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Author Topic: Unwanted Step Pulses  (Read 6385 times)

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Offline kcib

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Unwanted Step Pulses
« on: April 28, 2012, 03:17:17 PM »
I have a problem with the "Z" axis on my router , with the help of Tweakie I have made sure that all my cables are shielded and re-routed them I have also fitted capacitors on all my inputs , when I run the driver test I get a perfect straight line without any spikes , I have changed stepper motors over stepper drives over without any success , what happens is that whilst doing a roughing cut the "Z" axis starts to move very slightly up from the level it should be at then goes back down now this is not a real problem when roughing out but it does become a problem when doing the finish cut as it leaves lines on the work piece which after spending 3 hours or so on a 3D carving is a pain that I could do without.
Before anyone one asks my computer runs Windows 7, Quad 3.4ghz processor , 12gb memory and a 64gb solid state hard drive , apart from the operating system the computer is loaded with Mac3 and the Mach Standardmill screenset nothing else at all and is not connected to the internet , all drawing work etc. is carried out on my main computer and the via a USB key loaded onto machine computer, the software that I use for my carvings etc. is Vectric Aspire and Cut3D.
Any ideas would be greatly appreciated , and my thanks to Tweakie for all his help.
Attached is a pic of the sort of problem on a work piece. 

Offline ger21

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Re: Unwanted Step Pulses
« Reply #1 on: April 28, 2012, 03:43:04 PM »
Loose coupler on the Z screw.

Or, losing steps from too high accel. Lower accel by 50% and retest.

If it still does it, my vote is a mechanical issue.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html

Offline kcib

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Re: Unwanted Step Pulses
« Reply #2 on: April 28, 2012, 05:10:10 PM »
Coupler is 100% tight and all the "Z" axis all brand new , new ballscrew and nut plus all the other parts required and new Hwin linear rails and bearing blocks , there is for sure no loose fittings backlash etc.As for acceleration I have been up and down the scale with no effect , so if it is mechanical as you suggest where would you be looking ??
Thanks

Offline ger21

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Re: Unwanted Step Pulses
« Reply #3 on: April 28, 2012, 05:51:26 PM »
I've heard of couplers appearing tight, but are able to occasionally slip back and forth a little. Especially if they use setscrews.

Also, try going into the bios of the PC and disabling C1E and/or EIST if you have them.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html

Offline RICH

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Re: Unwanted Step Pulses
« Reply #4 on: April 28, 2012, 06:19:36 PM »
Alan,
I would suggest some simple pocketing ie; a few passes in the kind of wood / against the grain and at the cut depths you use for roughing.
If you do a straight cut over say 10" and the Z rises, then you would know that it's a mechanical problem because the code is not changing for the Z. Acceleration would not be factor.
You may want to just plunge directly in as that would put an upward force on the Z and over some travel it should come down as it's cutting the length.
FWIW,
RICH

« Last Edit: April 28, 2012, 06:22:30 PM by RICH »

Offline kcib

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Re: Unwanted Step Pulses
« Reply #5 on: April 29, 2012, 03:37:45 AM »
Hi Rich
I have already tried this and am certain that this is not a mechanical issue as the Z axis only moves up never down , only by a small amount but always up , if I watch the DRO for Z then where as it should be cutting at depth of say 5mm then it will alternate from the 5mm that it is supposed to cut to 4.9650 and then back to 5mm , as I say not a great amount , the other thing is that if I remove the stepper motor from the "Z" axis and just hold it in my hand you can see and feel the motor run down to where it would be machining at the required depth and then you can see and feel the motor move a small amount so I am convinced that this is an electrical problem and not mechanical
Thanks
Alan

Offline Hood

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Re: Unwanted Step Pulses
« Reply #6 on: April 29, 2012, 05:41:10 AM »
What drives? What BOB?
Do the DROs in Mach show the movement or is it just the motors move and DROs read correctly?
Hood

Offline kcib

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Re: Unwanted Step Pulses
« Reply #7 on: April 29, 2012, 06:20:02 AM »
Hi Hood
the DRO's in Mach show the movement , the stepper drives are from www.lamonde.co.uk and are STP-DRV-4850 and can be found here (http://www.lamonde.co.uk/acatalog/Drives_PSU.html) and the stepper motors are from same supplier and are STP-MTR-34066 fitted to the "X" and "Y" axis and STP-MTR-23079 fitted to the "Z" axis and can be found here (http://www.lamonde.co.uk/acatalog/Motors_Cables.html) BOB is a CNC4PC part number C35 and can be found here (http://www.cnc4pc.com/Store/osc/product_info.php?cPath=33&products_id=270).
Thanks
Alan

Offline Hood

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Re: Unwanted Step Pulses
« Reply #8 on: April 29, 2012, 06:32:35 AM »
If the DROs show the movement then Mach is commanding it and it is definitely NOT noise. Why Mach is commanding it is what you need to find out, is it definitely not in the code?
Hood

Offline ger21

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Re: Unwanted Step Pulses
« Reply #9 on: April 29, 2012, 07:02:03 AM »
Quote
the DRO's in Mach show the movement

For that to happen, that would mean the anomaly is in the g-code, and I doubt that is the case. If it were, you'd see it in the preview in Aspire. I've never heard of this occurring in either Aspire or Cut3D.

Also, that looks like much more than .035mm offset.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html