Different Fan Speed for Overhangs?

[rachael7 59]

Would it be possible to add a function to change the fan speed for overhangs of a certain angle?  Perhaps it could be rolled in with the (currently experimental) Overhanging Wall Angle and Overhanging Wall Speed function? I'm printing a lot of ABS, Nylon, and Polycarbonate these days, and those materials need to run without a fan for best layer adhesion. But the lack of fan makes overhangs come out less than pretty, even when they are only 10-20 degrees off of vertical. I got some improvement using the Overhanging Wall Speed adjustment, but if I could turn on the fans just for the overhangs, that would allow me to improve the print quality of the overhangs, without as much compromise of the layer adhesion (and hence strength) as I would get from running the fans through the whole print.

[GregValiant 984]

I usually open the gcode file and add fan lines manually.  You can try the ChangeAtZ post processor.  It had a couple of glitches if you were using "By Height" and there were Z-hops in a file, but without Z-hops and using "By Layer" it should be OK.  You would need one instance to turn the fan on and another to turn it off again.

[rachael7 59]

1 minute ago, GregValiant said:

I usually open the gcode file and add fan lines manually.  You can try the ChangeAtZ post processor.  It had a couple of glitches if you were using "By Height" and there were Z-hops in a file, but without Z-hops and using "By Layer" it should be OK.  You would need one instance to turn the fan on and another to turn it off again.

 

Thanks for the ideas, got me thinking!  Unfortunately, I do have (and need) Z-hops and it's not a by-layer situation for me.  The parts I'm working on are quite large, most of the area of the build plate, and only have overhangs in a few small portions of the perimeter. The fans need to stay off for the rest of the layer, to ensure good layer adhesion, and only come on for the actual overhanging portion. I suppose I could theoretically do it by manually editing the g-code, but that would really be a prohibitive editing process without much chance of automating it.

[GregValiant 984]

Somebody mentioned changing the cooling based on the feature.  That isn't all that hard to do as the features are in comments throughout the gcode.

Unfortunately within a gcode file you won't find anything that says "overhang starts here".  It would be really tough to code for.  If a support blocker could be configured...hold on... I feel a workaround coming on.

 

You must have "Enable Jerk Control" turned on for this to work and all the Jerk values need to be the same.  For this example lets say we have Print Jerk and all the little jerks at 10.  The fan speed for the overhangs will be 50% and the rest of the time the fan will be off.

 

So you take a support blocker and size it and place it covering the overhang.

You select Per Model Settings / Modify Settings for Overlaps and make "Print Jerk" one of the settings.  Set the Jerk within the support blocker to "1".

Every time Cura slices through the blocker it will add M205 X1 Y1.  When the nozzle leaves the blocker Cura will add M205 X10 Y10 (our default Print Jerk).

You add two Search and Replace post processors.  The first one is:

Search = M205 X1 Y1

Replace = M106 S128 (fan at 50% PWM)

and the second one is

Search = M205 X10 Y10

Replace = M205 X10 Y10\nM106 S0

The second replacement re-inserts the Jerk line so you don't have to go back and change the first line manually.

 

I like it.  Now it's up to you to prove why I shouldn't.

 

 

 

 

 

[rachael7 59]

2 minutes ago, GregValiant said:

Somebody mentioned changing the cooling based on the feature.  That isn't all that hard to do as the features are in comments throughout the gcode.

Unfortunately within a gcode file you won't find anything that says "overhang starts here".  It would be really tough to code for.  If a support blocker could be configured...hold on... I feel a workaround coming on.

...

I like it.  Now it's up to you to prove why I shouldn't.

 

I have to admit, that is pretty darn clever. I do use the jerk settings and could easily make them all the same, so that could work. The challenge will be to make the support blocker shape right to get the jerk changes to happen at the right points. Then again, once one has gone that far, why not just use the different settings for overlaps feature to change the fan speed directly? It would work the same, but without even the search/replace, right?

[GregValiant 984]

No travel settings and no cooling settings on modifier meshes.

 

Try again.

[GregValiant 984]

Close, but no cigar.  I don't think it will work.  It looks like the Jerk only changes when "TYPE:FILL" is there.  For the outer and inner walls the Jerk doesn't appear to be inserted.

[rachael7 59]

17 minutes ago, GregValiant said:

Close, but no cigar.  I don't think it will work.  It looks like the Jerk only changes when "TYPE:FILL" is there.  For the outer and inner walls the Jerk doesn't appear to be inserted.

 

Dang. Heck of a good effort though. I'll put in a feature request on Github and hope the Cura gurus manage to work it into the schedule at some point.