Hi Jason,
In another thread called `Balance Springs’ under `CLOCK’ topics posted on 29 June 2010, I asked for comments about wire for springs. The spring for my clock is helical in form and consists of about nine turns with a mean diameter of about 9mm.
Using moment of inertia as my basis, calculations showed that a direct replacement for a rectangular cross-section (0.020″ x 0.005″) would require a wire diameter of 0.207mm (0.00807″).
Where would I find this size of wire? It occurred to me that some guitar strings are made of steel. However, their magnetic properties might be disadvantageous in terms of the performance of a tiny balance spring.
My luck changed when I rang a friend who has a music shop. When I asked what diameters of steel guitar strings were available at around the above size I was told that the smallest was 0.008″ (0.20mm). What a coincidence! Their length was about 0.8 metres. Although I wasn’t too interested in anything larger, I think the next size up was around 0.010″.
I bought a couple at around $2.50. They are coiled up in an envelope which describes them as
PLAIN STEEL
S I T
STAY IN TUNE STRINGS
.008
0.20mm
BALL END
BALL END means that one end has been wrapped and anchored around a small brass bush. At the bottom of the envelope is printed AKRON OHIO – MADE IN USA.
The wire is bright and highly polished, and when removed from the envelope becomes fairly straight, ie. no kinks.
Although I haven’t made any springs yet I’ve found the wire to be very springy, and is instantly attracted by a magnet. Over a gas flame the wire burns (ignites like wire wool) very quickly giving off sparks which I assume are an indication of carbon content.
Upon release after a short length has been wrapped around a 4mm diameter mandrel, the wire coil increased to about 10mm diameter. I suspect that feeding the wire over a mandrel will be the most tricky part of making a helical balance spring.
Hope this helps.
Sam
Edited By Sam Stones on 16/08/2010 00:48:58