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Author Topic: Is my PC too slow or...?  (Read 8675 times)

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Offline mbele

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Is my PC too slow or...?
« on: April 18, 2013, 04:14:35 PM »
Hi,

I've noticed some time ago that when I increase feed rate via feed rate override in mach3 mill it looks like CV mode turns off (moves are not smooth any more). I'm able to reproduce this behavior now, so I'm posting my g-code and xml file. When program is running at 4000mm/min it runs fine, but when the feed rate is set to 5000mm/min or above (via feed rate override or in g-code program) moves are not smooth any more. What's more interesting is that, at raised feed, the first pass is smoother that the following passes :) I haven't noticed lost steps.

PC is based on AMD Athlon 2400+ 2GHz CPU with 1GB RAM running XP SP3 (Standard PC install). It takes one minute for the attached g-code to initialize (I've always experienced very slow initialization when program is based on arcs).

I get peak power from steppers at ~4000mm/min (~200RPM x 20mm lead direct drive 2.7Nm steppers 1/8 micro-stepping). Kernel runs on 25kHz.

I'd really like to be able to feed faster since my spindle is not very strong and I have to take light cuts.

Thanks,
Mihael



Offline stirling

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Re: Is my PC too slow or...?
« Reply #1 on: April 19, 2013, 01:02:29 PM »
You may want to take out all the unnecessary G17 commands. Takes the load time down from 1 minute to less than a second here.

Ian

Offline mbele

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Re: Is my PC too slow or...?
« Reply #2 on: April 19, 2013, 03:11:01 PM »
Thank you Ian!!! Not only that program initializes in no time, but the quality of motion is so much better. I'll take out redundant Gs too :)

Now it runs fine at 5m/min with 0.3G accel. For higher feeds I had to lower acceleration to avoid loosing steps. Above 5m/min with 0.1G accel motion is not smooth any more - slowdowns/speedups are noticable, but since accel is relatively low, the machine doesn't vibrate too much. Would higher acceleration make the motion smoother (actually, I tested that and the answer is no, but I cannot be sure since I'm on the limits of available torque) ?

Thanks,
Mihael
ps. I'm putting rhino script that generates g-code from arcs and lines in downloads section

Offline stirling

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Re: Is my PC too slow or...?
« Reply #3 on: April 20, 2013, 03:49:43 AM »
I would guess that the G17 on every line was killing the planner.

*generally* the higher the accel the better as long as the *robustness* of your machine can handle the increase in jerk.

Ian

Offline mbele

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Re: Is my PC too slow or...?
« Reply #4 on: April 20, 2013, 08:25:05 AM »
Can someone run attached test file @ 8m/min with 0.1G accel ?

I just managed to run it in the air @ 8m/min with 0.3G accel, and the motion is smooth, but these are not safe settings for my machine.
If I lower the acceleration (tried 0.25G, 0.2G, 0.15G and 0.1G) motion is not smooth any more - making slowdowns/speedups between segments more obvious as accel is more decreased :) 

So, my current conclusion is that there are "valid" acceleration and feed rate settings for CV algorithm to work properly, and that they are somewhat proportional (at least on my system/setup, running latest version of Mach3)
Actually, could it be that, because of the lower acceleration, CV is turned off so that cut accuracy wouldn't suffer ?

Thanks
Mihael

Offline Hood

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Re: Is my PC too slow or...?
« Reply #5 on: April 20, 2013, 01:38:43 PM »
Can someone run attached test file @ 8m/min with 0.1G accel ?


Set my accel down to 1000mm/s/s to get 0.1G, heres the video.
http://youtu.be/HwoikeEF2N0

Hood

Offline stirling

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Re: Is my PC too slow or...?
« Reply #6 on: April 20, 2013, 03:05:58 PM »
Well.... maybe not quite as impressive  ;D but I ALSO had to turn mine down to get 0.1G  :P

here it is at 0.1G

<a href="http://www.youtube.com/v/dDY0QXkL0ig?hl=en_US&amp;amp;version=3" target="_blank" class="new_win">http://www.youtube.com/v/dDY0QXkL0ig?hl=en_US&amp;amp;version=3</a>

and here at 0.5G

<a href="http://www.youtube.com/v/B03MQNLUuNc?hl=en_US&amp;amp;version=3" target="_blank" class="new_win">http://www.youtube.com/v/B03MQNLUuNc?hl=en_US&amp;amp;version=3</a>

Although it's OK at 0.5 you can hear it *bangs* a tad so that's why I normally have it backed off to 0.25G.

Ian

Offline mbele

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Re: Is my PC too slow or...?
« Reply #7 on: April 20, 2013, 04:11:11 PM »
Thank you Hood & Ian! I don't know what to say... guys, you're great :)

When I watched Hood's video, I saw the same behavior as in my system: machine slows down/stops three times during execution of one loop - only, on Hoods video it looks smoother than on my machine. I allready wrote the response, thinking that it's normal behaviour and that I'll have to live with that, but then I saw Ian's videos that do not show those 3 glitches :)

Ian, what are your CV settings / lookahead ? Maybe there's a catch...

Offline Hood

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Re: Is my PC too slow or...?
« Reply #8 on: April 20, 2013, 04:50:30 PM »
Ians does look smooth.
Are you using the parallel port?
Hood

Offline stirling

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Re: Is my PC too slow or...?
« Reply #9 on: April 21, 2013, 04:07:10 AM »
CV is plain "Mach out of the box" - lookahead 20, everything else off. System is an old AMD 1.5GHz / 512MB with onboard graphics and parallel port.

Ian