Powerscale doesn't seem to work

I have setup a test for engraving, I’ve marked on the sample what the power settings and power scale that was used.

They all seem the same with lots of char at each end of the pass.

Any thoughts on which setting I’ve missed somewhere or don’t fully understand?

This is modified K40 using a Cohesion Laserboard.

This board won’t let me include an image so here’s a link to it.


Hi David, Welcome to LightBurn

I had several initial trials that looked like this. For me I believe it was related to overspeed vs. acceleration / deceleration at the fill-line end. Dynamic Laser Power Mode (Edit: Not overscan), the math used to decrease the laser output when decelerating and accelerating seems somehow disconnected from the math used to reduce power output when the laser controller thinks it’s going too slow (everywhere else).

It could be a quirk in the algebra or a parameter that isn’t the same when the controller changes from power reduction during constant overspeed to power reduction when changing speeds - In all honesty - I’m not totally certain.

I believe that if you slow the process down the power output selected by the Dynamic Laser Power Mode at the end of the 70% line will level out and you’ll get a nice diagonal pattern of similarly solidly marked boxes across your bottom 2 rows. I’d also suggest changing it to 4 rows in your next test.

What units for velocity (cm/min, in/second, mm/s) is your software running in and what units is your controller looking for?

Kind regards,
[Edited terminology error]
Source: Grbl v1.1 Laser Mode · gnea/grbl Wiki · GitHub
Note: I’ll dig into the code a little more to back-check this and make sure I’m on track.

Hi John thanks for the reply. I’m using mm/s. So you’re saying to drop it to a slower mm/s? I’ll give 100mm/s a try and see what happens.

I have tried something like 250, 200, 150, & 100 mm/min on the same board. Then when I had something i liked I would proceed with future efforts at that speed.

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