Thanks to another post here in the forums, I found a helpful video from Carbide 3D explaining proper feeds and speeds for the Nomad bits in polycarbonate. Now that I have some ideas of proper settings, I am wondering if anyone can suggest different bits for this process. I know single fluted bits are less prone to melting the plastic? Any brand specific recommendations?
My previous results were… let’s just saying a learning experience.
Single flute cutters:
Yes! That’s the video I found this morning and it was super helpful.
I was curious if anyone has a favorite bit for cutting polycarbonate.
Not sure if I should be recommending this, but Datron’s general purpose single flutes are actually very reasonably priced. If you want to buy a set of good quality ER collets, you can use basically any size they sell. Otherwise, filter by 3.175mm shank (1/8"), and take your pick. They only come in metric cutting diameters.
rule of thumb: avoid heat. “O”-flute has one “tooth”, and minimal surface to rub on the material. To reduce friction(=heat) of the cutting edges themself / itself this should run as slow as possible: slow speed. But in order to stay as short as possible at one place move away the bit as fast as possible from the place: high feed.
Means: speed (rpm) as low as possible, feed as high as possible, with reasonable depth of cut: not to shallow, not too deep to avoid sheering with high feed. It makes a difference whether one uses cast or extruded acrylic: cast acrylic has a “paper” protection layer (the brownish one, usually not available in the big hardware stores), is slightly more expensive, handles heat better, is little less well bendable with heat. The extruded acrylic is better bendable with heat, therefore melts a little earlier with heat, so extruded acrylic is less favorable for CNCing.
DIfferences in cutting behaviour are minimal though. With proper settings even extruded acrylic can be cut nicely. I suggest some experimenting. You will break bits. I just broke a .25" O-flute, that is not a thin one, but broke during a just lengthy but otherwise routine job, tip did not look dull.
I also do not think coating of the bit is necessary for acrylic, possibly with metal? Have no experience with metals.
I’ve had pretty good luck with these:
https://www.amazon.com/SHARPRO-Carbide-Cutting-Diameter-Acrylic/dp/B0D1DS85TK?th=1
(EDIT: edited link down to only what was necessary, removing metadata)
I prefer the 1/4" shank as I cut aluminum with them as well.
I’ve had good success with the precise bits plastics tooling:
Downright pretty tools that eat acrylic and leave a great surface finish.
That said, any single flute will do you just fine. I’ve used the cheapest stuff you can find on Amazon and it works “ok” as well 
C3D, Amana, PreciseBits and Datron are all going to give you excellent results. Regardless, if you’re just cutting plastics the tool should last most folks a lifetime. Buy once, cry once.
And as UngerCNC said, the geometry works pretty well for nonferrous metals. Though I treat my plastic tooling like a nice non stick egg pan. It’s used for nothing else. A delicate and pampered tool that’s still sharp enough to cut you by looking at it wrong 
I don’t know how much crossover there is between machining acrylic and machining polycarbonate but it might be worth looking at some of the acrylic threads for tips and tricks. (A bit of soapy water on the surface made a big difference for my acrylic machining for example)
I tried a bit of soapy water last night just as a quick test. It definitely keeps the plastic from melting to the bit, but it also caused the chips to hang out in the groove and not be cleared.
I switched to a steady stream of compressed air and it worked great, although it makes a huge mess because it bypasses the dust collection.
That’s good info, thank you for sharing 
Maybe it’s finally time I post my idea for a compressed air assisted sweepy 
Basically a sweepy with an embedded ball joint/luer lock tip just inside. The idea being to inject a very narrow stream of high psi air directly at the bit tip inside the sweepy vacuum environment.
Clear deep slots with the high psi and have the swarf immediately picked up by vacuum. Will it work…who knows
Yes it will work.
I regularly use an air blaster with my dust boot when cutting hdpe. But it’s a 4” pence boot.
I’ve done over 100+ hours cutting on poly carb. Single flute and the default “hard plastic” settings in Carbide Create have worked just fine. I don’t bother with ramping. Unless I’m cutting something really small, I use the two pieces of painter’s tape with super glue method of part fixing and I put it on every waste board strip. I originally tried to skimp on this, but I found that even 6mm poly carb will flex and you get much cleaner cuts if it’s secure. When you get down to 3mm or thinner, you really need to secure it will or it will lift it off the surface temporarily. If you need to use tabs, I use 0.2" width, 0.04" thick. They’re thin enough that you can use a pair of flush side cutters to cleanly remove them. I dry cut everything with just the vacuum for chip removal. I actually find poly carb is easier to cut than acrylic.
Thanks for sharing your expertise, I’d like this post twice if I could 
I was wondering why would cut so much polycarbonate but your profile seems to tell the story. I imagine it’s a great material for the robots 
I have some single fluted bits on the way (suggested by folks earlier in this conversation). I’m excited to try it out. I have a bit more 1/4" polycarbonate remaining which I can “practice” on… then it’s game time.
If the part was silver, or transparent, it was cut on my CNC. 
We also prototyped most of the aluminum parts in poly carb first allowing us to quickly iterate on spacing and tolerances. The shooter turret on the left side is a combination of multiple 6mm poly carb layers including some cut as custom spur gears. The top cover is made of 3mm poly carb. And under that pile of balls is a circular structure to funnel all the balls towards the shooter made of 1mm poly carb.
I just received a 1/16" and 1/8" single fluted bit from these folks. Do you have any feeds n speeds recommendations for these? If not, I plan to call them after Memorial Day and ask.
I need to enter them in the Carbide library…
What manufacture? And are they called out as a plastic only bit or are they a generic o flute?
Amana/ tools today both have good feed and speed information on the product pages.
They have generic ( aluminum cutting) oflute and plastic specific oflute models.
The plastic specific models are usually much sharper and have a little deeper flute cut. To allow for larger chip extraction.
Precise Bits at Think & Tinker in Colorado.
These are specifically listed for plastic cutting on their website.
I’ve not cut much polycarb so getting some advice from them would be the best bet.
I tend to start with feeds and speeds from a similar tool in carbide motion since they tend to be conservative. Generally a safe starting point.
