Chapter 9: The EscapementOctober 9th - November 20th, 2005
This chapter covers the making of the escapement anchor (with its collet and arbor), the back cock assembly, suspension spring, and crutch.
These are pictures of the escapement anchor. You can see most of my original layout lines in the rough version. The anchor was sawn out of 3/16" tool steel sheet by hand using a jeweler's saw (the same as the click on the great wheel). After sawing out the click, I wasn't looking forward to it... but it actually went faster than I expected. Even so, I probably broke a dozen saw blades. The finished version has had the pallets hardened and the collet mounted. One problem with my anchor is that one of the screw holes is slightly off. I've managed to get it mounted on the collet anyways (by enlarging the hole in the collet), but it's a bit of a hack. If it turns out to be necessary, I'll make a new collet for it.
The back cock assembly consists of the cock itself, two small pillars to hold it off from the back plate, the pendulum support post, and an adjustable eccentric bushing which can be used to adjust the anchor-to-escape-wheel center distance. I thought that was a great idea, and I'm going to have to recycle it in my future projects. The slot in the pendulum support block was made with a .006" slitting saw (which looks like a tiny tablesaw blade if you've never seen one). I'd never used one before, so it was an interesting experience. It must be used at very low RPMs, and I cut it carefully on the milling machine in an attempt at accuracy. But you can see from the picture that the slot is not straight - the blade flexed as I cut it. I'm hoping it will be close enough, but otherwise I'll end up making a new block. This was also my first attempt at making a rivet, and I learned that many weak hammer blows are far more effective than a few strong ones.
Wow, it's really striking how well the thin lacquer has preserved the shiny finish on the decorative washers for the pillars, which I made over a year ago. Especially in contrast to the back cock, sawn out of plate only a couple of months ago!
The crutch is the lever that transfers the motion of the pendulum to the escapement to regulate the speed of the clock, and also transfers energy from the gear train and escapement to the pendulum so that it doesn't stop swinging. It consists of a steel body (cut from mild steel sheet) with a riveted pin on one end which engages with a slot in the pendulum suspension top block. It's mounted onto the escape wheel arbor using a brass collet on the larger end, which includes a set screw used for adjustment when putting the clock "in beat". Getting all of the curves and angles to look right on the crutch body was a little tricky and took a lot of work with the files, but I think it turned out reasonably well. It's still a little uneven, but I had the impression that I could have filed it it down to nothing before it was perfect. I also forgot to file and polish the outside of my steel stock when machining the crutch pin, and so you can see that the very edge of the flange is a darker color. It's not too noticeable on the final crutch assembly. Here are pictures of the crutch body, the crutch pin, and the finished crutch assembly (with brass collet & set screw installed).
The pendulum will be suspended by the top block and suspension spring. It will hang off the steel pin at the lower end of the top block (in the picture below), while the suspension spring is riveted to the upper end. The top end of the suspension spring is riveted into a folded piece of thin brass. The whole thing then slips into the slot on the support block, which holds it at the appropriate height for the crutch pin to engage the slot in the top block. The spring is made out of blue tempered steel shim stock (originally for making reeds for my concertina project, but efficiently repurposed here). To the left you can see the whole suspension system assembled and in place. The top block moves the crutch back and forth easily, and if you set it swinging, it will go for a surprisingly long time on its own. Next up is the pendulum, and then I can find out of this thing is actually going to run!
Here are a couple more pictures of the assembled clock in its current state. These were taken before the crutch and pendulum suspension were finished, but are otherwise current. Seeing it all put together like this gives me a nice sense of satisfaction. I've come a long way! It would sure be nice to know if it was going to run, though...