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Author Topic: Backlash Compensation Failure- Help is Appreciated!  (Read 3529 times)

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Backlash Compensation Failure- Help is Appreciated!
« on: March 08, 2012, 07:21:04 PM »
Hey everyone. I posted about this a few weeks ago, but the thread died and can't be accessed any more- so here it is again.

I have a 'JoesCNC Hybrid' that I have been trying to debug and I cannot get backlash comp to work properly. I suppose that's a bad way to describe it- from what I can tell, the software is taking up the correct amount of backlash, but the movement that follows is poor. This is an issue as the end mill really starts to warm up when the move is slow and rough.

I have read / watched Hoss' information on backlash compensation and the odd results, and as result, I had started out with my backlash comp velocity set to 100% and the shuttle accel to 0.005s. Obviously, this did not resolve the issue. I have played with several different combinations of shuttle accel and % velocity, here is I brief log:

1. Followed the advice of several threads by changing shuttle accel from 0.005 to 0.05, and then to 0.5. Each change made the affected movement more and more rough, 0.5 being the worst.

2. Given trend, placed shuttle accel at 0.0005s. The movement is still messed up (see videos), but this is the smoothest setting.

3. Any change to % velocity for backlash comp does exactly that, but after the backlash is taken up, it begins to move rough once more.

Here are links to videos that show the issue (CAM set to 80 ipm, but slows down to 20 ipm on negatives):

*http://www.youtube.com/watch?v=r5Q5VG9CGAE
*http://www.youtube.com/watch?v=HEaD1JbSfno

Given the number of different shuttle accel / % velocity combinations I have tried, I am really hoping there is some other setting that is causing the issue. I have attached my current .XML file for reference, but feel free to ask about anything.

Thanks,
Anthony

Offline RICH

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Re: Backlash Compensation Failure- Help is Appreciated!
« Reply #1 on: March 08, 2012, 08:01:16 PM »
Are you sure that there is not a chnage in the feedrate in your program?
What version of Mach are you using?

BTW, never experienced your problem...
RICH
Re: Backlash Compensation Failure- Help is Appreciated!
« Reply #2 on: March 08, 2012, 08:26:26 PM »
Rich,

Thanks for the quick reply. I looked through the code and it doesn't seem to change (attached). I have tried installed two versions and have the same results:

R3.043.058
R3.043.022

Glad to hear I'm novel!

Offline RICH

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Re: Backlash Compensation Failure- Help is Appreciated!
« Reply #3 on: March 09, 2012, 06:43:54 AM »
Frankly I don't know what the problem is.
Is the feedrate changing if your not using BC?
RICH
« Last Edit: March 09, 2012, 06:46:17 AM by RICH »
Re: Backlash Compensation Failure- Help is Appreciated!
« Reply #4 on: March 09, 2012, 09:39:41 AM »
The issue only arises when I have bc turned on. It seems like the general attitude is that I can just do without compensation... That is something that is yet to be determined.

The reason that this is an issue is due to the potential for acrylic re-weld. It's happened a couple of times on the slower sides.

Offline ger21

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Re: Backlash Compensation Failure- Help is Appreciated!
« Reply #5 on: March 09, 2012, 12:02:49 PM »
First thing I would try is to create a new .xml file from scratch and see if it still does it.
.xml files are known to become corrupt and cause all sorts of strangeness.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html
Re: Backlash Compensation Failure- Help is Appreciated!
« Reply #6 on: March 09, 2012, 07:32:23 PM »
I'm in the process of reformatting and reinstalling now. I guess I will just keep a frequent backup of the XML file so that can be part of my troubleshooting process.

Thanks for the input.

Offline ger21

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Re: Backlash Compensation Failure- Help is Appreciated!
« Reply #7 on: March 09, 2012, 08:08:54 PM »
No need to do all that. Just remove the .xml and restart Mach3, and redo all your settings.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html
Re: Backlash Compensation Failure- Help is Appreciated!
« Reply #8 on: March 09, 2012, 08:54:35 PM »
I have done simply XML rebuild several times with no apparent improvement. Prior to reading the horror stories about background or Internet functions causing issues with mach3, I had a bunch of stuff on there. Reformat will rule all that out (I hope).