Japy Freres pendulum sizing

Kurt Schulze

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Aug 15, 2018
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Bought a Japy Freres movement to replace a Marti movement in a crystal regulator frame. Movement works great. Tried to use the old pendulum from the Marti. Rod of old P too big a diameter to fit the fork on new clock. Old rod = 3.3mm for slot is a little more than 2mm. Now confused about sizing pendulums. Stamping on back plate is 96 and 36. Using the pouce lignes system length would be 2680mm. Afraid this newbe made a boo boo. Any advise would be helpful. Maybe the pouce lignes system was not used for the stamping.
 

zedric

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Aug 8, 2012
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Can you post a picture so we can see what you are seeing?
 
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Kurt Schulze

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Aug 15, 2018
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Attached are photos. Hope they help. First shows fit up of old pendulum rod (3.3mm dia.) into fork of old movement. Small side clearance as expected. Second shows attempt to engage the old pendulum rod (3.3mm) into the fork (width 2.1mm) of the new movement. Will not enter. Third photo shows stamping on the backplate of the new movement 96 and 36. Stamping on old movement is 4 and 8. Trying to find a new pendulum to fit the new movement. Case permits a max length of 6 inches.

old movement with rod engaged in fork of verge.jpg new movement showing rod too big in diameter to engage in fork of verge.jpg stamping of new movement.jpg
 

zedric

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Can you show a full picture of the backplate and wheel work of the new movement? More photos are always better..
 

Betzel

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Dec 1, 2010
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Yes to more pictures.

FWIW, this is the first of these I have seen that says "Made In France" which was not needed to explain to admirers who made it or where, as everyone already knew, and by French standards of typography and size, it seems pretty glaring. So, I wonder if one of the export regulations may have been in play at the time this was made? If so, how that relates to any change in measurement units, and the different sizes between the crutch and pendo rod, and its overall intended length, may be important.

Also, I have a Japy here (1860's?) that uses a 2.47mm rod fine with the original fork, and had one I gave away (not Japy) that took a modern replacement rod which was 2.45mm (round polished brass with the set-screw to adjust to the rod).
 

jmclaugh

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Jun 1, 2006
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I would think if the pendulum length is marked on the Japy movement it is more likely to be 3 6 than 9 6 as the latter sounds pretty long for one of these. However the length may be unmarked and 9636 refers to something else such as a serial number.
 

Curtis Brown

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Apr 26, 2019
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As there are 12 lignes to a pouce, any lignes count above 11 would not really make sense (and while experienced with French movements a bit, I am not an expert).
 

Kurt Schulze

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Aug 15, 2018
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Thanks for advice. I took a chance and filed the sides of the old Pendulum rod to fit the crutch. Ended up about 2.4mm width to match the slot for a good fit. Rod is 6 inches long and after installation, the clock runs and runs a little slow. Clamped trial weights on rod and it looks like about 3.5 inches from hook to center of mass is about right for pendulum bob location for proper time. Placed an order for a "French clock pendulum" - hope it come with the smaller rod size but can file if needed. Pendulum wasn't too expensive but the low value cost adder and taxes about doubled the cost. Ugh. Not sure what all that stamping was about but success in the end. Thanks again.
 

macaw

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Jul 23, 2014
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It uses a standard French pendulum and the distance from the bending point of the suspension spring to the center of the bob is 126mm. That's what the 4 & the 8 tell me.
 

zedric

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It uses a standard French pendulum and the distance from the bending point of the suspension spring to the center of the bob is 126mm. That's what the 4 & the 8 tell me.
Except those markings are on the old movement, not the replacement one..
 

wow

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Jun 24, 2008
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The pendulum you have should be fine. You will need to shorten it. Remove the hook at the top of the rod. Most screw on but some are soldered. If threaded, you need a die to match the threads. Cut new threads about an inch further down the rod. Cut the rod off about 1/2 inch and screw the hook back on. File the rod again where the crutch fork goes and try it at that length. If still running slow, cut the length and continue until the rating screw is in the proper range. Those numbers on the movement do not refer to the pendulum length (I think). Hope this helps.
Will
 

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