Twined strings

Dear members,

When doing string calculations how should one treat twined strings. E.g.: is a twined string of 0,40 mm equivalent to a string of 0,80 mm?

Regards,

Chris.

That is a very good question. I have no idea. What I can say is that on average to a fair approximation the mass per unit length would be double, so you could take the calcs from there. So probably, yes, but that’s assuming a loose sort of twining. If the string is tightly overwound then the mass per unit length would be higher, so the double factor would be wrong.

It would be great to hear from somebody who knows.

The person to ask about twined strings is Peter Bavington. He has studied and experimented with them in some detail.
Huw Saunders London

Surely there are many subtleties to consider, which others will be more qualified to address. However, just considering the cross-sectional area, which to a first approximation should determine the tension and also the mass, and thus pitch: two strands of 0.4mm wouldn’t equate to one of 0.8mm. Since area goes by radius squared, my rough calculation gives something like 0.56mm, as “double” 0.4mm.

These pages by Peter Bavington may be of interest:

http://www.peter-bavington.co.uk/stringwin.htm

http://www.peter-bavington.co.uk/twined.htm

Some time ago I wrote to Mr Bavington to invite him to join our list, but I have not heard back.

I think Andrew Bernard has the right idea. If the twist angle is rather small the mass per unit length is, to first order, simply doubled. If the twist angel is not so small, weigh a length of string. and figure out the mass per unit length, use that as a first estimate for the frequency calculation, the rest is (a small) trial and error adjustment.