Help with cutting

[tim_white]

i'm going to be cutting a acrylic glued to a gator foam sheet and was hoping for so help with feed and speed info so i don't chip the plastic or mess it up, (i'm cutting out letters)any help would be greatly appreciated, thanks again tim

[elcruisr]

I've handled those materials with spiral "O" flute plastics tools with good results. A lot will depend on wether you are using a spindle or a router, PRT or Alpha and the maximum allowable bit diameter. Generally with plastics the larger gullet in a larger tool will improve the edge quality a litle bit.

The old standby strategy is to keep the rpms down and the feed rates higher to control heat and welding the chips back into the cut. I did just try a new tool from Onsrud (I don't have the number handy but can get it) that takes a different tack. They recommend a feed of around 3 IPS and 16,000 to 18,000 rpm. Worked better than anything I've used before.

If parts and hold down system allow it you can also do a rough pass leaving 50 thousandths or so and then do a slower cleanup pass.

There are also about 20 different grades of acrylic. Some tooling manufacturers have different advice for different grades. If possible find out exactly what grade it is, select your tooling and talk to the manufacturer about their recommendations.

Eric

[artisan]

Good advice Eric. Tim, I'd like to add that heat is by far your biggest concern here. You've got 2 different materials that will heat up differently as well as some type of glue (flammable?)and I foresee tremendous possibilities for gremlins. Welding will be a major concern as well as deforming the foam core of the Gatorfoam.

I would advise (1) some coolant spayed constantly on your bit...I use water with a bit of Murphy's Oil Soap, (2) try to cut in stages the acrylic layer....then cut the Gatorfoam layer. Or (3) Cut the materials separately and then glue them together which is what I would really recommend.

Cutting layered materials is complicated and plastics are even more so. Finding the right feed speed will depend on the thicknesses of the two materials (.25 acrylic over .5 Gatorfoam ?) which you did not mention. When you find the bit that works and the speed that compliments it....give us an update. Good luck....D

[paco]

I've cut Acrylic sheet (1/8") with Cardide tipped 2 flutes 1/8" CED at 11 000 RPM at around 90"/min. with good results... but not combine with foam though...
As with this cutter; I have better results at bellow 125"/min. ... above that I get "chip welding"...
O-flute most be better for evacuating chip... but as for HIGH speed setting, ?????.........
Good luck!

[elcruisr]

Paco, you'll have much better luck with a single "O" flute. The new tool I was using was something my Onsrud rep recommended. It seems to break the rules on plastics cutting but works very well. It's also 3/8" diameter. Great chip removal and no welding!

Eric

[paco]

I have a 11-00 serie bit in order... We'll see... Did the rep. told you something bout feed and speed? I would like to improve speed some and get a smoother finish. But, as wrote, I pretty pleased with the result I got... Still, thanks!

[elcruisr]

Paco, depends on the material but I use their upspiral 1/4" diameter version in 1/4" acrylic at 3.5 to 4.5 in/sec at around 12,000 rpm.

On another note I'll be seeing all of you the other side of this bloody hurricane hopefully. The second in three weeks! This looks like a bad one and we're tieing down, locking up and hoping the shop survives. See ya all later.....

Eric

[artisan]

Good Luck Eric ! I'm in Myrtle Beach....looks like you guys will catch the brunt of this one and we'll be spared up here. If I can help in any way....Let me know.....Darrell

[tim_white]

thanks guys for all the help,