Pulsed vs Continuous laser power?


#1

I’ve noticed that in some recent work with 3mm acrylic, cut curves have a sort of stepped/ridged appearance. I’m curious if this is the result of stepper motor resolution, or perhaps the beam power being pulsed rather than continuous. Is this “typical” of “all” laser cutters?

The recommended settings for this material suggested a 5kHz pulse rate, suggesting non-continuous or at least non-flat laser power vs. time curve. I’m curious if we can expect similar appearance in cuts made with the Glowforge. Here are some images showing the cut edges, one with a penny for scale:

1, 2, 3

The designs were done in Illustrator, so I’m running on the assumption that the splines have no such edged detail in their representation. The cuts were made using an Epilogue laser. I took the photos with an iphone. (…holding a lens assembly scavenged from a recently disassembled Canon G9 to the iphone imager to get up close and personal with the subject. I’m calling the weaknesses of the imagery “artistic”)


#2

Penny? :relaxed:


#3

It’s likely the result of speed changes as the laser traverses the curve. Check your cut settings for linear vs curve speed. Since it’s moving in both axes at the same time, you can’t use the same setting as when it’s doing a straight line on a single axis.


#4

That looks like the sort of faceting artifact I see from CNC milling when the CAM software generates lots of small linear move commands rather than the desired circular move commands. That’s usually caused by an improperly set parameter in the CAM program that generates the motion control (G-code) file. I see the same thing on 3D prints of STL files and assume that is a result of some limitation or an improperly set parameter in the software that generated the design or the export of the design. What software did you use to generate the design and the cut file for the part? Can you share a version of the cut file in a format that is commonly readable?


#5

I think so too. To me, that looks like a problem with the input more than a problem with the output. The OP mentioned that they used Illustrator, which I also assume doesn’t facet curves like that, so maybe the problem is somewhere within the Epilog driver/software?

@jcberry, what file type is the design saved in? If it was saved as a DWG or something, I could see Illustrator adding facets in order to maintain compatibility with some versions of that file type. Perhaps saving it as a native AI file would make those flats go away.

One of the very, very few things I cut with a Silhouette Cameo ended up with faceted arcs. At first, I assumed the problem originated with the Cameo software, but after checking the file I noticed that SolidWorks had added the facets because the way it handles exporting DXFs is stupid.
(To anyone interested in SolidWorks’ stupidness, see the post from 10-28-12 9:50 (currently the last post) for a workaround - https://forum.solidworks.com/thread/57975 )


To adjust for kerf or not to
#6

I used Adobe Illustrator for the original files. The curves were created using the “live corners” feature in Illustrator, where I started with say, a triangle, then selected the corners using the direct selection tool, and scrolled the live corner handle to replace the points with fillets.

The result of the action is the replacement of a single vertex corner on a path with a pair of spline-handled vertices and a bezier curve in between.

When I go to cut the material, there’s a printer driver -like plugin for Illustrator which has a variety of settings for various materials. I’ve not attempted any deeper tuning beyond the simple selection of material. I’ll have to snoop around in there for details such as linear vs. curve speed, as @jamesdhatch suggested.

I’m running on the assumption that the driver software for the epilogue laser is responsible for generating any g-code intermediary representation, all under the hood/behind the curtains with respect to the user.


#7

I usually run curves at half the speed of the linear setting. My linear acceleration is 1000mm/sec and corner acceleration is 500mm/sec so I keep the same ratio for my cuts. Not sure what options you have with the Epilog drivers but it’s worth looking. Or asking Epilog.


#8

The Glowforge laser is continuous-wave, so it doesn’t produce those artifacts when cutting acrylic.


#9

Yeah, that doesn’t look like it has much to do with the laser itself (pulsed vs. continuous). But something in the path planning software or firmware is converting the smooth curves into line segments that are too coarse for your device. Somewhere there may be a smoothness/closeness of fit/precision control.