Hi,

I think you should halve the velocity and double the acceleration figures for all the axis and let it run a very long program, see if it faults,  it may be right on the limit.

Graham.

tried playing with the velocity and accelaration, even with the Z axis on 20mm/min and slow accel it still does it.

Weird thing is I let it be switched off for half an hour or so then I get 5 or 10 mins use and it buggers up again so unfortunately thats how I have to use it at the moment, its really driving me nuts!!! 


X and Y axis never miss a beat and I can run them whatever speed I want..

Have you had the Z axis in bits to see if there is a jamming condition, if I remember correctly these machines use plain bush slides, is one contaminated?

Graham.

I took the y drive plug out of the controller and swapped it with the Z plug on the front of the control box and then jogged z using what would normally be the y quick keys. problem didnt occur in z but does now appear in y. I didnt physically shift any wires inside

This proves that the motors were working correctly for both axes, so no need to upgrade those.
The problem occurs between the computer and the controller output.
Based on this it could be the controller board, PC port, or the software (including a software configuration error).

The fact that they state their preferred software works is significant - they probably also provide a config file which sets all the correct software config states up for their machine to operate

x axis is active low, other 2 arent.

X axis pin 2 direction   5v
X axis pin 3 step         5v

Y axis pin 4 direction   5v
Y axis pin 5 step         5v

Z axis pin 6 direction   5v
Z axis pin 7 step         0v ??

Very confusing.
I am wondering if you have mistyped something, and that x & y are active low, and z isn't. 
That would make more sense.
If that is the case, try changing the sense for the z axis step control.

Other thing from left field, is the PC doing something after 5 or 10 mins?
eg maybe a memory cleanup 'garbage collection' cycle or swap file flush etc.

I had a similar problem when I first set up my machine.
Trying to mill a test piece it would skip on the z axis at about the same place everytime (the 3D face test file, doing the fine cut about 5 mm into the side about level with the nose)
I finally fixed this by removing the ACPI chip driver and replacing it with the 'Standard PC' driver.
I presume some long delay interrupt triggers or similar, and windows gets sidetracked too long to drive the motors properly.
Now I have replaced the drivers, the machine has never skipped since.

I have had the Z axis apart and its smoooooth on the slides the only resistance comes from the antibacklash drive nut, its quite tight but then I guess it needs to be... 

Thought it might be a voltage issue from parallel port so got a PCI card, no different. Even tried it on two other computers and still the same!!

Hi, dougie329

A couple more things to try.

Some stepper controls are sensitive to leading and trailing edge pulses, set your z axis Dir., Step "LowActive" settings in config, Ports & pins, Motor Outputs

to the same as your X, Y. (It's a hardware change)

In Config, Home/Limits, You can change the Z direction if needed in Reversed coll-um for your axis.(It's a software change)

If that doesn't help in Config, Motor Tuning, Increase the Step, Dir Pulse's to 5. (This sends a longer pulse to your axis controls)

Hope this Helps, Chip

RE YOUR Z AXIS - What is it that you are trying to drive. - My Z axis or my milling set up is a very large milling head. As it was it was sprung UP  and I couldn't get the stepper motor to drive it down. Coming the other way it was fine. Yours is probably the opposite way - gravity helps it going down - but works against it going up (although I think you said you had tried a bigger motor).

I ended up gearing my milling head stepper down 5 to 1. I didn't need the speed, but I needed the power to shift this big lump of metal. Bear in mind if the motor is working hard, then the driver board will be working hard - and cut out if it overloads. There is also a warning on my stepper driver notes that if the voltage on the steppers falls below 12 volts, there is a danger the card will over heat - have you checked you driver voltages - you cannot be running them off the 5 volt computer supply.

You have proved (as far as I can see) by swapping the drivers round, that the fault lies on the pysical side of the equation, ie. the mechanics of the Z axis,  not on the electrical (computer) side, so the fault will lie somewhere in this area.

JIm.

Dougie what do you mean by "tight" on the Backlash nut? There should be very little resistance to turn the screw. If it is too tighten it may get worse as the friction heats up the components. Try losing the nut until the screw runs free turning by hand. Test the machine, retune the nut if needed. (;-) TP

Is the Z axis head counterbalanced?
My X3 has a gas strut to help balance the up and down loads
Large machines have a counterbalance.
It goes down OK, but has trouble going up.
With it all turned off try and measure how different the torque required to turn the Z screw up and down.
As stepper motors get hot, their resistance goes up, and if you don't have a contant current drive circuit, the torque will decrease as the temperature rises. Actually reducing the current limit on the stepper drive may keep it cooler. Z often gets a punishing because it does not move much.
If you do a lot of work where z does not need to move, consider locking the z and turning off the z drive unless you need it to move.
Best still balance the load.

Dougie said that when he swapped the y and z axis cables from the controller to the stepper motors, the problem shifted to the y-axis. 
That implies the driver electronics or software config -  pulse widths, pulse polarity and edge detection.
Or did I mis-read the thread somewhere?

If not there seems little point investigating the mechanics of his machine Z axis when now the movement of the Y-axis begins exhibiting the same problems.  Any problems with tight leadscrews/nuts or excessive weight of the Z axis machine head etc are not relevant if the Y axis suddenly starts doing it too.

He also said it did it when jogging around, so the heating affect ought to be minimal.