bottom radii not forming no matter what i do..

[mrfish]

Hi.. i really hope someone can help on this one..

i have managed to solve most s3d issues over the last couple of years but not this one..

Any part i design (fusion 360) spliced with s3d with a radius on the bottom face (trying to print a 4mm bottom rad on a rad) just will not form correctly.. overruns/misses the rad (see pic) i have tried just about everything i can think of different profiles, layers down to 0.15mm, speeds down to 20mm/s..

its almost as if the software can't actually compute the form?

Any input would be much appreciated..

thanks Will