Still more fine work on the detent blade. This time, I joined the detent blade to the jeweled barrel, jeweled the barrel, made a post for the assembly to ride on, and made a passing spring.
I soldered the jeweled barrel to the detent blade with Tix solder, which is a very hard soft solder which melts at low temperatures. The detent blade has been heat-blued, so I carefully filed away some of this bluing on the very end of the blade where it's to be soldered. I also used a little zinc chloride flux.
The trick in soldering such small things is to use only the minimum amount of solder, since any excess must be removed. I don't object to using soft solder, but I don't like to see it.
When the barrel was soldered to the blade, I used the Seitz jewel press to press the jewels into the barrel. The jewels have a 3 mm OD with a .90 mm hole through.
Next, I made a pivot post on the escapement pivot blocks. The pivot post is made from a needle, which is just a thousandth or so undersize the .90 mm hole in the jewels in the barrel. (The point and eye part of the needle can be easily ground off.)
I set the post by drilling a hole in the pivot block which is a few thousandths undersize the needle. Then I reamed it to a slight taper with a clockmakers broach. I tapered the end of the needle a bit with a diamond file, while turning it with a WW collet in the watchmakers lathe.
Then it's tapped into place, and the bottom ground smooth, where the bottom of the needle comes through the bottom of the block. Had this failed, I would have used Loctite to secure it.
The jeweled barrel will actually rest on a little bushing impaled on the needle. A convenient bushing is a bronze clock bushing with a .90 mm hole.
The "horn" of the detent blade is bent at about a 45-degree angle from the blade. It's exact place is determined by setting the escapement on the actual horizontal plate of the clock where it will reside. A tooth of the escape wheel is placed on its proper spot on the detent jewel and the horn is bent until it's in the right place in relation to the balance arbor. At this time, I also measured the distance between the horn and the balance arbor -- this measurement I'll use later to determine the size of the unlocking pallet.
The L-shaped part of the detent blade is bent so that it sits at a right angle to the detent blade. The passing spring rests on the inside edge of the L-shaped piece.
The passing spring slips through a hole in a small post, which is attached to the detent blade. I made the post from 1/16" brass rod. First, I drilled a .015" hole through the rod in a drill press. (Bits this size can be had from any tool supply house.) Then I chucked it in a 1/16" collet in the Taig lathe and machined a waist in the brass between its base and the hole in order to make it as light as possible. I used a triangular bit for this purpose.
Then I reversed the brass in the lathe and cut a .040" diameter spigot on one end. The spigot will serve to rivet the post to the detent blade. Then I cut off the post from the mother brass and rounded the end with the hole. I left this part a bit long, since it will be used to impart heat to the post when the detent spring is later "glued" in the .015" hole with watchmakers shellac.
The post is .260" long, measured from the base of the post to the .015" hole. This is the same distance as the end of the horn is from the blade, measured at a right angle. This makes the passing spring run parallel to the detent blade. That's why I wanted to bend the horn to its proper place before making this post.
It's difficult to hold a small part like this post while it's being riveted. To make it easier, I drilled a 1/16" hole in a bench block and upended the post in the hole. This provided a steady base for the post while it's being riveted with small taps with a small hammer. I made a few taps, just enough to set the post in the hole. Then I put a drill bit in the hole in the post and turned it so that the hole is parallel to the detent blade. When it's parallel, I set the post securely with a few more taps.
I hold the passing spring in the hole in the post with watchmakers shellac because the passing spring can be easily adjusted by warming the "glue", when the escapement is being set up to run at a later time. It's also quite secure stuff.
The passing spring is made from .007" thick music wire.
The detent blade is finished. It's extremely light, since the jeweled barrel is virutally hollow, with thin walls. The blade itself is light, as is the passing spring assembly. Good work, I think. Seeing this is one of the pleasures of doing this sort of work.
Todays links:
Seitz tool 1 Seitz tool 2 Pivot post with bushing Escapement assembly on clock plate Cutting the passing spring post Post with drill Post with perspective Post in bench block hole Aligning post hole Riveting post Detent blade done 1 Detent blade done 2 Passing spring and horn Detent blade drawing, GIF