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Messages - cncjerry

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1
General Mach Discussion / Re: issues with PCB milling - newbie
« on: May 02, 2012, 12:46:20 AM »
I played with PCB milling for years.  I never got what I called consistent results.  I even built a vacumm hold-down board to ensure the board was flat.  I changed all my screws to near zero backlash, etc, etc, etc.  I finally gave up.  There were a number of us working on the problems with outlining copper paths, tools overheating, gummy copper and other things.  I finally went to an outside processor, Sunstone, who makes the boards almost overnight and ships them drilled and plated for about the same cost as the carbide cutters I ruined over and over.

I finally found a solution, at least partially, by making a floating pen holder and using my mill as a plotter.  I used black and red sharpie brand pens and dipped the boards in hot FCL and they came out great.  If you go this route, you will need to drill after you plot since the gummy copper chips will spin on the drill bit and ruin the plot.

Jerry

2
General Mach Discussion / Re: Unwanted Step Pulses
« on: May 02, 2012, 12:36:37 AM »
If it shows up again (now that I see it was fixed) I had a problem way back in releases that had to do with mach3 not handling a consecutive sequence of very small moves well.  The cam software I was using for 3D surfaces was set to allow scallops of nothing higher than .0001".  So there were a lot of very small moves that were stacked-up in the gcode and they were going plus/minus on all three axis. I can't remember what fixed it - maybe something to do with look ahead?  I might have had backlash enabled to correct for .002" or something and maybe turned it off?  It could have also been a release upgrade that fixed it.  You might want to try a test where you make steps or blocks that are only a few mil high and in straight lines.

Jerry

3
General Mach Discussion / Re: backlash on Z axis
« on: May 01, 2012, 08:19:16 PM »
I suspect you are translating to english so I will attempt to explain this using words that will translate correctly:

I don't think your problem is backlash.

Backlash could be making it worse.

I think your problem is that your Z axis is dropping steps or losing position when it raises against gravity.

This will make successive holes deeper.  The Z axis moves less than the amount your G code specifies due to dropped steps and then does the drilling at a now lower position.

I have found that turning on backlash compensation makes stepper motor based systems more susceptible to dropped steps because of the way the backlash is done at a percent of maximum instead of accelerated.  This might have changed in recent releases.

Backlash will not be additive in any direction.  If you tell the Z to raise after it was lowered by .005 backlash + 1.000, Mach will do the number of steps to go .005" at a percent of maximum that you have specified.  This might cause your motors to miss steps since the heavier Z axis is not being accelerated correctly as it would under control when backlash is turned off.  If in this example, you then told the Z to move back, it will move the same amount of steps as it did to raise up.  Therefor even though the backlash has been removed by gravity, it will be forced back upwards taking up the backlash when the drill bit hits the work.  So you don't gain steps because of backlash compensation.

Jerry

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