I should just go with trial and error – the spring will expand diameter-wise when the winding tension comes off it.

Good morning Peter,

If you have a copy, I’m led to believe there are charts/calculations for winding springs in “Machinery’s Handbook”.

Model Engine Builder No 19 has a winder in it which I have. made and works well, allowing you to do close coils and vary the main pitch as well. Dersigned originally for model valve springs and allowing you to repeat so sets can be made.

Mark

On 9 January 2024 at 17:06 Mark Rand Said:

I’ve got a job where I need to coil a bendable heating element to be a firm fit around some stainless steel pipe. Fulmen’s calculator site seems to say that I should be aiming at about 1.5″ mandrel diameter to match the 2″ pipe.

I’ll happily use that value in the hope that it comes out about right.

If you look at Fulmens link there is a factor k used in the calculation, which not only seems to vary with material but also varies as to how that value is calculated so I would be very wary about the value for mandrel diameter calculated, it may take a couple of attempts to get the correct value, hopefully the heating element could be uncoiled and rewound if it comes out wrong. Having said that if you aim for a slightly  smaller coil diameter then possibly it would be a firmer fit when on the stainless pipe.

Paul,

That’s odd.

I used both the formulae and the “calculate” button in Fulmen’s reference and got exactly the same answer for mandrel diameter for each material as you would expect. What did you find ?

On 8 January 2024 at 21:10 Fulmen Said:

There’s this one: https://daycounter.com/Calculators/Springs/

I’m late to the party, but thanks for that link

Good to see an online calculator that clearly states its working, and credits the the source.

MichaelG.

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https://craftsmanshipmuseum.com/artisan/kozo-hiraoka/

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P.S. __ for the practicalities of making small extension-springs

https://www.homemodelenginemachinist.com/threads/springs-and-things.7552/