"Enable auto cooling" + "Combine infill every # layers" = bad print results

Hello,


If "auto cooling" is enabled, the fan speed depends on the layer printing time.
"Combine infill every # layers" creates different layer printing times and then the fan goes from fast to slow, to fast, to slow, ...


Simplified example:
0.2mm perimiters, 0.2mm infill; infill goes each layer
Layer printing time is 10 seconds, which needs only a low fan speed setting.

0.05mm perimiters, 0.2mm infill; infill set to combine each 4 layers
then the 3 perimiter layers will take 2 seconds
and the last perimiter+infill layer takes 4 seconds.

This causes layers without infill to be smaller (because they shrink more when the fans blow harder) than layers With infill.
Even though the average layer printing time remained about the same.


My fans sometimes go to 100% when printing a layer that does not have infill,
while this is totally not required since the next layer (with infill) will take a lot longer, and then it will cool down anyways.
This high fan speed causes the print to shrink so hard that it warps off the print bed.
I tried to disable auto cooling and set a value which is the average of what auto cooling does, and the print does not warp at all.


My suggestion is to calculate the "auto cooling fan speed" not over one single layer, but as an average over multiple layers.

Any thoughts on this?

Edited 1 time(s). Last edit at 12/17/2015 07:55AM by FalloutBe.

I use PETG and keep the fan off.

Ok, but I use ABS because I can smooth it with acetone :/

FalloutBe,
Fans blowing on the part are not recommended for ABS, because ABS is designed to shrink as it cools.

For ABS it is recommended to print more than one copy of a small part, or print a throw-away part like a cylinder some distance away, so that small features do not overheat.

If you still want to use a fan with ABS and use auto cooling, you can control the speed by setting both the min and max fan speed on the Filament settings, Cooling screen. If you set them both to a low value then perhaps that will suit?