Acrylic sheet

Mostly Printed CNC - MPCNC Troubleshooting
#1

I have successfully cut quite a bit of wood now I want to try some acrylic. I thought it would be fun to make some stencils with it. The stuff I got is 3mm thick from the hardware store. I tried a cut but it was melting and gummed up to the extent that it failed.

I am reading people say the problem is I should get cast acrylic and the hardware store stuff is extruded. I also read suggestions about moving faster with a shallower cut and using am upcut bit.

Anyone on here cut any and can share some tips? I got a 12"x24" piece so I am hoping I can figure it out and get something usable before I go through the whole thing :slight_smile:

#2

What bit are you using (type, diam, length) and approx RPM? What spindle, how long is your zaxis, how big is your machine?

Chances are really good you are spinning the bit too fast and taking way too small of a bite, causing the bit to just melt its way through the part, a larger bite means the bit will take the heated plastic out of the cut, metal is the same way, but is even harder to cut because too small of a bite and you will work harden it and break
your bit.

A single flute bit lets you spin it twice as fast as a two flute bit while taking the same size bit out of the material. We have a high rpm spindle single flutes bits are best and still slowing it down helps. If you can’t slow it down you need to move it faster. To move it faster you might need to take a shallower depth of cut to not cause too much tool deflection.

An upcut can pull the sheet from the table so unless you have it double sided taped down you should use shallow passes, just watch for the material to vibrate up and down and you know your too deep. A down cut can push all the material to the bottom and melt it, these are best with through cuts.

#3

I was trying a 1/8" 2 flute straight bit. I am using a dremel it was on max speed which is 30K I tried slowing it down and that made it worse. I was taking 1/32" cuts.

The machine has 24x24 cut area.

#4

I am not sure when a straight flute is to be used other than maybe a finishing pass. Dremel’s have horrible runout, anything harder than wood is going to be tough.

Upcut or down cut and best to make sure the end is meant for plunge cutting. I am pretty sure most straight flute can not plunge cut.

Here is a quick description, http://blog.cnccookbook.com/2012/04/06/cnc-router-cutters-types-and-how-to-use-them/

#5

I have been liking the straight flute for wood because it chips out less than the upcut.

Today I tried an upcut bit (because I keep reading people saying you need to get the chips out) with .01 depth per pass and I slowed down the rotation speed. It was going ok and not melting but then like you said it lifted the piece off the table. I may try with taping it down next but now I put the dewalt 660 on there and I don’t have a speed control for it. I might wait and get a smaller diameter bit and try that because I want some smaller ones anyway.