Compound shutter main spring?

[Tim Deming]

I know this is a long shot, but I've got a small, old compound 00 shutter (holds a 132mm f6.8 Collinear III) that came to me in pieces. Fortunately, I have most of the pieces and have it together again. The problem is the main spring (that is tensioned when cocking the shutter, and housed within the cylinder that the cocking arm mounts to -labeled as #4 in the image) is missing. Looks like someone a long while ago took it apart to get to this problem, and then gave up. I've worked on most every type of shutter, but never had to replace the main spring on a compur or compound before. Anyone with this experience here? Is it tricky to tension and install this spring?

I do have a larger, working compound I'm tempted to cannibalize for the spring, but want to make sure I dont decommission that if the spring wont fit (the winding mechanisms do appear to be similar is size and structure). Any help (including a cheap or donated broken compound for parts) would be appreciated.

thanks

Tim

[E. von Hoegh]

Your best bet is a similar shutter for parts. To duplicate the spring, you'd need the original for dimensions; it's not that horrendous a job if you have length width and thickness.

edit - Do not try to use the spring from the other shutter. You will almost certainly end up needing two new springs.

[Steven Tribe]

Does the spring reside in the round housing with the threads for attaching to the lever?
I have a number of scrap compur/compounds from 9x12cm folders and I think that many parts are the same size. Will check in good daylight tomorrow.

[E. von Hoegh]

Steven,
The structure at 3 o'clock in the larger view houses the spring, it's a relatively thick flat spiral of around 4-5 turns and the spring itself is not visible.

I'm not certain but I think the Compurs had a stronger spring.

[Tim Deming]

Does the spring reside in the round housing with the threads for attaching to the lever?
I have a number of scrap compur/compounds from 9x12cm folders and I think that many parts are the same size. Will check in good daylight tomorrow.

Yes, that's right, inside the approx. cylinder shaped housing that the cocking lever mounts to (marked "4" in the big image). Upon not too close inspection (i.e. I didnt remove the cylinders) of a few compounds and compurs, it does look like this housing (and/or spring inside) was fairly standardized for these shutters. Spring strength changing with compound vs compur and for different sizes is a good point, but I'll gladly try out any spares you can send my way

cheers

Tim

[Tim Deming]

edit - Do not try to use the spring from the other shutter. You will almost certainly end up needing two new springs.

Why? are they prone to breakage, or that difficult to remove?

cheers

Tim

[Steven Tribe]

The cocking spring of all the dial set compurs I have had, did have noticeable different tensions, without the function being much influenced.

[E. von Hoegh]

Why? are they prone to breakage, or that difficult to remove?

cheers

Tim

They're tricky to remove and reinstall without stressing the spring, which can cause it to break.

[Steven Tribe]

OK Tim, I have a "scrap" small compound that was sold by Goerz - I have taken out the Series III 120mm (?) cells long ago.
I feel pretty sure that this is the same size as yours ( external diameter 55mm).
There is is working spring in the housing.
Do you want this as a complete shutter (the dial and cocking lever/screws are gone) or would you prefer me to take out the housing + spring?
One disadvantage with the "complete" shutter is the US customs! Or you could send the remainder to our favorite shutter repair gal!

[Tim Deming]

Thanks Steven,

this looks perfect. Probably best to have the whole thing. I can either see how the spring is mounted now, to help reinstallation, or even rebuild your shutter with parts from mine if the threads are the same.

cheers

Tim