Today I made the click spring, the mainspring hook on the great wheel arbor, and the hook on the barrel. I also installed the mainspring in the barrel.

While it's a temptation to use a small spring from an old movement for the click spring, I prefer to make as many parts as I can, and it's fairly easy to make springs. The material is 0.010" music wire. The material is wound on an arbor made from rod about 3/32" in diameter. In the end of the rod I used a jewelers saw to cut a slit, whose purpose it is to hold one end of the wire as it's being wound. The rod is put in the chuck of the Unimat, whose drive belt has been unhooked, since this is a hand job. One end of the spring wire is slipped into the slot in the end of the winding arbor, then the drive pulley of the lathe is turned with one hand, winding the spring along the arbor. It is important to keep the spring wire tight and wound closely on the winding arbor. When the spring is wound, it can be slipped off the winding arbor, cut to length, stretched out if desired, and coils at both ends can be carefully bent out into loops.

The click is drilled with a 0.022" hole to hold one end of the spring. The other is held by a small post. The post is made on the watchmakers lathe using a graver, and slipped into a hole in the frame. If the post and the hole are a close fit, no other fastening is necessary. This will permit removing the post at a later time when the frames are given the final polish.

The hook (post) on the greatwheel arbor which holds the inside loop of the mainspring is also made on the watchmakers lathe. It has a long tang on it, which will go through a hole drilled in the arbor. It is riveted (mushroomed) on the opposite side of the arbor, which holds it tightly in place. The mushroom is expanded in a countersink in the hole.

The post which hold the outer end of the mainspring is made similarly. The tang of the post goes through a hole in the barrel tubing, which is then mushroomed (by small peening taps with a hammer) in a countersink in the outside of the barrel. All familiar stuff to clockmakers.

The mainspring (as bought) has a loop end. This must be broken off, and then the end is annealed and punched with a new hole. More stuff familiar to clockmakers.

The mainspring is 1/2" wide, .014" in thickness, and 86" long. Rather a long spring, but the greatwheel of this clock turns 9 times in the course of a weeks' run, so it must be rather long to provide power. There is also plenty of extra room inside the barrel, so that either a longer, thicker (or both) mainspring can be used if the clock requires that.

The length of the spring would also permit the use of a Geneva works (stop works, or winding limiter) if that would at a later time prove useful.

The greatwheel assembly -- the "powerhouse" -- is now finished.

Today's links:

Arbor hook
Great arbor with hook.
Spring in winding arbor.
Click spring.
Click and spring.