"Pegged" Casting Thermometer

[Bent Ramrod]

Somebody gave me a "Tel-Tru" thermometer that had been used for boolit casting. The dial goes from 525 to 825 F but at rest the needle is on 820 or so. When the probe is dipped in the molten lead, the needle goes completely around the circumference of the dial and past the 825 degree mark to the bottom of the thermometer where the scale ends.

Has anybody seen a casting thermometer get "pegged" or "tweaked" by too much heat? Or by some other means? Is it possible to recalibrate or reset the needle on these things? There doesn't seem to be a way of getting to the needle short of breaking the glass face or prying off the bezel.

[RobS]

I believe you are on the bad end of it all. I've had this happen to a cheaper thermometer, but not a higher end one. I believe Tel-Tru is a decent made thermometer but it may not matter at this point if it is cheap or not.

[fourarmed]

If you look at the back of it, there may be a way to hold the spike and turn the dial. Then you just need a standard to calibrate it. Either another thermometer or an alloy with a fixed melting point like pure lead or linotype.

[cbrick]

fourarmed nailed it. There should be a hex nut on the back side of the dial, hold that with a wrench and turn the dial with the other hand. Be fore warned, go the wrong way or too far and it breaks the spring, no going back from there (don't ask how I know). Being turned like this could well be the problem, since the needle goes all the way around it could have a broken spring.

Rick

[Bent Ramrod]

Thank you all for the advice. There is a hex nut on the probe side. I tried to turn the bezel on the dial with the hex held in a wrench but it wouldn't move in either direction. Does the probe itself turn in the nut? I could try that next.

[deltaenterprizes]

No, hold the probe with the wrench and turn the bezel.