Rough edges on PETG?

[Joe Kace]

I am hoping somebody out there has some experience in cutting PETG. I keep getting rough edges and little lines down the sides and can't seem to get the edges smooth. I have seen other laser cut PETG pieces and the edges are like glass, any tips for this? When I put on the air assist, it get's worse. I have also done a double cut and it gets a little better but not much.
Thanks in advance

Joe

[Doug Griffith]

I would question whether what you saw was actually PETG. It tends to have a melted edge when cutting and a slight lip on the surface. I've cut a bunch of it and never seen an edge that I would call glass.

[Joe Kace]

I have several pieces from another company I got as samples to look at. I didn't know what it was so I took it to plastic distributor and he said it was PETG and the company that makes the parts advertises it as PETG and the sides are glass. Do you think maybe they are flaming it?

[Vicki Rivrud]

Hi Joe,
We get the same result as Doug. We tried to finish it off flaiming it - but now we cut on the CNC Router - like glass and NO lip.

If you find a way to laser it with the glass finish please keep us posted.

Vicki

[Richard Rumancik]

I think that PETG will act similar to acrylic when cutting, in that it is pretty normal to get striations (curved lines) on the cut edge. In fact striations are common on with a lot of laser cutting, metals included. You won't see it so much on things like wood that decompose rather than melt or vaporize. With acrylic, if you have higher power, it can minimize the appearance of striations but you probably won't get rid of them completely. Air assist will blow out the vaporized or molten plastic from the kerf and therefore can make the striations more obvious.

Since you are probably running at 100% power already, increasing power isn't really an option. You could experiment with ppi (probably best if you can run continuous mode with no pulsing). The other thing you could try is a shorter focal length lens to get the power density up. This will act like a more powerful laser. Note that a shorter FL will reduce depth of field, so focus and flatness become more critical.

[Joe Kace]

Vicki - What type of cnc router are you using?
Richard _ thanks for the tips, I will try everything you said to do.

If I manage to get glass like results ( which I feel now is impossible ) I will be sure to update this thread.

Thanks everyone.
Joe