Bug: In perforation mode the speed of a cut depends on the angle of the line being cut. In this video the lines are cut with the same perforation settings but the fast one is horizontal and the slow one is angled by 0.8 degrees.
Perf speed.lbrn2 (3.6 KB) This is the file used in the video. I am on Windows 10, an Omtech laser with a Ruida controller, and Lightburn version 2.0.04. It appears a small stop happens when the laser turns ?on? ?off?. As per this, my idle_delay, start pause time and end pause time are 0. This makes laser’s speed erratic when cutting curves. Tabs/bridges have the same bug. Its not clear if this lightburn’s or Ruida’s issue.
I would not be surprised if this is something like… the issue happens when the laser has to turn off on the same frame the stepper motor has to spin.
I did some more testing you can see here with this file test 2.lbrn2 (11.9 KB). This issue didn’t seem to really affect perfectly horizontal lines. Also, the line being angled appears to matter more than the angle of the line. The smaller the perforation the more the affect on the speed. Even perforations of 0.3mm were affected. The effect really kicks in around 0.15mm perforations.
Scanning at non-90 degree angles is “emulated” using normal cutting moves.
This feels like the most likely culprit at the moment. Too many operations in a short time period. It would mean the issue is on Ruida’s side and not lightburn’s. Unless lightburn changes how it encodes perforations.
A “perforation” of 70 µm seems unusually small; what requires such a small perf?
Mostly to exaggerate the problem to make an example of it. But I know Tabs/bridges uses small perforations (0.1mm cut/skip?).
The laser head speeds seem equal for any perf spacing above 0.1 mm.
I assume you gave 0.1 mm a try and didn’t have issues?
The KT332N controller on my machine has only the Idle Delay parameter, so my machine is certainly different than yours.
Sorry, start pause time is a lightburn layer setting. That sentence had mixed device and lightburn settings in it.
Per the doc, that small spacing allows for fine-grained power control in the (rare, in my case) situation where you want partially cut tabs:
the width of the pulses used to simulate reduced power cuts
That’s different than Perforation mode, because tabs occupy a very small portion of the perimeter and a slight slowdown makes no difference.
I’ve used Dot Mode to similar effect, where short pulses with close spacing produces a nice trench in otherwise melty PETG sheet:
The actual speed is much much slower than the layer speed, but that’s irrelevant because Dot Mode isn’t intended for high-speed operation.
Given that there’s no slowdown while making “normal” perforations, a slowdown under perverse conditions is not so much a “problem” as an opportunity to get more control over the results.
I’d say the old advice applies: "If it hurts when you do that, don’t do that.
I think there’s some missed opportunity for high speed/quality cutting for some things like a melty PETG sheet, partial cuts on paper-based material (my case), ?maybe? an opportunity for less sooty cuts (my experiment), ect… But if the issue is on Ruida’s end because it can’t handle that many commands in the short period of time then that’s all a mute point anyways. I’ll add one more summary comment and mark it as a solution for the lost souls searching the internet.
I’d say the old advice applies: "If it hurts when you do that, don’t do that.
I think that’s how I’ll be handling this for now.
The laser does (slow down)/(speed up/down)/(have erratic speed) for tabs/bridges and for perforation mode when the perforations are small (<~0.5mm). It only happens when the laser is not moving at a non-90 deg angle. There is currently no fix. Its the laser controller’s fault not Lightburn’s.
When not moving at a 90 deg angle each on/off of the laser is probably being encoded as a unique command. At high speeds the laser controller probably can’t keep up with all the commands, and the machine slows down. Any value greater than zero for idle_delay in the machine settings, and start pause time/end pause time in the lightburn layer settings will make the problem worse. Thanks @ednisley for help getting to the bottom of what was happening.
