Can't find a usable temperature for PLA

Question

I have a Monoprice MP10 Mini, a cut-down Creality CR-10 with lobotomized firmware. Heated bed.

I'm trying to do PLA prints, but have been unable to find a usable temperature.

If I set the temperatures (either nozzle or bed) too low, the initial raft layers don't stick, the print shrivels up, and the result is a tangle.

If I set the temperatures high enough to allow initial sticking, the raft prints okay, but after that the filament leaks out of the nozzle during long moves producing strings (only a little unsightly when outside the print area, but causing bumps when moves over the build and eventually the nozzle knocks into them) and all solid flat areas (ceilings/floors) warp.

If I start with a high temp but reduce it during the print, the layers stop sticking to each other, solid areas still warp, and the printer eventually fails to extrude anything (presumably the filament congeals inside the extruder or tube, that's very unpleasant to recover from, fortunately I have some cleaning filament).

Tried with multiple types of filament and multiple models (from thingiverse, converted into gcode using cura 3.6)

What should I be trying?

Answer 1

First, you shouldn't need a raft for most PLA prints. That will help you get better bed adhesion at lower temperatures.

Second, you can reduce the stringing by increasing travel speeds (120 mm/s is not too fast) and a small amount of retraction: around 1.5 mm for direct drive and 5-6 mm for bowden.

With those settings, you should be able to print most PLA with a bed at anywhere from 50-60 °C and an extruder at anywhere from 190 to 215 °C.

Answer 2

Try bed at 50°C and hotend at 215°C, these are safe values.

Enable retraction in the slicer, to avoid/reduce oozing during long moves, but with Bowden setups finding a good value is trickier. Try with 6 mm.

Set the first layer height properly, but do it AFTER the bed has been heated for 5-10 minutes.

Answer 3

Here is the important information from your question:

If I set the temperatures high enough to allow initial sticking, the raft prints okay, but after that the filament leaks out of the nozzle during long moves producing strings (only a little unsightly when outside the print area, but causing bumps when moves over the build and eventually the nozzle knocks into them) and all solid flat areas (ceilings/floors) warp.

If you have material leaking from the nozzle during moves, this means your retraction settings are wrong - either off entirely, or insufficient distance. As I understand it your printer has a bowden extruder, so retraction distance needs to be at least 5 mm and probably 6 to 6.5 mm. Note that "Retract at layer change" is a separate and independent option from "Enable retraction", and is not really important; "Enable retraction" is the one that must be on. "Retraction Minimum Travel" should also be set very low (the Cura default of twice the line width, or slightly lower than that, is probably good).

Answer 4

If you get one of those lazer pointer thermometer things from the hardware store for checking the temperature of hot water pipes and stuff you can usually heat your hot end up and look at the actual temperature of your nozzle. If it's hotter or colder than the temperature that your filment is rated for them there should be a line of code in your firmware that will allow you to offset the temperature making it perfectly calibrated spot on. Then you should never have to change it ever again

Answer 5

As @Fernando Balthazar had suggested, the z-offset was wrong. I needed to bring the nozzle and the bed closer together. The printer's default is -0.50 mm, I had to change to -0.78 mm or so to get it to stick. But then I need to reduce set it back to -0.50 or -0.40 during the print to avoid the nozzle banging into the model.

I used 205C for nozzle and 35C for bed and it works great, virtually no warping.