Heat Treatment Oven Build Process
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Posted 13th February 2025
Advice on the MIG welding forum suggested that the thermocouples should stick out at least 50 mm or ten times the diameter of the tip. The tip diameter is 5 mm, so that tallies nicely! I replaced all three thermocouples; they all now protrude about 55 mm into the chamber:
I haven't trimmed the excess yet, but they'll all have to come back out soon as I need to paint the chamber.
The eagle-eyed among you will have notice that I've now wired up the door interlock, which should make the whole thing a lot safer.
With that done, the temperature seems much more consistent over the cavity (i.e. the thermocouples at the rear agree with the ones at the front). I also used a separate low-temperature thermocouple for some tests at around 200°C and that thermocouple agreed as well, so I think the extension of the thermocouples was well worth it. Tempering the little test blade produced a much better colour this time, although it was hard to photograph and I don't think the image shows the colour that well:
With the blade tempered, I could give it a bit of TLC in the form of some rubbing on wet-and-dry, some sharpening and the addition (with epoxy) of some wenge scales. With that done and a coat of Mike's Magic Mix applied, the marking knife is finished:
Side view:
This knife is well within the realms of things that could be done with just a blowtorch rather than requiring a big and complicated heat treatment oven, but I wanted to do something to test the chamber and this was a nice quick and simple project to use for the trial.
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