Cutting UHMW plastic

[Serb]

I purchased Amana 51410 O Flute, 1/8" bit that is suppose to be designed for cutting plastics and I'm totally dissatisfied with how it cuts or maybe I'm doing something wrong.

I wanted to replace the rubber spiders on my LoveJoys and decided to cut them out from a 1/2" UHWW plastic. The toolpath had 5 0.1" stepdowns and they came out full of burs as if I was using a regular end mill. I was just wondering if anyone had experienced the same problem with these bits or is there another bit or a way of cutting it smooth?

[ger21]

What are your feedrates and rpm? When cutting 1/2" plastic with an 1/8" bit, it's extremely important to get all the chips out of the cut, or you'll get melting.

[Serb]

At 20 imp the bit snapped within the collet so I inserted the leftover of it and was cutting at 10 ipm. The chips were getting cleared and there was no melting.

The first initial cut at 0.1" depth left a flare of a bur on the top edge.

[ger21]

Are you sure it didn't melt? You should be able to cut at that depth at 125ipm or more. What RPM?

[LeeWay]

I cut HDPE with just a straight plastic bit intended for polycarbonate. 3/16" bit. Probably 20,000 RPM at 80 to 150 IPM and 1/4" DOC.
The UHMW is a little denser of course, but my cuts are pristine. Your's should be too, so something is amiss.

[Serb]

Originally Posted by ger21 Are you sure it didn't melt? You should be able to cut at that depth at 125ipm or more. What RPM?

I am positive that the burs were not from melting.

I had a little Ryobi Speed Saw connected since I was using a 1/8" bit and that thing spins at 30,000 rpm with no load and having a 5 amps motor it couldn't have dropped down too much in speed.

I had about 1/2" inserted into the collet and running at 20 ipm on the 3rd stepdown the bit just snapped at the collet but I was still able to use whatever was leftover from it. I did some previous cuts on the same panel of UHMW with Osrud's 3/16 O Flute bit and it did have just a tiny bit of bur at the surface here and there but nothing like this Amana 1/8". Both of these cuts, 1/8" & 3/16" were made in a climbing mill fashion, going clockwise against the part and today I decided to do a conventional cut by going counterclockwise and it did a much better job. First 3 upper stepdowns had no bur and there was a little bit on the bottom 2.

I know that UHMW plastic is stringy compared to HDPE but I never had a problem with it when I was using a 1/2" straight router bit and doing it by hand against a pattern.

[ger21]

If you have 30,000 rpm, try 150ipm. You're generating way too much heat, which is probably why the bit breaks.

[joecnc2006]

I know with UHMW I get the fuzz you mentioned, however cutting HDPE and Plexi with the Amana 0 flute I get very nice edges, but I normally just cut everything with a 2 flute upspiral and still get acceptable results. Its the characteristics of the UHMW that is causing this not really the bit you will need to find the sweet spot to cut that material.

[TDA]

I'm with Gerry on this. I won't go slower than 170 IPM with a .125" 2 flute at 20k RPM in HDPE. Not the exact material you're cutting but 10 IPM sounds ridiculously low.

[stevespo]

I've cut (pocket and profile) UHMW and HDPE at speeds of 60-90 IPM with a .250" 2 flute spiral upcut bit and get very good surface quality. I definitely get a bit of a 'bur' on the top edge, which I just scrape off with a razor blade. Next time I'll bump up the speed and see if that helps.

Thanks,

Steve

[JerryFlyGuy]

I've cut it w/ just a carbide endmill even.. keep the speed WAAAAY up and if you can, shoot it w/ air while you cut. That will help clear chips and keep things 'cooler' at the same time..

[LeeWay]

My PC router does a fine job of clearing the chips. I have been cutting some double color stuff. Red outside and white inside. It makes millions of miniature matchsticks when cut with a straight flute bit.