Cutting Acrylic

[waltie]

I am getting melting when cutting acrylic using a PC router at 10,000RPM and 1.0 feed rate. Have tried other feed rates but same thing.

any help on speed and feed would be greatley appreciated.

[billp]

Waltie,
What kind of bit are you using...? THIS can make all the difference...

[paco]

Hi Waltie!

As Bill point, the kind of bit you use has it's value for the finish of the cut. Still, I have used standard 1/8" and 1/4" 2 straight flutes carbide tipped wood router bit without major problem... O-flutes are better for chip extraction and to avoid to get the bit clogged with debris/melted material.
Assuming that your trying yourself with straight edges wood bit, I would suggest to try 13000-16000 RPM, 1 to 1.25"/sec. feed, 100% stepdown or less for the 1/8" CED and a little faster for the 1/4" CED... and don't plunge too fast; if you can ramp in cut that would be better.

By the way is metling and welding to the bit or to the edge that's has been cut?
Is your cutter sharp?... VERY sharp?

Keep us informed of your finding?

[waltie]

I was using a 1/4 upsprial, weld is to the cut edge and bit is brand new

[kevinlreid]

waltie
I use a bit for plastic called a zero flute. Bought bit from Whiteside tools. I also blow air into the cut groove, and make passes at .25 inch deep per pass. Works good for me.
Kevin

[robtown]

There are different types of acrylic as well, cell cast and extruded. I've had better luck with cell cast.

[waltie]

Thanks guys for the help
the RPM of 16,000 and a feed rate of 1" in/sec
did a great job

Thanks

[paco]

Right Rob!

I always have a less good finish on CYRO Acrylite FF than any other; just today I cut a job out of two different material of the "same type" (1/4" thick white)... one was ??? and the other was CYRO Acrylite FF and the ??? came out very clean and easy cut non-rewelding chips while CYRO Acrylite FF came out with some "powdery rewelding" on the cut edge and clogging bit chips... I've tried 3 different cutters?!?!?!... I've tried air cooling with worst results!!!
Anybody have a good cutter with spec. for this CYRO Acrylite FF?

[paco]

Hummm... I'd be suprised no one encounter difficult Acrylic?!... did anyboby made similar observations and would like to share tips and tricks about it? I'd really wish I could get a better finish from this CYRO Acrylite... with a 1/8" tool bit that is...

[joe]

I would be most concerned with the type of acrylic. There are two grades I am aware of. The machineable acrylic doesn't melt back together so easily.

After all the bit suggestions, look at the material.

Joe

[paco]

Hi Joe!

Ok... but which is which? Type, made, brand, link for more info... Thanks in advance!

[joe]

Paco,

We order our plex with the suffix of SG. Some of the clear 1/4" plex we've received, did as you have posted, melted back together after routing. I really don't think it's the bits, speed, etc.

Joe

[paco]

Hummm... how to know in advance?... how to figure before getting the material?...

[Andy (Unregistered Guest)]

I use the following bit:

A 3.96mm diameter spiral down cutter. For Acrylics I use an RPM of 18,000 and a feed rate of 250mm per minute. With this cutter you can handle up to 6mm thick material in a single pass. The cutter is ground for clockwise rotation. (it's a cheap bit for a standard router although I'm running it in an Elte spindle)

I've found the feed is more critical than the RPM on the spindle.

I'm in the sign business so I cut a lot of Acrylic. There are two types as has been mentioned- extruded and cast. Cast is cheaper but is not as good quality wise- I have more problems with spoil welding on extruded over cast.

As well as there being two main types I find different brands vary hugely. Being in the UK we mainly use original branded Perspex. This machines consistantly and flame polishes perfectly right through the colour range. Other brands of acrylic I have worked with perform more like polycarbonate which is much more likely to melt up when cutting. Some of this stuff won't flame polish on colours or even clears- quality Acrylic will. Polycarbonate burns when you try to flame it and most of the cheap materials avertised tend to do the same.

I try to avoid using brands I've not heard of- there is a lot of cheap material from India & China floating about.

If you are using a good quality material a cutter like I'm using should give you a good edge.

In terms of lubricating the material I find a light maintenance oil like WD40 is helpful. The main thing you need is good extraction to clear the hot spoil as fast as possible- otherwise is gathers and cools.

Hope this is helpful

[Travis Vinson (Unregistered Guest)]

i went to home depot and bought some brand-x plexi which is melting the chips really badly. i had some of that aforementioned CYRO Acrylite FF which cut much better with less "chip-melting". but we broke our bit so we are using a different bit on the brand-x plexi. i am not sure if the bit is giving us different results or the plexi itself? what do you guys think? i am looking for the best possible combo of bit, speed, feed rate, and material?

[billp]

Acrylic and plexi are two totally different animals.
I've never had much luck in cutting plexi, and whenever I got the option I would use acrylic instead.
A spiral "O" flute works well in acrylic, but I haven't tried it in plexi. I usually cut acrylic between 10-13,000 prm, at speeds from 1.25-3IPS.

[joe]

When we order our acrylic, plex or what ever you call it, we ask for the SG grade. SG is a code for Sign Grade.

A good bit is necessary to do a good job but I don't think you can cut some of this material with a 000 upgrade , down grade spiral, sideways fluted, excess oval or etc. It's probably the materials.

Joe

[paco]

Hello all!

I've contact my supplier about this issue (mine at least) and he got back to me saying that I should order/ask for cast rather than extruded acrylic...

Bill,
what bit size with thoses spec.?
Do you use one flute or two (preferances) of thoses O-flutes?

[billp]

Paco,
I usually use a .25"single flute "O" bit.

[elcruisr]

I have a secret weapon for problem plastics and, so far, it's worked when the polished 1/4" o-flutes have been less than perfect. I got the tip from a guy who has seen alot of plastic run through CNC proccessing. Try an Onsrud 52-638. That's a two flute 3/8" o-flute upspiral for plastics. Then run it counter to conventional plastics wisdom and run the RPM's high and the feeds low. I'll turn 16,000 to 18,000 and feed it at 1.5 to 3 inches/sec. Sometimes I use a finish pass and sometimes not depending on the edge quality needed. I've cut extruded and cast acrylics of several brands and polycarbonates as well as some PVC. Best edge qualty I've had off of any tool and no melted chips in the cut. The idea is to get small chips and blow them out of the cut before they can melt behind the tool. I've used it on material up to 3/4" doing 1/4" passes with a .030 finish pass and had a really clean finished edge when done.
Eric

[cnctooling@upsharp.com]

Has anyone tried a cold air gun for melting problems? If so have you improved finishes or tool life?

[paco]

Hey Dan!

I've tried cool air while cutting acrylic (actually to remove chip from the kerf) and I got into worst; the melted material was hardening faster... on the tool bit...

[WCSG (Unregistered Guest)]

Cyro recommends 1/2" bit spiral -O 18,000 rpm's with 3 inch/sec. These bits are less susceptible to friction heat than smaller diameter bits.

12k-18k with feeds of 2.5-3inch/sec

[Andy (Unregistered Guest)]

In the perspex workshop handbook the recommended spindle speeds are 24,000rpm for bits between 6 & 12mm diameter. For bits larger than 12mm 18,000rpm is advised. HSS bits are preferred to TCT. Bits should have double edged cutters with a back clearance angle of around 12 degrees.

Optimum thermoforming temps are 170 degress for cast and 155 for extruded.

No mention of feeds in the book.

website;- www.perspex.co.uk (http://www.perspex.co.uk)

[cnctooling@upsharp.com]

Waltie,
Here's a suggestion you can call Onsrud Cutter, they have tools and can give you speeds and feeds. They log tests performed from all different material manufactures. 1-800-234-1560 ask for tech support.

[artisan]

I tend to agree with Andy,Joe and Eric on two key issues. Clearing plastic chips from your work is absolutely crucial....this is what heats up and fuses back to your work and your tools. If you are not removing chips, then coolant will not help you. Secondly, batches seem to differ wildly from each manufacturer even sometimes from batch to batch from the same supplier. There are a number of good bit configurations, but we always test the piece first to find and tune the better feed and speed rate no matter the bit style. Test your material and make the chips fly....D

[dmdraper]

Onsrud Cutter makes bits specifically for acrylic. The feeds and speeds charts are available at the link below under "Router Bit Search"

Onsrud's "Plastic" Web site (http://www.plasticrouting.com)