1520 plotter (was RE: Your VIC-20 is worth $300!!! W_at_W!)
> but the mould would be very hard to make (cutting
> internal teeth on a mould that size)
Wire EDM
Tony Duell wrote:
>
> > I've just been trying to locate replacement gears for my 1520 - So
>
> As is everyone who has this type of plotter mechanism. I have a 1520,
> Tandy CGP115, a couple of Sharp PC1500 printers, a Sharp MZ700 with
> built-in printer, an ORIC printer, and at least one other. At least half
> of them have this problem...
>
> > far, my measurements have yielded the following...
> >
> > 14 teeth
> > 0.175" tall
> > ~0.144" diameter (hard to get an exact measurement with my micrometer)
> >
> > I do not know the pitch or the depth. Not sure how to accurately
> > measure them except with a fine-pitch measuring stick and a magnifying
> > device (I have neither).
>
> There are various ways using rods of known diamater. You insert them into
> the teeth, and then measure the overall size with a micrometer. Rather
> like measuring screw threads.
>
> Or you can make a few good estimates using the known overall diameter and
> number of teeth.
>
> >
> > I do not know the shaft diameter yet, but that's only because I haven't
> > gotten the micrometer to where the plotter is.
> >
> > There are two of these gears in the plotter, one on the X and one on
> > the Y gear trains. They are the last step in the reduction. I have
>
> I would call it the _first_ step in the reduction. It's tbe pinion on the
> motor spindle.
>
> Unfortunately the service manual I have for the mechanism doesn't give a
> separate part number or description for the pinion. You're expected to
> change the complete stepper motor :-(. And don't ask me where to get
> those from either....
>
> > an Atari plotter with the same innards as the C= 1520 and both of the
> > gears in there are split along the bottom of a groove - thin material
> > there, plus a bit of stress and who knows what kind of thermal expansion.
>
> It's a very common problem.
>
> >
> > The local hobby stores do not carry gears with such a fine pitch. For
> > that diameter, they have 10 and 12 toothed gears, not 14. There are
> > gear specialty companies, but I don't have enough measurements to search
> > the catalogs or place an order.
>
> I've not found them ready-made either.
>
> There seem to be several possibilites :
>
> 1) Make a mould and injection-mould them yourself. I think the David
> Gingery injection moulding machine could easily do it, but the mould
> would be very hard to make (cutting internal teeth on a mould that size)
>
> 2) Use tranditional gear cutting techniques (dividing head and involute
> cutter) to make a replacvement from scratch.
>
> 3) Make a lantern pinion of the appropriate size. This actually looks
> very possible. The meshing gear's teeth won't be the right shape for the
> trundles of a lantern pinion, but that may not matter.
>
> 4) Kludge it. One suggestion is to make a groove in the teeth away from
> the meshing part and to bind it with fine wire. I've heard this can work,
> but I've not tried it.
>
> -tony
Received on Tue Jan 29 2002 - 20:57:22 GMT
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