Tension springs

[LF_rookie_to_be]

Has any of you experienced camera builders come across these types of springs? "Zugfeder" is the German term, the closest equivalent I found in English is "tension spring", perhaps there are other names.

Can these be used for a DIY spring back? The springs pictured are the ones I have and are pretty strong and stiff, but two connected together seem to have about the right tension for the 14mm thickness of a Fidelity holder. Any ideas? Thanks for your responses.

[Tracy Storer]

also called extension springs.
http://www.mcmaster.com/#extension-springs/=te4xna

[Dan Fromm]

The typical spring back uses a pair of leaf springs, one above and the other below the gate. See, e.g., fig. 4 here: http://www.cameraeccentric.com/html/info/graflex_5.html

In the typical spring back the ends of the springs hold the focusing panel against the back of the camera or, when one has been inserted, the film holder. If you can set up your coil springs to do that, fine.

[LF_rookie_to_be]

Thanks, Tracy and Dan. I've got a whole bunch of these small springs and thought to put them to use for a 8x10" sliding box camera I'm building. Seems that the connection of the hook to the focusing panel frame needs to be strong enough not to crack the 5mm-thick wood.

[Colin Graham]

One of the 4x5 Polaroid conversions uses springs like this on the back, can't remember which.

Canham uses compression springs and pistons housed in stays alongside the gg frame- pretty ingenious design. Torsion springs can also be used, like a graflock or Chamonix 4x5s. Depending on how complicated you want to get almost any spring can be used.

[Dan Fromm]

Torsion springs can also be used, like a graflock or Chamonix 4x5s.

Interesting. My Graflok focusing panels, all made by Graflex Inc., all have coil springs. One end of the coil bears on the panel itself, the other on the latching lever. My 4x5 Cambo international back has the same arrangement.

[Colin Graham]

We may be speaking of the same thing. If the load is radial like a mousetrap, I've always called it a torsion spring.

FWIW, I've only had one style of graflock back- sort of like this one- the torsion springs are housed on a mandrel in a void at the end of the ground glass frame casting, with the load on the arms. One side needs a left-hand wound spring, the other a right.

Attachment 120436

[LF_rookie_to_be]

Now I'm intrigued. Dan, if you could post a few pics showing details of the coil ends and the connecting latch(es), that'd be really helpful. Though my focusing frame will be made of wood, and I'm guessing Graflok and Cambo panels are all metal or maybe metal and plastic.

Or do you mean it actually uses torsion springs?

[Dan Fromm]

Colin, we're talking about the same thing. When I think of torsion springs I usually think of the torsion bars used in some Packard and Chrysler Corporation's cars' suspensions. These are straight rods that are twisted, can be thought of as coil springs that have been straightened out.

LF, here http://1drv.ms/1vsS48R are a few images for you. The first is the film side of a Graflok, the other is a Cambo bail back. A bail back is a fancier spring back with a device (bail) to pull the focusing panel out for easy insertion of a sheet film holder.

I think you'll find that making a spring back (with two leaf springs) is easier than making a Graflok with focusing panel like the one I've shown you.

Cambo made at least two different International backs for their 2x3 SC-1. One is a conventional Graflok, the other has a focusing panel that slips in. To take a picture with it, focus and compose, slide the focusing panel out and slip in a roll holder made to fit a 2x3 Graflok back; this version will not accept standard sheet film holders.

I see a way to make a back with a slide-out focusing panel that will also hold sheet film holders. Much easier, I think, to make than even a conventional spring back with leaf springs.

[jon.oman]

Good info here!