Making a mainspring Length Gauge with no moving parts
The following article is based on an e-mail to the Clocks mailing list from Michael J Helfrich
While preparing for an NAWCC workshop, a few years back, I ''developed'' the gauge.
| Obtain a 3''x5'' index card or a piece of cardboard from a shirt or any pad of paper that has a 90 Deg. corner. From the corner measure back 1'' on each side and mark with pencil. Connect the marks and you should have a triangle with a base length of approximately. 1 1/2''. Alternative materials can be Perspex or brass shim. These would be longer lasting. |  |
| Now the difficult part , scribe parallel lines from the base to the tip of the 90 Deg. angle. The more lines you scribe the more definitive the gauge becomes but about 1/16'' space will do. |  |
| To use, place the triangle flat against the open side of a barrel that contains the spring and arbor , with cover removed. Slide the gauge until one of the lines or spaces intersect the barrel I.D. and the arbor O.D. , the same line or space. Look down into the barrel at the tip of the gauge (90 Deg.angle). The tip (A) divides the barrel into two equal volumes/areas. This is where the end of the spring should be , plus or minus the amount of spring required to connect to the arbor, usually one coil. The gauge will work on any watch or clock barrel up to 3'' in dia. |  Gauge shows that the mainspring is too long.
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Simple , anyone can make and should have been'' developed '' a long time ago. No moving parts.
Hint: the more accurate you make the gauge the more accurate it is. This is a go- no- go gauge , it does not tell how long the spring is.
