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A "wound" on surface

Posted by tampano 
A "wound" on surface
June 26, 2016 09:45AM
I noticed this "wound" on the side of round objects (I'm printing my first experiments, not an expert) and I can't imagine what is causing it. Maybe calibration, but where/what?

I'm sure you may help me better :-)

It seems to be on every round object and always on the same side, let's say between hour 7 and hour 8 on a clock if you watch the printing surface from above.

I can't see anything similar on square objects.

open | download - File Jun 26, 14 24 54.jpeg (399.3 KB)
open | download - File Jun 26, 12 58 26.jpeg (478.4 KB)
Re: A "wound" on surface
June 26, 2016 10:42AM
Zzzz might need to Randomize Z start points (layer change), but even that can produce undeZirable Z artifacts.

Edited 1 time(s). Last edit at 06/26/2016 10:43AM by MechaBits.
Re: A "wound" on surface
June 26, 2016 11:06AM
It's probably subtler on square objects because it's starting the perimeters at a corner. You may be able to tune this some with coast settings depending on your slicer and firmware, you can change its appearance by switching between inside-first perimeters and outside-first perimeters, and you can make it a series of points rather than a line by switching to random perimeter start points, but the nature of FFF is that there will generally be some kind of evidence where the extrusion starts and stops.
Re: A "wound" on surface
June 26, 2016 11:58AM
As above, it's the seam where the head starts and finishes each line. It's normal, and yours isn't particularly bad - actually, pretty good.
Re: A "wound" on surface
June 26, 2016 02:25PM
Single line would be better, I'd be more interested as to why the stair step was coming from, Software or Z, or elsewhere?
Re: A "wound" on surface
June 27, 2016 04:11AM
I use simplify 3D and I've been trying to minimize z scar recently using the settings coast, retract, extra distance on restart and wipe nozzle. I have next to no Z scar anymore.

The Z scar is essentially the pressure that has built up in the nozzle being released, even if you are not doing a printing move. Coasting in S3D (not sure on other slicers) stops the extrusion before the end of the line so the pressure releases the filament.
Re: A "wound" on surface
June 27, 2016 06:50AM
What are your coasting - retraction - wipe settings in Simplify3D?
Re: A "wound" on surface
July 02, 2016 11:35PM
Try upping your Z jerk and acceleration in firmware. This will help make the layer change much faster, and reduce the scar.

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