Z axis moves below set zero

[Neale]

Once motor tuning is complete, if you don't confirm moves with a dial gauge you're on a hiding to nothing.

I'm a bit surprised that you said that. I would have thought that, given that you should know to the limit of manufacturing accuracy everything you need to calculate the "steps per unit" figure, calculating is the best way to get the right number to put into the configuration page. Yes, by all means check it afterwards, but even on my crumby old MDF machine, a quick check with a rule was enough to make sure that I had, for example, set the right micro-step value on the drivers. Any error will leap out at you - you are likely to be a factor of two or more out, not some small number of per cent (and assuming that you double-check your sums and data entry, of course). Any error so small that you could only measure it with a dial gauge is looking for design or build errors - too much backlash, not properly tightening the locking nuts on a bearing holder, or something like that. And in this case, you are checking that the dial gauge returns to the same value when you have moved off zero and then back again, not measuring travel. You will probably even check for missed steps by a "return to zero" test, rather than measuring travel. The idea mentioned elsewhere in this thread that you get the "steps per" value by measuring it suggests that the builder/operator doesn't actually understand how the machine works, and that is a worrying idea.

But I might have misunderstood, and if so I'm happy to be corrected. Always willing to learn!

On a different point, unfortunately, this thread has been riddled with typos (from the OP, it has to be said) that make many of the questions really difficult to understand. Please, please, read through any post before hitting "post" and make sure that it reads correctly! Predictive spell checkers really don't understand CNC terms and concepts and can't be trusted to get it right...

[magicniner]

My point is that so many half-informed attempts are made without a clue that double checking is always a good idea, even if you think you got your maths right, before assuming your software or hardware is broke because things don't do what you want.
I would never run a mill without checking some moves with a pointer on a rule then with a dial gauge and blocks, some might trust that the pitch of their screw is perfectly as advertised, I like to check actual movement.

[JAZZCNC]

I would never run a mill without checking some moves with a pointer on a rule then with a dial gauge and blocks, some might trust that the pitch of their screw is perfectly as advertised, I like to check actual movement.

Couldn't agree more on checking. Can't tell you how many times I've seen cheap drives with wrong Dip switch markings.
However to get the OP issue they would have to be massively wrong. Plus Mach's Auto Steps per option does a very good job of getting right provided accurately measured.

What his problem is I've no idea because is replies are much use fart in space suite.!

[magicniner]

this thread has been riddled with typos (from the OP, it has to be said) that make many of the questions really difficult to understand. Please, please, read through any post before hitting "post" and make sure that it reads correctly! Predictive spell checkers really don't understand CNC terms and concepts and can't be trusted to get it right...

At times I've wondered............