Drifting X-axis, making step ladders one side whereas other side is smooth- SOS

[khalid]

Recently i have retrofitted Radial drill machine and currently having  an issue with 'drifting' + in the X axis. I have a work piece on which i have drill some holes and then profile milling upto 4mm deep with 0.5mm DOC per pass... After centre drilling and final drilling of 7mm dia drill 4mm deep, i started milling with 3-flutes 6mm end mill... After 1 Hour the job was finished and the end mill went to its zero position about 2mm toward the positive X-axis...

I saw the profile and i found step ladder (each pass with little drift toward X) toward one side whereas i have removed material from the other end...In several levels in Z I can see by the faces of the pocket that it drifts (steps on one side, smooth on the other).. This figure will depend upon the length of program run, longer program, bigger drift. Any ideas?

I have backlash compensation On.
The computer is dedicated to Mach software only.

Material SS-316 solid bar
Depth per pass= 0.5mm
Feed: 2IPM
Dormer end Mill HSco 3-flutes
Spindle Speed= 800 RPM
Ramping


Kind regards
Khalid

[Tweakie.CNC]

Hi Khalid,

No much help really but I had a similar problem, long while back, where one axis only was gaining steps. These gained steps were produced from noise spikes which were treated by the controller as a genuine step pulse. Although they were random they were pretty consistent and my problem was finally solved by fitting another, better quality, breakout board which managed to filter out the extremely fast noise spikes.
Although it is unlikely to be the same problem I would suggest that you look for electrical noise as a cause of this event.

Tweakie.

[Hood]

Run it without cutting and see if there is a problem.
Hood

[khalid]

Hi Tweake,
Is this may be the problem of wrong calibration of X-axis? If the steps/unit are wrong for X-axis motor tuning then could this happen?

Hi Hood,
I will test a circle with a pen.. I will draw the same circle 100 times and will see if the axis drift?and then will post you the results...

Best Regards

[khalid]

Onething more, I get electric shock when touching the Control panel (BOB+Transformer+Drives).. Should this also the casue of the drifting problem to the machine?

[RICH]

Measure the voltage, say, from the control panel box to an earth ground / water pipe. Only a few milli amps can be a hazard.
You should not be getting any shock from the panel. So safety first. 

Trace out the wiring, draw a schematic, post it and someone will take a look to see what's  wrong.
Don't use it until you have made it safe.

RICH

[khalid]

Hi Rich,
Thank You.. On monday I will first check all the wiring and make them proper... I hope this will solve some of my problem...

[khalid]

Today I checked all of the wiring.. The problematic X-axis wiring , i have found short circuit situation.. The 6 wires coming out of Logic MOSFETS... The connect at the Motor power wire was darken due to continuous arcing... I think this may be the problem..

One of the motor coil was getting uneven voltages due to this arcing short circuit.. I don't know the right term... Is this may be Problem?\
Any Thoughts? How can this cause drifting of axis one side?

PS:
I also increased the Pulse width and ran it with 1/2 pulse sherline mode, but the problem was not solved...

Before opening the controller i checked whether the problem in the axis?.. For this i calibrated the X-axis , but every time i got drift toward positive X-axis.. As this was done during the calibration, so no cutting forces and no Quill clearance plays any role here...So the drifting was totally not related to mechanical... Then i swap the Y-axis motor with X-axis, and i always got the results within 0.03mm range for the same axis.. This means i have no mechanical problem..

[Tweakie.CNC]

Hi Khalid,

It is possible that the arcing has caused a problem with the driver for your X Axis. (Possibility - an arc produces so much energy that this could easily be translated into false step pulses by a driver).
Have you now replaced the damaged connector pin / socket and tried it again ?.

Tweakie.

[khalid]

Not yet.. Today i have spent a lot to organize the wiring... I make all the power wiring far away from the controller cards...So that interference zone should be far far away from the Step/Dir pulses....
Tomorrow i will retest the system.. I think this will eliminate the electrical issues too...

The attached picture shows the MOSFET wiring location to the connector.