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Spring Joint Caliper Replacement Spring

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HolyHarp

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#1
The spring broke on a pair of calipers. I'm considering just tossing them but I do like to repair things if possible. How could I find or make a spring for them?
 

HolyHarp

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#2
Here's a photo of the calipers with the broken spring. I'm thinking of trying to make a replacement from bamboo.
2018-08-09 11.21.07.jpg
 

francist

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#3
Well that will be interesting!

Many years ago I undertook the building of a violin from scratch. In order to accomplish the fairly tight curves in the ribs, the maple sides (about 0.50" thick maybe) are bent over a hot iron. You do this freehand, not over a form of any kind. It's actually pretty surprising how tight a radius can be accomplished with just localized heating of the wood and rocking it back and forth over the iron. Wonder if bamboo might respond similarly?

For what it's worth, my "iron" consisted of a short length of schedule 40 black iron pipe which I held in a vise and played a propane torch through the end. Worked great!

-frank
 

GrayTech

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#4
Recently did exactly such a repair. I cut a 1/4 section off a 1" spring steel split collar I picked up on the road. Worked perfectly. I could mail you a 1/4 section to use if you like.

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RandyM

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#5
In trying to avoid the this type of failure and to prevent the spring from losing its spring rate I store my calipers so the spring is not tensioned.
 

Cadillac

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#6
Don’t soak in vinegar to clean rust off with the hoop on. I bought three nice German made ones and went to clean them in vinegar. Came back about ten min later and the hoops were all in pieces :oops: :(. Haven’t figured a way to fix yet so I’m all ears.
 

BtoVin83

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#7
I have a small divider with the same problem. Mine are Mititoyo and I'm gonna see if they have parts or will fix them. I know they have a repair shop.
 

BtoVin83

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#8
Mititoyo was no help at all, might see if I can make my own.
 

francist

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#9
Wonder if one of these or similar might be able to be re-purposed for one?

image.png

-frank
 

HolyHarp

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#10
Recently did exactly such a repair. I cut a 1/4 section off a 1" spring steel split collar I picked up on the road. Worked perfectly. I could mail you a 1/4 section to use if you like.
Thanks for the offer. Let me keep that as a plan B for now. Please post a photo of your handiwork; I think it would be useful to others. I live in a small village in Thailand where there is quite a bit of bamboo but few spring steel split collars.
 

GrayTech

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#11
Here's the collar I cut. It's an old starrett caliper that was pretty rusted when I found it.
With a bit of fiddling the hose clamp pictured in a previous post would absolutely work. They are commonly used on hoses in car engines.


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Tony Wells

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#12
GrayTech, you should turn up the pivot for those calipers if it is lost, which often happens when there are issues with the bowspring.

Or is that a pin of sorts I see already there?

Just an aside, I have a pair of smallish OD calipers that are one piece. German made IIRC. It appears they simply forged the frame to be thin where the spring goes and omitted a pivot. If they ever break, there will be no easy repair.
 

GrayTech

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#13
GrayTech, you should turn up the pivot for those calipers if it is lost, which often happens when there are issues with the bowspring.

Or is that a pin of sorts I see already there?

Just an aside, I have a pair of smallish OD calipers that are one piece. German made IIRC. It appears they simply forged the frame to be thin where the spring goes and omitted a pivot. If they ever break, there will be no easy repair.
Hi Tony, I made the pivot pin that's in there too. I'm always picking up small pieces of useful stuff, or scavenging off tossed appliances etc. I have boxes full. Larger pieces of stock other than 1018 and 6065 is what I struggle to find. It's difficult to find and very pricey when I do find some. Wish I knew where to get drops at a decent price.

The calipers work as intended and should hold up well. I don't store them with the spring under too much tension.

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Tony Wells

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#14
OK, great....just checking.
 
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