Cutting speed for BALSA 9 mm

My hardware: CNC3018, GRBL Controller and 40W Laser.
First cutting job: Balsa 9 mm thickness.
As a beginner I have to cut 9mm balsa with a 40W laser. I chose 180 mm/min as the speed.
The nc file says 70% power, I changed that to 99%, S999 (according to recommendations from others).
The speed in the nc file is F6000; how come the speed of 180(mm/min) then is F6000?
Thanks for any help!

Help me get oriented to what you’re doing.

Can I infer that you’ve done the design in LightBurn with the speed setting set to 180 mm/min? Then saved to gcode from within LightBurn and are now reviewing the generated gcode?

Why did you have to change the power? Where are you seeing F6000? Are you sure this is not for traversal moves?

Share the .lbrn file you’re using to generate the code and the generated gcode file. You may need to change the file extension to .txt to upload here.

The contours were created with a CAD program and saved as a DXF, then imported into LightBurn. I specified 180 mm/min as the speed and then let LightBurn generate the nc file. You can open this with a text editor. The code is:
; LightBurn 1.0.06
; GRBL device profile, absolute coords
; Bounds: X4.49 Y4.08 to X15.51 Y9.92
G00 G17 G40 G21 G54
; Cut @ 6000 mm/min, 70% power
; Layer C00
According to my records, F is speed. G90 means absolute coordinates, S=spindle speed (apparently interpreted as % of laser power) and F=feedrate.
My question is how F6000 came out of 180 mm/min.

I’m guessing that it didn’t. I’ve never seen LightBurn get feedrate wrong. 6000 mm/min happens to be the default speed for LB layers so I’m guessing something else going on.

Can you review your cut settings to confirm that the layer you’re seeing is the layer that’s getting exported?

Or share your .lbrn file here for review.

There is only one level/layer. And that can also be seen in the code that I have shown. This is the code of one of these files:
; LightBurn 1.0.06
; GRBL device profile, absolute coords
; Bounds: X3.67 Y5.3 to X124.33 Y72.7
G00 G17 G40 G21 G54
; Cut @ 6000 mm/min, 70% power - Cut @ 6000 mm/min!!
; Layer C00
; return to user-defined finish pos
G0 X0 Y0

I’m not a G-code specialist, but I have some documents.
F= feed (but why 6000)
Since the Z speed in LightBurn is 600 could that also mean this Z-speed ?
G00 Drives full speed to origin position
G17 select X-Y
G40 Cancel all tool path corrections
G21 programming in mm
G54 zero shift
G90 absolute coord’s
M4 laser on
M9 coolant off
G0X9.629Y5.3 Traversing commands XY
G1X moves to X position (124.332) S700=percentage speed F6000=10x Z speed, unclear
; Layer C00=default layer, will not be switched (there is only one)
then coordinates follow

You cannot upload files to this help page.
But please only answer if you know about this G-code.
If I don’t find out anything else, I’ll do a test next Monday and measure the speed with a stopwatch.

Thanks anyway and have a nice weekend.

There’s an up-arrow icon in the top of the reply box to upload a file.

Please attach your LightBurn File so we can have a look.

You can also drag-and-drop your LightBurn file into the reply box when you reply. That should work for you as well.

I see the G-code. I’d like to look at what you’ve instructed LightBurn to do with your imported DXF.

Thanks everyone for the many tips. In the meantime I have read a lot and also received direct help from LightBurn.
It’s a bit unfortunate in the main menu when you set a speed there and choose ‘Create GCode’, because the speed set on the main monitor isn’t transferred to the GCode, but that of the layer.
Cutting balsa 9mm is possible, but this material in this thickness leads to a relatively thick burned contour; if you grind them off, the result is a reduction. So you would have to factor in a corresponding allowance to get the exact part you want after grinding down the edges.
Since my small machine can laser and also mill, I milled these parts mechanically and thus got an exact result.
On the other hand, I am very satisfied with the laser cutting of plywood (3-5mm thick). Only the smoke is a problem, for which I still have to get an extraction device (or laser on the terrace in summer - the machine is on a roll container).
For all other questions I was very well informed by the support of the software manufacturer.

Where can you set the speed other than on the ‘layer’.?


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