Leaving Thermometer in Pot

[Bent Ramrod]

All,

I set up a Lyman casting thermometer on a base and position the base so the thermometer probe is about 1/4" off the bottom and sides of the pot but well down into any reasonable amount of molten lead on the bottom. Since it is pretty much out of the way I used to just leave the thermometer in the pot when casting was finished and the pot shut off.

Recently a friend told me he is on his third lead pot thermometer and says the previous two were ruined prematurely because he left them in the pot. Since then I've been taking the setup out and repositioning as best I can after the lead has melted.

There is no reason I can think of why the thermometer should be ruined by leaving it in the small amount of lead that remains to solidify and later melt again in the pot. It seems to me that the thermocouple in the probe will expand and contract as the probe heats up whether it heats slowly or is heated rapidly in the already molten metal. Lead shrinks as it cools so I can't see the probe being crushed by a pressure situation like a ship freezing in the ocean.

Has anybody here had a thermometer damaged by having left it in the pot this way? I can't recall any warning or instruction that says anything about taking it out at the end of every casting session.

[Springfield]

I cast 2-3 times a week with my Magma, and I have been leaving my thermometer in the leftover melt for 4 years now will no ill affects.

[Walter Laich]

Been leaving mine in for over 10 years--only one that broke was the one I dropped on the garage floor

walt

[dragonrider]

I've got about 15 years or more on my Lyman Thermometer and I seldom remove it from the pot.

[madsenshooter]

Thanks for bringing this up. I was wondering myself since I left mine in the pot and turned it all the way down. I just bought the thing last week. Note, I often leave my pot on, though turned down for days at a time since I never know when I'll be able to grab a few minutes of casting time and I'd prefer not to wait for it to heat up starting from room temp.

[frankenfab]

The only drawback I see to leaving the thermometer in the pot (which I do) is that it is held very rigidly by the lead and therefore more easily damaged should it receive an impact while the lead is solid.

[Stampede]

Hello Bent Ramrod,

There is actual a little bit of truth in that (the breakage).

At my factory we produce high end temperature sensors for the industrial & maritime market and have therefore some experiences with this topic. Sensor probes (the tube) really can be messed up by leaving the probe in the lead, but to start with: it is fortunately not a common event.

My self, i have a RCBS thermometer that i bought about 18 years ago (before i started my current company), and i leave it all so in the pot without any problems. So you should be fine just doing that. Did your friend actually messed up 3 thermometers that way??? (what is he doing with them?) As you can read nobody has real problems with leaving it in the pot.

The reason why a thermometer will malfunction is 9 of 10 times about the cooling and “crimping” reaction of the lead(mix). This “can” cause collapsing of the tube and/or the inner mechanism. A quality thermometer has a “thicker” probe/tube to protect the mechanism. For low(er) grade thermometers with “thin” tube walls we have name: “Triple-C” : Cheap Chinese ****.

I all so produce thermometers much like we bullet casters use, but than of a much larger size. These are used in industrial melting pots and casting baths for a quick temperature “reference”. The only way that these things break is when they cool to fast from the “melting” temperature back to a too cold temperature, this is a shock effect! Or let the sensor fall on to the ground. The mechanism can’t handle that. Personally i don’t mind when they break the probe that way, i sell the factories gladly new ones.:p

Since i all so do “official” certification of temperature sensors at my factory i did checked my RCBS lead thermometer recently if the reading is still accurate. Much to my surprise the thermometer lost about 22°C (71°F) of it’s accuracy after al these years, that is quite a bit! But not that bad for personal/private use in the melting pot.

You can make your own “digital” temperature read out set up if you are a bit handy with electronics. For instance the probe diameter can be brought back as far to: 0.039" to 0.078" this safes you a lot of handling space in the pot and you can leave them in it for ever.

My concurrent in the USA sells those probes for a nice price, less than $ 35.00 (without the digital indicator). See: www.omega.com and look for Thermocouple “K” with Inconel 600 or 304SS sheaths. I do make them my self as well, but sending them to you (overseas) is not at all cost effective for a single probe. Omega can and will set you up without any problem, if you like to go digital. NOTE: most professional bullet manufactures use this kind of temperature reading.

By the way, quit recently we had on the “Chat” a extensive experience swap out with this kind of temperature reading/controlling. It seems a couple of us make use of such a system with very great success for just a couple of bucks.

Peter (Stampede)

[mdi]

The only reason could think of is the difference in expansion rates of lead vs. glass, so I've removed my thermometer after each use. Besides, when I'n done with a particular project, I put away my tools (I had that beat into my head from a mechanic father; my tools are cleaned and returned to their storage place, with very few exceptions). That way I know where they are and that they are in good condition, which has served me well for 30+ years as an Electrician and Mechanic...

[Bent Ramrod]

Thanks to all for the info. I guess I'll leave the thermometer in the pot, for the most part.

Peter, my friend casts a lot more boolits than I do, and maybe to more exacting specifications as he's a BPCR competitor. However, I don't know what he does to wear out the thermometers; he uses the same metallic probe-and-dial that Tel-Tru, Lyman, RCBS, etc. all sell. I've never seen any evidence of crushing or damage to the probe, and I'm careful to keep it in the melt and not touching the sides or bottom.

We used Omega thermal sensors at work but I would think they'd be overkill for the casting I do. I'm more interested in knowing the temperature isn't swinging wildly and that the latest refill of the pot is fully up to the temperature setting than the actual degrees F or C. It's also good to see an actual temperature differential when I cut the heat back after the moulds are up and running well, but again, an absolute value doesn't seem to be necessary.

Thanks again to all for your inputs.

[John Boy]

Thanks again to all for your inputs.
And Thank You for an interesting and educational thread!
PS: Mine goes in the box after every casting session ;)

[hes]

Thanks for the info.

[metweezer]

Why would anyone want to keep the thermometer in the mold pot anyway?

[geargnasher]

Why would anyone want to keep the thermometer in the mold pot anyway?

Some of us like to observe the temperature at which the lead "just" begins to melt, useful for determining tin content, etc. It's always good to know exactly the temperature spread of the much phase, and a good way to verify the alloy before each casting session (if you leave the pot full of clean alloy like I do, it heats faster that way and saves time fluxing).

Gear

[JDUBS]

Glad I found this, Ive been wondering about that. Ive only been casting a year and my thermo has not been taken out once. No problems yet.[smilie=w:

[Sonnypie]

I've been leaving my probe in for as long as she'll let me....
Oh... wait.... nevermind. :oops: