Hello all.
I have a Shapeoko Pro with a Compact router and I’d like to cut some plexi, but need to know if I could cut it with what I have or rather what is needed to do so. Do I need a special bit?, do I need water? or can I do it with just what I have.
First question is the plastic cast or extruded?
Cast is far more readily machined than extruded (it usually comes w/ a paper backing).
A single flute endmill will help, but we have feeds and speeds for “Hard Plastic” in Carbide Create which should work.
See the videos on single flute tooling and similar plastics at:
I believe it to be the plexi that you can buy from your general local hardware store. Acrylic Plexi is what I think it is. But I’m not sure if it is extruded though
I use a two-flute cuz that is what I got right now. A one flute would be better.
If you are cutting shapes out. You do not need lubricant. Play with your speeds and feeds to get nice chips
I cut images on the stock at .001 or .002 depth. I use WD40 to lube the surface when cutting. An extra step to wash it, but in my experience, it works to make a better-looking cut.
Good Luck
A Huge thank you to you both. all great advice.
@Will: I looked at that link, that is a great resource.
@Zman: Im in that same boat. Ill be doing a contour cut to create a glass cover for another project. I will be using what I have and will use the settings provided via the link that Will provided.
Again, thank you both for all the information. I really helped.
If the plexi is a thin sheet more then a few inches in size and you are cutting through the sheet you will want to use the tape and glue workholding method. I typically tape and glue the whole bottom of the sheet just to be sure it stays where it is supposed to. If you just clamp it and the bit flexes/lifts the sheet Bad Things can happen.
Nice benefit to tape-and-glue is you don’t need to use tabs for most cut outs since both the silhouette and the finished piece are still tape/glued down. I use the “hard plastic” setting in Carbide Create with a standard #102 1/8" bit, no lubrication. I have used that on both cast and extruded acrylic and it has come out decent enough for my use (arcade control panel tops and an acrylic edge light sign).
Plexi and acrylic are 2 different materials. Both will cut fine though, extruded or cast. I cut ribs off both and HIGHLY recommend a single flute. Faster feed rates and lower depth of cut help as well.
Though there are different types, plexiglass is acrylic. Plexiglas® is a brand name for acrylic which I believe is always cast sheet.
@EXtinguisher79 It would be helpful to know exactly what you have. Regardless, you want to feed faster than you’d think.
Ah… you’re right. I’m mixing it and Lexan. 
Easy to do. Lexan is polycarbonate. Also great for machining. Again go fast, but with shallower passes.
Thank you all for every bit of the advice. It will all be put into practice.
The Plexi that I intend to cut is from the local hardware store and is .08" thick (Of the stronger type).
Additionally, when you guys say to “go fast”… what exact RPMs & Inches per Minute are you talking, as well as the Depth per pass?
A Two-Flute 1/4 & 1/8 is what I have to cut with at this time.
Like Will mentioned, CC has a few preset feeds and speeds for hard plastics, for example for the 1/4" 2-flute #205:
Hmm… gonna have to look at those. Are those able to be adjusted, and can those adjustments be saved for later use?
Those are predefined sets of values that are reasonable starting points, once selected you can override the values manually for a given toolpath, but those modifications can’t be saved for later reuse. If you would like to make a custom preset with specific values of your own, the best is to create a new “tool” in the library (meaning a new tool/material/feeds and speeds combination, really)
Ahh I see.
So in other words, If I wish to create a custome setting for an existing tool then I do just as you mentioned. perhaps it would also be helpful to name that tool setting something specific
That depends on the endmill.
There are a lot of threads on the forum about acrylic (use that to search instead of “plexi”) that may give you a better indication.
With a single flute, 1/8" cutter I’d start between 100in/min. With your thin stock, I’d be tempted to take in one pass, but the depth of cut is where you can be more conservative. Go two passes. The chipload on these settings is higher than what you usually see, but I’ve had good results with my SO3XL. With a 1/4" cutter, you can be more aggressive.
Make sure your material is really secure with tape and CA.
A note for @EXtinguisher79 since you mentioned you only have a two-flute 1/8th on hand for now, that recommendation would become 200in/min then (but @neilferreri is maybe assuming a higher RPM than 10000RPM?). But actually, it would be a better idea to order a single flute O-flute endmill if you are going to cut acrylic. More flutes means more risks of clogging them with melted plastic, and nobody likes broken endmills (but we do like you, @BrokenEndmill 
)
The bottom line is, plastics like high feedrates, so if you start with a small depth per pass, you should be fine with experimenting a little. The real risk in plastics is feeding (or plunging) too slow.
I have had my doubts, but it is reassuring to get it in writing 
WOW! Everyone is getting into cutting plastics with CNC. Just received an eMail from Popular Woodworking and went to the article here - a very long URL: Cutting & Carving Plastics with a CNC Router
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%20Weekly%20Newsletter&utm_medium=email&_hsmi=208354870&_hsenc=p2ANqtz-_lkCdSEcvgU5nzwMZsD1-
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Hello friends…
Update… the Acrylic Glass Cutting was a success.
Just want to say thank you to all for the insightful information.
It all came in handy.
