How to choose an extrusion temperature? From what I've been able to find out, online sources recommend around 205ºC for PLA and around 240ºC for ABS. But these are only guidelines, of course. Optimal printing temperature can be different depending on the printer, the filament, the model and other slicer settings.

For example, I've had success printing black PLA at 190ºC, but silver PLA of the same brand is giving me trouble. I'm having a hard time figuring out the general rules. So I would like to see a general guide for this, based on (at least) the following questions:


Which known factors before a print can help determine the right extrusion temperature? Obvious example: ABS vs PLA
What can happen during or after a print when the temperature is too low?
What can happen during or after a print when the temperature is too high?


An answer to the first question could take the form of a lookup table, or similar. The second and third could help someone adjust their temperature based on the symptoms of a failed print.

I understand that the failure or success of a print can depend on many more factors than extrusion temperature, but I didn't want to make this question too general. I may later ask the same question for other settings (e.g., print speed). However, do let me know if this question should be expanded or improved to make it more useful.
Printing temperature basics
Manufacturers generally specify a somewhat wide range of printing temperatures, and what temperature you should actually need can only be determined by trial and error:

The thermistor in your hotend is not 100 % accurate and may have an offset of a few degrees compared to its actual temperature.

Your hotend has a small temperature gradient, the place where the plastic is melted may have a higher/lower temperature compared to the temperature of your thermistor.


2 is further exacerbated by

As you print faster, you need more heat. The cold filament rapidly moving through your hotend will cool it down locally, meaning that the temperature will be cooler than what the thermistor measures. Faster prints equal bumps in the temperature up to 10 °C, and for a really slow print you might turn it down 10 °C from where you normally are.

This is a minor issue, but different colors of the same brand and material might work better at different temperatures. The pigments used can affect the melting point somewhat. Different brands also might have different temperatures.


Some symptoms may give you a guide as to how to adjust your temperature:
Printing too hot

Small/slow prints may not solidify quickly enough, leaving you with an ugly blob.

Stringing/bad bridging.

Plastic in the heatbreak may soften, leading to clogging.

You might burn/degrade the material (but for this you would really need to go outside of the temperature range).


Printing too cool

Too much force required to extrude, leading so skipping/grinding of the filament drive.

Layer delamination: the plastic needs to be hot enough to partially melt the layer below it and stick to it. Objects printed at a colder temperature tend to be weaker at the layer boundaries.


Furthermore, hot prints can sometimes have a more glossy finish than colder prints.