Acrylic and Polycarbonate

[Pete Andrew]

It seems most of you old hands on this forum have tried most things with your lasers - has anyone managed to cut shapes cleanly out of CDs? One might want to ask why.... it is a long story for another day. My understanding is that they are made out of polycarbonate, and having had a shot at it, I have managed to cut some shapes out, and it has taken more power than the equivalent acrylic (perspex/plexiglass) would have done. However the cuts are not as clean as acrylic, presumably because of the difference in the material, and the fact that there is a layer of aluminium in there too, confusing things. However, is there a guiding principal as to how I might adjust things such as PPI? I mean is it just a question of trying different settings, or should I be thinking along the lines of "more PPI means smoother edges..." Could lower PPI conceivably give me smoother edges? Or have I just to find that optimum setting....?

And finishing acrylic and polycarbonate - I have previously used Brasso (silverware polish, spirit based with fine abrasive suspension in it) to polish the edges of acrylic (I needed a bevel which I did by paring it down with some scissors....) without any knowledge of the possibility of stress cracks appearing. So far this hasn't happened, but when I cleaned up the CD pieces with Brasso, stress cracks appeared immediately all along the cut edges (sort of perpendicular to them). You could actually hear them forming!

Whats the thinking on this? Is polycarbonate more prone to stress cracks, maybe due to the extra power needed to cut it and its re-setting in a stressed way? Or does acrylic just not get stress cracks? Or not as easily...... or what?

Any help please. .... and the weird text sizing thing happening here is a bit confusing too....

Pete Andrew

[Aaron Koehl]

Adjusting PPI will depend on your laser manufacturer, but as far as choosing a setting, it is usually trial and error.

What is the text sizing problem you're having?

[Michael McDuffie]

It's been my experience (worked in CDROM manufacturing for 6 1/2 years) that CDs are looking for an excuse to explode.
I wouldn't use anything stronger than soap and water or rubbing alcohol to clean them and wouldn't try to run a laser cut CD in a player.
The shaped CDs are molded that way from the start.
A worn cutter for the center hole can lead to stress cracks and we had a few returned that exploded in drives under normal use.
We had a solvent for the screen printing presses that if you wiped it on a CD, would leave no evidence of trouble. If you bent the disc even slightly, it would fragment into shards instantly.

Michael

[Rodne Gold]

I have had a CD grenade in my player and in my puter. As Michael said , they are incredibly stressed. Cutting polycarb without burnt edges requires high power and inert gas blankets.

[Pete Andrew]

Thanks guys

Aaron - the text size thing is just that half of my post seems to be in a smaller sized font - I guess because I am not as succinct as I could be and the space allocation means some of my waffle gets shrunk down a size!

It sounds like CDs are a trick unto themselves, and I will at some stage have to explore the inert gas idea if I am to do many of these. Interesting about the solvents though - I would hope that something akin to the fluids sold to clean CD's would be pretty safe and not lead to stress cracking. What is that stuff anyway - is it something approaching the soap & water that Michael suggests? Soap & water seems to be getting a pretty good press on these boards recently - maybe that needs exploring more too!

[Aaron Koehl]

Thanks guys

Aaron - the text size thing is just that half of my post seems to be in a smaller sized font - I guess because I am not as succinct as I could be and the space allocation means some of my waffle gets shrunk down a size!

If you pasted in from a word processor (such as Microsoft Word), it often leaves artifacts of HTML, resulting in strange font combinations. If this is the case, try pasting into Notepad first, then copying and pasting into the editor window.

[Joe Pelonio]

I have cut and engraved on CD's with good success. Even was ableto engrave on a data CD and still have it work after. It's not the power or speed as much
as the frequency setting that affects the smoothness of cut. Also, the cracks
on this or Acrylic are caused by interaction with the material that has been
changed at the molecular level by the lasering. The worst thing you can use
is denatured alcohol, but many solvents will do this. The only thing I have found
to clean well without the cracking is Rapid Remover by Rapid Tac Co., available
at many sign supply stores.