Contemplating a pyrometer

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bjalongi

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Oct 23, 2006
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I have a limited budget for tools and steel because I'm a full time student at the UW and living off the measly GI Bill.

If I were to purchase one more item for my shop, it would have to be a pyrometer for my forge. I'd like to buy a new grinder, a better anvil, the list goes on... But I am tired of guessing and feel I won't progress to the next level until I know exactly what's going on in my forge chamber both during forging and HT.

Can anyone give me some advice about the most economical pyrometer that is reliable and will last at least a few years. There are many choices out there, including cheap Ebay items, but I'm unsure what's good and what's cheap import garbage.

Thanks,
Brook
 
bjalongi,

I've been using an Omega (www.omega.com) HHM63F , handheld K-type thermometer/ multi-meter, $102 current price, for four years, with KMQXL 125G 6" probe, $31, reads to 2440F, probe lasts year or so in propane forge at welding temp, 2320F

John
 
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Like John, I use an Omega handheld and electrode. Good stuff.
This Auber Instruments unit is probably one of the least expensive quality meters you will find outside of Harbor Freight. While it is also a controller, you would find it fine to use just as a pyrometer. The drawback is that you will need to supply power.
I converted my analog Paragon to digital using Auber components (except Omega thermocouple) and have been entirely happy. I assume it will last many years, as I have read no complaints.
 
Can you use an infrared or laser type thermometer to check the temps? I want control over forge temps too but have no knowledge about thermocouples/probes.
 
The laser type can be used for temps, or should I say some do use them. The higher temp models are a bit more expensive, last time I looked 500+. You can get a Auberins controller and a $40 omega probe and still have change from your $100 bill.
 
Pottery supply places handle a variety of pyrometers. If you can't afford digital, Skutt makes a very good analog one for about $100.00.
 
beta_medic88 said:
So what's the difference between a thermocouple and a pyrometer?
Click to expand...

A thermocouple is the probe portion, where a junction of two wires generates a signal based on temperature.

I don't know for sure if the term "pyrometer" is accurate in this case, as older pyrometers were optical devices. It might still apply because of the high temps. It might be better simply to call a thermocouple in combination with an appropriate meter as a thermometer. I'm not certain.
 
Do most knife makers use a thermocouple? Are they easy to work with? Sorry for a lot of questions, just trying to figure out how to make this HT I'm about to do accurate.
 
A thermocouple/thermometer is probably only going to be of use if you have a decently enclosed space like a furnace, salt pot, or forge, that can maintain a "space" at a relatively consistent temp. In other words, if attempting to heat treat with a torch or one brick forge, I can't really see where it would be of much help.
 
I'm planning on going tomorrow to get the stuff to make a coffee can forge with some furnace cement and a bernzomatic propane torch. I'm hoping that will keep a somewhat consistant temp. I know the HT is extremely important and I don't want to ruin my knife with a poor treatment.
 
Don't mean to hijack, but I need some info also. Grounded or ungrounded T/C? What diameter, 1/8" or 1/4" ? Also need input on extension wire from T/C connector to display.
Thanks.
 
nc_cooter - 1/4" type K. It doesn't matter if it is grounded or ungrounded for our purposes. The connecting wire needs to be thermocouple wire. I have plenty,if you can't get it with your thermocouple.You also should get a ceramic sheath thermowell.If you don't use a thermowell, get heavy gauge probes, See below.

beta medic88 - This is how a pyrometer ( pyrometer is the term used for a high temperature thermometer ) setup works for a forge.

You need a thermocouple that is made to read in the range we are dealing with, and sturdy enough to survive the environment inside a forge. The range type is called type K, and will read to around 2500F. It needs to be robust enough to not melt or burn up in the flames, so a 10 or 12 gauge solid wire unit is the best.these come with ceramic spacers that protect the leads .The tip is the only part that reads the temperature,BTW.It is there that the junction of the two dissimilar wires create a bi-metallic joint, which creates a small electrical current, variable by the temperature. The thinner gauge units will work, but will not last as long. The best setup is to install the thermocouple in a thermocouple well, ceramic being the best, but a stainless piece of 1/2" pipe will do fine. Put a cap on the end in the forge and slip the thermocouple down it.

The thermocouple needs to be wired to the reading device with a special wire called thermocouple wire. The connections need to be secure ( twisting the wire around the thermocouple leads won't cut it) and a thermocouple head block is the best way, but Kearney nuts will work fine. Using regular copper wire may make the readings off.

The thermocouple needs a device to turn the small electrical current it generates into a digital or analog reading. This can be a simple as a multimeter (not usually very accurate) ,a specialized pyrometer unit ( Auber instruments and others), or a PID ( what most knife guys use). The PID is readily available on ebay for about $30-40. It can be simply connected to the thermocouple to read the temperature ( ignoring all its other functions). If you later on decide to control a device ( toaster oven for tempering ,or a controlled forge) it can be hooked up to do that,too. A PID and a thermocouple will cost about $75 on ebay. The other items needed to hook it up can cost from a couple dollars to $50, depending on how you want to do it.

There have been several threads lately on PID controllers.

A coffee can forge with only refractory cement will not be a very well controlled heat source for HT. There also may not be much room for the thermocouple. Check out building a simple 12" gas forge , it is not expensive. There are guys here who have done it for $30-50, with a little smart scrounging.It is easily done for $100.

Stacy
 
Stacy, thanks for the info. I have a 9" x 18", two burner forge. It's about 5"ID with a movable back wall. Most of the time I only use one burner.
I plan on buying the Auber PID that Mike recommended and a Super OMEGACLAD XL T/C probe. I can get a 25' roll of T/C wire for about $20. This will be less than $100 total. I don't plan on controlling, just for measurement.
Thanks everyone for all the input.
 
Troop,Good luck with that laser pyrometer.
The problem is that you are at the end of the range, and the emissivity of the forge is above the range. The readings can be very erratic and often totally wrong. I tried using a $500 IR laser unit and had poor results. A $15 HF digital thermometer and a $20 ebay type K probe read perfect.
I hope you have better results.
Stacy
 
bladsmth said:
Troop,Good luck with that laser pyrometer.
The problem is that you are at the end of the range, and the emissivity of the forge is above the range. The readings can be very erratic and often totally wrong. I tried using a $500 IR laser unit and had poor results. A $15 HF digital thermometer and a $20 ebay type K probe read perfect.
I hope you have better results.
Stacy
Click to expand...

Well, that lesson just cost me $ 199.00. I'll let you know how it works.:(
 
I have the PID from Auber Instruments. I love it, I was running my forge way too hot in the past. I still had the metal at the right temp but was wasting a lot of gas doing it. If it hasn't paid for itself already it will soon. Plus now it makes it easier to soak blades.
 
I bought a Fluke thermometer and a type k probe.

I only insert the probe to check the temp and then set the forge with the needle valve. The forge will stay fairly constant, you can check a couple times to get the fell for it.

IMO it is much chaeper to spot check the temp than replacing thermouples or buying thermowells...unless of course you get a themowell on the cheap. :)
 
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