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Author Topic: Backlash strangeness  (Read 4616 times)

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Offline Ansen

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Re: Backlash strangeness
« Reply #10 on: December 07, 2012, 08:18:13 AM »
Rich,

I am absolutely sure that the 1/4" gaps are due to backlash compensation. Here's that file. If you want to, run it once with BC on and once with it off. I would be interested to see if you get the same results.

As for the banding, I fixed a farly significant "hardware" issue last night which brought my backlash down considerably. X=0.003, Y=0.001, Z=0. I'm going to try the face file again this morning with BC off.

Thanks for your help, guys!

Offline RICH

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Re: Backlash strangeness
« Reply #11 on: December 07, 2012, 06:33:59 PM »
Anset,
Dry running in MACH here with or without BC made no difference.
Backplotting the gcode dosen't show the large gaps nor any missed holes.
So not the gcode in my opinion.

Attach your xml file.

 How many runs did you do with BC? Just the one or numerous? If more than one with BC, are the results around the same line number?
ie; Is the skipping location rather consistant?

Steppers or servo's?

Rather hard to say it's a BC setting or your machine at this point.

RICH
Re: Backlash strangeness
« Reply #12 on: December 07, 2012, 06:35:18 PM »
Ansen,

In your gcode file, the first gap in the bottom row of dots (right side of block 1 to left side of block 2) is 0.1278765 inches wide.  This is not caused by backlash.  Shows up in my tool path very plainly.

Regards,
John Champlain
www.picengrave.com

Offline RICH

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Re: Backlash strangeness
« Reply #13 on: December 07, 2012, 06:44:15 PM »
The spacing varies between the dots........so does the depth.....
RICH
Re: Backlash strangeness
« Reply #14 on: December 07, 2012, 06:49:46 PM »
OK,
Further exam shows I was not looking at the code properly.  My apologies.

This may not be a backlash problem, but may be a screw pitch variation issue or sticky axis bearings .  I see similar banding with my laser diode machine when burning images if the oilite bearings and shafts are dirty.  
John

Offline RICH

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Re: Backlash strangeness
« Reply #15 on: December 07, 2012, 06:59:33 PM »
Pic to portray depth changes......
RICH

Offline Ansen

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Re: Backlash strangeness
« Reply #16 on: December 08, 2012, 12:14:21 PM »
Rich,

I ran the pattern several times with and without backlash compensation. The results were always the same. Gaps and (even missing holes) in the same locations with BC on.

My machine uses steppers on all axis.

Attached is the XML.

Thanks for your help.

Offline Ansen

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Re: Backlash strangeness
« Reply #17 on: December 08, 2012, 12:17:53 PM »
One more thing: to drill this pattern, I use a v-groove bit with a 53 degree angle. This make the Z axis plunge depth the same as the hole diameter at the surface of the material.

Offline RICH

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Re: Backlash strangeness
« Reply #18 on: December 08, 2012, 06:10:03 PM »
Ansen,
At least you have repeatablity for the problem and that is good in the sense that one can try a few things to see what the cause is.
I would start with trying to find out why the first 1/4" gap is happening ( didn't notice any holes missed in the first section).

Lower your velocities 50%, set backlash speed to 50%, you can play with the shuttle setting or leave as is at .01.

Here is my 50-50-50 rule which you may want to consider:

50% - The max velocity is 50% of where your steppers will start to skip
50% - Set the shuttle Wheel setting in configuration to .0050  to .050 ( .5 too slow )
50% - Backlash speed

----------------------------------------------
I have numbered your gcode file and around line 590 , before/at/ or after is where your skipping.
You don't need to run the whole program so you can edit out a lot of code and see the affect with changes.
See attachements.

RICH

Offline Ansen

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Re: Backlash strangeness
« Reply #19 on: December 09, 2012, 10:14:45 AM »
Rich, Tweakie and all,

Problem solved. After some testing, all I had to do was move the Shuttle Wheel Acceleration to 0.03 instead of 0.01.

Many thanks for your help. I'm off to the races.

--Ansen
http://ansenseale.com