[CAD_CAM_EDM_DRO] Spindle, inverted taper

Some musings, if anyone would care to comment...

Spindles, tool holders and collets are a difficult item for the hobbyist,
especially if you are after an ATC of sorts, and expensive if you want to
mount all your tools.

What I've been wondering about is the general, current methodology of
inserting a tapered toolholder into a spindle(ISO15, 20,30,40 etc).
Perforce, the spindle nose has to be quite large to accomodate the widest
part of the taper. The bearings then need to be of quite a large diameter,
which also affects the top speed attainable, unless you raise the spec of
the bearing. The R8 system lowers the required bearing diameter somewhat.

Now consider a spindle, which exits the motor as pointed rod, same 7/24
taper. The tool-holder, then fits over this, as opposed to into it. For the
hobbyist, it means that almost any sturdy motor can be used as a
spindle(with a few mods).

There is the concern of a lengthened tool, but if one looks at the kind of
milling done with a BT30 spindle, I'm sure some watering down would suffice
for the hobbyist.
http://www.youtube.com/watch?v=7q-Z7uqlxZg
http://www.youtube.com/watch?v=8f6I3hKg6vA

So the spindle would have an external point, with a small threaded hole in
the end, or a small through hole for a drawbar, and each toolholder would
have an internal cone and a stud of sorts.
So the idea is not to reach high speeds, or take hugh cuts, but to be able
to make ones own spindle using a steel shaft(~3/4") and regular bearings, or
directly use the motor shaft. Obviously the toolholders would have to made
to suit.

I did come across a driven spindle like this once, but I think it was off an
old tape reel-reel data system.

Regards
Roland


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