Now that I'm very used with 0.4mm layer thickness printing using ABS, I want to try to go down to 0.25mm.

With 0.4mm LT (Layer Thickness) I was using 1.8 for the "Perimeter Width over Thickness" (PWoT) which was giving me a 0.72mm perimeter width (0.4 x 1.8 = 0.72).

With 0.25mm LT, I plan to have a perimeter width (PW) of 0.4mm. So my PWoT is going to be 1.6.

Now I have to calibrate my speeds so that the formula LT x PWoT = PW is respected. I decided to not change my printing speed of 16mm/s (Feed Rate) but to adjust my extrusion rate instead (Flow Rate). After a few tests I ended with a Flow Rate value of 135.0 (tests done with BfB white ABS).

With the machine now calibrated for 0.25 LT prints, I decided to re-print an allready 0.4 LT printed object for comparison. I choosed to re-print the female torso.

And here it is out of the box :

ABS 0.25mm LTABS 0.25mm LT

The print went out really nice except a few burns and scars and the very last layers that have failed.
I don't know exactly what happened there because I was not in front of the Rapman when the last layers got printed.
But I guess it's because each layer time get too small so those layers didn't have enough time to harden when another layer was put on top. Thus making the top layers of the neck molten.
But I'm not sure because I think I used the Cool plugin. I usually do for such cases... So I don't know.

Compared to a 0.4 LT print it doesn't look that much better at first look. But when you have a closer look you can see the layers are way much thinner.
It is a "bumpy" effect that doesn't make it look as good as what it should. And this bumpy effect comes back at regular layers thickness. We can see here that every 8 layers some layers are not perfectly aligned, giving it the bumpy look.
This is due to the "XY woble" and not much can be done I guess...

XY wobbleXY wobble

Still my settings show that printing at 0.25 LT with 0.4 PW is not a problem for the Rapman.
But for printing time reasons I will use that setting only for objects that need fine printing and keep using 0.4 LT for the others.