I tried my hand at cutting 3/16" plexiglass last night. I got a porter cable 10 amp router that spins up at 23K or 28K RPM. I used a 10 IPM feed, and 1/4" 2 flute spiral up cut bit.

The material appears to have melted more than cut. I had to use a chisel to get it off the table! After some handy work with a utility knife, I got to a clean enough edge, but there's got to be a better way to work this stuff.

Does anyone have any suggestions, bits, feeds, speeds?

Thanks,
Dean Brock

Plastic cutting bits are usually straight cutters. No up or down cut. They don't do much rubbing this way. I use 3/16" 2 flute straight cutters made by Onsrud. I cut lexan, which has a higher melting temp. I cut with a feedrate of 80 IPM for tight arcs and 150 for everything else.
I think with a slow feedrate like you were using, you are componding the heat issue.
Speed it up if you can. Multiple passes might help too. If you can't speed it up on feed, then slowing the router might help some too. I use a cheap router speed controller on my PC 690 when I need to slow it down.
The torque falls off with the speed, but then if I make a couple passes, it works great.

Slow your rpm down to 23K, and up your feedrate to about 100ipm. With a 1/4" tool, you'll probably still have trouble due to the chips packing in the cut, unless you can blow compressed air on them to clear them out. You're best bet would probably be to try to rough cut them about 1/32" oversize, remove the surrounding scrap and then run a finishing pass.

Conventional cutting (vs climb cutting) helps too- the chips don't get stuck to each other. I'm milling the stuff at 2.4K rpm (WAY below you) and about 11ipm with an 18mm end mill. Rack the RPM down until you get a steady stream of individual chips coming off the cut then increase it while catching the chips in your hand- you will be able to tell when the chips are getting too hot and this is your optimal cutting speed/ feed. If they come off all gnarly and stuck together you're going too fast.

I know I'm using a mil and you're using a router, but the main reason cutting acrylic or other polymers fail is the spindle being too fast... it melts (and smells lol).

2 flutes are better than 3 or 4 which whak the material too much

I engrave plexi plates(with v bit) for foundry match plates and end up sitting there with a stick constantly knocking the little blob of plastic off the end of the bit. If not the blob just gets bigger and ruins the letters( usually 1/8 to 1/4 high)
Dave

I know it's a router, I have a 2 1/4 hp PC on my K2cnc and manufacture a box out of 1.00 cast sheet and I cut .750 deep and I [ food grade mineral oil ] in a squirt bottle, light spray, or silicone spray non flamable. works for me. And if you have a dust exracter, it's even better as to keep it out of your router. and if you not going very deep you can use wax.

9lrac9

I engrave plexi plates(with v bit) for foundry match plates and end up sitting there with a stick constantly knocking the little blob of plastic off the end of the bit. If not the blob just gets bigger and ruins the letters( usually 1/8 to 1/4 high)
Dave

Try using liquid Dish-Soap mixed with a little water, it washes off easy, and the plastic will never stick to the tool!
It also makes the finished part more transparent, instead of dull frosted look.
The nice thin is you don't need a lot, just paint the area prior to machining!

Widgit

Try using liquid Dish-Soap mixed with a little water, it washes off easy, and the plastic will never stick to the tool!
It also makes the finished part more transparent, instead of dull frosted look.
The nice thin is you don't need a lot, just paint the area prior to machining!

Widgit

The downside is it leaves a few clean spots in the shop so the really dirty spots stand out more. ;)

Try using liquid Dish-Soap mixed with a little water, it washes off easy, and the plastic will never stick to the tool!
It also makes the finished part more transparent, instead of dull frosted look.
The nice thin is you don't need a lot, just paint the area prior to machining!

Widgit

I will give this a try
Dave

Widgetmaster, You rock!! It never ceases to amaze me how the little things make all the difference. Cut a plexi plate last night and used the soap-- came out beautiful.
Thanks a million!
Dave

If you want to cut plex and have it come out crystal clear like a window use Kerosine for the cutting fluid. An old trick I learned at a Plastics Machine Shop years ago. You will be amazed by the results.

I've got some 3/8" cast acrylic to cut with the paper backing, when you guys are talking about the soap/kerosine, are you removing the paper first before cutting or leaving it on? I've just got my CNC, so anything more detailed about this method would be a big help.

