mainspring.

[bobpat]

looking for a mainspring, no luck. Best I could do was a Bestfit # T320-2, can’t find a cross reference or nothing close. Dennison width is .23, strength is 00 😯 <<<<<< This is what I feel like after searching on the web for a couple of hours

[tmac1956]

Bobpat:

I think I ‘ve missed something…. For what watch are you looking to replace the mainspring? It can be difficult, but not impossible. Please post and let us see what we can find. It’s possible that I’ve missed the post, so forgive me if that’s the case. My attention span is pretty limited these days.

Later,
Tom

[bobpat]

Radium?????? Tom?

[bobpat]

Tom,Its an old Ingersoll cheapie, nothing special, I am pretty persistent, or call it stubborn but I am determined to get her running.I have all the measurements, but I can’t even come close. tried all the sites you gave me and then some,,

[randy]

bobpat,

Do you have a movement number ( caliber ), name, etc ?
Wrist /pocket watch ?
All of the mainspring width and thickness dimensions in millimeters instead of Dennison ?
( you give the length in inches )

[bobpat]

pocket watch, dennison # are. width is 23. strength is 00. its an old Ingersoll cheapie. I have 546mm for length, I measured it, it was about 21 1/2 inches.. only number I have is 26682986. I found a match in an old bestfit book. Its t320-2 but I cant cross reference it ti nothing …. Thanks Randy for replying to me

[arutha]

They used the same mainsprings in these cheap watches as in the Smiths pocket watch, its funny because I was working on one of these recently for a customer, they didnt want to pay £15 for a new mainspring so I managed to fit one from an old Westclox dollar watch, the spring was just a fraction thinner but still runs the watch for 30 hours and keeps good time.
http://www.ebay.co.uk/itm/Mainspring-for-the-Smiths-Empire-and-Ingersoll-Pocket-Watch-/201072373704?pt=UK_Jewellery_Watches_WatchAccessories_SpareParts_SM&hash=item2ed0d8efc8
You can buy one of these if you have no luck elsewhere.
Paul.

[bobpat]

thank you paul. Most likely I will be using this one. So, tell me how you found this mainspring, to fit. did you compare sizes?. I looked everywhere and I couldn’t even come close. Again, Thanks Paul

[randy]

Right on Paul…that was one of the candidates I was looking at also.
You confirmed my suspicion !

Take care

Randy

[chris mabbott]

Bobpat,

Identical mainsprings are often difficult to find, I had the same problem many times. You guys are going to get sick of me quoting de Carle but he states in one of his books that for older watches, (this book was published in the 50s so I assume he’s talking about 20yr old pieces and not our, now 80-120 yr old ones)
that older watches, because of lack of available parts, and due to wear, technology etc, CANNOT be expected to keep 100% accurate time as they did when they were new from the factory, there will always be a certain time loss, due to frequent positional changes, shock, dust, temp changes. condition etc etc

I’ve had the same problems finding specific Rockford, South Bend, Seth Thomas parts, specifically mainsprings. So I’ve taken to making my own best fits 😆 I’ve had good results simply by matching width and trying to stay with the consumed space requirements of the barrel (length) i.e. 1/3 for the spring. I also try to stay within the model specs, 18s, jewel count and train type, IF possible.
As Paul states, you can easily achieve the 30hr plus running time by fulfilling these two out of three requirements. The strength… I try to stay as realistically close +_ to the specs, but it isn’t always possible..

If you have the Chicago watchmaking book, there is an in depth chapter on MS, where the author experiments with a correctly sized MS, then proceeds to shorten it and test the reaction, surprisingly, the watch seemed to perform better on a shorter spring, although this is not a reason to start cutting down MS length 😮 ..

[bobpat]

Thanks chris.I kinda figured it would be looking for a close fit.The mainspring across the pond is $25 plus $8 for shipping..More than I paid for the watch, but I am determined to get it running, I will look around here for one, if not, I will get the one Paul found…. THANKS GUYS

[arutha]

Hi Bob,
as the customer didn’t want to buy a new mainspring I just looked through what I had and the Westclox mainspring was the closest, as Chris said, in some cases you cant get a perfect match so you just get as close as you can.
Paul.

[david pierce]

These posts bring up an interesting thought. There is a misconception that when something is designed a bunch of engineers pull out complex math formulas , the products are made from these and then shipped out the door. This is not the way things are really done. That is the reason airplane factories have wind tunnels, testing facilities and test pilots. When that watch was designed and manufactured the watch company went through the same process in selecting the mainspring that Paul went through. This means that the watch will work properly within a certain range of selections and the replacement does not have to be an exact match to the origional. As long as the selection makes the watch work within certain performace parameters, it is an acceptable choice.
david

[tmac1956]

Bobpat:

If you don’t already have one of these you might want to pick one up. You can punch holes and modify the ends of mainsprings with it.

http://www.ebay.com/itm/VINTAGE-WATCHMAKERS-POCKET-WATCH-MAINSPRING-HOLE-PUNCH-/291148084045?pt=LH_DefaultDomain_0&hash=item43c9c7334d

Additionally, a good book for modifying mainspring barrells and springs (and just about everything else) is entittled: “Practical Benchwork for Horologists by Louis and Sam Levin.

I hope this helps!
Tom

[Author]

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