Jtech laser and Xcarve feeds and speeds question


3.8 w jtech laser mounted on Xcarve,
grbl 8000 mm/min max feed rate X&Y

same rate set in PicSender,

Machine doesn’t run anywhere near that when trying to burn a straight line,

reset 4500 mm/min and still nowhere near those speeds,

Im sure it could run a lot faster , when I burn at 0-255 it often burns deeper than i want,
I can halve the max power to 0-127.5 and it travels same speed,

Is it running as fast as GRBL can feed it?
the router can run at high feed speeds,

how can i move that gantry faster :slight_smile:

grbl 9g jtech version



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Hi Greg,

Have you made any performance changes to the grbl settings? More info here:

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Thanks for the info

I had all those settings in except the very fast accel rate,

as i added accel rate in GRBL the machine engraved faster until i was at 5250 mm/min feed and 12,000 mm/min accel rate , this accel rate can be a bit shaky as gantry is carrying a makita router, but, if need be can easily enough be removed

this dithered bmp is 190mm across and took 2+ hours

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That post I linked showed an accel of 8000 and max feedrate of 4500mm/min for the X-Carve’s X&Y axis in the J-Tech grbl settings.

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True , I had scrolled down further and found this and took it as gospel and set off to be Buzz Lightyear and Laser a hole in the universe :slight_smile:

another error on my behalf was I was using the J tech settings page , when i changed to GRBL PWM and tried again the machine tried to finish the next clock in 5 minutes, this was awesome fun to watch but was going to shake my table to bits such was the force of the direction changes,

So i will indeed reset grbl to 8k and 4.5k mm / min and report back .

I am now the most awesome Dad in town , My boys 12 th birthday party and I managed to strap the Laser to my arm and run around in the night cutting branches off trees yelling “PEW PEW” while star wars music played , :joy:


Ok , Jokes aside

this took 27 minutes , same size as last one , more detail, better burn ,and 90 minutes faster ,i also used skip white feature, I will slow it down some more though, change of direction is still an slight issue for me,
Im not sure how to use the laser edge feed reduction yet, i keep getting errors and obviously my doing,

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What errors are you getting? Have you input a Width in Pixels value? That value is multiplied by the Pixel Resolution setting for the distance it travels past the engravings edge before it reverses directions. You will have to experiment with the feedrate for the Extended Edge so you do not experience any mechanical ringing/jarring that can show up in the laser burns.

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Hi Pic2

im getting an “unkown USB error”
or program just freezes ,

the only thing i have changed (i think) is the edge setting

i will try and replicate the error and post a screen shot

do PEP5 1 bit images need to be dithered ?
does extended edge work in with skip white enabled ?



here is a screen shot,

I will try an updated arduino driver as i found 1.6.8 on my system and 1.6.12 is out

Hi Greg,

Yes it is recommended to Dither the image to 1bit. Without dithering, there are grays in the image that will cause ramping and the S commands will not be just Min and Max values.

If you use the Analog/PWM engraving profile, dithered image and Skip White, the Extended Edge will work also. Dithering the image ensures the Skip White works properly.

The USB Issue error is the PC & PicSender lost communication with the UNO & grbl. Check if your USB cable is faulty and the USB Power Management in Windows is disabled. Do you have a high power draw equipment starting such as an air compressor or air conditioner causing a voltage drop (brownout) to your PC? I have a battery backup on our PC for a voltage conditioner. I have read others use a powered USB hub to eliminate this problem.


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Hi Greg,

There is a known limit to the feedrate using the J Tech GRBL version 0.9g due to the stepper implementation in the main GRBL branch. There is a lot of floating point math in the stepper ISR that will cause a limit on the feedrate allowed. This is not a huge concern for using the CNC, but can be a problem when using a laser.

Sonny and I are working together on the laser implementation on the new version 1.0 of GRBL main branch. We have merged the J Tech firmware laser implementation with his main branch and it should be able to do 8000mm/min. In the meantime, you might just need to lower the power if you are hitting the maximum feedrate limitation due to the stepper math. The new version of the firmware should be available soon. Sonny is working on it now and we will be testing it shortly. It will be a big advancement for all the laser users who use GRBL and for us as it is a big task to try to update our firmware every time the main branch does something new. J Tech Photonics is proud to be an official sponsor of GRBL and we look forward to this new release. We will keep everyone posted on this upcoming release of the new firmware!

Best Regards,

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Jeff & Jay

Thanks guys for the input , very much appreciated

I’m getting a much better handle on the diode and software ,
I’ve turned out some decent results and my speeds required have been nowhere near the upper limits of GRBL ,
This is good as it shows I most likely had something set incorrectly

A new USB cable in a different port seems to be better
No errors since

i still have many questions
But another time

Thanks again


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