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Dead beat escapement problem


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I'm building a clock with woden gears and have set up the escapemant with which I'm having some problems. The clock is pendulum driven and the mechanism is driven through a chain wheel. I have been testing the escapemant without the gear assembly to eliminate any issues from that.

I've used the design provided in Brittens Watch and Clock Handbook for the Dead beat escapement with 30 teeth on the wheel. The pallet is solid and made from steel whilst the wheel is made from aircraft grade aluminium. (I tried making it from brass but the teeth profiles were poor). They are both CNC machined and are to a good tolerance. However, the pallet, when manufactured initially had a small amount of asymettry and this was corrected by grinding one of the locking faces. As a consequence one of the inpulse faces is slightly narrower than the other.

The bearings supporting the shaft were initailly plain PTFE bearings but in order to reduce friction I changed them to knife edge bearings with with the edge of the knife on the centreline of the shaft. This the nreplicates exactly the rotatin of the shaft. The knife edge sits in a 3D printed fitting and i can adjust the distance between the wheel and pallet shaft by printing different fittings.

The pendulum bob weighs about 110grams and is supported by a 2.5 mm steel rod via a pendulum spring to the pallet shaft.

For testing I have wound a piece of string around the second/escapement wheel shaft with a small weight on it. The weight is 6gr on a 6mm shaft.

If I swing the pendulum and release the weight wrapped round the shaft all goes well. There is good engagement of the lock faces and the tik/tok sounds balanced. However, with time, the amount of lock decreases and themechanism stops.

I have varied the seperation of the two shafts and the size of the weight driving the second wheel with little effect. 

I'll post some images when i've worked out how to do it.

Any help would be appreciated.

 

 

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IMG_1560 

This shows the Knife edge bearing and the lower impulse face narrower than the upper.

IMG_1557

View of escapement and pendulum arrangement.

IMG_1558

This shows the knife edge in it's fitting.

A point i forgot to mention earlier. 

It seems the pendulem is not getting enough energy from the escapemant so i increased the weight driving the wheel but this only seems to have the effect of making the movement clunky. The wheel rotaes faster and the pallets don't have time for the locking faces to enter properly.

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Hi Bob,

The first I have to say is that You missunderstand the aim of escapement parts. If the pendulim is suspended on knife bearings, why in the world is that suspension spring there??? The suspension spring is needed to avoid friction in pendulum suspension. But the engagement between pendulum and palet MUST be hard, not via spring!!!

If You ask me, this type of pendulum suspension will last no long, as the knifes will cut easy in the printed bearings... Make the bearings of steel an harden them, also harden the knifes too. Throw away the spring and replace it by rigid piece... Or, do everything as it is in the traditional design!

The pallet must be hardened and polished, and the wheel must be of brass. Oil mus be aplied on impulse surfaces. The CNC mashine doesn't work good with brass? Then throw it away, the files are invented lond ago...

By photos only, I can't say if the escapement parts are in correct colaborration. Make a video and show it!

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