Post process not working correctly

[litodrums]

Hello and thank you for you input. I'm replacing my spoil board and I'm using the facing operation in fusion 360. My CNC machine is not acting correctly. When I press run the Z axis travels up to the limit switch and stops.  I'm enclosing the file for review. 

Thank you for your input. I've been at this for two days before posting this.

[weber_dominic]

Can you share your NC-Code and tell us where exactly the error occurs?

[engineguy]

@litodrums 

It is likely that the Post Processor is generating either a G53 Z0 or a G28 G91 Z0 line of code at the start, this is usually a safety move on most machines to lift the Z axis up so that it doesn`t crash the tool into the stock/clamps when moving to it`s start cutting position.

If the CNC has been "Homed" correctly at start up then there should be no problems, without knowing which Post Processor you are using and also the Control used at the CNC then there is mot much more can be said, except that it may be that your PP has been updated and if it had been edited then the edits may have been overwritten.

Can you upload a copy of the Post Processor that you are using and details of the Control at the CNC.

[litodrums]

Thank you for your time to look at this.  I'm using a benchtop cnc using Grbl 1, python3, on a MacBook Pro computer. I generate PP from Fusion 360. Before I begin my machining operations, I always Home my machine then find my X0 Y0 Z0 coordinates. Thank you

Thank you here is the code:

(spoil bd facing)
(T3 D=1 CR=0 - ZMIN=-0.02 - face mill)
G90 G94
G17
G20
(When using Fusion 360 for Personal Use, the feedrate of)
(rapid moves is reduced to match the feedrate of cutting)
(moves, which can increase machining time. Unrestricted rapid)
(moves are available with a Fusion 360 Subscription.)
G28 G91 Z0
G90

(Face2)
T3
S5000 M3
G17 G90 G94
G54
G0 X15.8779 Y16.55
Z0.65
G1 Z0.197 F39.37
Z-0.02 F13.12
Y16.25 F39.37
Y-0.25
X15.262
Y16.25
X14.6462
Y-0.25
X14.0303
Y16.25
X13.4144
Y-0.25
X12.7986
Y16.25
X12.1827
Y-0.25
X11.5668
Y16.25
X10.951
Y-0.25
X10.3351
Y16.25
X9.7192
Y-0.25
X9.1034
Y16.25
X8.4875
Y-0.25
X7.8716
Y16.25
X7.2558
Y-0.25
X6.6399
Y16.25
X6.024
Y-0.25
X5.4082
Y16.25
X4.7923
Y-0.25
X4.1764
Y16.25
X3.5606
Y-0.25
X2.9447
Y16.25
X2.3288
Y-0.25
X1.713
Y16.25
X1.0971
Y-0.25
X0.4813
Y16.25
Z0.65
G28 G91 Z0
G90
G28 G91 X0 Y0
G90
M5
M30

[engineguy]

@litodrums 

I see in your code a G28 G91 Z0 line, that is what will be sending your machine to it`s Z0 (Machine Z zero position)

How do you Home your CNC, is it to the actual X,Y,Z switches and after homing they become limit switches, if so then you probably need to remove that G28 G91 Z0 line of code at the start and I think that your Grbl control has a Z clearance height that you can set at the control itself so if so then you can set that to whatever clearance you need to be safe at and if you can upload a copy of the actual PP that you are using it can probably be edited so that it doesn`t generate that G28 G91 Z0 line of code at the start.

I see that you also have the G28 G91 for the Z axis and the X/Y axis at the end of the code, do you want to keep those lines of code ??

Hope this helps 🙂

[programming2C78B]

common GRBL issue with people not zero'ing out their Z's. Just remove g28 z0 from the post settings before you hit Post 

I always manually jog z to the top, then reconnect the machine so that it treats that as machine home,0.

[litodrums · Accepted solution]

I discovered the problem. I recently ran some programs that worked correctly so I open up their g code to find that G28 G91 Z0 was in every program I was running.  As a friend of mine once told me if there is a problem start with the plug coming from the outlet. Well I don't know why this happens but I unplugged the power source from the cnc control box then plugged it in again. An all the programs I've been having problems with are now working.

 I want to thank you all for your input. I'm not a programmer but I really enjoy working in this environment. Many years ago I did go to boces to become a machinist so I have some knowledge under my belt but I'm still just a novice in the CNC world.

Thank you for your input and suggestions I appreciate it very much.

[programming2C78B]

Is it because you power cycled, or was the machine Z at the top when you unplugged it? Then you just did what I suggested, just more coarsely.