Oh dear: shouldn't have touched that 'calibration' screw...

[dchisholm]

. . . soldering irons aren't amazingly powerful and if you ask it to heat up something inside a container . . .

I thought his iron didn't have a readout, just a dial - right?

My apologies for the confusion - I should have explained myself more thoroughly.

I was thinking of a soldering station with some kind of readout (LCD or 7-segment LED; or even a "bargraph" of LED's) of the tip temperature, generated from a feedback signal (created with a thermistor, thermocouple, etc). The procedure would be similar to:

• Use a suitable appliance (kitchen stove, hotplate, solder pot, etc) to heat the container of oil.
• Use the cooking thermometer to measure the temperature.
• Immerse the soldering iron tip in the heated oil bath.
  (For best accuracy you could apply power to the solder station and try to adjust the unit's temperature control until it was in the middle of its hysteresis range.)
• Observe the readout on the solder station's indicator.
• Repeat at a second temperature. Ideally, you'd probably want to choose two temperatures that represent the lower portion, and the upper portion, of the solder station's expected working range.
• Make calibration adjustment(s) until the errors at the two temperature readings is acceptable.

Obviously, this won't work if there isn't any kind of readout. If you only have, e.g., a potentiometer for setting the soldering iron's temperature you could immerse the soldering iron in the heated oil, then adjust the solder station's temperature setting until the unit is right on the edge of cycling the heating element. Comparing the dial's calibration marks to the measured temperature of the oil bath will give an indication of the temperature accuracy.

Safety is certainly a concern. (I know a guy or two who would probably like to buy drinks for my widow, or otherwise comfort her in ways I wouldn't approve of, and I have no intention of giving them the opportunity to do so.) Our cooking thermometers have graduations marked to 400F, and deep-fat frying typically uses 350F or a bit more, so I'm not especially worried about the thermometer exploding unless its heated well beyond the indicated range. A greater concern is the oil catching fire if heated above its flash point. I mentioned the synthetic motor oil because I believe its flash point is higher than other oils. Some other material with a high boiling point but lower flammability - perhaps pure ethylene glycol, or the stuff used for moth balls (don't recall the chemical name at the moment), etc - may be a better choice for the heated bath material.

Dale

 

[AndrewT]

When I adjusted my set point to 190ºC, the solder (63/37) finally melted.
I had been gradually increasing the set point by ~2C so that I did not overshoot.

This indicates that my readout is ~7C high at 183ºC, if I have repeated the experiment correctly.