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K40 Laser Power Before & After

Perhaps this is just in my mind, but interested to know if others noticed this..  (or my tube is starting to age..)  Ever since the install of the Gerbil board I feel my tube has "less" power.  With the stock Moshi board, I was able to cut an object out of 3mm (1/8" birch plywood with 1 pass 8mm/s @ 32% power.    Now I can go 6 passes at the same speed an power (according to my values in the software) and don't even break to the other side sometimes..  Is it possible there is a static value stuck somewhere behind the scenes where its set to lets say 30% power, and im only adjusting 0-100% within that 30% max value?

don't think im due for a new tube yet, just seems to be a dramatic difference.  I may swap the Moshi back in to confirm tests.


I have needed to adjust the $30 parm to various levels depending on the print I am using.  Lowering the $30 to 100 for some jobe has given sufficient power to give a decent print and some prints need to be at 2000 or higher.  Every print needs to be at a certain level to come out right and I expect the same will be true for cuts.

You can adjust the $30 value with cncjs - it's free.

So, I have been avoiding this question to look like a n00b...  But what are all these values your adjusting..  $30 means nothing to me..lol   I'm sure there are values and parameters for EVERYTHING like X axis limits, Y limits...bed size....etc..  but how does one know WHAT to adjust, and why.    I guess my question is what IS $30.   Is there a key that defines values?  min vs max?   I currently use CNCjs, as well as lightburn.  Both have access to console.  Thanks, and apologies for cluttering up the forum..


Hi Derek,

The $ prompt is the grbl firmware config values. You can enter those via the command section in cncjs (black screen block, just double click in it and enter $$) or any other gcode sender.

$$ - View Grbl settings

To view the settings, type $$ and press enter after connecting to Grbl. Grbl should respond with a list of the current system settings, as shown in the example below. All of these settings are persistent and kept in EEPROM, so if you power down, these will be loaded back up the next time you power up your Arduino.

$0=10 (Step pulse time, microseconds)
$1=255 (Step idle delay, milliseconds)
$2=0 (Step pulse invert, mask)
$3=2 (Step direction invert, mask)
$4=0 (Invert step enable pin, boolean)
$5=1 (Invert limit pins, boolean)
$6=0 (Invert probe pin, boolean)
$10=3 (Status report options, mask)
$11=0.010 (Junction deviation, millimeters)
$12=0.002 (Arc tolerance, millimeters)
$13=0 (Report in inches, boolean)
$20=1 (Soft limits enable, boolean)
$21=0 (Hard limits enable, boolean)
$22=1 (Homing cycle enable, boolean)
$23=3 (Homing direction invert, mask)
$24=100.000 (Homing locate feed rate, mm/min)
$25=1000.000 (Homing search seek rate, mm/min)
$26=250 (Homing switch debounce delay, milliseconds)
$27=1.000 (Homing switch pull-off distance, millimeters)
$28=0 (default laser pwm mode)
$30=2000 (Maximum spindle speed, RPM)
$31=0 (Minimum spindle speed, RPM)
$32=1 (Laser-mode enable, boolean)
$100=160.000 (X-axis travel resolution, step/mm)
$101=160.000 (Y-axis travel resolution, step/mm)
$102=250.000 (Z-axis travel resolution, step/mm)
$110=3000.000 (X-axis maximum rate, mm/min)
$111=3000.000 (Y-axis maximum rate, mm/min)
$112=500.000 (Z-axis maximum rate, mm/min)
$120=500.000 (X-axis acceleration, mm/sec^2)
$121=500.000 (Y-axis acceleration, mm/sec^2)
$122=10.000 (Z-axis acceleration, mm/sec^2)
$130=320.000 (X-axis maximum travel, millimeters)
$131=220.000 (Y-axis maximum travel, millimeters)
$132=200.000 (Z-axis maximum travel, millimeters)

See https://github.com/paulusjacobus/grbl/wiki/Configuring-Gerbil-Grbl-v1.1e

For example if your machine homes in the wrong Y direction you could specify $3=0 rather than swapping the Y axis connector 180 degrees around...

Hope this helps.

Cheers, Paul awesome.tech

Thanks Paul, I have seen that menu before in console, but have not messed with any settings, so at least I was in the right place...  So based on the $30, spindle speed, is that equal to laser power?  So I guess my question is, which value should should I look at and play with settings.  Is spindle speed is equal to power, what would my min, and max values be?   Example.. 2000=100?  I want to say mine is set to 1000 currently, as that's what it was default.

Thanks in advance,  Also, thought I would mention not all software shows the information in the console.  Some shows just the value ($132-200.000)  and other software shows the explanation as below.

$132=200.000 (Z-axis maximum travel, millimeters)

grbl 1.1 removed the descriptions to save space for more code - good plan...

Quote from BlazinLazin on January 24, 2018, 11:41 am

So based on the $30, spindle speed, is that equal to laser power?

$30 is the laser pwm range 0=0mA and 2000=18mA. Depending on the age of your tube you some set this value. See the calibration guide on awesome.tech! Gerbil Engraving Calibration Guide

Cheers, Paul awesome.tech

Thanks Paul, I'm guilty of missing that guide..  My bad, I will play, test, and report back my results.  Thanks again!


No worries Derek, it just shows that I need to fine tune my instructions. Hopefully I get better at that!

Cheers, Paul awesome.tech

Finally had a few days off to play with the mini-gerbil.  Installation was easy (later power supply with the plugs.. easy to get pwm working.

I love this thing.. I guess its because I am an engineer, so I go into the plugin code and your settings to understand what is going on.

What does "spindle speed" mean when you are setting $30 ?   This seems to be a measure of max power going to the laser from the power supply.. but I don't understand the term "spindle"..

I would like to get the test button working again, but don't understand the technical drawing.. can you explain that better?


Yes $30 is basically the power range (0-2000 = 0 - 20mA). Since LightBurn has the default to 1000 in their laser cutting software, we have set it default to 1000 to ease the configuration for the users.

The test button can be switched on via a light burn macro.

Right click on the macro and give it a title - test button config

$32=0 (cnc mode)

S100 (laser strength low)

M3 (or 4 laser on)

P4  P1000 (dwell 1 sec to power the laser)

M5 laser off

$32=0 back to laser mode

Cheers, Paul awesome.tech

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I recently purchased and installed an MG3 and right from day one I noticed that the power was weaker. I too thought maybe my tube was aging. It just wasn't the same as the M2 Nano board. I cut mainly 3mm acrylic and I normally cut at 15% power on my digital k40 which is about 50% tube power or about 9mA. Cuts like butter with M2 Nano. However, once I installed the MG3 board and used the same settings in Lightburn, I couldn't even make it through the same material. I even tried 28% digital power/100% tube power/18mA in Lightburn and I still cannot get through 3mm acrylic. I got frustrated so I disconnected the MG3 and went back to the M2 Nano board. It cuts great again at 15% digital power/9mA.

When I get a chance I'll plug my MG3 board back in and check the $30 setting. Perhaps it's set lower than it should be.

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