Introduction and plea for help

Hello group,

With a bit of luck, this list will be the best thing in my life (sad
eh?)

As some of you know already I repair and restore high class watches and
small clocks and I am wanting to find a way of making small parts easily
and accurately. A typical problem might be that a complicated
chronograph may come in, having suffered the attentions of an 'expert',
with one or more of its internal operating levers missing. At the moment
the only way I can reliably make a new part is to cut and fit it
gradually bit-by-bit using the remains of the movement as a guide - a
very hit-and-miss affair. I have worked out that, by taking digital
photos, importing them into Autocad and drawing over them, I can design
the required new part to a high degree of accuracy and confirm that it
will work OK before I cut any metal BUT I then have the major problem of
transferring the designed shape onto the metal and cutting it
accurately - a scribed line in my scale of things can be half the width
of the finished part!
So, I have been playing about for some time with ideas to make a wire
EDM and a miniature CNC miller - each with a table size of only about 6"
x 6". However, I have continually fallen at the first fence as I don't
seem to be able to get a stepper interface working properly. The
steppers I have are marked 'Step-Syn' type 103G770-0344, 24 volt, 0.22
Amp, 1.8 deg/step, 5 wire. I have tried a number of published stepper
driver circuits but these are mainly for low voltage motors and seem to
give up when I try to hang a power darlington output stage on them to
handle the higher voltage. I must admit to not having tried Dan's
circuit yet but, after so much wasted time and expense, I'm a little
sceptical of paying out for 24 transistors on a maybe! (Sorry but I am
the archetypal Yorkshireman - deep pockets and short arms!) I tried
running an emulation of this circuit on an electronics workbench program
and it seemed to work, although with apparently jittery outputs - then I
moved and reconnected a wire I had connected to the wrong place and it
stopped working!
Can anyone advise me on the practical solutions they have found and,
also, can anyone tell me how the feedback circuits of a wire EDM work -
I'm sure this is really the machine I need for most of the work I want
to do.
Some of the watches etc. I have been working on recently are on my
web site at http://www.iw63.freeserve.co.uk/watchreps.html

Best wishes

Ian

--

Ian W. Wright LBHI
Sheffield Branch Chairman of the British Horological Institute.
Bandmaster and Euphonium player of the Hathersage Brass Band. UK.
See our homepage at:- http://www.iw63.freeserve.co.uk/ or
http://www.iw63.demon.co.uk/ or
http://www.GeoCities.com/Hollywood/6067/

'Music is the filling of regular time intervals with harmonious
oscillations.'