Z Problems! (New to CNC)

[CADTechnician]

Hi all,

I work in a school and we recently purchased a CNC machine to expand the capabilities of the department. Since buying it we have not been able to run it properly without running into a few problems. The first issue we had was it carving in reverse, this was sorted quickly by changing the X and Y axis'. The second more annoying problem is that when running a job it will do part of it then it will move up too much on the Z and continue to run cutting at the wrong depth, then not cutting on the material at all. I've slowed down the acceleration on the Z axis, made sure all parts are tightened correctly and made sure it isn't hitting the end stop but still the problem occurs. Any help would be greatly appreciated.
We run VCarve Pro and Mach 3.

Max

[PaulRowntree]

It sounds like you are losing steps on the downward Z motions. If you are absolutely sure that the Z is mechanically solid, then you should look at the electrical side. This starts at the parallel port, and includes the cables, break-out-board, and the actual stepper drivers. The software is not the issue. On my machine it is always mechanical, no matter how many times I think I have verified it.

It may be useful to set up a job that causes problems but offset the Z higher in Z so that the tool never touches the material. If Z remains inaccurate (ie Z offset shifts up after the job) then the problem is not load related. Could be a bad connection on the Z motion. Try swapping the entire Z wiring with X or Y : the bad connection should move to the swapped axis.

If Z offset is now constant no matter how many times you try it, the fault is load dependent, possibly a bad driver or again a bad connection (but less likely).

Cheers!

[4DThinker]

What Brand/Model of CNC are you using?

[mike1966]

I had that same problem with mine a couple years ago. It was a bad ground wire.
another thing it could be is the z is to tight or binding, un hook the motor and try turning it up and down by hand.

[Roly]

I had a similar problem when I first started with mu machine. It turned out that I had not properly tuned my machine to Mach 3. Once I completed doing that the problem disappeared. Hope it gives you another option.

Roly

[CADTechnician]

I run a Routout CNC Z90SL using Mach 3.
I'll have a go at what has been suggested when I get a spare hour, I'm just loath to start playing with the electrics as this will void the guarantee.

Cheers guys

[David Rueth]

CadTechnician

It could also be you are using a short bit and it can not reach all the way to the table top. Make sure the bit you are using can be jog to the top of the table or at least to the lowest point that must be reached in your work pice.

Dave