Accuracy Of Casting Thermometer

[detox]

I have two thermometers from two different manufacturers and there is a 50 degree difference between the two. 50 degrees is a big difference to me. I trust the readings of my RCBS more than the cheaper $35.00 version. The RCBS reads hotter. Has anyone else ever compaired readings.

[theperfessor]

Have you checked to see what either of them read when put in boiling water? Do you have any pure lead you can use to check the melting point (651F IIRC)? I wouldn't trust either one unless I did that. Maybe they are both wrong!

[doctorggg]

Have you checked to see what either of them read when put in boiling water? Do you have any pure lead you can use to check the melting point (651F IIRC)? I wouldn't trust either one unless I did that. Maybe they are both wrong!

That's a great idea because I have the same exact problem as the OP. boiling water should work. Mine is more like 30* difference.

[dromia]

There is a table somewhere on here with boiling points of pure water at different altitudes which I have used to calibrate my thermometers, It will no doubt be on the web some where as well.

BTW do you know which thermometer you dropped? :wink::grin:

[detox]

My RCBS is 15 years old and has been dropped a couple of times, but i bet it is more accurate than the cheaper version. I will do the boiling water test.

[Dale in Louisiana]

Check your local businesses for an industrial calibration service. They routinely check such things. there is going to be a fee involved, but you end up with a device that is of known accuracy, traceable to NIST (National Institute of Standards and Technology).

Or, if you know somebody who works in industrial instrumentation, quite often they have bench test standards that will perform the same function at only slightly degraded accuracy.

Dale In Louisiana

[RickinTN]

I purchased a thermometer on "sale" back around Christmas and after a few uses the stem began to rotate where I had to set it at ambient temperature before using each time. I sent an e-mail and soon received a replacement. Comparing the two, I have an 80 degree difference. I just yesterday received an RCBS thermometer which I purchased and have higher hopes for it's accuracy. I have been having poor fillout on the driving bands and frosting in the same area. It seems it is difficult to keep my aluminum molds cool enough, and have to leave the molds open between cast longer than I think I should for cooling. I'm thinking I'm on to the cure and will find out soon. I usually purchase top quality loading equipment but in this initial case did not. Every now and again I need a reminder it is best to start with quality equipment and avoid the headaches that come with sub-quality equipment.

Rick

[GP100man]

I checked my Lyman against boiling water & it was only 10 degrees off adjusted & it is very close to the pure lead melting point.

Before I sprung $$ for it I used a cheapo grill thermometer & it was way off but still gave me reference points to where certain molds were happy with alloy temp.

Knowing what I know now I doubt I`d turn the furnace on without 1.

[TenTea]

I have noticed temp readings will vary based on the probe (stem) depth into the melt.
I thought this was kind of odd, but my 2 thermometers read the same when inserted to the same depth of ~2 inches, so I trust they are close to accurate.

[John Boy]

My RCBS is 15 years old and has been dropped a couple of times, but i bet it is more accurate than the cheaper version.I'll cover your bet for $500.00! Want my mailing address?
Buy a Tel-Tru for 21 bucks instead of buying the vendor rip off's with RCBS & Lyman, etc logos for 48 bucks
http://www.teltru.com/p-272-big-green-egg-primo-grill-dome-kamado-replacement-thermometer-lt225r-5-inch-stem-2001000-degrees-f.aspx
Under the dial on Tel-Tru is a calibration nut!

[williamwaco]

JB is correct.

Truth be known, the RCBS IS a "cheaper version".

It is the Tel-True with an RCBS logo.

Tel-True makes about 90% of all the industrial dial thermometers in this country,

And both of them are inexpensive versions of their normal thermometers.

http://www.teltru.com/default.aspx

[detox]

I just did the boiling water test. For my altitude the boiling point of water is 210 degrees.
http://www.csgnetwork.com/h2oboilcalc.html

The old RCBS measured 199 degrees
http://www.midsouthshooterssupply.com/item.asp?sku=0004481175

The cheaper Altraco (different design) measured 175 degrees
http://www.midsouthshooterssupply.com/item.asp?sku=00036MTH1000

[detox]

What is the Teltru part number for the RCBS version?

[Dale in Louisiana]

I just did the boiling water test. For my altitude the boiling point of water is 210 degrees.
http://www.csgnetwork.com/h2oboilcalc.html

The old RCBS measured 199 degrees
http://www.midsouthshooterssupply.com/item.asp?sku=0004481175

The cheaper Altraco (different design) measured 175 degrees
http://www.midsouthshooterssupply.com/item.asp?sku=00036MTH1000

Typically, mechanical analog meters are given an accuracy rating in percent of full scale. If yours is 2% of full scale, that's plus or minus 20 degrees - anywhere on the scale. That means 200 indicated could be anywhere between 180 and 220 and still be within specification. It will also be plus or minus 2% at a thousand degrees, which means 980 to 1020, a lot less significant error.

That said, a decent meter (or thermometer) will be repeatable. In other words, if you melt to 750 indicated this time and a week from now do that same indication, the actual temperature both times might be not exactly 750, but what it was last time, it will be pretty close this time.

Electronic meters, the more expensive ones, have the ability to be "spanned" to give the best accuracy across the range, as well as calibrated to a specific spot temperature, so you can take an electronic thermometer (thermocouple device) and check its calibration at a specific temperature, for instance, 750 degrees. Of course, these are a bit more expensive, and to calibrate, you need access to some trusted standards. If you calibrate to boiling water, you are pretty secure in that knowledge, but you're also five hundred degrees away from the range you actually want to measure.

dale in Louisiana

[John Boy]

What is the Teltru part number for the RCBS version?
Call RCBS and ask them ... if they answer the phone!

BTW, the best casting 'thermometer' is when the sprue puddle frosts in 5 seconds for little bullets and 8-10 seconds for the 500+gr ones, alloy dependent. I've done the 'frost thermometer' many times and then put the Tel-Tru in the pot to see the temperature and mark the paper I keep in the mold boxes for reference. Then the next casting session, bring the pot & mold up to temp with the thermometer and you're good to go

[detox]

Using boiling water I calibrated my Altraco by holding nut on back then turning face to 210 degrees. Now pointer will not return to near zero when cool. It is stuck on 100 degrees.