I have a customer who is using GRBL 1.1f and Phil Johnsons Demon controller with Arduino UNO to run a plasma table with a J Tech 7W laser on it.
It looks like it starts going and then abruptly stops. I mentioned it might be USB, but it looks like it does this right at the beginning every time. Any help would be appreciated. Here is the video of the issue.
https://1drv.ms/v/s!AtkWa_K9eiIJie4Y-t0Z3_1oslXTkA?e=McRa3F
Jay
@JTechPhotonics I’m sure that I’m too new to this to be able to help, but I hope that you don’t mind a question. What is your $30 value? The screen is too blurry for me to see it. It looks like 3000 to me.
Here it is:
$30=1000
$31=0
$32=1
We changed the machine size to larger and also changed the maximum speed settings and this started. We don’t have homing, soft, or hard limits enabled.
Machine jogs just fine. You can jog all over the table. Just when you start the program it stalls in 2 seconds every time.
Best Regards,
Jay
@JTechPhotonics Tks, Jay. I can’t be of any help, unfortunately. I have more experience with CNC routers than with lasers. I’ve only recently added a diode laser to my CNC router setup.
In the router forum that I inhabit, stalls and stops are frequently caused by noise getting to the motor cables. I don’t know if the same is true with a setup like yours. Also, these problems generally occur further along in the gcode.
I’ll be watching to see if anyone can help you, of if you figure it out by yourself.
Good luck.
This video pauses at all the things I don’t need to see, and shakes badly over everything I’m trying to read, but it sounds like the axis just seizes. I couldn’t read the settings clearly, but it looks like the X & Y axis steps are set to 500 per mm. Since 8 bit GRBL can only pulse at 30,000 pulses per second, the user would have an absolute maximum speed of 60 mm/sec (3600 mm/min) but appears to have the machine set to allow up to 8000. If he exceeds 3600, GRBL will just internally seize up. That’s my best guess.
hello all! I am the manufacturer of the Demon shield. I believe I have been emailing back and forth with this person, unless it’s a different plasma cnc.
To my knowledge and experience, the sudden stopping is from noise/interference/static. you have to fully vet out the grounding and separate the DC motor signals/cables from the AC and or the plasma power lines. among other steps to further isolate the issue.
Try keeping all plasma components off and air cut. if it completes, it’s definitely the plasma end of things.
If that is the case, he can set the micro stepping at 4x ( I send out the controllers set to 8x). sacrifice a little accuracy for speed.
Hi Oz and Phil- Thanks for responding. I am assuming the $101 and $100 settings will be based on his steppers, so I don’t think he has calibrated it already. I told him to lower the $100 and $101 to 100 and see if it will move. If it does, then this would make sense.
He told me originally that the machine was too slow and I noticed Phil you had the max speed set to be something like 47inch/min, so I bumped it to the 300inch/min number. Probably my fault then if this all works with lower steps/mm values. 
I’ll look at your site to see how to change the micro stepping.
The controller gets sent out per cnc for newbies settings. Which is about a 157" a minute Max on a screw drive. I can tell you that The controller has sent out can go way more than that Only changing the Max rate. If it really was 47, that means he changed the settings
I run my Demon Controller at 315ipm max with 8x micro stepping no problem.
The thing that matters here is the total number of steps sent per second - how you get to that number is irrelevant. If 8x microstepping on your setup at 315 ipm is putting out less than 30000 steps per second then it would not be a problem.
315 ipm is about 133 mm/sec, and 30000 / 133 is 225.5 steps per mm. You didn’t mention what your $100 / $101 settings for steps per mm are, but if it’s less than 225 then you wouldn’t be hitting that 30000 steps per second limit.
He had the $100 and $101 set to 500 and he was trying to go pretty fast. When he first got it set up it was working, but slow. He also wanted to have 1.1f on the machine so it will work with lightburn.
I believe he had updated the firmware to GRBL 1.1f because Larry’s firmware that was installed on the arduino doesn’t support the M4 command for lightburn and the dynamic laser mode. I think his values for everything have been reset to more “default” values and now he is in this situation. Hopefully if he can calibrate his steps/mm to lower than 500 this should work. I’ll check with him and see.
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