Machining plastic please advise

[stk2008]

Hi all I need some advice.

I have loads of black plastic its kinda soft.
It is 2mm thick and is shiny on one side and the other looks dull.

I really think its for laser cutter I am not sure

here is a picture of some thing I have made

http://i39.tinypic.com/iy0qgx.jpg

When I cut this I had to file (only lightly to get rid of what looked like fluffy edges.

I have now wanted to cut some thing out again using this plastic using a 1mm end mill.

I have done every thing slow feeds high speed,high feeds low speeds,reversed cutting direction etc etc and still get a crap finish.

The thing is the part I cut out looks terrible but the hole left that I don't need looks a lot better.

Please advise you may say it is for laser cutters but I will try and get some real close pictures of the material soon for you lot to look at.

Thanks in advance.

[fixtureman1]

It looks like Sintra. You should not cut Sintra with a laser as it gives off dangerous gasses and it is corrosive to the parts of a laser. If you say that the hole looks better then you need to change the direction of your cut. If I use a Gerber gold bit P80368A it does a nice job cutting. The one I listed is long because I cut 25 MM Sintra.

[stk2008]

Hi thanks for the reply.

I have to go out soon but when I get back I will take more photos of the finished item and the hole.

I have reversed the cut it did help a little.

Damn this is a pain the plastic is soft.

I have cut perspex out with a very nice finish that's because its harder.

I have looked on some sites and some people say to freeze the plastic makes sense.

[RCaffin]

I have loads of black plastic its kinda soft.
It is 2mm thick and is shiny on one side and the other looks dull.
When I cut this I had to file (only lightly to get rid of what looked like fluffy edges.
The thing is the part I cut out looks terrible but the hole left that I don't need looks a lot better.

Machine a nice square and measure the density (mass/volume). Then check on a plastics web site.
It sound a bit like polyethylene (or maybe PP) with the feathered edges. That stuff drills OK but machines poorly. Rake angle matters.

Freezing would help: makes it harder.

Cheers

[stk2008]

Machine a nice square and measure the density (mass/volume). Then check on a plastics web site.
It sound a bit like polyethylene (or maybe PP) with the feathered edges. That stuff drills OK but machines poorly. Rake angle matters.

Freezing would help: makes it harder.

Cheers

Hi thanks for replying.

I am sorry you have lost me on cutting a square?

Should I machine a 1" square then weigh it?

Do you have a link to a plastic web site that would then give me the information your referring to?.

I cant see how I could change the rake angle?.

Thanks for the help

[WarOzz]

The fury edges and softness you describe sure does point to polyethylene. Trick with this stuff is a super sharp tool, less flutes the better and fairly high spindle speeds. Make sure to climb cut for finish pass and leave a good .01 or better for that pass or it will just melt the edge.

[RCaffin]

Should I machine a 1" square then weigh it?

Well, basically yes, although a 200 mm square might be easier to weigh if you don't have a lab balance. :-)
Just as long as you can measure the square accurately to calculate the volume accurately.

Do you have a link to a plastic web site that would then give me the information your referring to?

Sure. Try
Density | Plastic Properties Tables | Plastics Technical Properties | Dotmar

I cant see how I could change the rake angle?

True, unless you make custom tools. Follow suggestions from WarOZZ below.
Making up a custom cutter might not be a silly idea though, if you can do that. But it has to be polished and SHARP!

Cheers

[stk2008]

wow thanks so much for all your input.

I will try a finish pass an I will all so cut a square (200mm) and post my results.

I will all so try freezing it but I will try doing a final pass.

I will all so look into getting a single flute cutter.

[CaptainVee]

Reading trough this quickly it does sound like PE. I use the same stuff (4 mm) and have had good results with a wood router bit (4 mm 1 flute) and even better with 4 mm negative spiral 1 flute.

Also high feeds and low revs. For 4 mm I think i used 15000 revs and 1000 to 2000 mm/min.

The fluff lets itself be scraped very well with a box cutter.

[ssutton]

I have successfully cut soft plastic with my machine. The formula for me was this;

single flute 3/16 cutter (Amana, for aluminum. They make them for plastic to)
.050 depth of cut per pass
175 ipm speed (or as fast as you can go)
8000 rpm spindle speed

AND VERY IMPORTANT!

I have attached an air gun blower to the bottom of my z axis to blow compressed air on the bit while cutting, this keeps chips from recirculating around the bit and melting and helps to keep the cutter cool.

Scott