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Deadbeat tooth design on the escape wheel

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Chris TickTock23/10/2020 17:47:43
605 forum posts
43 photos

Hi Guys,

Currently trying to understand the deadbeat escapement. All is fine apart from none of my books appear to state any design criteria for the selection of the angles of the back slope and undercut for the teeth. Yes they all state they point forwards for an escapement going clock wise but it would be nice to understand how such angles are derived.

Any pointers gratefully recieved

Regards

Chris

John Haine23/10/2020 18:29:53
3422 forum posts
184 photos

You think there is science behind them?

Chris TickTock23/10/2020 18:44:06
605 forum posts
43 photos
Posted by John Haine on 23/10/2020 18:29:53:

You think there is science behind them?

 

There is some but there is apparently a selection of shapes possible. Still need more detail to voice a more solid opinion. With triangular teeth certainly some science that could be used...that's as far as I have got. There appears to be a relationship between the number of teeth and the angles. I suspect many old clocks were made by rule of thumb. But even rule of thumb escapes me at present.

Chris

Edited By Chris TickTock on 23/10/2020 18:44:35

martin perman23/10/2020 18:51:03
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1891 forum posts
78 photos

Having done a quick search on the internet and looked in the books I have I tend to agree with Chris's rule of thumb idea but I've found this http://www.davesclocks.net/uploads/5/8/9/1/5891949/dcr_deadbeat_calc.xls which may be of use to you.

Martin P

Chris TickTock23/10/2020 21:06:10
605 forum posts
43 photos
Posted by martin perman on 23/10/2020 18:51:03:

Having done a quick search on the internet and looked in the books I have I tend to agree with Chris's rule of thumb idea but I've found this http://www.davesclocks.net/uploads/5/8/9/1/5891949/dcr_deadbeat_calc.xls which may be of use to you.

Martin P

Thanks Martin, I have this spreadsheet it does not explain any formula though. Obviosly there must be a limit on forward tilt of teeth as well as back slope. Circa 20 degrees forward slope is about the mark. Still on the case.

Chris

Michael Gilligan23/10/2020 23:32:28
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16616 forum posts
723 photos

The choice of angles on the wheel teeth is pretty arbitrary ... the cleverness of Graham’s idea really lies in the shape of the pallets.

Have a look at these three videos:

**LINK**

**LINK**

**LINK**

MichaelG.

Bazyle24/10/2020 00:00:30
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5555 forum posts
207 photos

All the formulae are given on the other page of the spreadsheet. It is just 'simple' geometry to give clearances. The teeth are triangular only because it is an easy shape to cut - they could be arcs matching the curve of the pallet movement - just no point in being that complicated.

The only places where any science or even much choice comes in to it is to decide on the angular movement of the pendulum which depends on how much circular error you want in relation to your other choices of temperature compensaton etc.

Chris TickTock24/10/2020 11:20:04
605 forum posts
43 photos
Posted by Bazyle on 24/10/2020 00:00:30:

All the formulae are given on the other page of the spreadsheet. It is just 'simple' geometry to give clearances. The teeth are triangular only because it is an easy shape to cut - they could be arcs matching the curve of the pallet movement - just no point in being that complicated.

The only places where any science or even much choice comes in to it is to decide on the angular movement of the pendulum which depends on how much circular error you want in relation to your other choices of temperature compensaton etc.

Thanks for this Bazyle, I missed the other pages at the bottom initially. Largely I agree with your take. all I would add is this;

On the standard deadbeat escape wheel providing you first understand how it works then you have a fair bit of leeway in the tooth design. Teeth slope forward (CW wheel) and a minimum of 6 degrees is recommended as Thornton's cutters. Equally to much forward slope can weaken the teeth so Wild recommends keeping this to under 10. Backslope on the teeth not critical again but too much may impair clearance during the run on lock, so ball park 18 to 21 degrees may be a good starting point. As usual Tooth witness (tip flat) should be there but small so I would go for 0.5 a degree.

Chris

Bob Stevenson24/10/2020 11:34:27
440 forum posts
7 photos

I use a fly cutter for making escape wheels and shape these along the curve of the wheel blank...has always worked well for me...remember to 'pin' the blank during cutting as the action of the fly cutter being assymetric can nudge the blank making a not very happy day!

Chris TickTock24/10/2020 15:08:51
605 forum posts
43 photos
Posted by Bob Stevenson on 24/10/2020 11:34:27:

I use a fly cutter for making escape wheels and shape these along the curve of the wheel blank...has always worked well for me...remember to 'pin' the blank during cutting as the action of the fly cutter being assymetric can nudge the blank making a not very happy day!

Good point with the pins Bob...cheers.

Chris

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