Small Part / Thin Section Fails

[robfawcett]

Hi All,
We are trying to print a small part in ABS with a slot in the middle and 2 thin wall sections either side of the slot. The part is about 25mm by 10mm and the wall thickness is 0.8mm at the minimum with a nozzle size of 0.4. We keep getting a rippling buildup of excess material on the outer wall of thin sections, the inside is fine. We're using an Sigma BCN3D printer & Simplify 3D slicer. We have tried a range of temperature settings, from 245 to 260 and various speeds and have tried to back off the extrusion rate to 90% with no success. Also, when we use Cura slicer for the same model and settings we get similar results but it's not consistent with Cura as can be seen in the attachment where all 10 parts were printed with a single run and 4 out of 10 failed.
Any thoughts appreciated!

[gearsawe]

From the photo it appears you do not have retraction enabled. When it moves from island to island it oozes and looses pressure. Which is the build up you see along the sides of the thin walls. This will make other features fail when it started to extrude again. since it take a little distance before pressure is brought back. The fault retraction may be little to small. And different materials will need more. Direct drive less then Bowden. My Bowden tube uses about 4mm with 1.75mm filament. for yours try starting with 1.5mm retraction.

[robfawcett]

Good thought, thanks, and we do plan to experiment with the retraction but we see the same issue when we print a single part which is the top image (black). Diagonal buildup of what looks like excess material. Interestingly, when we reprinted the batch of 10 parts the same positional 4 failed..

[gearsawe]

So looking at your Factory File the retraction is off. and looking at the movements in red is where you are seeing the build up of material

[robfawcett]

That took care of the excess material, thanks load gearsawe!

Interestingly, we also had the Thin Wall Behavior, External Thin Wall Type parameter set to 'Allow Single Extrusion Walls' which, oddly I think, made S3D choose to use a single extrusion for the wall, even though the nozzle size is 0.4 & the wall thickness is 0.8 & the 'Maximum Printing Width' is 150%. You can see this in the animation image attached where the wall is shown as a darker blue for single extrusion. When we change the Thin Wall type to Perimeters Only, it printed using 2 passes which is structurally much stronger.

Part looks good now. Thanks for the help.

[PhillipM]

I've had similar, where the thin wall fill completely ignores the minimum and maximum thickness and tries to fill a gap anyway.
Even worse on my printer is, whatever generates both the skirt and the thin wall paths, seems to make loads of tiny sections to do it, and the printer vibrates like crazy even with jerk down at 10mm/s, then the flow is inconsistant and it leaves weird patterns on the outer - interestingly, they look just like the pattern you get there.