Large print issues

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Large print issues

Postby chappy1978 » 2016-May-Tue-16-May

Hello, All
The printrbot is having problems with very large prints. I have a fan cover I want to print out on my Metal, simply put the cover is 145mm square. Its really close to the full dimensions of the bed. I removed the brim so that it doesn't go over the 150mm max. What the Metal does is check its test point for leveling and the starts to print. Its prints from back to front (Z axis) with out issue but when it comes down to the first line in from left to right (X axis) it seems to start to far to the right and finally grinds the belt. Ive seen this happen in Cura and Simplify 3D. Ive worked with the offsets without luck and thought? Included is a STL of the Fan case.
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Large print issues

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Re: Large print issues

Postby lairdb » 2016-May-Tue-18-May

chappy1978 wrote:Hello, All
The printrbot is having problems with very large prints. I have a fan cover I want to print out on my Metal, simply put the cover is 145mm square. Its really close to the full dimensions of the bed. I removed the brim so that it doesn't go over the 150mm max. What the Metal does is check its test point for leveling and the starts to print. Its prints from back to front (Z axis) with out issue but when it comes down to the first line in from left to right (X axis) it seems to start to far to the right and finally grinds the belt. Ive seen this happen in Cura and Simplify 3D. Ive worked with the offsets without luck and thought? Included is a STL of the Fan case.


Does it "start to the right" by about 18mm?

You may be running into an issue I found, which I solved (though never quite got to the bottom of.) (Also, the details are fuzzy because it was about a year ago.)

IIRC, the 3 point calibration actually messes up the home offset. (Fuzzy recollection, don't trust the details, etc.)

This can be fixed with improved start code.

IIRC the key change was moving the G28 X0 Y0 command above the G29 and adding the G92 with magic numbers to tell the head where it *really* is after calibration (X132.4, Y20). (Important: My current start code has several other changes (e.g. warming the head and the bed at the same time, raising the Z arbitrarily, etc.) which you may not want; do not blindly copy it.)

This is my current start gcode:
Code: Select all
M140 S{print_bed_temperature}
M104 S{print_temperature}
G21 ;metric values
G91 ;relative pos
G1 Z+20.5 F{travel_speed} ;move Z up
G90 ;absolute positioning
M82 ;set extruder to absolute mode
M107 ;start with the fan off
G28 X0 Y0 ;move X/Y to min endstops
M190 S{print_bed_temperature}
M109 S{print_temperature} ;wait on temperature line
G28 Z0 ;move Z to min endstops
G29 ; Auto bed levelling
;G28 X0 Y0 ;move X/Y to min endstops
G92 X132.4 Y20; Reset actual position after G29 bug
G92 E0 ;zero the extruded length
G1 F{travel_speed}


(and for completeness, my end gcode:)
Code: Select all
;End GCode
M104 S0                     ;extruder heater off
M140 S0                     ;heated bed heater off (if you have it)
G91                                    ;relative positioning
G1 E-1 F300                            ;retract the filament a bit before lifting the nozzle, to release some of the pressure
G1 Z+0.5 E-5 X-20 Y-20 F{travel_speed} ;move Z up a bit and retract filament even more
G1 Z+45.5 F{travel_speed} ;move Z up
G28 X0 Y0                              ;move X/Y to min endstops, so the head is out of the way
M84                         ;steppers off
G90                         ;absolute positioning
;{profile_string}


Here's some test squares (20x20, 140x140, 150x150) that should be simpler test prints than your real object. (Those are the outside dimensions; there are chamfers so they're not a PITA to peel off the bed, and the ribs should be 2mm in all of them.) If you can print the 150, you've solved your problem.

square thing - Square 20.stl

square thing - Square 140.stl

square thing - Square 150.stl


20:
Image
Image
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Simple Metal Kit, heated bed
Mods: blower fan with self-remixed blower duct
Usually PLA on kapton with AquaNet.
Usually Cura.
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Re: Large print issues

Postby chappy1978 » 2016-May-Thu-11-May

Hey lairdb,
That did the trick prefect. The g-code fixes totally put the extruder right where it should. Thanks for the test prints that really helped
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Re: Large print issues

Postby PxT » 2016-May-Thu-16-May

Just for reference: the home point is likely offset because of a bug in Printrbot's firmware constants. See discussion at https://github.com/MarlinFirmware/Marlin/issues/732
The G92 command is the right workaround, re-organizing the other start parameters shouldn't matter.
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Re: Large print issues

Postby lairdb » 2016-May-Thu-18-May

chappy1978: glad it helped.

PxT: Thanks -- when I was first fighting this people seemed to think I was insane for daring to suggest it might be a firmware issue. Nice to feel slightly vindicated.

Not entirely sure I agree about the reorganizing (though I have to admit I've lost track of what the original start code was):
- Isn't a G28 X0 Y0 necessary before the G29?
- ...and then it would be necessary to insert the G92 immediately after the G29...
- ...and then I've seen it said that a G28 resets the G29 readings, so it is necessary to suppress or move the G28 that follows the G29?
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Simple Metal Kit, heated bed
Mods: blower fan with self-remixed blower duct
Usually PLA on kapton with AquaNet.
Usually Cura.
lairdb
Waiting for extruder temp...
 
Posts: 81
Joined: 2015-May-Tue-13-May
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