Turning acrylic/plexiglass rod on a lathe

Hello,
I know this is not specifically metal related, but we have some acrylic rod that we are trying to machine using a lathe. The problem
with acrylic is that it melts as the bit is cutting into it. We have tried various speeds, with little effort. Would it help to keep the material cool using a water spray or some other means? Is there a particular bit/material that is good to use?
Thanks for any ideas or pointers.
Mike
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Mike, HSS with very high rake for OD turning, same for boring. Small tool tip radius and Diamond honed very sharp. Surface speed is very tolerant. Light feed rates are fine, Shop Vac is good to keep the snow off everything.
Drilling is a whole n'other story. Zero rake, slow PRM's slow feed. Peck a lot to remove the chips.
Plastic polishing compound as a lube, for drilling and tapping
Dave

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I have generally found polycarbonate easier to turn than plexiglass. Polycarbonate is not immune to the melting problems but it tends to cut at typical metalworking tool speeds/angles rather than melt and gum up everything.
For drilling plexiglass, or cutting plexiglass, there are special drill and saw blades, but I didn't find anything special for turning plexiglass that actually worked for me.
Tim.
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eljainc wrote:

Try soapy water as a coolant/cutting fluid. Be sure to clean up well afterwards (rust). RR
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On Tue, 27 May 2008 22:04:15 GMT, Randy Replogle

Slow and easy, scary sharp tools.
For drill bits, shallow rake and scary sharp - the plastics centers sell the right drill bits already pre-ground for use. If you try modifying your own drill bits for plastics, use a Drill Doctor or other precision sharpening jig. If the point is sharpened off-center that drill bit will try to make a conical hole, or a hard left turn, or other disasters.

And whatever you do, DO NOT use any solvents or lubricants on the plastic (either acrylic or polycarbonate) that are not specifically approved for use on it - Read The (Friendly) Manual.
Solvent embrittlement can destroy the item in 15 seconds, or set up a 'slow burn' that will wait a few days before it starts crazing and cracking.
--<< Bruce >>--
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As you have found, heat is the issue. The cutting edge has to stay under a couple hundred degrees or it will gum up. Tooling has to be super sharp. A finely honed HHS bit is the only way to go, don't even think of carbide. Use lots of rake on the tool but be careful that the rod doesn't buckle and dig in. An air blast directed at the cutting point may keep things cool enough to avoid the dreaded melt and gummy stage that you are experiencing.
eljainc wrote:

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I use carbide on polycarb all the time, but that's just me....

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Slow, sharp tools works well. Do not use a coolant. All plastics will absorb the coolant and swell. Some plastics more than others, but all plastics swell when exposed to coolant. After a few days your work will be undersize as the coolant dissipates. A directed air blast will not only cool, but eliminate chip galling and the related heat that problem generates. Steve

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Keywords:

A vacuum cleaner provides a little less airflow, but you don't have plastic dust or chips flying all over.
"Coolant" doesn't always mean "solvent". I've used soapy water with great success, and never had a problem.
Doug White
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On 29 Maj, 02:42, snipped-for-privacy@alum.mit.edu (Doug White) wrote:

Every time I been jigsawing acrylics I used alchohol to cool , that work .Isn't alchohol also the choice for Aluminium, only asking to avoid bad jokes !
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wrote:

I've used and recommended alcohol for cutting aluminium, it keeps the tip temperature down and stops it from trying to weld to the cut surface. This allows for a very fine finish compare to dry. It will also air dry without any residue, which can be important. It is for the aluminium samples collected for chemical analysis by spark spectrometers like I work on.
Grinding of soft metals is also not preferred due to the amount of crap from the grinder that is ground into the surface. Hope this helps, Peter
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Alcohol can be bad for acrylics. I'd stay away from it. I once tried to clean an acrylic pen with alcohol and the whole surface became checked.
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I suggest a test . But it's allway's important to remember, that much denatured Alchohol contain uo to 8 pct. water plus the denature agent , it might be what caursed the problems. Othervise it would be an idea to look for the right speed and the right angles to use for the cutting piece
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I suggest a test . But it's allway's important to remember, that much denatured Alchohol contain uo to 8 pct. water plus the denature agent , it might be what caursed the problems. Othervise it would be an idea to look for the right speed and the right angles to use for the cutting piece
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I suggest a test . But it's allway's important to remember, that much denatured Alchohol contain uo to 8 pct. water plus the denature agent , it might be what caursed the problems. Othervise it would be an idea to look for the right speed and the right angles to use for the cutting piece
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wrote:

Run the test with the acrylic both stressed and unstressed. If my memory serves, acrylic is prone to crazing when exposed to alcohol only if it's stressed to a significant percentage of its tensile strength. The pen mentioned above may have had residual stresses left over from the molding process. Sawing or turning with sharp tools that don't overheat the plastic are less likely to leave the part stressed. I've seen acrylic parts with very deep drilled holes craze when exposed to alcohol.
--
Ned Simmons

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Ned Simmons wrote:

I don't know if short-term exposure would expose a crazing risk, but it should be pointed out that Plexiglas also absorbs plain water. This can cause the part to distort, which may affect the precision of any machining.
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On Tue, 27 May 2008 12:47:26 -0700 (PDT), eljainc

Others have posted good info about sharp tools and solvents. Steve said not to use coolants. However, I have machined lots of acrylic using pure water and have not had any problems with the plastic shrinking. It is vitally important to keep not only solvents but also any oils away from acrylic. Any oil on acrylic will eventually cause cracking. If stressed the plastic will crack faster. Even acrylic pepper grinders eventually crack from the oil in the peppercorns. Use only polishes made for plastics. Tap Plastics sells drills and polish for acrylic. ERS
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There's cast acrylic and there's extruded acrylic.
Cast acrylic is very easy to machine. For turning, I use sharp HSS tools and no lubricant. For drilling, 0 rake and a lot of water to keep it cool. And lots of pecking. There are special drill bits with sharp points but I can't use those because I'm generally drilling blind holes.
Extruded acrylic is a real pain to machine. Use cast.
Which are you using?
-Bruno
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