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Spring Tension


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I need to replace all of the springs in a 48 key Wheatstone concertina because they have become weak and some even have trouble exerting sufficient force to seal the pads properly. I've bought the springs and I'm ready to go but I have no idea how to go about setting the springs to give a fairly uniform tension of around 60g force throughout the instrument.

 

Obviously the longer levers will overcome the spring pressure much more easily than the shorter ones so I assume that some kind of force meter is required in order to ensure that the keys have a uniform response. I googled around a bit and was alarmed by the cost of proper test instuments. So is there a simple method of setting spring tension? Is there some simple device I can cobble together myself that will give me a near enough indication without resorting to laboratory test kit?

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Obviously the longer levers will overcome the spring pressure much more easily than the shorter ones so I assume that some kind of force meter is required in order to ensure that the keys have a uniform response. I googled around a bit and was alarmed by the cost of proper test instuments. So is there a simple method of setting spring tension? Is there some simple device I can cobble together myself that will give me a near enough indication without resorting to laboratory test kit?

Yes there is. I'm sorrry, it's late and I can't search up the thread and owuldn't knwo how to cite it in here if I did, but one of the well-known makers posted a description and photos of a simple force guage.

 

Basically, it's a rod you hold vertically over the button being tested; it slides in a sleeve that you hold, and you stack washers on top of the rod until the button depresses. You adjust the spring until the button just depresses with the right number of washers. You only need a postage scale to weight the washers to calibrate the gadget.

--Mike K. (whose Stagi Hayden has no two rows of buttons with the same resistance ;)

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I need to replace all of the springs in a 48 key Wheatstone concertina because they have become weak and some even have trouble exerting sufficient force to seal the pads properly. I've bought the springs and I'm ready to go but I have no idea how to go about setting the springs to give a fairly uniform tension of around 60g force throughout the instrument.

 

Obviously the longer levers will overcome the spring pressure much more easily than the shorter ones so I assume that some kind of force meter is required in order to ensure that the keys have a uniform response. I googled around a bit and was alarmed by the cost of proper test instuments. So is there a simple method of setting spring tension? Is there some simple device I can cobble together myself that will give me a near enough indication without resorting to laboratory test kit?

Once you get one button set to the corect weight, I think you'll find that your own fingers provide an adequate and accurate force gage. In the end it is your fingers that do the judging not a gage when you play. I have both an accurate dial gage and the weight on a post type, and while they work fine, My finger feel is much faster. Having a uniform keyboard is a great thing, and on an english is pretty easy to do. some anglos because of radically different lever lengths are harder to make even andd some compromise must be made.

Dana

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I made a simple guage using an old pen. I glued on a brass rivet to the pen core to press against the button, kept the spring and some of the pen body. The gauge was calibrated with US coins (a nickel = 5g.). I'm sure it can be improved but this cost me nothing and took about 15 min. to make.

post-948-1188398924_thumb.jpgpost-948-1188398953_thumb.jpg

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Many thanks for all of the input, I'm just sorry I missed the original thread and went back over old ground. It turned up a few more interesting comments and ideas though. :)

 

I've got my eye on a second hand gauge but the shop was closed for a half day today. If that doesn't work out I'll be making something to set the first key accurately and then trying out Dana's idea (while double checking my accuracy with the gizmo).

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