Vertical walls close to edge of buildplate sloping inwards

[avogra 68]

I had my first larger print this weekend. It is a an air guide for an adaption of the crossflow approach for the UM2. It is quite okay except that at the edge of the buildplate the walls between the air channels are all sloped towards the center of the buildpate.

The first full horizontal layer seems to restore dimensions. On the second level of channels the same happened to a less extend.

The inner walls are 0.8mm, the outside walls are 1.6mm. I had to print it 45° rotated to fit on the plate.

Filament is Colorfabb leaf green. Settings were 50mm/s, 100µm layers, 0.8mm walls, 15% infill, fans 100%.

My first thought was, that the inner walls are only 2 lines, one going front the other back, so there might be some torque forcing the walls to bend. But that would make them all bend in the same direction and at the other end of the part, they are also bent inwards.

Any ideas what has happend?

btw., the function is lousy :PAirflow is quite uneven across the length and mainly dictated by where the radial fan blows. Next design will put much more resistance against the flow and instead of straight channels I want to try a kind of a streched nozzle als used in some airdoors by teddington.

[Edit:] I forgot to write printing temperatures: it was 205°C / 60°C

Edited October 7, 2015 by Guest

[avogra 68]

I think I have found the reason: this might just be shrinking: When the first solid layer is printed after the walls, it will consist of 90% overhangs. This first layer will cooldown and can easily contract, because it only has to bend those walls a bit. The next layer will see much more resistance, as there is one solid layer beneath. So within a few layers, there is hardly any more shrinking and dimensions are as intended. Then the next walls are raised perfectly straight. When the first solid top layer is printed, the same happens again.