Sizing a new mainspring to a barrel arbour

[DrHWO]

Until now I've bought model correct, branded mainsprings which drop nicely into the barrel. Recently I've had to go a bit off piste and use a bit of Alex maths to source generic mainsprings which gave good fits for the height, thickness, length and barrel diameter but were too large in their inner terminal coil to catch on the barrel arbour hook. Have I missed some essential piece of the specification which identifies the barrel arbour diameter? I did learn the hard way that you can't just grab the terminal curve in your smooth Spencer Wells forceps and try to fashion a tighter curve, mine just snapped through the slot in the mainspring. 

[Neverenoughwatches]

39 minutes ago, DrHWO said:

Until now I've bought model correct, branded mainsprings which drop nicely into the barrel. Recently I've had to go a bit off piste and use a bit of Alex maths to source generic mainsprings which gave good fits for the height, thickness, length and barrel diameter but were too large in their inner terminal coil to catch on the barrel arbour hook. Have I missed some essential piece of the specification which identifies the barrel arbour diameter? I did learn the hard way that you can't just grab the terminal curve in your smooth Spencer Wells forceps and try to fashion a tighter curve, mine just snapped through the slot in the mainspring. 

Eyup Doc. No you haven't missed any spec. Height thickness length and inner barrel diameter is all that is required, sometimes the barrel size is overlooked. What you may have missed out is the process of annealing the inner coils that you wished to manipulate into a tighter shape to fit the arbor. Tempered steel will bend some but not as easily as annealed steel, so it broke at its weakest point. The steel's molecules need to be less rigid to bend easier and further, heat the inner coils up to red and allow to air cool, you can practice this with your broken spring to see how much more malleable the steel is. After reconfiguring the inner coils size, re harden and temper back, this is best done in a dark area so you can see the colour changes.

[DrHWO]

Is anything in watchmaking ever easy? So, I need to add metallurgy to metrology, stereotactic brain surgery and an ability to cuss fluently in half a dozen languages. I'm truly doomed.

[rehajm]

I've found my expertise from grade school of avoiding work by figuring out all the shortcuts is really paying off. I think some of you here are compadres in that regard...

Have you seen this?

 

Edited June 14, 2023 by rehajm

[Neverenoughwatches]

12 hours ago, DrHWO said:

Is anything in watchmaking ever easy? So, I need to add metallurgy to metrology, stereotactic brain surgery and an ability to cuss fluently in half a dozen languages. I'm truly doomed.

Join the club Doc.

[DrHWO]

And after burning off the fingerprint from my right index finger, creating an art deco mainspring shaped pattern on my sycamore self built desktop and an acrid stench to rival that in my bathroom after curry night, I decided to look at my barrel arbour carefully. Perhaps I should have looked before I beeped.

 

[Neverenoughwatches]

3 hours ago, DrHWO said:

And after burning off the fingerprint from my right index finger, creating an art deco mainspring shaped pattern on my sycamore self built desktop and an acrid stench to rival that in my bathroom after curry night, I decided to look at my barrel arbour carefully. Perhaps I should have looked before I beeped.

 

Once again, join the club Doc. 

[DrHWO]

So, Before the hookless barrel arbour debacle, I did get out my thermally controlled soldering iron and gave the heat treatment (300C if interested) to my busted spring parts. The technique worked well (in that they didn't snap). I needed to make the diameter 2mm to account for the "spring back" to 2.5mm. Thank you all for the advice. 

[steinpom]

Hell everyone,

 

I need to replace the 2 mainsprings in my model 1910 Waltham size 37s car clock.  Since I am new at this, how does one accurately measure the length of the spring since it remains coiled up even after removing them from their barrels.  Thanks for any suggestions.

 

Danny

whoops I meant to type Hello not that other place

 

[JohnR725]

4 hours ago, steinpom said:

I need to replace the 2 mainsprings in my model 1910 Waltham size 37s car clock.  Since I am new at this, how does one accurately measure the length of the spring since it remains coiled up even after removing them from their barrels.  Thanks for any suggestions.

 

Danny

whoops I meant to type Hello not that other place

Ideally it would be best if you started a new subject as you are doing what I call hijacking an existing discussion. In the previous discussion we don't actually know what this person's Trying to find a spring for so we really can't be very helpful.

Basically to get the length you would just stretch them out.

Goriest look on older mainspring list or anything that lists Waltham mainsprings as that's a standard at least I assume it standard hillbilly tell when you see the size that matches the width and thickness that you have.

Then the other thing that works really well is just going to your favorite search engine and searching you might find link like this one

https://timesavers.com/i-9994854-waltham-37-hole-end-mainspring.html

I also snipped out an image out of one of the later parts books that gives some specifications.

Then we discussed Waltham Springs before on the group somewhere there's issues with this type of end. Then in addition to that little problem which is a little this is a really big Spring.

Also want to make sure that the sizes I have listed below match the size of whatever your spring are.