View Full Version : Z axis motor 'lifting'..

02-08-2010, 10:21 AM
Hi all..

Well, finally rebuilt my cnc router, first one was mdf (big mistake, nasty stuff) and have now redone it out of aluminum extrusion.. Using 3N steppers and system 3 board..

Fired it up and hey, worked first time..! Jumped in at the deep end and tried to do some 3D routing which I worked out as about a 6 hour run for the finish cut.. But about 2 hours into it, the Z axis lifted by about 10mm, although mach 3 thought it was in the correct position..

I re-referenced the tool and it started the cut from the beginning, then again (not in the same place) about 2 1/2 hours into it, it lifted again.. I did not see it happen (short attention span), and from the cut, it did not lift in one go but steadily got higher until it was not cutting any material at all. But after checking, and re-checking everything, the only thing I could find was that the z-axis motor was way hotter than the others..

So, first my question is.. Is it right that a motor that is under power, but not moving, should get so hot? The x and y axis motors were doing all the work and were quite cool, but as I said, the z axis was very hot and doing nothing.. Was wondering that maybe it had overheated and when it had to start moving, maybe started stalling or losing steps?

I could fit a heat sink and cooling fan to it if that is the case..

Anyone had this problem or any ideas about it..?


02-08-2010, 10:43 AM
the stepper will get hot when powered and not moving, as it's being held in position.

02-08-2010, 10:55 AM
Hi i2i..

Forgive the newbie questions, but is it simply that a hot motor will drop steps or stall? Think that would be easily fixed if so..


02-08-2010, 11:21 AM
The Z motor must have been moving a bit though for a cut program of that length in time...I can't imagine that it was at the same depth for 2.5 hrs?

But yes motors do get hot when stationary as current is still passing through them to keep their position locked & stationary.

As for the Z axis being off....there could be lots of reasons - something in the code that you missed, something mechanical in the Z drive train that could cause it to bind in one direction, interference in cabling could cause dropped steps...& probably many other things as well.

02-08-2010, 11:45 AM
Hi Crafty..

Yep, 2 hours of flat cutting before the z axis has to start moving (0.01mm cuts).. Bit extreme I know, but I figured I would get to see any of the problems by cutting this part this way.. Will fit a heat sink and fan later, then do some proper testing to check it out properly..


02-08-2010, 12:40 PM
Bloody hell ....a 6 hour cut? I go purple & cover the dog in spit if my simple 5 minute cut has a problem half way through - I'd need valium & a bottle of Vodka if doing a 6hr cut.

02-08-2010, 01:23 PM
hmmm... if it was a lot hotter then this suggests it was being overdriven (wrong current limit) or was in a state of stall (mechanical binding) All the motors are permanently energised so should all get to roughly the same equilibrium temperature. At high temperatures the motor could lose power (magnetics lose force with temp) and therefore a 'down' step could miss-step so the returning 'up' step is too far up... hence the decreasing z-depth over time...

The cutter you were using was a plunge type? you weren't trying to plunge something with no cutting tip? that would stall the motor or at least make it work hard...

02-08-2010, 02:33 PM
Good flippin grief...

It was the power lead to the spindle, got snagged on a burr on a piece of aluminium at the top of the z axis.. Sorry guys... On the plus side, when I do make an appearance on this forum, I do seem to make you all sound like geniuses!!!!

Going to have my thumb surgically removed from my ass before seeing if I can create another 'high tech' problem..

Thanks all..!

02-08-2010, 03:07 PM
If only all problems had such a simple solutions, :wink: ... Mind you then the resident geniu (is that the plural of genius) on the Forum would be sat there twiddling their collective thumbs!!:whistling:

02-08-2010, 06:46 PM
something else to also think about is connections. The motor will get hot if the windings are not receiving equal current.

03-08-2010, 08:19 AM
Hi Ze0paz.

After the first debacle and your compelling point, am going to go right through all the wiring and give it a check and a tidy up..

On a really cheap note (done this whole thing on the cheap), has anyone tried using pipe lagging (the foam tube type with a slit down the length,) as a cable tidy? Dead cheap, very light and flexible.. Gonna get a bit and try and try to set fire to it today, unless someone knows a compelling reason not to (excluding pyrophobics)...


03-08-2010, 11:44 PM

Get down the pound shop or ikea and grab the stuff used for tidying up the tele cable clutter??????????? its a pound