Hi John B, Your suggestion of using a piece from the mainspring of a clock for a compass needle is quite a good one - I have done this. It needs to be tempered by heating and then allowed to cool slowly first. However, the disadvantage is that the material tends to be rather thinner than is ideal (0.3 to 0.5 mm seems to be normal) and so there is less 'magnetic moment' when the needle is in place. This makes it more sensitive to the 'stiction' of the pivot. Regards, John D ----------------------------------------
Dr J Davis Flowton Dials --- On Sun, 8/7/12, Morgie Terwilliger <[email protected]> wrote: From: Morgie Terwilliger <[email protected]> Subject: Re: making a compass To: [email protected] Date: Sunday, 8 July, 2012, 0:40 John's ideas are all right on. John mentioned a piece of hard steel. I wonder if a piece of clockspring would have the right properties. You can take a clockspring out of the drive drum of a junk windup clock, and at least the outer coils can be straightened out flat. I've seen magnetizing coils. They are air-core solenoids (helical coils) of heavy gauge wire and they are energized by capacitive discharge using capacitors such as are found in photo flashes (strobes) Best, John Bercovitz
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