Top layer height

[Fabiuz 2]

Hi all,
I would print an object (let say a cube 1x1x1mm), and the height should be very as precise as possible. The layer height is 0,15mm so cura will print 1/0,15 = 6,6layer, truncated by Cura to 6 layers, resulting in 0,9mm height. Is it possible to tell Cura how it should handle this special case to get exactly 1mm height? It could print "half" layer (only 0,1mm), or a taller top layer (i.e. 0.25mm). I am aware of "initial layer height", but it may be set to different (bigger) values to improve adhesion to the build plate.

[GregValiant 1,412]

The layer height may be input at 3 decimal places.  In your example, if the layer height was .143 and Initial Layer Height was .142 you would (theoretically) end up at exactly 1.00.

BUT...If that block had a step at .5, then the step would end up at .428.

 

I don't know the Ultimaker machines so this next refers to my Creality machine.

Given the 1mm tall block and all layer heights at .15 then at the start of the top layer I could change the Home Offset Z with an "M206 Z-0.1".  The result would be to fool the printer into moving the last layer up an additional 0.1mm.   But all the E numbers for the top layer were calculated at a Layer Height of .15 which I have effectively turned into .25 and so the flow is wrong.  An M226 S166 would be required to adjust the flow to compensate.  That's a lot of Flow for my hot end.  It might be necessary to reduce the speed as well so M225 S33 to drop the speed by about the same amount as I increased the flow.  At the end of the Gcode file I would need to straighten all that out setting the Home Offset, Flow and Speed back to the defaults.  It would certainly be easier if Cura could admit that it needs another layer of  0.1 height to complete the print.

But what if the step was the important feature and needed to be an exact height?  What if I had a 40mm tall part with 10 steps of varying height that were all important?

 

"Everything effects everything" and taking the human mind out of the loop and letting the software decide what's important isn't ready for prime time yet.

[Fabiuz 2]

Thanks for replying.

I was thinking that "layer height" was somewhat "fixed" by predefined settings, next time I will tune the layer height as you said. It seems the most effective solution to now.

 

I had understand your solution, it is feasible but it seems more an hacking than a final solution. As you had pointed out, printing another layer would be a more elegant solution.

Edited December 3, 2020 by Fabiuz

[GregValiant 1,412]

One more thing about layer heights.  I have come across some posts here and there regarding the Creality machines that say to use even number layer heights.  .20, .18, .16, .14 are good.  .13, .17 etc, are bad.  It has something to do with the way numbers get rounded off during the calculations in the printer.  I know in Cura it was an issue when calculating the E numbers and that is why the E resets every 4157mm of filament (10,000 mm of extrusion).