Subject: Coming up dry for Alps/Radio Shack/Atari/Commodore plotter gears

From: Ethan Dicks <[email-masked]>
Date: Wed Apr 23 12:59:06 2003

Having worked out the pitch of the broken drive gears (120), and
having looked on a couple of web sites _and_ contacted someone
at Boston Gear, it's looking grim.

According to the e-mail I got back, Boston Gear doesn't carry anything
finer than a pitch of 64.  When I asked who did carry such gears, the
answer was: "I am not familiar with any company that makes miniature
gearing." :-(

My goal all along has been to find a company that has a bag of these
on the shelf.  I had no idea it was such an unusual item.  I don't
relish the idea of fabrication, but maybe that's what we're facing.

Rather than machining each gear, I wonder how hard it would be to
make an extrusion die to pump out a long gear and cut it into 5/32"
slices?

-ethan
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From: Mail List <[email-masked]>
Date: Wed Apr 23 13:00:49 2003

Hello Ethan,

Internal splines, which is basically what that extrusion die would be are
much harder to do than cutting gear teeth on the OD of a gear blank.
The internal splines would have to be done on a slotter ( or possibly
a shaper with the right set up, i.e. some cutting machine with a linear
reciprocating cutting motion ) or cut into the die with EDM or wire
EDM processes. Much more difficult, and therefore more expensive
manufacturing processes. Original gears probably were shot in a
plastic injection mold, but the mold making is very expensive too, and
not something to do for very small production runs. Too bad you couldn't
find someone with a broach, because broaching internal splines might
not be as expensive a manufacturing process as long as you found
someone with the broach already made up. To have a tool and die maker
have to make a broach would also be expensive. Also extrusion die blank
material would have too not be too hard to broach. But then you have to
have the extrusion process set up and run. All in all, if you can't find them
already made up, milling the teeth into blanks or slotting on a lathe are
probably going to be your only really feasible options.

Best Regards

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From: Don Maslin <[email-masked]>
Date: Wed Apr 23 13:07:30 2003

> answer was: "I am not familiar with any company that makes miniature

Ethan, there is an outfit Sterling Instrument/Stock Drive Products
at 2101 Jericho Turnpike, Box 5416, New Hyde Park, NY 11042-5416,
phone 516-328-3300, fax 516-326-8827 who may be able to help out
in the 64 pitch game.  The address and phone data is some years
old, but may well still be valid.

						- don

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From: Don Maslin <[email-masked]>
Date: Wed Apr 23 13:09:01 2003

- don

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From: [email-masked] (Tony Duell)
Date: Wed Apr 23 13:09:30 2003

> make an extrusion die to pump out a long gear and cut it into 5/32"

There are 3 ways that instantly spring to mind for making this gear, 
using the sort of tools you'd find in a good amateur workshop (i.e. no 
CNC tools).

1) Mill it a tooth at a time on a dividing head. The disadvantage is that 
this is slow. The advantage is that the equipment needed is not too 
exotic. The pitch sounds simmilar to small watch or clock pinions, so a 
tooth cutter for those might be able to be used (but be warned such 
cutters are _very_ expensive).

2) Cut it on a hobbing machine. Once set up, it'll just cut the gear -- 
you don't have to index the blank round and feed it past the cutter by 
hand. The problem is that hobbing machines are not common (although not 
impossible to make either). Where you get a suitable fine pitch hob 
is another matter...

3) Injection mould it. David Gingery has written a book about making a 
small injection moulding machine which I think would be suitable for 
making these gears 1 or 2 at a time. The problem is making the mould. The 
obvious way to make something of that size would be by EDM. The electrode 
could be made by one of first 2 methods (you'd only ever have to make one 
of them :-)). EDM is not impossible in the home workshop, or so I am told...

Methods (1) and (2) have the advantage you could make the gear in brass, 
which would easily outlast the owner of the plotter :-)

-tony