I am hoping I can get some help. I recently replaced my Gshield and Adruino boards on my controller. I checked my wiring and my belts everything looks good.
For the first 2 minutes of the carve it looks great, but as it continues it starts to shift and gets messed up. I played with the voltage on the motors, which seemed to help some, but it’s not perfect.
What do I do?
Most likely stalled steppers due to insufficient torque.
What bit, feed rate, RPM, depth per pass?
What PSU voltage do you use?
What have you set your reference voltage for each axis to?
What are your micro step setting?
What are your values for GRBL parameters $1, $100-102, $110-112, $120-122?
Let us know 
I diagnosed a motor pulley without a set screw and a loose belt. I got it dialed in on the test cut. Trying another cut now.
In the g shield, it’s not hard to overheat the driver. If it continues to work well at first and then start to develop poor performance, you can be overheating the driver. I had massive issues with this when I first started using my shapeoko 2.
I was using a 1/8" downcut on MDF. I was using the standard feed rate. I found a missing set scree and a loose belt. I also have a V-Wheel that’s messed up some how.
Here is another carve i tried. It looked good except the outer circles are off.
So what do I do about this overheated the driver?
I tried again with a 1/32 bit, 30 in/min feedrate.
I’m not sure what you mean by the voltage questions an the micro step setting.
How do I get the GRBL parameters?
This is all pretty new to me.
You either need to dial down the current with the potentiometer as long as the new current provides enough driving power, or you need to improve the cooling on the driver. I ran with the gshield and uno for a long time with great success, even running Nema 23 motors. When I finally blew one of the gshield drivers, i upgraded to a better driver setup and havent ever looked back.
One of the problems I found with the cooling fan on the gshield (assuming you have a fan) was that the fan was close enough to the drivers that the hub for the fan was directly over the Y axis driver which essentially put that driver in the “eye of the storm”, preventing it from getting much flow. To fix this, I Turned the fan to blow out rather than in, and then drilled some holes in the Uno/Gshield mount housing to allow airflow under the gshield, then pulled out over the top. This also took some tape/foam on open areas to ensure the air flowed properly. Just start thinking about how air moves and youll start to see some things you can do to improve cooling. I did also add heatsinks to each of the drivers on the gshield.
How do I check the voltage and reference voltage?
How do I check the micro step.setting and the GRBL parameters?
This is new to me and I have never been able to get this thing working and ready to just toss it.
Here is what I have GRBL:
$0=10 (step pulse, usec)
$1=255 (step idle delay, msec)
$2=0 (step port invert mask:00000000)
$3=3 (dir port invert mask:00000011)
$4=0 (step enable invert, bool)
$5=0 (limit pins invert, bool)
$6=0 (probe pin invert, bool)
$10=115 (status report mask:01110011)
$11=0.020 (junction deviation, mm)
$12=0.002 (arc tolerance, mm)
$13=0 (report inches, bool)
$20=0 (soft limits, bool)
$21=0 (hard limits, bool)
$22=0 (homing cycle, bool)
$23=3 (homing dir invert mask:00000011)
$24=25.000 (homing feed, mm/min)
$25=750.000 (homing seek, mm/min)
$26=250 (homing debounce, msec)
$27=1.000 (homing pull-off, mm)
$30=12000. (rpm max)
$31=0. (rpm min)
$100=40.000 (x, step/mm)
$101=40.000 (y, step/mm)
$102=188.976 (z, step/mm)
$110=8000.000 (x max rate, mm/min)
$111=8000.000 (y max rate, mm/min)
$112=500.000 (z max rate, mm/min)
$120=500.000 (x accel, mm/sec^2)
$121=500.000 (y accel, mm/sec^2)
$122=50.000 (z accel, mm/sec^2)
$130=750.000 (x max travel, mm)
$131=750.000 (y max travel, mm)
$132=100.000 (z max travel, mm)
