Only a few parts remain to make to finish the escapement. One of them is a detent spring. I had originally intended to use an alarm clock balance spring for the detent spring, but I thought of an easier way to make the spring. I made a small block with a .013" hole in one end for the spring, a .033" hole in the other end to mount it to the needle which is the post for the detent blade and its jeweled barrel, and a transverse tapped hole in the end for a 0-80 set screw. The spring itself is a piece of .007" music wire, held in the .013" hole with my favorite watchmakers shellac. The assembly can be rotated a bit to increase or decrease the tension of the spring against the detent blade. The adjustment is important, since too little tension will result in unreliable return of the detent blade against the banking, while too much wastes escapement energy -- the balance must press against this spring to unlock the detent, and any energy used to do this is lost when the detent blade snaps back against the banking block.
Another piece to make is the banking stop. This functions to stop the detent blade when it moves back to rest after unlocking the escape wheel . Banking must be adjustable, since it controls the amount of the escape wheel tooth that will fall on the detent jewel. There should be enough lock to ensure that the detent won't bounce out, but not so much that the blade must move a lot to unlock the escape wheel. Too much movement also wastes escapement energy.
The banking stop is a simple angular piece of brass, with two 0-80 screws which mount it to the escapement base plate, and a long, stainless steel 0-80 set screw which will adjust the lock. I milled it from 1/8" brass, milled to an L-shape with an end mill. I drilled the holes with a drill press, after first "clamping" it with Super glue to the escapement base plate in the proper place. You drill the small holes first (those for a 0-80 tap), then oversize the holes in the L-shape for the outside diameter of the 0-80 screws after the piece is unglued. The long, stainless steel screw which serves as the stop will eventually be secured with a lock nut.
I also made the unlocking table. This part holds the jewel which will press against the detent blade to unlock the escape wheel. It is a simple lathe job, with a .033 hole drilled through for the steel pins on the balance shaft, a cross-hole drilled and tapped for another 0-80 set screw, and a hole for the unlocking jewel, which is another Brocot escapement jewel. The jewel is held in place with Loctite, the flat part of the jewel being on a line with the center hole in the unlocking table.
To finish off the escapement, I decided to "snail" ( also called "spotting" or "damascening") the escapement base plate, just for looks.
To do this, I mounted a piece of aluminum angle in the big vise on the big mill, and used a flycutter to flatten the top of it. Then I "glued" the escapement base plate on it with watchmakers shellac.
The snailing itself was done with rubberized abrasive (Cratex) with the abrasive cylinder screwed directly in the mill's drill chuck. I moved the mill's x-axis crank one turn for each row of the snailing ( on my mill, 1/8"). I brought down the mill spindle and made a spot, then turned the y-axis one turn, and made another spot, continuing until a row is finished with spots. Then I turned the mill x-axis another turn to begin a new row, and repeated until the piece is finished. The effect is gratifying.
The piece to be snailed must be pretty well finished before the process is undertaken. The process will not cover finishing sins.
Todays links:
Detent spring block Banking block Unlocking table and jewel Escapement done Machining the snailing mount Mount on mill for snailing Base plate snailed Pretty escapement