Horizontal shrinkage at the first 2 mm

[Pilzefreak 2]

Since I updated Cura and UM2+ firmware to version 15.04.5 last week I can oserve a strange effect on my PLA prints.

The first 2 to 3 mm of a model seem to shrink and are noticable drawn inwards. Looking at the bottom surface the corners have not lifted. So it is not a problem of bed adhesion.

Has anybody observed this effect and is there a way to fix it?

[Coyote_Blue 0]

Hello, I have recently seen the same distorsion while printing single wall structures in PLA-PHA from Colorfabb on a heated bed at 60°C. My first thought was that it could be linked to a thermal shrinkage when leaving the heated zone. First experiment yesterday was to stop heating the bed. This effectively removed the shrinkage but there was some warping and the part did not stick to the bed until the end. More tests to come. I'll be very intérested to read about possible solutions

[IRobertI 433]

Check at what point the fans are set to turn on. I'm guessing they turn on later than you're expecting which can cause this defect.

[gr5 1,061]

The problem is that it's too warm down there. PLA is like a wet rubber band when it extrudes at the moment it is still liquid. Like snot. Or mucus. It pulls inward going around that corner. Because the layer below is above the "glass temperature" it pulls the layer below inward a bit and "warps" it.

Usually with a bed temp of 70C you get this badly. At 60C I never see this problem anymore but I also have the fan at full speed by .5mm from the bed. So IRobertI might be right about the fan speed. Or possibly your bed is hotter than you think and you should go down to 55C?

I used a thermal temperature sensor on my 60C bed and the sensor said it was 60C over most of the bed and 55C around the edges (the last 2cm).

[Pilzefreak 2]

Thanks for your replies. Lowering the fan speed to 80% improved it. Next I will lower the bed temperature from currently 65°C. This is probably too hot.

I like your snot and mucus comparison ;-)

[jechsturk 3]

Thanks for your replies. Lowering the fan speed to 80% improved it. Next I will lower the bed temperature from currently 65°C. This is probably too hot.

I like your snot and mucus comparison ;-)

 

I have had this problem once with PLA-PHA when my bed temperature was higher than 60°C. So lowering it to 60°C solved this problem for me! Stucking to the heated bed is still no problem then, even 55°C is enough for PLA-PHA.