On Mon, 18 Aug 2003 14:51:40 -0500, Jon Elson
wrote:



random wrote:

I'm looking for wisdom, subject is drilling a 4" long 9/64" hole
through a rod of extruded acrylic. After about an inch and a half the
acrylic and/or the bit are hot enough to melt the acrylic. I've tried
various speeds and find that 80rpm is about least bad. I've tried
various grinds on the tip. Bottom line appears to be 80 rpm for the
first inch then take it out of the lathe and woodpecker with a
variable-speed drill, hoping someone knows a better way. tia.


I think you have to peck at this, allowing it time to cool. You could
drill about 1/2" each peck, then retract. Leave the tailstock base
unclamped, and just slide the whole tailstock forward to drill, and
pull back to extract the chips. This is much faster than the crank.
Use a wet brush to cool the drill and knock the chips off it. The chips
carry much of the heat, so getting them out of the hole is important.
Also, they make a lot of friction when packed into the flutes.
Use a squirt gun or little pump sprayer bottle to get water all the way
back in the hole. If the hole needs to look good, drill undersize and then
ream, or make a custom boring bar just a hair under the full hole size.

Finally, when you are just about to break through, clean off the bit and
advance real slowly with the crank, to minimize chipping of the exit hole.

Jon

In the machine shops I work in, they simply use flood coolant just
like they would with metal. Seems to work for them. Oil for the most
part, though some use toilet water.

Gunner

"The French are a smallish, monkey-looking bunch and not dressed any better, on average, than the citizens of Baltimore. True, you can sit outside in Paris and drink little cups of coffee, but why this is more stylish than sitting inside and drinking large glasses of whiskey I don't know." -- P.J O'Rourke (1989)
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