cutting plastics

[puzzlemaker]

We use HDPE copolymer plastic for some of our furniture parts.Usually .220 thick.I am getting chatter marks along the edges,mostly on arcs.Sometimes on straight cuts as well.Some people say to cut as fast as possible,others say slow it down.Does anyone have experience with plastics,and how fast should I go?I've tried 50ipm,and up to 200ipm.My personal theory is that it is too soft and tends to flex,thus causing the chatter marks,but what do I know.

[Keith Graydon]

define the source of the chatter.

 

tool

part

fixture

machine.

 

Use Sharp Tools. Coated HSS is fine. dull tools are bad,very bad. go fast dont dwell.

 

 

HTH

-KLg

[Roger Peterson]

sharp tools, sharp tools, sharp tools. If that doesn't work try using sharp HSS tools with a high helix and make sure your finish passes are taking off at least .010" for HDPE, it's pretty gummy. I'm guessing your running a router with a vacuum table so your fixturing should be pretty good. So I would concentrate on tooling and machining practices. Conventional milling can yeild a better surface finish especially if you are not using sharp tooling. If you give some more info I'm sure you'll get some more answers.

 

 

HTH

[puzzlemaker]

As far as the source of the chatter,I'd have to guess, part and machine.The edges are rather choppy looking, espacially on smaller radius.I am using a Vortex single edge "0" downcut spiral (carbide).I always start out with a new bit but doesn't seem to matter.I don't have a vaccuum table.Just a few clamps and some well placed screws.My cutter is only .1875,so am using only one pass,no finish pass.Maybe thats the problem?

[CAM-mando]

+1 on the sharp tools

 

Also consider the effect of internal radii. The greater the ratio of (cutter radius / part radius) the greater the effective feed rate.

 

For example a .375" Corner Radius with a .500 Dia. Tool the program feed rate of 10 ipm produces an effective feedrate of 40 ipm in the corner.

 

Consider slowing down in corners.

[Roger Peterson]

To me it sounds like the fixturing is the root cause. It doesn't take much vibration to create a poor surface finish. I don't think clamps and a few screws are going to cut it on thin hdpe like that. As was mention internal corners only amplify the problems. There are some extremely thin double sided tapes that could be used in strategic areas or just run some strips of it the length of your sheet. Depending on the size of what you are working with vacuum chucks are not hard to make and work very well.

 

HTH