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Our printer has been working very well lately and we tried printing a larger part. It is an arm for a 3DRobotics IRIS+ quadcopter.

Rostock Max V2, PLA, Part length about 21 cm (8.5") width 3.5 cm (1.25"). The only setting that we have changed from earlier prints is changing Outer Surface - Perimeters from 2 to 3.

After about 10 layers, the printer goes crazy. It is traveling length wise along the part and all of a sudden it starts lifting off of the bed as it travels down to one end of the part and simply extrudes filament into thin air. The hot end is about 1 inch above the part at this point. It travels back the other way and goes down toward the bed. This has happened three times now. Two of those times it has tried to go below the level of the part and digs into the already deposited plastic. In those two instances I switched off the printer immediately so I don't have any video imagery of that action.

Two of the attached photos are frame grabs from a video sequence showing the motion. The third shows the part with the detached filament that was extruded into the air.

(I was unable to upload these photos to the forum and have instead provided the following google drive links. I tried accessing the forum via chrome and firefox. The photos (JPEGs) range in size from 46 kilobytes to 113 kilobytes. Frustrating. It has not been a good day.)

https://drive.google.com/open?id=0B83XK ... WR3M05CcjA
https://drive.google.com/open?id=0B83XK ... jNjdjdjYTA
https://drive.google.com/open?id=0B83XK ... jBFSG1paEE

It is as if the printer suddenly thinks the bed is slanted and tries to accommodate for that slant.

I have run calibration for z-height and TOWER CAL. Software Print Leveling is enabled.

Any ideas as to how to overcome this problem would be very welcome.

I think your travel speed is too fast for the proximity to the bed, and thus some steps are being missed, either at the motor or controller (I'm not really sure which). I believe you'll need to drop your travel speed a good bit for it to be happy. Try cutting it in half real quick.

I will try that. Thanks for the suggestion

Xenocrates, thanks for your suggestion. I slowed non-print travel speed from 300 to 100 mm/s and the print finished. It did so, however, with many more stringers than I normally get. I will bring the speed up a bit to see if I can reduce the stringers but at least I have a part and I can clean most of the stringers.

Photo at google drive: https://drive.google.com/open?id=0B83XK ... UpkWHdrdWc

It's a bit of a balancing act. You could potentially bring your PLA temps down, and play with retraction (Quite slow or quite fast could be your solution, it's hard to tell since so many respond differently to it) as well.

I am glad it's solved though.