Rebonjour Cher Monsieur SMBaker,
Bravo pour votre efforts thermocouple.
We have had consistent results on solder iron tips,as well as,solder pots,,for both leaded,,and RoHS solder since,15 years.
We used Omega K TC, plugs,and cables, and Keithley and,Fluke types K TC meters.
We calibrated the meters,and TCS with ice,bath and boiling water.
Important to select a thin guage,TC,wire eg,#30AWG, and insulation rated for solder temps like Kynar, Téflon, etc.
DIY TC must be welded or braised.
We get very consistent tip temps.with both old Hakko 926, 936 and our 1992 Metcal SmartHeat SP-200 500 kHz solder stations with Metcal handles and tips.
As we,have several of each type iron, we have both large,chisel tip and small cone tip irons on the bench.
We use wet sponges to clean off dross and original Hakko and Metcal holders.
Remarkably we,have yet to change a tip in decades....but we are doing bench work perhaps once a month nowadays.....
Hope this mémoire is of interest
Wishing you an absolutely fantastic weekend
Jon
pix one bench Tektronix scopes 7000 plug-ins, Yokogawa digital scope and in background the Hakko and Metcal irons....