Perfect sphere, rubbish collar!

[slugbut]

I'm still new at this game and would REALLY appreciate some help.

I'm printing a semi-sphere (40mm Dia) with a 4mm collar.
I'm using the Qidi Tech 1
Printing using ABS on a heated bed set at 110, extruder set to 230
I use 5 layers of skirt! but have also tried 10. I have also tried a raft.
The sphere and collar are hollow so the walls are 2mm thick


The problem is that the sphere prints really well but the collar seems to warp inwards slightly. The area next to the bed is a perfect circle but once away from the bed, it seems to bend inwards. Once the sphere prints on top it makes it look like a bulge, but its not the sphere but the collar.

Could you please help as I think I've now printed about 20 of these trying different settings and getting in a right mess

[Angus]

It's caused by your heated bed. You'll find further information here: http://support.3dverkstan.se/article/23 ... wallcavein

[wirlybird]

I would say to start lowering the bed temp after the first layer. Maybe even start a little lower. Another thing I do for ABS is the have the skirt/brim build up several layers to help hold heat in against the part. Sort of like building a wall around the part. I get the offset at about 2 so it is real close to the part.