making a jig for springs

[nicx66]

I am interested in making a simple jig for springs to replace them when they fatigue and break. It has happened twice in the last 2 months so I am anticipating future spring failure. I have done a good bit of carpentry over the years and made jigs for window sash, etc. My concertina is a 30 key Connor C/G, his standard model. I had to salvage a couple of springs from a spares/repairs concertina that I have, however I realize that the springs are made to fit and not interchangeable. I watched an instructional youtube video on making this type of jig. I am curious about where to source the right gauge/type of wire and whether or not I should stick with the type that John Connor used? It seems quite thin, but I am sure that he used it for a good reason. 

[RAc]

This has been discussed several times before, you may for example start here (there are other back links to previous threads in that thread).

[Don Taylor]

I bought some phosphor bronze wire from the Instrument Workshop in Oregon,  their .020in premium coil works well for me.

http://www.fortepiano.com/index.php/products-menu-item/wire-menu-item/copper-alloy-menu-item/phosphor-bronze-menu-item

Edit:

I am sorry but I made a mistake in my original post.  I am using their .020 premium coil (16301-20) not the 0.025 as I originally said.  I have both sizes but find that the .025 fractures very readily when bent at right angles.  You can feel it give a little crack and see the fracture in the bend.

Edited June 1, 2018 by Don Taylor
Corrected size of wire from original post.

[Dana Johnson]

When making new springs, don’t copy the ones that have broken.  In my experience, poor spring design has dramatically increased their fatigue.  Each diameter and material of spring wire will begin to fail if bent around too small a diameter a mandrel.  A small increase in coil size can drastically increase the life of a spring.  When I first started making springs, I got about 100,000 cycles before failure.  By increasing the mandrel size, to 3mm, the springs would go for over 4 million cycles without failing.  With the right coil size, springs will effectively last indefinitely.  Heavier wire needs larger coils.  ( this relates not to spring tension, but to the microscopic damage done when the metal is bent beyond it’s yield point.)  find a safe coil size, then determine the number of coils for the desired force range.  

Dana

[Chris Ghent]

You can make more than adequate springs on a very simple jig, all you need is a four inch nail, a brad, and a piece of round wooden rod. Drive the four inch into the end of the wood and cut it off at about 4mm. Put the brad in 15mm away and cut it off at 2mm. 

To use, put the bend into the wire for the foot, hook it around the brad, make three turns around the four inch holding the wire low as possible to keep the coil tight, and stop bending when the top run is at at or near the required angle for the preload. Cut the wire a little long.  Form the hook directly above the foot and cut off the excess. Correct the foot and hook angles. If you want to make it look flash you can bend the top run over sideways as it comes off the coil and then reverse that bend a little further out so top and bottom runs are in the same vertical plane. 

Sorry about the mix of imperial and metric, a four inch nail is a colloquial term here, they used to be 4 inches long and 1/8" in width so about 3.25mm in width. 

[Anglo-Irishman]

23 hours ago, Chris Ghent said:

Sorry about the mix of imperial and metric, a four inch nail is a colloquial term here

Don't worry, Chris! Even here in Germany, where the building trades have been metric for generations, carpenters still talk about four-inch nails (4-Zoll Nägel). Not a colloquialism - correct trade jargon!

German organ builders also use the non-metric foot (Fuss) to denote the pipe registers.

Old ways die hard!

Cheers,

John