Paul Garnier Chaff Cutter Escapement

[wls1971]

I have a wooden cased carriage clock dating from about 1840 fitted with a Paul Garnier "Chaff Cutter" Escapement, has anyone ever worked on or come across one of these it was a fore runner to the platform escapement, It runs but seem to have a arc of swing on the balance wheel of about 60 degrees is this correct for these escapements ?, it does run well and if the balance is gently stopped it springs back to life instantly once released, I have read that the action of the escapement is of a dead beat variety and is in some way related to a verge escapement but I can find very little on the web about them., It consists of two club toothed discs that make up the escape wheel, with a half circular disc with sloping edges on the staff, that releases and locks the opposing discs on the escape wheel as it swings.

If anyone has any info or knows of a site with any please let me know.

[nickelsilver]

This was a variation of Debaufre's escapement, which was interrelated with several others all trying to deal with the massive recoil of the escape wheel in the verge escapement. There is a good description in Paul Chamberlain's It's About Time.  Like a cylinder or most any frictional rest escapement amplitude is normally quite low and you may find that there is a pin on the balance to prevent it going too high- though perhaps not on a stationary clock like this. One interesting thing with frictional rest escapements is they are somewhat self regulating regarding isochronism, as when power goes up the friction during the non-escape time goes up too, limiting the amplitude.

 

60 degrees seems a bit low, I would imagine about double that if everything is in good order and lubricated. But if it's working well it's not really a huge issue, the fact that it self starts right away is a very good sign.

 

There is a good chance there is some sort of adjustment for the depthing of the escape wheels to the impulse table on the staff; most verge escapements had this too. When one escape tooth has just "escaped" the following tooth should land on the flat surface of the impulse table. If it's landing on the sloped surface the depthing is too light.

Edited January 6, 2020 by nickelsilver

[wls1971]

Thanks, I have managed to find a cheap copy of "About Time" so have ordered it,  I could not find any videos of a running example so had no idea what the amplitude should be like.

[nickelsilver]

It's a fantastic book, and usually not cheap!

[wls1971]

My heart did sink when I saw the prices for it on Amazon and Abe books, but Ebay came up trumps

[oldhippy]

You don’t get much of a swing from the balance with this type of escapement; it is nothing like the swing of an anchor escapement. They are slow in comparison much like as you say a Verge. The ones I have worked on I think 3 or 4 after a proper O/H always seemed lazy in the rotation; it’s as if the balance wheel was too heavy for the hair spring. I don’t see much oil on the two club toothed discs, this might be to do with the photo. Not a very popular escapement, which might be due to its poor action.  

[wls1971]

25 minutes ago, oldhippy said:

You don’t get much of a swing from the balance with this type of escapement; it is nothing like the swing of an anchor escapement. They are slow in comparison much like as you say a Verge. The ones I have worked on I think 3 or 4 after a proper O/H always seemed lazy in the rotation; it’s as if the balance wheel was too heavy for the hair spring. I don’t see much oil on the two club toothed discs, this might be to do with the photo. Not a very popular escapement, which might be due to its poor action.  

Yes as you say the action seems Lazy in comparison to a platform lever or cylinder escapement, they also seem to inhabit a short space of time in carriage clock production 1830-1850 , with platform escapements soon superseding them. I did oil the escape wheels but just a small drop of oil on one tooth on each , it has been running three days now but I have not measured time keeping performance yet but I should imagine it will run far short of a good platform escapement.

[Lenj]

5 hours ago, wls1971 said:

I have a wooden cased carriage clock dating from about 1840 fitted with a Paul Garnier "Chaff Cutter" Escapement, has anyone ever worked on or come across one of these it was a fore runner to the platform escapement, It runs but seem to have a arc of swing on the balance wheel of about 60 degrees is this correct for these escapements ?, it does run well and if the balance is gently stopped it springs back to life instantly once released, I have read that the action of the escapement is of a dead beat variety and is in some way related to a verge escapement but I can find very little on the web about them., It consists of two club toothed discs that make up the escape wheel, with a half circular disc with sloping edges on the staff, that releases and locks the opposing discs on the escape wheel as it swings.

If anyone has any info or knows of a site with any please let me know.

What a great movement..

 

[oldhippy]

If you have time I'd like to see the hands, dial and case. 

[WatchMaker]

This page might be interesting: http://www.my-time-machines.net/chaff_cutter_detail.htm

If you click on one of the main pics it will take you to a further page with extra pics / breakdown detail. Also note the video download links (1,2,3) at the end of the first paragraph.