PLA printing temperatures and settings

[mxk]

I print almost everything in PLA. Some people say its harder to use, others say it easier. For me, since I don't yet have a heated print bed on any of my printers, it's a no-brainer (you need a heated print bed for ABS).

I had some bad experiences with inexpensive PLA bought off of eBay, and now buy all of my filament from Ultimachine. I would love to sample the color choices offered by Faberdashery (http://www.faberdashery.co.uk) but the shipping rates are too steep for me to bite that bullet. Ultimachine filament has always been consistently round and of uniform diameter along its length, long-time reprappers I respect and admire say similar things about Faberdashery.

Different colors of filament print optimally at different temperatures. Because everyone has different hot ends and different thermistor placement, take what follows as guidelines not as absolute numbers.

I find that the translucent filaments work best around 180 degrees. I usually print the first layer at 185, then run at 180 thereafter.

Colored filaments work best for me with the temps set about 5 degrees warmer. The more richly colored filaments, blue and red especially, seem to be softer so I have to adjust the idler on my extruder to grab them a little tighter. Black, on the other hand, is hard like the transluscent colors and works at the same lower temps.

Temperature variations are A Bad Thing. A 5 degree swing in temperature, not uncommon using bang-bang temperature control, will make the difference between solid layers with filaments lay nicely against each other with no overlap and stretched filaments with breaks in those lines and/or little spiky things blemishing your print job. If you are using the latest Marlin firmware do use the M303 setting to do the auto-PID tuning, let it cycle four or five times, then recompile your firmware with the suggested values. (I am still using a beta release of Marlin and had to figure it out by trial and error, lots and lots of error).

On blue painters tape I set the first layer height ratio to anywhere between 0.5 and 0.75, depending on the layer height. It sticks great for me, and only rarely do I have the tape peel off with the print job. My zero Z setting is where I can barely fit a business card beneath the nozzle and feel it dragging as I tug it back out, measured with the hot end hot.

Every spool has different diameter filament. Measure it carefully at several places along the length and in different orientations (in case it's not round). Use at least two decimals precision when telling slic3r what diameter filament you are using.

Raise the print head a few cm above the print bed and extrude some filament into free air. Measure the width of this extruded filament. That's roughly your upper limit on layer height. My 0.50mm nozzles extrude at about 0.64mm into free air, and print very well with layer heights of around 0.35mm to 0.50mm. My 0.35mm nozzles print at layer heights of around 0.18mm to 0.28mm. You CAN print with smaller layer heights, but you have to slow down, lower the temperatures, and increase the number of solid layers. At very small layer heights, increase the first layer height ratio, or else you will have a harder time pulling the printed object off the print bed and may end up with blue glue on the bottom.

Hopefully this was helpful to some of you. I would love to hear if anyone has different experiences or other advice.