CNC Router shoots up z axis at start of operations

[Anonymous]

So I am trying to do a test model for a project, which involves cutting a few recesses and a couple holes in the piece (all pockets). After several other successful tests the router is now playing up. At the beginning of the operation, it goes straight up the z axis to its limit and wants to continue going up. I think it thinks that its position is way below where it actually is so shoots up to get to what it thinks is the zero position. 

Have checked the g code and the operation info and it all seems to be correct. Any suggestions would be helpful, thanks

[engineguy]

@Anonymous 

Usually a dodgy limit switch or (depending on your control software?) the Z axis settings have been changed somehow.

Regards

Rob

[seth.madore]

Could you share your file and the posted code? 

[Anonymous]

So we tested this code against, using code from vcarve set up to do the exact same thing. The vcarve did as it was supposed to but the code from fusion moves it upwards.

(1001)
(KILN TEST)
(T1 D=10. CR=0. - ZMIN=-18. - FLAT END MILL)
G90 G94 G91.1 G40 G49 G17
G21
G28 G91 Z0.
G90

(2D CONTOUR1)
M5
T1 M6
S1750 M3
G54
M8
G0 X158. Y101.
G43 Z15. H1
Z5.
G1 Z4. F30.
Z-2.
G18 G3 X157. Z-3. I-1. K0.
G1 X156. F350.
G17 G3 X155. Y100. I0. J-1.
G1 Y50.
Y45.
X45.
Y155.
X155.
Y100.
G3 X156. Y99. I1. J0.
G1 X157.
G18 G2 X158. Z-2. I0. K1.
G0 Z5.
Y101.
G1 Z1. F30.
Z-5.
G3 X157. Z-6. I-1. K0.
G1 X156. F350.
G17 G3 X155. Y100. I0. J-1.
G1 Y50.
Y45.
X45.
Y155.
X155.
Y100.
G3 X156. Y99. I1. J0.
G1 X157.
G18 G2 X158. Z-5. I0. K1.
G0 Z5.
Y101.
G1 Z-2. F30.
Z-8.
G3 X157. Z-9. I-1. K0.
G1 X156. F350.
G17 G3 X155. Y100. I0. J-1.
G1 Y50.
Y45.
X45.
Y155.
X155.
Y100.
G3 X156. Y99. I1. J0.
G1 X157.
G18 G2 X158. Z-8. I0. K1.
G0 Z5.
Y101.
G1 Z-5. F30.
Z-11.
G3 X157. Z-12. I-1. K0.
G1 X156. F350.
G17 G3 X155. Y100. I0. J-1.
G1 Y50.
Y45.
X45.
Y155.
X155.
Y100.
G3 X156. Y99. I1. J0.
G1 X157.
G18 G2 X158. Z-11. I0. K1.
G0 Z5.
Y101.
G1 Z-8. F30.
Z-14.
G3 X157. Z-15. I-1. K0.
G1 X156. F350.
G17 G3 X155. Y100. I0. J-1.
G1 Y50.
Y45.
X45.
Y155.
X155.
Y100.
G3 X156. Y99. I1. J0.
G1 X157.
G18 G2 X158. Z-14. I0. K1.
G0 Z5.
Y101.
G1 Z-11. F30.
Z-17.
G3 X157. Z-18. I-1. K0.
G1 X156. F350.
G17 G3 X155. Y100. I0. J-1.
G1 Y50.
Y45.
X45.
Y155.
X155.
Y100.
G3 X156. Y99. I1. J0.
G1 X157.
G18 G2 X158. Z-17. I0. K1.
G0 Z15.
G17

M9
G28 G91 Z0.
G90
G28 G91 X0. Y0.
G90
M30

[seth.madore · Accepted solution]

I'm betting that it's the G28 G91 line. If your machine doesn't have limit switches, this is likely what's happening.

[Anonymous]

Thank you Seth, that was the one. All working as it should do now