Cura Position issues

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Cura Position issues

Postby SkyeFire » 2017-Jan-Sun-19-Jan

This one is quite strange.

After having very good experience with a PB Play as an entry-level printer, I bought one for my (not technically inclined) schoolteacher-aunt for Christmas. And while I was helping her get it set up and running, we got about 6-7 hrs of good printing before something really odd began happening. Suddenly, if the print was centered on the bed in Cura, it was printing way out at the far positive end of the X axis, so much so that the extruder head was bouncing off the X+ end stops and wrecking the print. The part was centered properly in the Y axis.
I homed-- no change.
I checked M212. The X value was +20 (which seemed odd). I tried changing it to 0 -- this had no effect at all (?!?). Neither did making some random changes in the +/-50mm range, just for kicks. I eventually set M212 X = 0 and left it.
I moved the print in Cura to the far X- edge of the bed, and it printed on the far X- side of the bed, exactly where Cura showed it.
I centered the part in Cura and tried printing again -- it ran off the far X+ end.
I centered the part in Cura, then by trial and error moved the part in the X- direction juuust enough to get it to print within the X+ limit of the bed. It printed perfectly, but far to the X+ of where Cura showed it.
I centered the part in Cura, then saved the G-Code. The X values ran out to the 90s and above.
I moved the part to the far X- edge in Cura, and saved the G-Code. The lowest X values were down in the 2-5mm region.
The obvious answer seemed to be a step/mm ratio for the X axis. But printing a cylindrical part (http://www.thingiverse.com/thing:1460364), at multiple positions on the bed along the X axis, produced a perfectly cylindrical part -- the nut and bolt threaded properly, and even mated properly to an industrial 16mm threaded bolt. So there's no issue with the calibration of the machine.
Given that the error is coming from the X values in the G-Code Cura is producing, it has to be a Cura issue. But it's not an offset, since the part prints where Cura shows it when I drag it to the X- edge of the bed in Cura. It's almost as if Cura's concept of the X axis is at fault somehow. But I have no idea what setting in the machine profile could cause this, especially since this just started happening for no reason in between a perfectly good print and the first one that started running off the X+ edge.
I've run out of things to try. It prints well as long as I pull each print to the X- edge in Cura. But I'd really like to know how to fix this.
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Cura Position issues

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Re: Cura Position issues

Postby RetireeJay » 2017-Jan-Sun-20-Jan

I assume that you are executing an X homing maneuver before the print starts - either manually or as part of the print G-code. What does the User Interface say the X position is when it's clearly not printing where you expect it to be printing?

In Cura, try looking at your Machine Settings. The little check mark box for saying the machine's center is at 0,0 should NOT be checked because Printrbot machines have 0,0 at one corner of the bed.

Then take a look at the Startup G-code to make sure there's not a G92 lurking in there which is resetting the X = 0 location.
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Printrbot Plus operational January 2013
Brass threaded rods (5/16" X 18) & nuts for Z axis
GT2 belts & pulleys
Cable chain to reduce probability of fatigue failure in wires
E3D V5 Hot End, 0.4mm nozzle, also 0.8 and 0.25 in use occasionally
PB fan mount + 40mm fan -- using printed mount adapter, not the E3D supplied fan
Injection molded extruder gears
Optical Z "endstop" (custom designed and built)
Have used many pounds of T-Glase filament. Now also doing some work with Ninjaflex SemiFlex
Print on glass with Scotch Craft Stick or other glue stick
"My next printer is..." Prusa i3 MK3
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Re: Cura Position issues

Postby Mooselake » 2017-Jan-Mon-09-Jan

Is the problem always with the same part? What is it, I'd like to take a look at the STL file. Does the gcode preview look OK?

You mention successfully printing another part, which suggests the issue is part specific.

