machine tool accuracy and materials...
 

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Copyright (c) 1997 Douglas Dana Goncz

Doug Goncz
Replikon Research(ers)



On Thursday, September 11, 1997 3:00:00 AM UTC-4, The Dougster wrote:
Dear Bill,

You asked,

If I
want a CNC machine to machine complex shapes out of styrofoam, can
I build a lathe or mill entirely out of wood?


And the answer is YES, but it doesn't make sense to build a machine that
looks like a regular mill or lathe out of wood. Wood can be light, strong,
stiff, and stable when milled, sometimes laminated, and varnished. The
whole idea of CNC is to let the computer compensate for the geometry. So
why not set up something a little more frame-like, like a robot arm, or
gantry table? A hot wire cutter might be more useful, as "machining" any
shape at all out a styrofoam produces extreme digs and surface roughness
with conventional end mills or lathe tools. Are you familiar with the hot
wire method of forming tapered foam blanks for model aircraft wings? This
works for real airplane wings, too. Or get a plotter with a hot wire
attachment. You can build great custom cars this way.


Carrying this to extremes, can I start making structural machine
pieces (say, riser blocks for a lathe) out of plastic or hardwood
if I'm planning to machine softwoods andd softer plastics?

Sure, but you will be stuck with them, and may have to make another of
better material later.

It has a lot to do with beam theory. A plastic lathe like the Unimat One
makes a fine finish on a little aluminum plug, but to get a long shaft (the
one fundamental machine component) to stay straight, you need a stable
base, and a traveling steady rest if it is a skinny shaft. The shaft acts
like a beam, and the math is VERY non-linear. Anything can be done with a
bench and a ruler if you can take a fine enough cut and then measure the
result. That's how machine tools are built de novo. It takes a hell of a
long time that way.

Also, a medium size toolroom lathe is a wonderful piece of ergonomics. I
ran a 15" Clausing ten hours a day for a while and didn't get frustrated or
tired. Little machines are not very well adapted to the human body.

On the other hand (he said, gesturing with his third hand so far), people
are mobile, and mobile machines are a good match to that spirit.

I have a kickstand on order for my moped. The new part has nice hollow
pads on the bottom that can accept a sturdy rod, to keep it from falling
over while operating the Crapmaster, which easily fits on the back, if I
ever get around to mounting to the existing rack in a removeable way.


Yours,

Doug Goncz

My Soc. Sec. card says right on it:
"FOR SOCIAL SECURITY AND TAX PURPOSES--NOT FOR IDENTIFICATION" !
(Form OA-702 Rev. 9-61)

http://users.aol.com/DGoncz (sonoluminescence)
http://users.aol.com/ReplikonVA (machine tools)