The escapement works – it’s alive! The escapement has been installed and the lifting arms trimmed to the correct length. According to the books we’ve read the pendulum should swing 3 degrees (each way), but nowhere does it say what positions the arms should be lifted to before the pendulum reaches them and how much further they should be moved by the pendulum. The more they are lifted by the pendulum the more energy the pendulum will lose on the upswing and so the less of a push, relatively, will be given to the pendulum on the downswing. This was a simple bit of trial and error, positioning our temporary pendulum manually (the arch pattern was helpful for holding the pendulum, see the pictures below) and seeing where the arm rests on the block and how much the block moves with the rest of the swing. The result we were happy with was lifting the arms to a position reached with the pendulum at 2.5 degrees. This let the arm of the escapement sit about about a third of the way on to the block. When the pendulum pushes the arm the rest of the way to 3 degrees it moves the block enough to unlock the escape wheel with a reasonable looking clearance.
I have uploaded two videos to YouTube showing the escapement in action. In the first video the clock would only run for 5-10 minutes at a time. In the second, after all the new parts had bedded in a little it will run for hours. The blocks you see next to the bracket are in place of the banking pins, which haven’t been made yet. There is a extra collar on the pin at the bottom of the left arm because the arm needs a slight tweak to it’s angle. The pendulum is temporary and too short, so the clock is running faster than it should.
It’s been a while since my last post about the turret clock restoration project, not least because there wasn’t a lot of progress over the winter. For a long time we were struggling to work out how the double three-legged gravity escapement itself was constructed. Unfortunately, several offers of help with this didn’t come through but we have managed to work something out that that fits the brief. As always there are a number of ways something like this could be done, but we wanted to replicate the original. Visually we have done that so we must be pretty close, but we don’t know how close.
The method we used was to turn down a hexagonal bar to make the arbour, leaving a short hexagonal section on which to mount the two escape wheels. The hexagonal mount gives the wheels good solid attachment to the arbour preventing any rotation as they hit on to the blocks and stop moving. We can see no way that they could have been pinned to a round arbour and we didn’t think silver soldering them would be sufficient due to the repeated blows they must endure. A small section of brass tube fits over the hexagonal section between the two wheels to keep them the correct distance apart. The three lifting pins are installed between the two wheels in simple holes straight through. A boss fits on either side to sandwich the wheels and tube together and keep then in place, as well as covering the pin holes to keep the pins in. The bosses could be pinned to the arbour, but they don’t appear to be on the original. The arbour isn’t a large diameter and the bosses don’t have a lot of depth to take a pin. As they only need to hold the parts of the escape wheel together, they don’t take any force, we decided to silver solder them on to the arbour. Overall we think our construction technique must be pretty close to that used on the original, but it’s hard to inspect this part on a working clock – our reference clock is viewed from eight feet up a ladder, with the escapement at the back and everything is moving.