# Overhangs lift up

My printer is exhibiting a problem wherein it's as if the nozzle pulls up on layers. I don't think it used to do this - it seemed like it manifested after I replaced the broken x-carriage with a printed one, but I don't see how that could have caused the issue. It's possible something else I did or replaced caused it; not sure. Allow me to give an example:

I'm trying to print a worm gear, with a tooth size of about 2mm. The teeth, as they appear in the stl, look kinda like

 ____________
<            >
>        <
<            >
>        <
<____________>


However, when printed, the edges are pulled upwards, looking more like

____________
\          /
_\        /_
\          /
_\        /_
\          /
\________/


I originally noticed the pull-up in the surface finish of flat things - there was a grid of raised bumps on the top layer, I believe corresponding to the empty points between infill walls. That wasn't an effect that mattered to me, though. The effect on the worm gear is much more significant.

Anybody know why my printer is pulling up on layers, or whatever it's doing?

• props for amazing ascii art. Does this happen when printing larger overhangs as well? Jun 5 '19 at 18:15
• @Nach0z Yes it does, you see this effect many times, e.g. at the bow of the Benchy, myself I experienced this with X-axis idler mounts with 45º slanting slopes.
– 0scar
Jun 5 '19 at 18:39
• @Nach0z Haha, thanks. Mine seems to happen primarily with thin layers - but on the other hand, I don't usually print large overhangs, anyway, so that may just be data I don't have. Jun 6 '19 at 14:56

If you print (overhanging/slanting) fine edges too hot with too little print part cooling, they curl up. Please increase the part cooling fan percentage or try printing with a lower hotend temperature. Another possibility is to print slower, this way the filament cools better for the same fan RPM settings (fan spends more time in the hot region).

The Simplify3d slicer website has a print quality troubleshooting section that describes the up-curl of edges, they also hint to overheating as the source of your problem.

• This is absolutely correct. On my Ender 3 I get the effect only on one side of the threaded shaft due to unequal air flow. Going to do a custom fan duct to mitigate it, but short of that, longer cooling and slower printing mostly suffice. Jun 4 '19 at 23:04
• Well, I reduced the temperature all the way down to 175, but there was no change. I do have a cooling fan enabled, though it's kinda homebrew. I'll try slowing down the print. Jun 5 '19 at 0:55
• Yes slowing down also should work, for similar print cooling fan settings, cooling is more effective.
– 0scar
Jun 5 '19 at 18:42
• That looks like a hotend fan setup not one for cooling the part...? Jun 7 '19 at 12:52
• @R.. I think the right part is the print cool duct, and indeed it is a very bad design, the area narrows too much for the fan to push air through. There are way better print cooling ducts to be found.
– 0scar
Jun 7 '19 at 14:52