Trouble when I cut large files - fails down or up Z axis

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09 Sep 2019 15:32 - 09 Sep 2019 15:33 #144610 by zaxlex
When I try cut files with more than 500k rows, I get fails down or up Z axis (fails down happens more often) and my CNC keeps cutting lower (or higher) the level at which the Z axis failed.
For example, I have the 1500K rows 3D relief G-code on which I failed.
After it I insert after each 250k rows pause on 1 hour (G04 P3600) to be sure that it problem not mechanical (or heat for example) and got same failure result.
After it I split this large file into several small 250K rows each and run one after other without any delay - and I cut everything well and got a positive result.
I think it's a problem to work program with RAM or some thing else. I found in it topic - G-Code file size limit post where was write -

Practically it is about 500k lines on P4 2.8Ghz, 1GB ram, geforce 2
And you can turn off the preview in AXIS.

I tried turn off preview in AXIS and switch to other minimal interfaces without backplot, but no get positive effect.
But I have 3Gb ram (1Gb+2Gb) and I think LCNC work with 1Gb RAM at first and after it with second 2Gb RAM.
And when it switch to read from first 1Gb to second 2Gb it get fails.
I think it is BUG of LinuxCNC
I think it needs to be fixed. But I do not even know where to start looking at the source code to understand what needs to be fixed and how.
The second option is to write a script that would load the file for execution in separate parts, so as not to waste time dividing a large file into parts and not to load each part separately - it is very tedious, especially if you have to wait in the middle of the night when one part is cut to run another
I think if I insert one big RAM memory or two identical, it problem will stop for my case of 1500K rows, but if I load much more rows. when it begin switch again between two RAMs - it problem come up again
So manipulating memory is just running away from problems, not solving them as such.
May be some body can help me, or give me some advice how to solve it problem.
Thank you.

:~$ lscpu
Warning: Spoiler!

:~$ lshw -short
Warning: Spoiler!
Last edit: 09 Sep 2019 15:33 by zaxlex.

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09 Sep 2019 17:10 #144615 by tommylight
1.5 milion lines !!!???
You can try dissabling "lookahead" but i do not know if it will help.

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09 Sep 2019 17:25 #144617 by PCW
I would guess a hardware problem is more likely especially with Z only issues
Sounds like lost steps

Can you try with you Z axis acceleration reduced by say 30%?

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09 Sep 2019 18:20 - 09 Sep 2019 18:22 #144619 by bevins

And when it switch to read from first 1Gb to second 2Gb it get fails.
I think it is BUG of LinuxCNC
I think it needs to be fixed. But I do not even know where to start looking at the source code to understand what needs to be fixed and how.


I cut an 8 foot 3d relief header 8 inches wide and it took 12 hours on my router. It finished it fine and I had 2 gig ram.
Sounds like a hardware issue to me.
Last edit: 09 Sep 2019 18:22 by bevins.

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09 Sep 2019 19:35 #144622 by zaxlex
no, it can not be hardware issue. I run 7 parts of it file without delay and no problems, I agree may be that is not correct work linuxcnc with RAM memory. But I want cleary understand what kind of problem I get and how to try fix it.

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09 Sep 2019 19:38 #144623 by PCW
I would first try reducing your Z acceleration...

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09 Sep 2019 19:56 #144624 by zaxlex
it was allready made with half of my usually accelerations and velocity, and you do not hear me - it runs good only when load parts separately one by one and no other any changes

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09 Sep 2019 20:18 #144625 by PCW
Loading parts separately would be different because startup gcode would be run for each part (not the case for the complete job)

It really does not seem like a memory issue to me,. Note that LinuxCNC does not necessarily load the entire gcode file into memory (though the backplot will run through the entire file), and that there is nothing special that happens at 1G.

What interface hardware do you have?

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09 Sep 2019 20:33 #144627 by zaxlex
I have mesa 7i92m ethernet
but it problem I had and on older PC with lpt port
and yes I try other minimal interfaces without backplot

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10 Sep 2019 14:40 #144703 by rodw
I don't think it reasonable to be guided by a 10 year old post about memory limits on a P4 PC.
There have been plenty of posts where people are cutting similar size files without issues but they d turn off the back plot.

Like everyone else, My money is on lost steps on the Z axis. In my experience, this usually happens on up travel with the weight of the Z axis pushing down.

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