On Sun, Aug 13, 2006 at 12:41:50AM +1000, Tony Smith wrote:
> > Very common mistake to think one type of drill bit will work 
> > on all materials for sure... My tool catelog collection has 
> > drill bits for, in some cases, even specific types of 
> > plastic, nylon, teflon, peek etc.
> > Hyper-optimised so much it's rediculous for anyone not making 
> > thousands of parts on high-end machines.
> 
> 
> Ah, feed, not RPM, you're right.
> 
> Machining plastic sucks anyway.  It either chips, melts or flexes.  I'll add
> catch fire for celluloid.  What do you use celluloid for these days anyway?
> Aren't table tennis ball celluloid?

They are, only modern use of celluloid I've ever heard of too. The guy
said he was completely mystified as to why they needed the part out of
celluloid, some research project aparently, so who knows?

Can't blame him for turning it down, hell, machining some of the more
flammable metals, like magnesium and titanium, is bad enough as it is.

> But you can't compare plastic to metal.  The hole gets bigger when heated,
> unless there's some other force involved, like clamping or stresses with the
> metal.

But see, the clamping force is the *surrounding* material. If that
material stays cool, it's not expanding along with the hole, so it forms
a perfectly good clamp. It happens with plastic because of the very low
termal conductivity combined with the ability to agressivly drill the
stuff.

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