Missing corner

I've noticed that several of my test prints have a small triangle on the very top layer missing. You can see it quite clearly in the nearest corner of both cubes here [goo.gl] . The printer gets to very near the end of the run, then lifts away and stops. I've noticed that it moves the head a short distance from where it was printing, then makes the motions it would to draw the last few parts of the corner in mid air.

Does anyone have any insights into this? I am printing in PLA at 185C on a Folger 2020 using Repetier 1.0.6 and Slic3r. It could be some setting to Slic3r or maybe a firmware issue. The preview shows this is not a characteristic of the models.

Edited 1 time(s). Last edit at 06/19/2015 11:48PM by animoose.

First are you sure Slic3r was done? The reason I ask is that on more than one occasion I just assumed it was and loaded up a gcode that was not 100% complete.

Next I would suspect maybe the original file was bad.

In repetier can you see the problem? if so then it's something in the file, if not then it's an issue in the printer.

It looks good in the preview in Repetier and it has happened on multiple files, including ones from a widely used calibration set. So I think it isn't the file.

I'm fairly confident Slic3r is done. I watched is closely on the last couple of runs and it looks like this:
- slic3r prints the top layer
- when it's almost but not quite done it moves the head away and then makes the last few zig-zag movements that it would have made to finish the top layer
- then it executes its normal end of print commands (M104 S0 ; turn off temperature
G28 X0 ; home X axis
M84 ; disable motors)

I found an answer to this in a very old thread: [forums.reprap.org]. My end gcode was moving the head away and turning the motors off. You have to issue M400 first to let the buffers clear. Problem solved.

Why isn't the M400 in the end code by default? Seems bizarre.