Coming up dry for Alps/Radio Shack/Atari/Commodore plotter

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Tue Apr 22 18:34:00 2003

> 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?

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
Received on Tue Apr 22 2003 - 18:34:00 BST