Kirk
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Re: Cura Position issues

Postby SkyeFire » 2017-Jan-Mon-13-Jan

The positional issue is not part-specific -- I had it turn up with several different STL models, before I buckled down and started seriously experimenting with this issue. The experiment series was all done with the same STL model, to satisfy the "One change, one test" rule.
I didn't look at the positional readout during the various tests, but manually positioning the head, either by Homing then jogging, or by executing G commands from the command line, matched up with the results when executing the same X values in the G-Code output. After going through all that, I'm pretty confident in calling this a Cura issue (or possibly something in the specific Cura config). What's puzzling is that *my* Play at home, using the same version of Cura, and the same Play machine profile file from PB, has been working for nearly a year without ever showing any remotely similar behavior.
While I didn't check the "machine 0,0" check box specifically, when I deliberately placed a model right up close to the front-left (X~0, Y~0) position in Cura, it printed right there on the physical bed. So I think I can rule that one out.
The Play X axis has 100mm total travel, and the Cura machine configuration is set to that (I checked). If I placed the test model (~20mm diameter) as far to the left as possible, the G-Code X values ranged from (X<5) to (X~25), which is exactly what you would expect. But if I centered the same model in Cura, the G-Code output X values ranged from (X~85) to (X~105). Obviously, the average X value *should* have been 50.
The "Start GCode" has a G92 E0, but no other G92 commands. I'll have to do another set of tests and check the final G-Code output to be certain that Cura isn't adding any, but it seems unlikely -- Cura would have to be adding it for parts centered on the "virtual" print bed, but *not* adding it to parts positioned at/near the left edge.
Hm... since cylindrical test prints come out perfectly cylindrical, we know it's not a *scaling* issue in the slicer or the machine. But... what controls the "scaling" relationship between the "virtual" print bed and the real print bed? What I mean is, is there a setting/scaling factor in Cura that would make the virtual and real dimensions incorrect to each other, but would *not* effect the actual X *size* of the printed part? It would have to be something that *only* affects how Cura "scales" the "motion" of a part as you drag it around the virtual print bed.
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Re: Cura Position issues

Postby RetireeJay » 2017-Jan-Mon-14-Jan

You might try comparing the two .ini files that your two different installations are using. On Windows computers, you will probably find them under
C:\Users\[yourname]\.cura\15.04.6
You could also post the problematic one here if you can't pick out anything that looks "off" to you. When posting the file contents here, if you click on the "Code" button and then paste the file contents between the opening and closing Code block delimiters, then it will show up in the window here as "scrollable". Or you could Attach the file. Either way is fine.
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Printrbot Plus operational January 2013
Brass threaded rods (5/16" X 18) & nuts for Z axis
GT2 belts & pulleys
Cable chain to reduce probability of fatigue failure in wires
E3D V5 Hot End, 0.4mm nozzle, also 0.8 and 0.25 in use occasionally
PB fan mount + 40mm fan -- using printed mount adapter, not the E3D supplied fan
Injection molded extruder gears
Optical Z "endstop" (custom designed and built)
Have used many pounds of T-Glase filament. Now also doing some work with Ninjaflex SemiFlex
Print on glass with Scotch Craft Stick or other glue stick
"My next printer is..." Prusa i3 MK3
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RetireeJay
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Re: Cura Position issues

Postby Mooselake » 2017-Jan-Mon-14-Jan

The DOS command COMP (for compare) is still around (it's still in my Win10 IP edition), and might be interesting to see what the differences in the two files are; comp /? will show you the options. the *nix diff command would be even better if you're familiar with it.

If you've installed Repetier-Host slic3r comes along with it. Using a different slicer (slic3r, craftware, KISSlicer, etc) would definitely eliminate Cura as the source of the problem.

The machine center 0,0 option makes the center of the bed 0,0 (instead of the front left corner) is only for delta style printers and should definitely be turned off. Being on could be the cause of your problems. Ultimachine doesn't make deltas and they removed/depreciated/something the option for a while and caused a big to-do in open source land - not that that is hard to do, the hard-core open sourcers are pretty prickly.

Kirk
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