Z axis error woes

[Jonathan]

it could be noise making the z step randomly

I just plotted the point list:



That doesn't look very random! In fact that's an excellent linear correlation (R²=0.9996) so it looks like an alignment problem to me. If you hadn't said that the bed was surfaced I would say that it is the gantry that's not level and if you hadn't said that the cut with a V-cutter looked fine I'd say it was the bed/PCB that's not level as a straight line like that implies one or the other is inclined.

One way to test if it's a cumulative error, for instance missing a couple of steps for every down move (seems unlikely but you never know), is to just do two points. One at Y0 and one at Y10 and see if the error is a 50th of what you just got from measuring 50 points.

This is why I sent you the 1mm endmill - with that the bed can be a lot further from level as the width of the cut does not depend on the height. Only problem is 1mm it a bit useless for anything but the simplest PCBs. I bought them on eBay as the seller said they were 0.5mm, but they weren't hence I've got no use for them.

[JAZZCNC]

That doesn't look very random! In fact that's an excellent linear correlation (R²=0.9996) so it looks like an alignment problem to me. If you hadn't said that the bed was surfaced I would say that it is the gantry that's not level and if you hadn't said that the cut with a V-cutter looked fine I'd say it was the bed/PCB that's not level as a straight line like that implies one or the other is inclined.

Yes Machine setup was my first thought Jonathan but the leveling of the bed rules this out.! Not sure the pcb would be so consistant increasing thickness.?

Thats why I turned to pulse timing issue.? This would be repeatable to this level.!

I feel for hank because things like this can drive you crazy.!!

[Jonathan]

Yes Machine setup was my first thought Jonathan but the leveling of the bed rules this out.! Not sure the pcb would be so consistant increasing thickness.?

Yep, the PCB itself has good thickness tolerance so I was more thinking the PCB itself might not be stuck down flat, but as we both said... that makes no sense! Maybe the gantry slipped at one end? Again unlikely.

I doubt it's the USB cable as interference or interruption in the USB signal would cause all sorts of problems, not a nice linear error. Similarly if the motor is connected wrong it'll either break, not spin at all or spin the wrong way.

Out of the causes you suggested I think the acceleration setting is the most likely cause as that could well induce a consistent error. Testing on a different axis, or even probing a grid so we can plot a plane is also a good plan.

Try running the probing routine exactly as before, but twice in a row ... probe from Y0 to Y10, then start again at Y0. If the two point lists are virtually identical you know it's not a motor or motor tuning problem as those problems would make the second probing routine output different to the first.

I feel for hank because things like this can drive you crazy.!!

Yep.

[JAZZCNC]

Similarly if the motor is connected wrong it'll either break, not spin at all or spin the wrong way.

No it will work fine but as you say spin in reverse, changing the pin hi/lo setting is what most folks do to get round this. But wrongly wired polarity of motor/drives is known to cause this kind of error, it comes up every so often on Mach Yahoo forum.! . . .Yes I know this is USB but still motor/drive issue so still possible.? Certainly worth checking as it's 5min job.!