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Author Topic: Not getting the desired cutting speed  (Read 2208 times)

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Not getting the desired cutting speed
« on: January 18, 2011, 05:16:11 PM »
Hi to all,
I have built my own cnc router about 3 years ago, as most of you guys did on this forum and have a small setback that
has been bothering me for a while, so I was wondering if anyone on the forum has ever come across this one. My cnc
router runs perfectly fine in all aspects when running at a cutting speed below 28mm/sec. As soon as I take it up to
say 50 or 60mm/sec, my cutting path gets messed up.
My current configuration / setup is as follows:
1 - PC Pentium4 core II 2
2 - Servo drivers from Rutex R990 type
3 - running software Mach3 at max clock speed on OS WinXP
4 - encoders on servos 500ppr
5 - cnc structure mild steel
6 - driver motors - servos rated at 6000rpm at 60V and supply voltage 58V DC (As seen here
http://www.servosystems.com/electrocraft_dcbrush_rdm103.htm )
7 - gantry driven by belt and pulley at a step down ratio of 4:1
8 - Using ball screws 10 travel per rev and gantry sliding on brass bushings
9 - working area 750mm x 550mm x 250mm


Now the problem is that when running at "higher cutting speed" the cutting path seems to initially loose orientation
but then comes back to the right path as can be seen in the attached photos showing "V" gap between cutting path. According to my calculations I should
be running at least 200mm/sec.

I have thought the following but could not figure out what could be wrong:
1- There doesn't seem to be any lagging between the gantry and the signal from the driver cards cause the gantry
starts going back a short distance clearly indicating it's way out of line.
2- I have tried a higher encoder resolution - no improvement
3- running mach3 at a lower clock speed - no improvement
4- checked servo actual running voltage - OK
5- Changed servo bearing the whole gantry movement to a more powerful one (type
http://www.kelinginc.net/KL34-170-90.pdf ) but running at voltage of 58V DC.

That's as far I have gone but to no avail and the only against me is the weight of the gantry which is about 20Kg
but nothing the motors cant handle.

Any comments please.
Thanks
marting

Offline Hood

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Re: Not getting the desired cutting speed
« Reply #1 on: January 18, 2011, 07:13:44 PM »
Can you attach your xml and also the code please.
Hood
Re: Not getting the desired cutting speed
« Reply #2 on: January 19, 2011, 12:56:47 PM »
Hi Hood,
Not surprised some setting here would be the culprit and although I have read the manual and set Mach3 to the best of my understanding, I would not exclude that there may be some fine tuning that I may not be aware of. So here we go ... attached is the XML file for mach3 but the cutting path is lost somewhere on my hard disk as this was done in the early stages of my cnc build, however on the other hand the file seems to be OK after having run it on a piece of waste material at a lower cutting speed. You think you would still need it? If so I'll try to find it somehow.
Thanks
marting

Offline Hood

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Re: Not getting the desired cutting speed
« Reply #3 on: January 19, 2011, 02:10:05 PM »
Ok, first thing I see is you have the kernel set to 100KHz
Your motor tuning suggests that 25KHz kernel would be more than enough so I would set it to that. Having a faster kernel than you require has very little benefit and often does a lot more harm and especially as high as 100KHz as you need a very fast computer to be capable of that..
Hood