That $400 heat treat furnace I bought secondhand keeps drifting 50 degrees on me

I used to just eyeball the color of the steel for hardening (you know, cherry red and hope for the best) but after my last batch of hammer heads cracked from uneven heating I finally coughed up the cash for a used furnace. The controller is supposed to hold within 10 degrees but lately its been wandering all over the place and ruining my quenches. Any tips on recalibrating these old analog units or should I just save up for a PID upgrade?

2 comments

2 Comments

wadefoster18h ago

Hold on, is a 50 degree drift actually ruining your quenches or is that just what you're telling yourself? Old analog controllers are janky but people have been hardening steel with them for decades, maybe check your thermocouple before you blame the whole unit.

jamierodriguez11h ago

The real issue might be that old analog controllers don't hold calibration steady when the shop temp changes through the day. I've seen units that read fine at 60F start drifting bad once the air gets warm around them. Could be your thermocouple is fine but the controller itself just needs to sit in a more stable environment.