Top Surface Flaking off...

[Chuck B]

So I'm making a 2"x1.5"X8.5" box to encase a product prototype I have made. The walls of the box are 1/16th (.o625) thick. Naturally, I sliced the part into two halves (each 3/4" high) in my cad system and turned both halves on their back so that the STL file would not have to deal with an impossible bridge (a top spanning 1.5 inches). I plan to stick the two haves together with Acetone later, since they are made of ASB. The prototype slips into the case from the small end (into the rectangular tube).

As the parts begin to be printed, the first 4-5 layers have no problem, and due to some generous brims the corners are staying down on the plate. The 2 x 8 slabs continue to go along wonderfully as the extruder runs back and forth at a 45 diagonal along the length of the part - BUT when the final layer is laid down on the next pass, it abandons the diagonal pattern and settles into it's East, North, South, and West pattern of ever decreasing squares until the inside is finished.

Now here's the mystery, when finishing off this final layer (before it starts building the 3/4" high walls around the perimeter), the extruder was heading east down the length of the 2 x 8 square and the filament went down beautifully. But when the extruder ran west along the length of the top surface, it resulted in flaking ribbons that did not adhere to the last surface. What makes this even more intriguing is that it did it on both halves, but only in the west direction.

Someone elsewhere suggested I should turn the bed down after the first 4-5 layers as the heat actually builds up as the layers increase. But how does that explain the flaking happening ONLY in one direction, and not in the opposite direction?

Any 3D Sherlock Holme's out there know what causes this?

[Glacian22]

Any pictures? Might help us diagnose the problem.

[Chuck B]

[img]http://i.imgur.com/t31buA9.jpg[/img]
Sorry the image is not so great, but you can see the flaking in the right side of the part on the right (I already cut away all the flaking on the the left part. And as you can see, the flaking only happened in one direction.

[nitewatchman]

The nozzle is likely tilted and dragging on that side.

[DavidF]

im wondering if there is some sort of error in the cad file, or if the slicer is misinterpiting something?

[Chuck B]

I agree the nozzle might be tilted and dragging on one side, but if this was the case, how would you correct this?