When I started waxing my own skis last year, I was too cheap to buy a proper wax iron, so I dug up my mom's 1950's vintage GE non-steam, solid baseplate clothing iron and used that. It worked....well, sort of. The mechanical thermostat has a wide "dead-band", making the temperature cycle up and down over a 20 deg C range. I set it so that, at its hottest, it just melted the wax, but then at its coolest, it didn't melt properly, making it a pain to use. I was afraid to set it hotter for fear of damaging the bases.
The other day I was rummaging around in my basement and came across that old iron, and I thought this year I'd better buy a proper one. Then the proverbial "light bulb" came on.... Why toss out my poor derelict GE iron? Why not bring it out of the dark ages and into the computer age?!!
Out of my years of accumulated gizmos, I dug up a thermocouple and a PID process controller (that's short for proportional-integral-differential, in case there are any other engineering geeks out there :-) I opened up the iron, removed the original mechanical thermostat, and installed the thermocouple so that it could feel the temperature of the baseplate from inside. Here is the result:
On the right is the original power cord, and on the left, poking out through the hole left by removing a light bulb that used to be there, is the lead from the thermocouple.
Then I assembled the process controller and its associated power relay and an outlet box so that it would use the signal from the thermocouple to control the iron.
I didn't have an enclosure handy, so I just attached everything to a piece of wood for now.
Now for the test....does it work? Well, in a word, yes! In fact, it works incredibly well. Here is a picture of the iron holding a temperature of exactly 100 deg C with less than +/- 0.5 deg C variation. The green numbers on the controller are the thermocouple temperature and the orange numbers are the setpoint. The thermometer I put on the sole of the iron confirms the temperature read by the thermocouple.
That sure beats +/- 10 deg C with the mechanical thermostat.
Of course, the real test will be to see how it performs when waxing skis. That's coming soon, I just have to clean up the mess in my basement so I have room to work :-)