Dark Lady Clock

Sorry I was reading what you posted on the 14th

Well with a 3kg weight attached from the ratchet assembly only I get this...

Edited By John silver on 26/10/2016 17:20:04

Edited By Neil Wyatt on 26/10/2016 18:13:10

You can hear it speeding up and slowing down, it definitely is hesitating on some teeth, its as if the shape of the edge of some teeth gives it a 'kick' while others hold it back?

Neil

Edited By Neil Wyatt on 26/10/2016 18:13:30

Watch the video carefully. The first time it nearly stops the tooth at the left looks much rounder in cross-section (looking at the tip).

Neil

Hi Neil,

I think I see what you mean, the teeth that are more curved on the edges are allowing the pallet to wing further round, making have to travel further back the other way losing momentum all the time.

I wondered if the pallet was re-made with the curved sections closer to the shaft then the pallet movement would be reduced and more likely to return the other way to complete the cycle. To be fair the teeth were all square on the leading edge and I thought easing the sharpness of the edge would help in operation but I still think the pallet shape is the problem, especially when you compare Brian's extrapolated pallet (from photo) to the one I certainly started with using the starting cutout from the dimensioned drawings.

At least my experience with wooden clocks has shown how critical the escapement is for reliable operation

All the best

John

John,

From your video it is clear that there is too much friction in the escapement. To minimise the friction the working surfaces should be highly polished and the pallet should be very hard. I don't know what you have made the pallet from but if it's mild steel (lead free) it could be case hardened. Better still to use gauge plate and harden it with no tempering.

The design of the pallet looks wrong to me.

Assuming very little friction the impulse force provided to the pallet by the escape wheel tooth will be perpendicular to the working surface of the pallet. To maximise the effect of that force in maintaining the swing of the foliot that force should act perpendicular to a line drawn from the centre of the pivot to the contact point. That is far from the case with your design. At first thought it would seem to imply that the sliding surface of the pallet should be radial to the pivot. Perhaps a bit of playing about with the operation on a CAD program (or on paper) would help with understanding it?

Russell.

It can't be truly radial, or there wouldn't be any impulse?

Neil

That would be true for an anchor type escapement but not for this geometry.

If the surface of the pallet is radial to the vertical pivot of the foliot then the impulse vector, perpendicular to the pallet surface, will give the maximum moment to that pivot. With John's design the impulse vector is almost in line with the centre of the pivot just before release so provides virtually no energy to the folio.

Russell.

Sorry muddling radial and tangential

Neil

I do things like that but put it down to age. What's your excuse

Russell.

Interesting contributions chaps

It looks to me that my pallet is incorrect. Although I did cut it as per Brian's dimensions (shown in blue). As I said, I have overlaid what I believe is Brian's pallet taken from a photo.

What I started with, is shown in magenta ie using the dimensions shown in blue - there's quite a difference between the two. There's no way you can get the red pallet from the blue dimensions

BTW the pallet is mild steel and not hardened

I think your pallet should look more like this:

The angle between the faces is 90°. The radius should be as per the original. Yours was too big and there was more rubbing than necessary. Make it from gauge plate, harden it, polish it, and fix it to a bush with Loctite high strength retainer.

Russell.

OK ..time to start again with both variants The 122deg Brian pallet and Russell's suggested 90deg pallet

Bon chance!

Russell

Time for an update

I can't get reliable operation of the clock and found that when it stopped, you could pull the Foliot up and the gear train was stuck!

Investigations found a few issues:-

(1) Main wheel brass bearings were very tight?? I'm sure I reamed these out but had to ream some more.

(2) I looked at the pinions and found that one of the pins was wonky making the spacing to the next pin too large.

Now I had a look through John Wildings Alarm clock which the Dark Lady clock seems to be based on. Interestingly, there is a very detailed diagram explaining who to shape the pallet.

What was also interesting is that although John uses 'bird cage' pinions he did in fact use a commercial involute gear cutter for the main gears.

Checking my first pinion to the main wheel showed that they could be very closely meshed. However on the escape pinion, the wonky pin meant that I had to widen the spacing between the gears leading to excessive backlash - which I believe and hope is the reason why the gear train locks up periodically.

So I am going to machine new pinions and then I will have to re-make and drill the bushes.

When the clock was running it was running quite smoothly and evenly after I rounded all the escape wheel teeth (And polished them) and also ensured that the pallet shape was evenly shaped and polished.

I'm sure I'll get it running but at least I know I don't have to re-make the gear train and Involute gear pattern is fine with 'bird-cage' pinions

Edited By John silver on 08/12/2016 10:22:45

I found a tapered reamer at a boot fair which was perfect for the bearings. I cut them quite slack as the frame moves noticeably when loaded and running.
This week the clock started 'running away' and had to be adjusted by 10minutes in 24 hours.

Friction is your problem. In an earlier post you said that the pallet is unhardened mild steel - not good for low friction. You could case harden it before polishing but personally I would use gauge plate and fully harden it without tempering. It would then have to be glued to the bush. The working surfaces should be polished to a mirror finish.

Oil - just use the barest amount on each pivot and just a drop from the end of a fine needle on the pallet face. Preferably clock oil but, for that clock, I would think a thin sewing machine oil would do. Don't oil the gear teeth.

Russell.