On Sat, Aug 12, 2006 at 11:09:25AM +1000, Tony Smith wrote:
> Unless you can come up with a good reason to rapidly heat the inside of a
> 20mm x 20mm cylinder with a 1cm hole drilled in it, it's a contrived case.
> Getting the inside of a large gun barrel to size is about the closest case
> you'll get.  Regardless, it doesn't matter.

Well, you can heat up that cylinder's hole very rapidly by drilling
it... I do a fair bit of machining, and I've heard people say that while
doing high-speed drilling work with some types of plastics the heat from
the plastic was both unable to escape due to low termal conductivity,
and caused the plastic to locally swell enough to grap the drill bit.

This is unlikely to be the drill expanding as some plastics can have a
much higher COE than drill bits.

The cure is oddly enough to drill the hole even *faster* by increading
the rate, the feed rate, at which the drill plunges into the work. That
way more of the heat gets ejected in the thicker chips and there is less
time for the drill bit to rub against the plastic..

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