1520 plotter (was RE: Your VIC-20 is worth $300!!! W_at_W!)

From: Ethan Dicks <erd_6502_at_yahoo.com>
Date: Wed Jan 30 00:20:17 2002

--- Tony Duell <ard_at_p850ug1.demon.co.uk> wrote:
> > I've just been trying to locate replacement gears for my 1520...
> 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.

That's an interesting idea. I hadn't thought of it. All I need is some
fine, precision wire...

> Or you can make a few good estimates using the known overall diameter and
> number of teeth.

I thought of that, but I wasn't sure how to validate/cross-check my
estimates. I really can't estimate if the depth is 0.1mm or 0.05 mm
or what. Not without some sort of precision measuring device.

> > 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.

Not in mine... it's the farthest gear from the motor spindle that's
broken - it's the gear on the shaft that runs the width of the printer
mechanism, for one. Perhaps we have different broken gears in ours...

> 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....

Eastern Pennsylvania, no doubt. A long, long time ago, in a Galaxy...

> 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)

Might not produce a clean casting, either.
> 2) Use tranditional gear cutting techniques (dividing head and involute
> cutter) to make a replacvement from scratch.

I would try that if I had access to the equipment

> 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.

I don't recognize the term "lantern pinion" - is there an American
term for that?
> 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.

I hadn't thought of a wire binding, but I did think of epoxy... kinda
permanent, though. If it breaks further, it'd be difficult to clean
up the mess.


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Received on Wed Jan 30 2002 - 00:20:17 GMT

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