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03_Calibration.md

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Extruder calibration

To ensure the stepper movement translates into the piston movement accordingly to the g-code, it needs to be calibrated properly.

Calibration set-up

In principle, the calibration set-up requires:

  • CNC control of the piston powering motor (we use Nema 11 with a planetary reductor)
  • the assembled extruder (at least the moving parts)
  • a precise displacement measurement device (calipers, etc., high precision indicators are preferrable)

The calibration protocol requires a set-up, where the piston translation, can be precisely measured in the axis of extrusion. For this purpose, the measurement device is fixed on the extruder in a way, that the extruder movement is translated directly into the measurement.

Calibration procedure

  1. adjust the steps/unit value of the motor settings in the cnc control software (or use default values)
  2. command piston movement for an exact distance
  3. measure the real movement distance and compare
  4. repeat steps 1-3, until the g-code value coincides with the measured value

For a Nema 11 motor (with a planetary reductor) + an M5 spindle (0.5mm pitch/rotation), the default STEPS/UNIT value is 37914.30.

Thermistor calibration

Every thermistor analog output values have to be mapped to actual temperature values via an equation. Every thermistor needs to be calibrated as described in this section.

EQUIPMENT: thermo block/plate (heat source), alcochol thermometer, thermistor, setup for reading analog signal from the thermistor, oil, glass.

  1. pour a small glass of oil (50mL or so)
  2. place the glass on the heat source
  3. fit a thermistor to the alcochol thermometer
  4. sink the thermistor - thermometer setup into the glass with oil
  5. prepare the system to read analog values
  6. turn on the heat source and record sensor analog output at every 1°C increment
  7. plot data (x - axis: analog output, y-axis: real temperature)
  8. fit the best trendline to the data obtained (MATLAB or EXCEL are good tools for completing this task but there are also others)
  9. software will yield a fit line equation which then has to be transcribed into microcontroller firmware (we used Arduino Mega)

Now your thermistor will give out the right temperature values.