Mention has been made of using a solenoid, and I believe that this is not the sort of thing Jackie will have in her 'silver' workshop.
Let us not forget that the traditional method of magnetising something is to stroke it with another magnet, as was done BF (Before Faraday) with a lodestone. Nowadays we have access to very strong magnets to do this job. Not quite good enough for making a compass, but is it normal domestic experience that knives and scissors will become magnetised by the earth's magnetic field and will mysteriously pick up paper clips and pins. Whole ships become magnetic too, but that is yet another story! In fact the opposite requirement is essential for a watchmakers workshop - that of a de-magnetising tool. I have made a compass for teaching purposes using hard spring steel sheet guillotined to size, a brass insert and steel sewing needle for the pivot, but its large size will hardly suit Jackie. Regards, Doug On 8 Jul 2012, at 09:34, JOHN DAVIS wrote: > 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 > > > > --------------------------------------------------- > https://lists.uni-koeln.de/mailman/listinfo/sundial >
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