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Unitas 431 Ratchet Wheel Screw - LH threaded?


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Hi, I just managed to break the head off a ratchet wheel screw (not the crown wheel screw which is LH threaded) on a Unitas 431 in a Waltham 25 jewel railroad watch. I assumed it was RH threaded and was frozen (which it might well have been for all I know presently). I had previously successfully worked on a Unitas 6431/6445 variant and didn't have any problem with the ratchet wheel screw so I was a little too sure of myself with this one. 

I did source a new arbor for the 431 but I can't find a new loose screw. I don't have a screw machine (I might ask my jeweler to make one).  Does anyone have any experience with this movement? I'm under the naive impression that there can't be much difference between the barrel/arbor/ ratchet in Unitas family 431 cum 6431 cum 6445 cum 6497. Is this screw indeed LH threaded? Will a ratchet wheel screw from a 6497 fit a 431 arbor? I'm waiting for delivery of the arbor before I can test it.

I assembled the movement and I was successful in restoring it with the exception of the arbor/screw. I was able to wind the watch to test it without the screw but obviously this is only temporary.

I did check Dr Ranfif's webpage and he cautions that the 431 might have a LH thread, but he also says this about the 6431/6445 which I didn't experience.

If anyone has any information I would appreciate it. I'll publish my findings in the hope it might help someone else...J.

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13 hours ago, Watchoutnow said:

a ratchet wheel screw

I have a link to a parts listing where we have a mystery. So they list the ratchet wheel screw not sure if we can get one but which one did you want to left-handed or the right-handed one? This is one of the problems of watches that have been made over time you can end up with variations. Like I see this for different balance completes for this watch that's always a clue of made over time with variations.

then when you figure out which screw you need you click on it and give your cross referenced all the ones that have the same screw type. You can also take the suitable part number and go to their home page enter it in and see if they have one

http://cgi.julesborel.com/cgi-bin/matcgi2?ref=UT_431

http://www.ranfft.de/cgi-bin/bidfun-db.cgi?10&ranfft&0&2uswk&Unitas_431

 

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Thanks, I see the link in Jules Borel but can't seem to be able to order either part. I have an arbor coming but I don't know if it is a RH or LH. What baffles me is that the mainspring is a RH winder, which means that turning the ratchet screw to the left would put resistance against the click pawl which would allow me to unscrew it. If I turned it to the right it would only wind the watch, so how could it be a LH screw? Would I have to have been holding the winding stem crown to put resistance in the RH direction? This seems strange. ..J.

 

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I also see in JB's index that the UT 431 RH screw 5415/607 cross-references to the ratchet wheel screw on a UT 6497 which are easily had. So, maybe I'll get lucky and receive a RH arbor that matches a 6497 ratchet screw. I also searched this pn on Otto Frei's parts look up and it too references the UT 6497. Maybe the arbor for a 6497 might also be compatible, something else I could try. 

Otherwise I'll need to find a 5415/375LH screw, or have a screw made or have the arbor I have with the broken screw machined out and re tapped to fit an available screw...J.

Edited by Watchoutnow
wrong lh screw pn
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6 hours ago, Watchoutnow said:

have a screw made or have the arbor

you must live in a different part of the planets and I do because getting a custom screw made would cost more than the whole watch. I don't even know actually who would make custom screws. Typically when I need a screw I open up my box of miscellaneous screws and go through all the little containers so I find something that works. Or I have physical material houses I could send the watch down and see what they have or see if they would even have the part this is one of the minor catches to online material houses they don't actually list everything. So if you had the luxury of living in a location that had a physical material house you could ask them or even some of the online ones you can ask if they have the part

6 hours ago, Watchoutnow said:

Maybe the arbor for a 6497 might also be compatible, something else I could try.

if you click on the arbor for your watch at the link I gave you it gives you the cross references and the 6497 is not a cross reference part. So while the screw might fit the arbor will notplus of course the barrel does not fit either.

Then a course is back to eBay to see if can find a broken movement. Then this is also the probably working on older watches is defined spare parts. Or for that matter find you spare parts for just about any watch can be a challenge depends upon what it is

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I resolved my problem. I was able to back out the broken screw in the arbor and confirmed that it was indeed LH threaded. I found a LH screw for it in a box of mixed ratchet wheel screws. I also received the replacement arbor I ordered and found that it is indeed RH threaded. I found the matching screw for this in the same box of screws. I decided to install the RH arbor instead of the original LH arbor in order to spare some future watchmaker of the same frustration. I would think that since this movement was a mass produced item that the screw couldn't be that hard to find.

I even found a match for the missing dial feet screws in another box of mixed df screws. CK has nice mixed lots of assorted screws for various functions at a very reasonable price. 

I still wish I had a mini lathe and a set of screw dies. I'm a retired engineer and it was too easy to ask someone at work to make something every time it was need...so that's the "parts of the planets" I'm from.

I didn't try a ratchet wheel screw from a 6497 to test to see if that was compatible but I may if I get a loose one, I just didn't feel like opening up the 6497 I have cased. The arbor and barrel is much smaller but I did test the ratchet wheel and the square matches the arbor but the wheel diameter is also much smaller.

I hope this helps someone else someday...J.

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7 minutes ago, Watchoutnow said:

I resolved my problem. I was able to back out the broken screw in the arbor and confirmed that it was indeed LH threaded. I found a LH screw for it in a box of mixed ratchet wheel screws. I also received the replacement arbor I ordered and found that it is indeed RH threaded. I found the matching screw for this in the same box of screws. I decided to install the RH arbor instead of the original LH arbor in order to spare some future watchmaker of the same frustration. I would think that since this movement was a mass produced item that the screw couldn't be that hard to find.

I even found a match for the missing dial feet screws in another box of mixed df screws. CK has nice mixed lots of assorted screws for various functions at a very reasonable price. 

I still wish I had a mini lathe and a set of screw dies. I'm a retired engineer and it was too easy to ask someone at work to make something every time it was need...so that's the "parts of the planets" I'm from.

I didn't try a ratchet wheel screw from a 6497 to test to see if that was compatible but I may if I get a loose one, I just didn't feel like opening up the 6497 I have cased. The arbor and barrel is much smaller but I did test the ratchet wheel and the square matches the arbor but the wheel diameter is also much smaller.

I hope this helps someone else someday...J.

Also a retired engineer...electrical. I love my lathes. Recently re-pivoted a center wheel. This morning I made a setting lever screw for a member of this forum.

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as we like to dream about making things here is a book that talks about making things. Making things by machinery unfortunately they don't break each machine down to its components which would be rather nice. I rather like page 48 the steps of making a balance staff by machinery.

https://archive.org/details/evolutionofautom00mars

 

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