Do any slicer programs decrease the layer height when there is little to print on a Z layer? How do you think that would affect the print speed and quality? I was thinking that shorter layer heights could be done instead of decreasing print speeds in such situations where the top layers would turn out poorly when printed at normal layers at full speed. I am sure a number of you know the “minimum time per layer” setting in Cura. I am sure other slicers have that too. I was thinking a shorter layer would cool off quicker and print better allowing for faster speeds and an overall 1.5 times the speed of using a minimum time per layer height.
A shorter layer is more likely to allow more heat to be injected into the part. You’re just going over the same small portion over and over and over and over and over…
Skeinforge had the ‘skin’ feature, which would make the perimeters a much much smaller layer height, and then combine infill layers. So outers could be 0.05mm, and infill could be 0.2 and it would be done every 4 layers, for example.
Slic3r also has that option, I’m not sure about others. I’m not sure making lower layer heights would help anything. I suspect it would actually make it worse.
@NathanielStenzel Here’s an example of the top side of a sphere printed at 0.05mm layers. It shows small area thin layer printing at the peak. Thantik is likely correct about extra heat as the print generated some deformation from it at the very top since I did not have a second piece to move to or set a minimum time between layers. I do have a really good part cooling fan duct on my printer which helped. Faster speeds on such small areas can trigger a skip from the short direction changes depending on the geometry. Over all not likely to save any time. Curved and slanted surfaces do come out really nice with thinner layers.
https://plus.google.com/u/0/113930448883604105560/posts/361D47NphPq
Well, the layer height would not go smaller than 1/2 or maybe 1/3 the normal for what I was thinking and would be similar to the smaller perimeter layer heights that you mentioned. It would just be triggered instead of a wait time for when people want speed.
Cura can do different layer heights for infill at least
Yes. I have seen the affect of short print times on a layer causing deformities before. The debate I was hoping to make was if (A) making the layer height shorter than default could be a good alternative to (B) slowing down or pausing the print till X time is up. The logic being that a thinner layer should be able to cool off faster than a thicker layer. Yes, it would also probably take twice as long, but when I set a minimum layer time I end up seeing more than half of the time in some of the layers being wait time.
Then per your debate topic I can confirm that thinner layers do cool off faster with dwell times being equal to thicker layers. I get much flatter bridges (less than 0.1mm of sag per 25mm of span) and much less curl if any on cantilevers with thinner layers. So even if you don’t save time (double the layers but no pause/wait for 50% of the time - cancel out?) you can get a better print quality.
If your print areas are multiple points but with a small overall area this concept of yours could be effective and not trigger deformities from heat radiation.
@Jeff_Parish thanks for the confirmation of that. Just to be sure, 2 thinner layers taking the same time as the one normal thickess layer. We are thinking the same thing, right?
Yes, the thought is that one normal thickness layer with a cooling pause would be about equal in time to two thinner layers with no pause if the cooling pause is 50% or more of the layer time on a thicker one as you mentioned seeing sometimes. If the cooling time is less than 50% of the total amount, then your print time will go up with thinner layers. That’s why it may not save time. This thinking is in the context of a small area print geometry on each Z layer.
Although I have not done any definitive measurements it seems that thin layers cool off a little more than twice as quick as a double thick one. In addition the already cooler plastic below a new thin layer does not absorb heat at the same rate as a warmer one especially if it has transitioned across the glass temperature. Thick layers seem to hold their heat a little longer so if the passes are short even with a pause thicker layers may still be warmer than one thin layer at the time of a second pass. It is very dependent on the geometry how effective this might be.
This would be an interesting experiment to quantify. 
This is more for better quality where it’s needed, but probably could also be used to make thinner layers at hights where pauses are needed becuse of too short passes.
@cprezzi indeed