Thread: Mach 3 - "Goto zero" moves Z negative and below zero

Have you homed the machine before zeroing the axes?

Originally Posted by Bernmc

Have you homed the machine before zeroing the axes?

Thanks.
Yes, after homing the machine, I definitely set the axes to zero.
To be specific, X0 and Y0 to material's bottom left hand corner.
And Z0 to the top surface of the material.
Cheers
D

What direction does Z move?
What does the DRO in Mach3 show after it has down to this Z move down?

Chances are you have it set up so that Z moving down is positive.

Z moving up towards the sky should be positive (value increasing)
Z moving down towards the ground should be negative.

Convention is to have Z all the way up as zero, and all the Z axis travel is negative (in machine coordinates).

Important to understand machine coordinates (G53) vs work coordinates (G54)

I suspect your GCode program has a line like
G0 Z10
Then
G0 X0 Y0

If you have Z set inverted, this will result in a plunge down 10mm then move to X0Y0

If you post the GCode we may be able to comment further.

Good idea to proof new g code by running it in air, well above workpiece.

Are you setting z height with a probe or manually?

There should be a probe thickness setting that might apply an offset automatically and make it think is a distance above the workpiece when it isn’t.

Originally Posted by pippin88

What direction does Z move?
What does the DRO in Mach3 show after it has down to this Z move down? "-10"

Chances are you have it set up so that Z moving down is positive.
When Z moves up the DRO number increases.
In my explanation above when I set the zero to the top of the work, If I move the bit down it will then read --18 on the surface of the spoil board.

Z moving up towards the sky should be positive (value increasing) Yes it is
Z moving down towards the ground should be negative. Yes it is

Convention is to have Z all the way up as zero, and all the Z axis travel is negative (in machine coordinates). (I will check this)

Important to understand machine coordinates (G53) vs work coordinates (G54) Yes

I suspect your GCode program has a line like
G0 Z10
Then
G0 X0 Y0
Issue occurs when I press the goto zero button on the Mach 3 screen, I do not need to have any gcode loaded

If you have Z set inverted, this will result in a plunge down 10mm then move to X0Y0

If you post the GCode we may be able to comment further.
Apologies, I should have included the word "button" in my ooriginal post.
It is when I press the "Goto zero" button just below the 3/4 DROs in the middle of the Mach 3 screen that the Z axis moves from zero or a number above zero down (and unfortunately proceeded to jam the end mill into the work piece and then snap it off when moving to X0 and Y0!)

Good idea to proof new g code by running it in air, well above workpiece.
Yes

Responses in red alongside your points and questions

Thanks, I'll check, but I think I had given up on the probe at this point (as the probe was giving unexpected results too).
FWIW, When the X, Y & Z are all manually set relating to a specific job, everything is OK. We have successfully cut out shapes several times.

Given a manual setting works ok it sounds like a toggle in the software is wrong.
I use a setting to change the zero reference between the material surface and the machine bed, depending on the job I want to do.
If I set the toggle to material surface and zero to the bed the behavior I get is as you describe.

Unfortunately I don't know Mach 3 at all and am no help about where to look for a similar setting.

Thanks Bone Inspector.
That sounds interesting.
What is the the software you're using and what is the name of the toggle?

Vectric and fusion.

but this is in the software that generates the g code.

I use UGS to stream code to my cnc and there is stuff there too for setting up offsets with my probe.