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An unusual problem
« on: January 09, 2016, 06:56:56 AM »
As the title suggests, I have come across an unusual problem with my router.

Occasionally it will change its cutting path mid-run without apparent reason.

I was cutting an a double Archimedian spiral out of 4mm plywood, it ran the first spiral of 5 passes perfectly, then started on the second spiral, it ran one and a half passes on the second spiral Ok, then suddenly shot off at an angle and continued to cut the path from another position.  The two paths had be drawn in Illustrator, taken into Aspire 4.5 and calculated there, then exported as a .txt file to run in Mach 3 as a complete path, not separate for each spiral. I stopped the machine and put it down to a glitch without exploring what had happened.  I ran the toolpath again in the air, and there as no problem.

A couple of days ago I was machining and lozenge shaped bowl which again I had generated the outline shape in Illustrator, taken it into Aspire to model the bowl, exported it as a roughing cut and as a finishing cut.

I ran the roughing cut without problem, changed tools and started the finishing cut, after 30 seconds or so of the finishing cut, again it displaced and continued cutting the bowl, this time I let it complete and when I returned the tool to zero, the zero x had moved to the right by around 25mm and the zero y had moved down by about 6mm.  As the shape was regular, I was able to save the work by running the toolpath again a couple of times, displacing the x axis to take account of the error, then cleaning up by hand after.  I ran the path a further 4 or 5 times to correct the bad cut, and each time it ran perfectly without error.

The router and computer are both on a UPS so there should not be any problem caused by power fluctuations etc, but I am at a loss to understand what is happening, I have since run a lot of other toolpaths without problem.

Any help, advice etc. gratefully accepted.
Re: An unusual problem
« Reply #1 on: January 09, 2016, 08:04:17 AM »
A UPS will clean up the mains to the point where the operation of a PC, TV or other household item will not be affected by mains fluctuations, more sensitive equipment (including many, but not all CNC systems) can still be affected.
Freezers, Fridges, Central Heating Gas Control Valves and lots of other things can still kick out enough RF interference to cause a glitch,
Regards,
Nick
Re: An unusual problem
« Reply #2 on: January 09, 2016, 09:03:54 AM »
Dear Nick

Thanks for the thoughts, the UPS is a Riello Vision Dual VSD 3000ER which is apparently powerful enough for the job, we are in a dirty current area but the UPS has smoothed out all the apparent surges, dips etc, so I think you could certainly be on the right track.  If this is Radio Frequency interference, how can I shield my machine from it, what is affected? the pc, the control board< the USB cable?

Re: An unusual problem
« Reply #3 on: January 09, 2016, 10:29:43 AM »
I have an mains RF filter on a VFD which knocks out a lot of noise, if you can identify the source of a noise problem that's the best place to deal with it,
Regards,
Nick
Re: An unusual problem
« Reply #4 on: January 09, 2016, 10:47:01 AM »
Dear Nick

Sorry again in English please  :) Electrickery is not my strong point  :-[
Re: An unusual problem
« Reply #5 on: January 09, 2016, 11:11:43 AM »
Sorry, assumed level of knowledge & all that :-[
VFD - Variable Frequency Drive - I use them to run 3 phase motors at variable speed with a single phase supply, some are nice and clean but I have one real dirty one in the workshop that knocks out the radio and causes jitter on my CNC machines. 
RF Filter - Radio Frequency Filter - a tin box your mains passes through to get to the load, it's a low pass filter that presents negligible resistance to mains frequency but which blocks the passage of the higher frequency nasty stuff on the power lines,
Regards,
Nick
Re: An unusual problem
« Reply #6 on: January 10, 2016, 01:29:46 AM »
first, make sure all the equipment is properly grounded.......if you're using a Spindle Drive make sure the cabling is either shielded or none of the signal wiring is in close proximity to the power wiring. If it is use shielded cabling or separate the wiring. Its also good practice to not run the signal wiring parallel to the power cabling. If you're using steppers there is no easy method to determine if the controllers are either 'seeing' additional pulses or having pulses negated by noise. If either is happening, you'll be off some amount depending on how many pulses are compromised. And it shouldn't be consistent. I would doubt the issue is coming from noise on your incoming power supply (120v?) unless you are in relatively close proximity to something very, very, very dirty (electrically generating a lot of high frequency noise)......Also, I know of two Mach3 users who had somewhat similar issues and it turned out all they needed to do was reload the Mach3 configuration files. One of the applications would go 'awry' whenever Mach3 would turn on the spindle. Even if no spindle drive was actually in use.
Re: An unusual problem
« Reply #7 on: January 10, 2016, 05:50:09 AM »
Many thanks for the comments, I will now go away and try to shield as much as possible as it would appear from replies here and from other sources that it could well be RF interference causing my problems.  I certainly have not been taking excessive cuts on the toolpaths, so hopefully mechanical issues should not be a factor.

Thanks again for the swift response, much appreciated.

Offline ger21

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Re: An unusual problem
« Reply #8 on: January 10, 2016, 07:39:48 AM »
I doubt that this is a problem with your power.

Do you know if it loses position during a rapid move?
Try reducing your acceleration by 50% and see if it still does it.

Gerry

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Re: An unusual problem
« Reply #9 on: January 10, 2016, 07:43:32 AM »
It does not appear to loose position under any particular set of circumstances, so far it has been random with regard to tool, type of move, cut position on bed, time during cut etc. Then next time it will run the path perfectly.