Spiralize bottom layer

[Cura_Mura 0]

hi guys, currently i'm working on a project, in which i need to print a lampshade in petg. while the wall be printed in the "spiralize outer contour" mode, the bottom layer is printed in "concentric" mode. spiralize outer contour does a great job by making the seamless wall, but the first layer has, due to it's pattern, still see a visible seam.

my question is if you know a cura setting or way that can a enable a (somewhat) seamless first layer, like spiralizing first layer?

best reguards✌

Edited November 3 by Cura_Mura

[Slashee_the_Cow 480]

TL;DR: Manual post-processing is your best bet. File, sandpaper, abrasive implement of choice. You can try increasing the maximum jerk but beware of stability issues, 

 

The main part of the problem is that a concentric top/bottom pattern does a bunch of rings rather than a spiral pattern:

Doing a spiral on a flat surface is hard because you'd need to properly taper the flow rate at the start and end to achieve a "seamless" look (which is near impossible for a lot of printers, especially those with Bowden extruders, because they don't have anywhere near the precise control over flow rate required).

 

The second problem is that PETG is very stringy once it gets up to printing temperature. On incredibly short distances like this, it will ooze out of the nozzle chamber even if it's not being actively extruded. That's what's happening here - it's doing complete laps, but as it moves out to the next lap it drools a bit where it's been and a bit where it's going to be (which it then prints on top of). A retract won't help because it'll just make the nozzle stay in place longer, and it won't really be retract what's left in the nozzle chamber anyway. Not to mention you'd be chewing up the filament a bit.

 

So what can we do?

There's manually filing/sanding the lump. Hurts the concentric rings look unless you're being veeeeeeeeeeery careful. In which case it just slightly hurts the look because you're not going to get the lines that were on top of the lump. If this is on the bottom inside of something, you may want to pause after it prints the first layer so that you can get in there with easy access.

 

I haven't tried this one, but you could also increase the jerk value, but just for the first layer. Jerk is how much the X/Y speed of the print can change instantly, like at a corner. If you set this high enough maybe it will do the move to the next ring quickly enough to avoid a lump, since you're reducing it having to slow down at the end of one ring, move a little bit out, and start moving again. Setting this really high is generally a bad idea, you risk your bed/tool slipping a step or two if it makes a sudden movement, but sometimes you have to take extreme measures. Fortunately Cura includes a post-processor which allows us to change it just for the first layer - but still watch it print to make sure it doesn't go out of alignment. Anyways, in your quality settings enable Speed > Enable Acceleration Control and Speed > Enable Jerk Control. In the Cura menu bar click Extensions then go to Post Processing > Modify G-Code, in the drop down menu on the left find "Limit the X-Y Accel/Jerk" and click that to add it. Change the settings so that it'll change the jerk but only for the first layer:

Make sure to change the "From Start of Layer" to 1 and "To End of Layer" to 1 (it defaults to -1).