Determining the temps and speeds for DIY printers? I've been going down the learning road with two broken printers that I'm rebuilding with better parts and electronics.

One thing that I've recognized is that there is a pretty low likelihood that any hotend or heatbed that has had the thermistor/thermocouple and/or the printer board swapped with a non-OEM part can be trusted to accurately report it's own temperature.

Sure, there are lots of things I can (and do) do to try to make it as accurate as reasonable like calibrating with thermistors from multimeters, IR thermometers, etc., but each method has limitations.  You never know if the 2nd thermistor is mounted both correctly, or if it is reading the same local temp as the printer thermistor.  IR thermometers have issues with reflective surfaces (like aluminum hot ends and build plates)  Calibrating the thermistor constants from experimental data isn't perfect.

IMHO, any hotend/heatbed temp on a DIY setup might be off by a constant &plusmn;&nbsp;5&nbsp;&deg;C or so, more if it is poorly calibrated.

Printers use PID controlled heaters to keep oscillations down to a degree or two Celsius, because people say it impacts print quality.

Is there a good visual or experimental way to know whether your temperatures are "correct" for your printer/filament?  IOW, if my filament was supposed to be heated to 220&nbsp;&deg;C, how would I know if my printer was having issues because the "true" temperature is only 215&nbsp;&deg;C (or 225&nbsp;&deg;C) when it is reporting 220&nbsp;&deg;C?

One common problem I've experienced is the nozzle clogging after the transistion from layer 1 to layer 2.  (Layer 1 = higher heat and slower speeds, Layers 2+ = lower heat and faster speeds.)  It's been a struggle to know which factor (lower heat or faster speeds) are to blame for the clogs after the transition.
The short answer is, you use the temps and speeds that give you good results. It's trial and error. 

The temperature number your printer reports really doesn't matter. That's just a process control variable: it needs to be consistent and repeatable, but it doesn't need to be accurate against an independent reference. What you should care about is your print results. 

Some signs your printing temp is too cold:


PLA printed parts have a dull, matte surface
Poor layer adhesion
Extruder stalls or strips the filament at fairly low printing speeds for your extruder and nozzle size


Some signs your printing temp is too hot:


PLA printed parts have a very shiny surface
PLA has a very strong sugary/waffle smell, or any material smells burnt
Stringiness during travel moves that you can't eliminate by tuning retraction
Excessive oozing while the nozzle is stationary off the print
Bubbles or cloudiness in extruded strands in extruded strands even with dry filament


You will also calibrate speeds via trial and error. There are two main speed limits for a printer: how fast the motion mechanism can move the nozzle without running into issues or unacceptable print quality degradation (which is also a function of acceleration settings), and how fast the hot end can heat up and melt filament. 

The mechanism speed limits you have to find via trial and error. Pick a test print you like (such as Benchy) and repeat it with different tuning until you find your preferred limits.

Melt flow restrictions are slightly more complex, because they are a function of VOLUME flow rate, not commanded speeds. Make a large boxy test print (with long straight lines) and multiply extrusion width times layer height times feedrate. That will give you your approximate flow rate in mm3/sec. Generally speaking, every extruder + hot end + material combo will have a maximum feasible flow rate. For example, most "average" hobbyist printers with 0.4&nbsp;mm nozzles and good extruders can extrude about 4-8&nbsp;mm3/sec with PLA. PTFE-lined hot ends are at the lower end, all-metal hot ends are at the higher end. The value will depend on your hardware. But you can do a few quick benchmarking tests to find the limit, and then use that to determine peak feedrates to avoid exceeding the melt capacity of your system.