Hi! I have a problem.
I have installed grbl on my arduino uno and I’m using Cnc shield v3 to control my machine. Everything is correctly set up.
When I try to make a job slicing a .svg or .dxf file and I make multiple passes a strange error occurs. After the first pass the machine offset a undefined distance on my y axis only. For example i have a text and in the second pass it goes all over that specific text, offsetting in y.
is that a slicing problem/Laserweb problem. I tried it on windows and mac and same issue. Does the passes feature works in this way?
Not sure I get what the problem is, could you have some point astray over the other side?
Basically when I generate the Gcode for my laser, I set laser cut option. Then in the option that say Passes I put 2. I start my job and it makes the first pass with no problem. When it is time to do the second pass the machine offset positively on my y axis by a distance which is the file height ( y range) + a random spacing. Let me know if i’m being more clear
@Marco_Dal_Lago understood, never have ive seen such an issue not has someone reported something like this.
Does the gcode show such a move?
Maybe a too high speed and skipping steps in rapid movements? A loosen pulley?
So here’s the problem. I made some tests to understand some facts. In photo there’s a laser cut of two circle made at 4mm/s. I made a process of 3 passe. As you can see y (which is vertical) is perfectly made (proportion are correct) and it offsets between each pass.
I have to say that I have not set any homing with endstop yet.
Here’s is the Gcode output of a single horizontal line with 3 passes.
G21 ; Set units to mm
G90
;
; Operation: 0
; Type: Laser Cut
; Paths: 1
; Passes: 3
; Cut rate: 4 mm/s
;
; Pass 0
; Pass 0 Path 0
G0 X0.00 Y5.74
M3
G1 X189.12 Y5.74 S1000.00 F240
M4
; Pass 1
; Pass 1 Path 0
G0 X0.00 Y5.74
M3
G1 X189.12 Y5.74 S1000.00 F240
M4
; Pass 2
; Pass 2 Path 0
G0 X0.00 Y5.74
M3
G1 X189.12 Y5.74 S1000.00 F240
M4
M5 ; Switch tool offEnd
So… Y position is the same on each pass.
I tried to make a single pass. Then used the macro GO TO X0 Y0. And then start the same job again, but it still shift.
Maybe I need to understand how the software set zero. Maybe it is a Grbl configuring issue… For me it is kinda strange.
Btw thank for the help so far 
(movements are low, stepping is correctly set and belt well pulled and not too tight)
missing/deleted image from Google+
Very strange indeed . If there are no mechanical issues idea say maybe it’s not going 0 before each pass. Did you use the grbl default machine profile or you made changes?
@Ariel_Yahni_UniKpty yes this is grbl default machine profile. I saw that in the console it says work offsett 200 o y axis. Does the set zero button set the work offsset parameter on grbl?
Maybe I’ll try to reflash the arduino and cancel eeprom values first.
Btw it is kinda strange to me that a work offsett would change between each movement home position
I don’t know what to make out of this. Do you have machine show machine ON in settings/machine?
Set if off
A similar thing is happening in a personalized 3d printer Marlin, every time it homes, it adds the offset to Z. I think it’s related to write the offset Everytime it homes to the eprom. But didn’t found any success.
In your case, if you restart grbl, it homes to the last offset?
Hello guys! A quick update to let you know how I managed to solve the problem.
After the arduino uno decided to burn itself, I ordered a new cnc shield on amazon and now everything works fine! Original arduino, original a4988 driver, but chinese shield.
Thanks for the support!!!