I leave the protective backing on when I can. If you are just cutting the edges or a profile, I don't think it will hurt anything.
I get lexan sometimes with paper backing rather than the normal plastic. It holds much better while milling or routing.
Less chance for chips to scratch the surface.
I have heard about soap before, but never actually tried it. I might have to to see if it makes a difference in lexan.

kerosine may make the paper mushy but....

keep the paper to protect it from scratches. you will be amazed how clear the plex will be.

If you want to cut plex and have it come out crystal clear like a window use Kerosine for the cutting fluid. An old trick I learned at a Plastics Machine Shop years ago. You will be amazed by the results.

If you go back to the first post it says: " I got a porter cable 10 amp router that.....". This router, like most routers, is a universal motor (I think that is the correct name), a motor with a commutator...that makes sparks...you can see them when the motor is running. Kerosene is flammable, and when heated vaporizes. You could be quite thoroughly amazed if you managed to heat things up enough to create kerosene vapors that got sucked in by the cooling fan on the router and ignited by the sparks in the commutator.


Use soap like Mr Widgit recommends; I have never heard of soap vapors causing an explosion.:D

Soap is fine but the finish will be frosted not clear. Working with a sparking router that can cause a fire is not safe under ANY circumstances.

Soap is fine but the finish will be frosted not clear. Working with a sparking router that can cause a fire is not safe under ANY circumstances.

The finish is frosted no matter what you use as a lubricant, once you have washed all traces of the lubricant off. And if you are going to avoid working with a router that has a universal motor because the commutator sparks you will never use it; it is impossible to run a commutator motor without some sparking.

No you're wrong. If you use Kerosine it comes out chrystal clear like the rest of the material. If you haven't tried it you don't know.

I have to say I would be leary of using any type of solvent or fuel or oil on plastics. I have experimented with some and it becomes unclear and clear why I shouldn't have done that. ;)

Most of the cuts I make on lexan are then welded with solvent later. They clear up some just from that. Upon second thinking, a lube would be yet another set I would have to wash off.

A torch also works well to clear the edges. They have to be pretty smooth to begin with, but flame licking the edge will make it clear and shine. It like most thing, takes practice to get good at it.
Too much flame will be self evident. ;)

No you're wrong. If you use Kerosine it comes out chrystal clear like the rest of the material. If you haven't tried it you don't know.

Read what I wrote: "once you have washed all traces off". It is quite difficult to get every trace of kerosine, or any mineral oil, out of the minuscule roughness in the machined surface and these traces make the surface seem clear. Soap. of course, washes out easily.

I have machined acrylic, lots of it, experimenting with different liquids as a lubricant/coolant. Here is an example:

http://www.cnczone.com/forums/showthread.php?t=46464

Yup, you can clearly see the brushes sparking while the porter cable running, but it doesn't seem like much of a danger, if you're not using kerosene cutting fluid.

I've caught my JGRO on fire already, but it wasn't commutator sparks and kerosense, it was running a dull bit which made an ember that was fanned to flame by the dust collection. Thankfully, I was around to keep it from getting out of hand.

I think that's a more significant fire danger with homemade CNC routers. A dull bit, producing an ember, that gets sucked up into the vacum bag, with lots of wood dust and fresh air circuilating in it... That could be tricky to extinguish.

By the way, I ran some more plex, with a 1/8" 2 flute spiral bit at 20 IPM, and it made a huge difference. It still stunk, but it didn't fuse to the bed this time. :^)

Thanks, yall.

deanbrock,

Sounds like words of experience. :D

Soap is fine but the finish will be frosted not clear. Working with a sparking router that can cause a fire is not safe under ANY circumstances.

I used to work at a sign-shop and they treated the frosted finish using either a small propane torch or a welder's torch heating the 1/4"-1" thk edges of the routed plastics.

A gentle flame, held 4-6" away from the frosted edges would produce edges like glass. You can easily "finish the edges" of a piece 3'x4' in less than a minute

I used to work at a sign-shop and they treated the frosted finish using either a small propane torch or a welder's torch heating the 1/4"-1" thk edges of the routed plastics.

A gentle flame, held 4-6" away from the frosted edges would produce edges like glass. You can easily "finish the edges" of a piece 3'x4' in less than a minute

I am guessing you worked with cast acrylic. I tried this on extruded acrylic one time and just got a bubbly mess; it seems to have a much lower softening temperature than cast