Bottom 2-3mm always misshaped like a bell

[kenneth 0]

I've got a relatively new UM2, and have been quite pleased with my results....above the bottom 2-3 mm or so (bottom defined as the part touching the build plate).

For some reason the bottom 2-3mm seem to be "flattened" outward like the bottom of a bell. If the core of the print is hollow, that hollow space is narrowed by this effect as well. Everything above that prints just great!

This effect happens across multiple models/prints, so I don't believe it has anything to do with my model files. Is the bed temp too high? Anyone seen this before?

Thanks.

 

[illuminarti 18]

There are multiple theories about what causes it. One thing I recommend is lowering the bed temp to 60º, rather than the default 75. Also, try having the fan come on earlier or later, and see what effect that has.

 

[gr5 2,004]

75C as default bed temp for PLA is a very bad thing. Should be 70C. Or lower.

 

[yellowshark 153]

Personally I would say there is no need to exceed 60c for PLA even for pieces taking the entire bed area; I have never intentionally gone above 60c.

I have had the effect on some pieces and overcome it by reducing the area of the bottom 0.3mm (i.e. layer 1) of the model by 0.1mm all-round. Effectiveness of course probably does depend on the geometry but e.g. I always design a cylinder with 0.1mm taken off the diameter if I remember.

 

[kenneth 0]

Great - thanks for the suggestions - I'll lower the bed temp and let you know how it goes.

 

[thehitman04 0]

Ive just done this and it worked for me so id go with what the guys are saying

[kenneth 0]

Turning the bed down to 60 helped immensely... also made the glue from the gluestick hold the part on stronger (had to remove the glass to get the part off). Thanks again!