Cutting Acrylic Plastics

[steve1000]

Does anyone have any experience with cutting acrylics on their Shopbot?
I am cutting pieces that are roughly rectangular in shape, about 16" x 8" x 3/16, sometimes 1/4". I am not happy with the cut edge, it is very rough and choppy. I have tried many feeds and speeds but havent found anything good yet. Best results have been at a feed of about 2.5" and a router speed of 13,000. I'm using a quarter inch carbide upcut spiral bit but still getting a pretty rough edge. Any advice anyone can provide would be appreciated.

Cheers

[pkirby]

Steve,
To get clean cuts in acrylic I use Onsrud Bit 63-530 at 16,000 RPM and 0.8 IPS. I don't cut acrylics that often, but this setup has always worked well for me. Also make sure your hold down is tight and not causing chatter.

[knight_toolworks]

I use 1ips 8k and at most 1/4" per pass that gives decent results with an endmill.

[steve1000]

Steve,
To get clean cuts in acrylic I use Onsrud Bit 63-530 at 16,000 RPM and 0.8 IPS. I don't cut acrylics that often, but this setup has always worked well for me. Also make sure your hold down is tight and not causing chatter.

Thanks Paul,
can I ask what thickness you generally cut, and do you do multiple passes and do you use a clean up pass, and are you using a conventional or climbing cut?
Thanks,
Steve

[steve1000]

Thanks Steve

[jerry_stanek]

I have been using 2.8 ips at 9000 rpm I normally cut .125 deep If I need a real nice cut I will use a clean up cut. .25 Gerber gold bit

[pkirby]

I was using it on 0.220" thick acrylic with a conventional cut. I cut the majority out on the first pass leaving a 0.035" onion skin layer. Then cut all the way thru with a second pass (still in conventional cut).

[steve1000]

Thanks, Paul Jerry
I tried .8 ips,with a speed of 16,000 rpm. Used multiple passes of about .060 climb cut. I used used a finishing pass at 1.2 ips at .020 deep, conventional cut. I held it down with Super 77 spray adhesive, which did a good job of keeping it in place. I used an Onsrud 63-718, 3/16" tool, which is an upcut spiral flute.
It was by far the best result yet. After a little rub down with .220 grit wood sandpaper with a litte tool lubricant on it I though it looked pretty good. However, still not the glass like finish that my boss is looking for.
Thanks everyone for your help.

[steve_g]

To get a "glass like" finish Onsrud has a diamond bit that polishes the cut $$$$$$ or you can flame polish a 400 grit edge with a hydrogen torch...

[bleeth]

220 is not fine enough. Going finer with wet sandpaper and using some oil for lubricant will also bring up a gloss edge although it is slower then flame polish.

[steve1000]

Thanks Dave

[jkaras]

We do this all the time. You will be amazed what a flame polish can do after 220 sandpaper. You can use a simple propane torch from the hardware store. The key is you have to move across the acrylic edge with a good consistent speed and 90 degree angle. If you flame too slow you will get bubbles, if you go too fast you will miss areas. If you go too fast and miss areas, wait for it to cool down before flaming again. It will bubble much easier if its still hot. Keep the acrylic edge consistently at the end of the blue flame. Stay perpendicular with the edge or your corners will bubble. Be prepared to blow out small areas of corners that catch fire. Remove protective paper out of the flame area. Make sure you remove sandpaper dust. The key is one clean, consistent and even swipe with the torch. We typically flame polish 1/4 to 1/2 inch acrylic. Good Luck!

[twelchPTM]

Flame polishing will give you a glossy look but in my opinion nothing looks better then a hand polished edge. I sand in steps up to 1500grit adn then finish is off with Novus step 3,2, and 1 acrylic polish

[cnc_works]

OK, I'll add my polish technique used on plex up to 4" thick. Cut, sand through the grits with a hard pad sander through 1500, (after 320 it is all wet or dry lubed with water), then buff with a wheel on my drill with white compound. If the piece is small enough to pick up I like to use my big wheel on a bench mounted polisher. You can quit at 1000 and it just takes a little longer with the wheel and you get the same result. Perfect transparency.

With my cnc, sometimes I will joint a straight surface because it is a little easier to clean up that surface than my router cut.

By the way, my plastics guy says that flame polished edges should not be used as an edge to glue to in structural projects. The flame changes the chemical characteristics of the plex and makes it more likely to fail.