Thermistor vs. Manual Control

I understand that the thermistors register voltage to give temperature readings to the electronics. I understand that if the temperatures for extrusion or bed temps changed dynamically during a print why this would be advantageous. Since the temperatures are supposed to be static, wouldn't a better idea just to have a manual temperature control (calibrated with certain notches for certain temperatures, like an oven) that controlled the temperature with a knob on the front of the printer work just as well and eliminate a little complexity?

That idea works for heated beds, many people use a fixed current and resistance to arrive at a fixed temperature, but for an extruders hot end as you push plastic thru it the plastic itself absorbs the heat so you need to dynamically adjust in order to keep the nozzle temperature stable. Also, as you print faster for larger surfaces you need to heat up the plastic more than for smaller objects i.e. the ears on a bunny, for example need the nozzle to move slower so you don't just drag molten plastic around in blobs, and since you are moving slower you extrude less plastic, and therefore want to cool down the hot end. Make sense?

Since you need the thermistor circuit and the heater circuit anyway, adding a knob and a temperature controller is adding physical complexity to replace firmware.

I use different temperatures on the first layer, for both the bed and the plastic, so manual control would not be practical.

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[www.hydraraptor.blogspot.com]

... on my CNC-repstrap I use separate temperature controllers for the nozzle and heated bed, which i can set and adjust by 1 centigrade accuracy.

For this i have to remove all G-codes controlling the temps.

For changing the temperatures during print I can insert a pause-G-code, so the print stops and waits until I hit the continue-button ... this is usefull not only for manually changing the temps, but even more for aftercuring and layer-treatment by per-layer-prints with UV- and IR-curing pastes and powderbed-SLS.

But I have to manually change the G-codes of the common slicers or write my own slicer+host ...

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Viktor
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