Fan fixtion...

I've been playing with my new 3DRobo, and learning the tao of successful printing with PLA. I've not yet had anything that I'd consider a 100% successful print, but several have come close.

One variable I'd like to limit, or at least understand better, is the fan. Default settings turns it on too soon and too high. My print of the 15mm cube has lamination issues, because the fan came on full bore two layers in, almost immediately the tip cooled below 160°, and I had a partial pass with no extrusion. Caught it, shut of the fan manually, and the rest of the print was perfect... but of course the second layer delaminated almost immediately after I pulled it off the surface.

So, I found the settings in Slic3r and shut the fan off. Printed the 5mm calibration cube. With no fan, most of the item printed well, but the very top slumped from being too hot; and the bridges were a bit saggy.

So, all the way off is bad. All the way on is bad. Anyone have some good middle of the road settings they can recommend as a starting point? I know I'll have to tune it a bit for my environment and project... but I'd rather not flail at random. I'm running out of PLA!

 

Hmm sounds like there needs to be a setting in the softwares that let you control the begining, middle and end of the print fan speeds?
;

 

There is a control to shut off the fan for the first X passes. The rest of the variables have to do with turning on the fan or slowing down the print head if the layer size is smaller than a given variable.

Another data point: with the fan off, the thermistor keeps the print head right at the preset temperature just fine. But the model still needs cooling, without killing the temp on the nozzle. My wish is that with the fan on, the thermistor would up the power to the nozzle... but possibly it can't keep up.

So, the question is which parameters to tweak? Fan speed: max and min? Layer size?