I've drilled holes in 5/8" acrylic to depth of about 3" with the lathe
at about 500 rpm and using my not-too-expensive 118 degree bits. I use
Cool Tool II or some other coolant and don't drill more than about
1/4" at a time without withdrawing the bit to clean and apply a bit
more coolant if necessary. Given the limited tailstock travel, I am
also readjusting that a lot. So it takes a while to get to full depth,
but it works.

I've read that a wider drill angle (e.g. 135 degrees) may be better,
but I have not tried that yet.

First time I tried, I melted it too.

-Bruno

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.

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

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.

Good words from others. I think it's also important to grind a flat on the
cutting edge so it scraps instead of cuts the plastic. Similar to drilling
brass when you don't want the drill bit to grab.

Earle Rich
Mont Vernon, NH

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)
--------------------------------------------------------------------------------

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.

If this is a one-off, just tough it out with what you've got. But
if you're going to be doing a lot of this work, you really want to
get a drill bit ground specially for acrylic, like at

http://www.craftics.com/products.cfm...ken=3841 3811

Most plastic dealers/fabricators will have these drills in stock.

When I did stuff like this we used "plastic polish" (a white creamy fluid)
as a lubricant.

If you're really making a tube out of a rod, and you'll be doing a lot of
it (thousands of pieces), you can probably get these cast exactly to your
specifications.

If the properties of acrylic aren't essential you might want to try Delrin
or Nylon as a raw material, it's a whole lot nicer to work with.

Tim.

Maybe a pilot hole and then the regular size. With a pilot you could push water
through the hole from the bottom. Anything to get away from WD40.
Bob AZ

Spray mist would be nice. You have the right idea with low rpm. You will
need to peck with a small amount of time in cut and enough time out of
the hole for tool to dissipate heat. If mist (or flood) is not an
option, use an airgun with a small orifice to direct air into the hole.
Plastics generally develope heat rapidly and usually shrink back when
tool is removed and part cools. When you put tool back into hole it is a
bit smaller than the drill, but usually not so much that the drill cuts,
rather it rubs and expounds the heat problem. A coolant fed drill would
be a good thing, but the smallest size available seems to be 3/16.

michael

If you switch from Extruded rod to Cast rod, your task would be easier. The extruded rods, and sheets for that matter, have a tendency to gum up no matter what you do, even cutting on a table saw.

I would also like to chime in on using tube instead of rod too. Advantages here are having the inside of the hole clear too, something not likely to happen with drilled rod. Hopefully sizes are a bit flexible.

Generally with acrylic you would want a pointier bit rather than a flatter bit, but sharpness is very important. As mentioned before, you want to let the bit scrape or cut the hole, not just creating heat and melting through. Lubrication is very important. At Just Plastics (another plug!!) we use 3 differant things, though not at the same time. In this case, we would rub the bit with soap. You would want to use a soap without perfume or color as they might attack the stressed material (we use IVORY). Second is flooding it with water soluable oil. A bit messy, but can give you a beautiful hole with some patience. Third would be some sort of Silicone spray lube.

Good luck and feel free to contact me if I can be of any more help.