info for cutting acrylics and lexan

[Ajcoholic]

So I've been using my machine for 4 1/2 years now, and believe it or not other than some solid surfacing, I only cut sheet goods (ply/particle core/mdf) and solid wood. I would appreciate some advice from the forum..

Today I picked up my new truck from the local sign and graphics place I deal with (getting my company logo put on), and we got to talking... seems they order a lot of pre cut letters and numbers from a larger manufacturer and pay through the nose. I want to try cutting some acrylic and lexan for them. Ill assume 1/8" to 1/2". I do have a few of those O flute bits which I assume are for plastics, but can anyone suggest a feed speed and rpm to start at? They are to give me some material to test and I dont want to experiment too much on their material - if I can get a good base start point.

Also should I try and cut in one pass or leave a thin skin to go and clean up? I do have a good universal vacuum on my machine.

Thanks!

Andrew

[RossMosh]

If they're talking about Gemini, then it's really hard to beat their pricing as a wholesaler. Acrylic is just too damn expensive and hold down for lettering can be a pain in the ass compared to a laser. Not to mention, a laser leaves a much nicer finish and is typically much faster.

As for the machining process, 60-90ips at 12-15,000RPM with 2x DOC works pretty well. O flute bits will help prevent stalling/snapping due to heat/build up.

[Ajcoholic]

Have no idea, but they would be in the Toronto, ON area. Im in Canada, in Ontario.

[Ajcoholic]

If they're talking about Gemini, then it's really hard to beat their pricing as a wholesaler. Acrylic is just too damn expensive and hold down for lettering can be a pain in the ass compared to a laser. Not to mention, a laser leaves a much nicer finish and is typically much faster.

As for the machining process, 60-90ips at 12-15,000RPM with 2x DOC works pretty well. O flute bits will help prevent stalling/snapping due to heat/build up.

Thats a lot slower than I'd have started at. (Im assuming you meant 60 to 90 IPM or 1 to 3 IPS?)

The prices they were telling me... I dont think it will be an issue to match the cost. I know the material cost can be pricey (Ive bought lexan for windows) but they were talking crazy money.

[willmorgan]

I use a Onsrud 63-718 and cut in one pass.

[knight_toolworks]

hold down is always the issue with acrylic and even worse with lexan. depending on the parts I will use spray adhesive or vacuum or a pressure foot. I cut a whole sheet of .125 4x6" rectangles I used a 1/8" o-flute and two passes at 1ips and vacuum and a pressure foot they all stayed in place. when I did 2x3 rectangles I sued spray adhesive and glued them to the spoil board. lean is softer and pretty grabby like most soft plastics and it will scoot around much worse.

[dana_swift]

I have cut a fair amount of lexan which is a PITA, to get descent results, I use vacuum hold down, a 1/8" bit and leave a skin on for the first pass. That holds everything together and on the table until allmost all the cutting is done. Then a final pass to cut-through and break the vacuum when the cutting loads are very light because all the high forces happened during the first pass. That "usually" works.

Lexan is bad about sticking to the bit, which tells me my bit is getting too hot, so that calls for less aggressive cutting, same feed rates, but less pass depth.

Hope that helps.

D

[GeneMpls]

The best way is a laser- the edges come out 'flame' polished. Crappy pict but it is 3/4" acrylic. Gene

[Alex Naumenko]

I cut all my acrylic from 1/8 to a 1" with .25 single flute bit. 120 ipm 0.25 pass. I do laser some of my acrylic up to 1/2 but my laser is only 18x24

[Ajcoholic]

Thanks everyone - this will help when I get to test cut some!

Just a question, has anyone tried using compressed air piped right at the bit (maybe an 1/8" diam or 3/16") and let run steady to cool the plastic as the bit runs around? To try and stop the gumming up? Or just push the feed and keep the rpm down?

[Burkhardt]

.... has anyone tried using compressed air piped right at the bit (maybe an 1/8" diam or 3/16") and let run steady to cool the plastic as the bit runs around? ....

Yes, I have done that when I had to cut clear extruded acrylic sheet (which really melts easily and is a mess). See the 1/4" aluminum tube on the left. It is pinched flat to a nozzle and fed with about 20 psi.
This was for a reverse lithophane, roughing with an 1/8" end mill and finishing with a 0.025" radius ballend.

I am not sure if it is really cooling much but at least it helps clear the swarf from being re-cut. Anyway, it worked for me.

https://lh4.googleusercontent.com/-aU7bxVkbYNQ/V1ISXMb3NAI/AAAAAAAAGSY/QvKDrMxLgr8LbRbp27i1H9XIZfgYZ66KACL0B/w1024-h579-no/4-DSC00597.jpg

[blackhawk]

Andrew - I have been cutting a lot of acrylic and Lexan lately, mostly Lexan. I have been using an Onsrud 63-775 1/4" bit. I have a PC router and run it at 16,000 rpm. I cut 1/8" deep per pass at around 2 IPS. I have never had any problem the Lexan melting at the bit. I don't use any cooling. My edge finish is good, I wouldn't call it great. I have used an 1/8" bit in the past with success, but they will break. Stick with a 1/4" if you can, I have yet to break one of those (knock on wood).

[myxpykalix]

The guy on here who cuts alot of plastic is "Xray" and he would be the guy to get some good cutting advice from.

http://www.talkshopbot.com/forum/member.php?5242-Xray

[knight_toolworks]

Andrew - I have been cutting a lot of acrylic and Lexan lately, mostly Lexan. I have been using an Onsrud 63-775 1/4" bit. I have a PC router and run it at 16,000 rpm. I cut 1/8" deep per pass at around 2 IPS. I have never had any problem the Lexan melting at the bit. I don't use any cooling. My edge finish is good, I wouldn't call it great. I have used an 1/8" bit in the past with success, but they will break. Stick with a 1/4" if you can, I have yet to break one of those (knock on wood).
With 1/8" you need to stick with 1ps I use 1/8" a lot to keep the small parts in place. I cut upto 1/2" thick with a 1/8" bit.