TPU overhang layering artifacts
Hey all,
I've been printing 95A TPU relatively successfully on my MK4, but I get an occasional issue.
See my crude drawing below of a front-view of what I'm printing (it has some depth in the Y axis too):
Imagine the brown sheet is the printbed, and the black bit is what I'm printing.
The bottom solid part prints absolutely fine, but when I get to these thin overhang parts, I get a layering artifact at the exact same point each time. We've tested this on multiple MK4s, and the layering artifacts happen at exactly the same point each time.
I've got some images below - but basically the bit where there's loose filament strings is on the underside of the overhang, and the line gaps is on the other side of that.
The first image is that underside, and the other two is the other side of that overhang.
My interpretation of whats happening is that the nozzle is likely hitting the overhang as it travels over, and pushing it out of the way, meaning it prints onto nothing, creating this stringing issue. But I have no idea why the nozzle would be hitting the part (my retraction is set to 5MM!), or why it happens in exactly the same place every time.
It seems to be centered around the holes in the overhang, possible filament is building up at the point where it retracts for the holes? But how do I solve this?
Does anyone have any ideas?