View Full Version : No smooth edges on Acrylic

Andrea Weissenseel
06-24-2009, 6:31 AM
When I cut acrylic, even the 3mm width, the edges don't have a clean cut - they rather almost look like the edge of a coin. Is this a problem of the material or the machine ?

Thanks, Andrea

onur cakir
06-24-2009, 6:41 AM
Hi Andrea,

what are you settings ?

Mike Null
06-24-2009, 7:36 AM

Try increasing your frequency setting.

Rodne Gold
06-24-2009, 7:54 AM
Its normally a "problem" with the air assist and the melt ejecting thru the cut , it's almost impossible to get totally smooth edges without striations with a laser. You can minimise it by using higher PPI's (freq) and setting the exact correct air assist pressure and direction of air assist flow.
If you dont use air assit , this can be even worse as the melt does not get properly ejected and resolidifies making the edges worse.
Apart from this , if it's worse on curved sections , it can be motion slop in the machine itself.
The fact that persepex expands when heated makes things worse as the pex itself is "alive" when you cutting it.

Frank Corker
06-24-2009, 9:03 AM
....and this could lead us on to why we have been discussing 'flame polishing'. The edges are sometimes rubbed down with gritted paper and heated very quickly, this will re-melt leaving a much smoother edge.

Rob Bosworth
06-24-2009, 9:45 AM
Andrea, the above responses address the processing parameters very nicely. Another thing to contemplate would be the condition of the movement system of your machine. How old is your machine? When was the last time you replaced belts, bearings, idlers on the system. Have you gone through and made sure your all the bolts and clamps are tight. Wear on these machines can usually be seen in a raggedy processed part. Dirt build up in drive gears and belts can also effect end results. Jagged edges on either raster engraving or vector cutting or scribing can be a sign of a machine needing a little TLC (and a few dollars of parts.)

Andrea Weissenseel
06-25-2009, 2:30 AM
Goord morning,

@Onur, I cut 3mm with 1.6 S and 95% P

@Rodne, Mike - the frequency is at the maximum. For acrylic I allways use the air assist. I know how to adjust the pressure, but that means only that I know how its done :rolleyes: the instructions are pretty vague.

@Rob, my machine ist 8 month old, at the beginning I had some stripes when raster engraving so they changed the driver of the x-axis and its gone since. If TLC means grease, and I clean the old one off and put some new on pretty regularely.

Last but not least @Frank - why did I know when I asked the question that I will get an answer on flame polishing :D so I got prepared

onur cakir
06-25-2009, 3:55 AM
Goord morning,

@Onur, I cut 3mm with 1.6 S and 95% P

And the freq. ?

I set my epilog to S5 P100 FQ5000 and it cuts like hot knife on butter with perfect edges.

Stephen Beckham
06-25-2009, 7:52 AM

Not sure if this helps, but I've accepted the fact that I get cheap plastic (from Mexico to my understanding) occasionally from the supplier. It has the same effect as yours everytime. I pop in a piece from Cryo and it comes out real nice with the same settings.

Tim Bateson
06-25-2009, 8:02 AM
Thank you Andrea.:p:p:p:p What about it Frank, are you going to change your Avatar?

sean m. titmas
06-25-2009, 8:25 AM
i dont have any experience with the machines you all have but flame polishing is a good skill that you might want to learn. its a bit old skool but produces a very unique edge that is very organic.

Martin Reynolds
06-27-2009, 1:48 PM
Several things come to mind.

First, the laser software on my machine converts curves to a bunch of short lines. There's a setting for speed and accuracy - more speed means longer lines. Note that the motion control system is capable of doing curves, but the controller still does lines. This approximation appear to be true for all the smaller lasers, so your machine naturally wants to cut many little flat edges.

Second, cast acrylic shows these little lines way more than extruded. Extruded flows a little more after the cut, and smooths the edges. Have you tried extruded acrylic? It is usually only easy to find in clear, colors tend to be cast.

Third, how is it at cutting squares? Squares only use one axis at a time, so if there's a motion problem, it won't be so likely to appear.