation will eventually hold the pin which acts as the detent pivot.
Next I cut the brass block in two. The part with the simple hole will become the fixed mounting block, the other part -- the part with the elongated hole -- will become the movable block.
Then I used a machinists square to vertically clamp the moveable block in the mill vice and cut the slot for the micrometer screw collar. I cut it with a .012" slitting saw, which makes a slot which is too narrow, so I raised the vertical axis of the mill a bit and made another pass or so, until the slot is about .040" wide.
The blocks can now put temporarily put together by inserting a pin through the hole in the fixed block and the slot in the moveable block. With the blocks perfectly aligned, I drilled and tapped a hole in the fixed block for the 0-80 locking screw, using the slot in the movable block as a guide, being sure that the screw was placed so that the movable block can move about 3/16".
Next, I made the escapement plate from 1/16" thick brass. I drilled a 1/16" hole in it to mount the fixed block on it. The hole is countersunk on the bottom to hide a flat head screw head.
Then I drilled the bottom of the fixed block with the holes necessary to mount it to the escapement plate. One hole is drilled and tapped for the 0-80 flathead screw, which used to screw the fixed block to the escapement plate, and further "clamped" it to the escapement plate with Super Glue.
Next, I drilled a shallow 1/16" hole through the escapement plate and a bit on into the bottom of the fixed block. This hole will hold a steady pin so that the fixed block has a two-point mounting. I used a steady pin instead of a second screw because a long hole would interfere with the micrometer screw hole, which is directly overhead.
Then, I trimmed both blocks to their proper length, and drilled and tapped a 2 mm. hole in the end of the fixed block to hold the micrometer screw.
The micrometer screw is made from 3/16" mild steel. First, I turned the 2 mm part (which will be threaded), then I cut the shoulder which fits into the notch in the movable block. At this point, I removed the incipient screw from the lathe, cut the threads and tested it in the blocks. This makes it possible to close-fit the shoulder to the notch in the moveable block, and to see that the head of the screw is tight against the edge of the moveable block, in front of the notch. Had I needed to trim a bit from the screw, I could have put it back in the lathe for trimming.
Then I polished and parted off the screw. I cut the screwdriver slot in the head by hand, with a jewelers saw, then heat blued the screw with a heat gun. The results are very good -- the micrometer adjustment screws easily, with not a wobble anywhere in the blocks. A good week's work!
Today's links:
Milling the slot
Aligning mother block with pins
Milling edges
Cutting notch for detent pivot pin
Mother block
Sawing notch, movable block
Moveable block almost done
Blocks together
Mounting hole in fixed block
Drilling escapement plate
Escapement plate bottom
Escapement plate drilled
Cutting micrometer screw
Fitting micrometer screw
Micrometer screw
Screw in notch
Blocks, side
Blocks, end
Blocks, top
Blocks 1, GIF drawing
Blocks 2, GIF drawing
Escapement drawing, GIF