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Experiments with pallets not dropping to lock


Boz
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I bought an old mantel clock as a practice piece. It might be based on a Smiths car clock movement, I'm not sure.

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These have the feature of having relatively soft plated pivots so there was plenty to get on with. It is scratched and rusty in parts so I'm not worried about experimenting on it. One notable issue was the escapement which did not drop to lock on the exit pallet. Whilst there is wear to the escapement wheel tips the entry pallet did lock so there was some uneveness there between entry and exit that might not entirely be due to wear of the tips of the teeth. The escapement safety functions and pivots are OK. I showed the movement to some friends at a local horological society and was advised that it looks like the pallets might have been moved. Given that is is a non functioning clock and I have another scrap ABEC platform to play with I thought I'd have a play

I made a little brass heatsink, and measured the pallet from the back of the fork

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I started gently heating the warmer until I could feel the shellac was soft, using a mini bunsen on yellow flame. I did put a fibreglass mat on the bench first for heat protection! First attempt and the pallet was not quite straight. I was aiming to increase the depth by 0.10 mm. I managed 0.08mm

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And gave it a try. Still not quite locking, but an improvement from fully impacting the impulse face to just meeting the end of it.

I repeated the process and pulled it out another 0.05mm

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Now it drops to lock at a depth similar to the entry pallet.

I set the banking pins to give approximately equal total lock.

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A quick clean and I popped it back in.  The movement runs even at a low wind :Smiths car clock movt

Having succeeded in my initial objective- to learn a new technique - I'm doubtful whether it was the correct solution. I suspect that I'm compensating for wear to the escapement wheel.  That said, it was an interesting experiment and as it turned out, quite straightforward.

Next stop, check it's in beat. It sounds OK and self starts so no a bad start. 

Edited by Boz
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