Re: The Impulse Roller & Shape of Pallet
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Interesting experience with reshaping your impulse pallet. Some years ago I actually machined one from a solid lump of brass (and it's still running well). Until then, I wasn't aware of the radius on the impulse face. To machine this, I mounted the pallet on rod clamped to a moveable, but essentially fixed, vertical slide and ran a milling cutter in the lathe chuck. You will have to imagine the set-up. By this means, I could manipulate the pallet as I milled the impulse face.
Having seen many Synchronomes over the years, I think that there IS a great deal of in-built tolerance to the design which is a testament to the original idea. Note, however, that very similar results can be obtained with a straight, flat impulse pallet - as Mr Parsons & Mr Ball found.
From: Chris <chris.b@...>
Sent: Sat, 14 Nov 2020 7:24
Subject: Re: [synchronomeelectricclock] The Impulse Roller & Shape of Pallet
Hello Michael and Welcome to the forum.
Let us not forget that the impulse curve is also rotated about radii struck from the center of the rod. Which makes me wonder how the factory shaped the impulse curve on the raw pallet casting. Perhaps they used a high speed, copy lathe using a pantograph mechanism?
My own [pre-gravity arm buffer] 1919/20 Synchronome had apparently been run for decades with the pallet badly skewed to the plane of the arc. Requiring careful work to reshape the impulse curve. I used the highest speed in my old S&B lathe and various grades of abrasive paper. Wrapped and glued tightly around a slightly undersized rod to reshape the impulse curve in 3-dimensions. It would have required much higher speed to allow a form tool to shape the impulse curve due to extreme chatter and the weakness of the original casting.
Only after re-assembly did I realise that I had altered the overall length of the pallet slightly. Requiring the pendulum be moved bodily to the left. With further adjustments to suit. It has been running steadily for at least 35 years in my care so my "botching" seems to have worked. Or perhaps Synchronomes can shrug off the worst offences that can be thrown at them. Like being run out of line for long enough to wear the original pallet curve askew. New pallet castings became available later but it would been even more difficult to copy the original exactly than to "repair" it.