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This is a close up of the mini/ Flat Pin junction. Again, two inputs on the display, both the same Flat Pin. The negative terminal on the Male side is wider than the negative.

Mini K Type Thermocouple.png

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And the Round Pin K-type thermocouple. The probe from Omega came with a quick disconnect, which is more or less a female plug that you attach a wire to. The female plug is where I put the clipped end of the probe that came with the display unit. You can also see in the top half that there are two slits below the round holes. Those are for the Flat Pin K-type input. Two different sets of holes, same function.

K type Thermocouple.png

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  • 4 weeks later...

So John did you find probes for HT temp and for forge welding temp like you wanted to do ??? and can the probes stay in the heat or do you need to stick it in check the temp then take it out?? Just wondering because I want/need to make a HT forge and a forgeing forge and a welding forge so it would be nice if you can leave the probe in the forge and just hook up the readout to which ever one you are using at the time ...

 

Thanks

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The probes I eventually got from Omega are usable up to 1335°C (2440°F), which is fine for HT, although I haven't used it for welding yet (and I don't know how hot it would be, as I have only done it based on colour and the borax activity). For the use it has gotten, I have left it in the forge for the duration of the work, and it has shown no wear yet other than slight discolouration. They are cheap enough that you should be able to leave them in and then replace them when needed. The thermometer I have has two inputs, so theoretically you can have them both connected at all times, and simply push a button to change which one it is reading off of.

Hope this helps, and I'll get some info on the next welding project I do.

 

John

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If you really need to contiuously measure welding temperature, you'll almost certainly need to go for a Platinum-based thermocouple with a ceramic sheath.

 

The Omega thermocouple John uses is really about the upper limit for base-metal thermocouples. Where I feel it is most useful for the novice forge-welder is in establishing whether the (gas) forge is hot enough to weld high(-ish?) carbon steels.

 

My feeling is that it's unlikely to help the experienced guys much, if at all. I originally recommended it because I feel that it offers the most bang for the buck. Over here, the additional cost for the Omegaclad XL sheath versus a 310 Stainless sheath from another supplier, works out at around 10 bucks or so. Once you factor in shipping and the readout, it adds less than 20% to the total system cost to get the extra 200 degC of usable range and this is enough to just get into the welding range.

 

I come at this as a bit of a geek with an interest in tools and a background in gas burners and process control, rather than as a maker of knives. I had no idea at all what sort of temperature to aim for when building a propane forge a couple of years ago. I struggled to find objective information online, so I went to a hammerin, watched lots of folk making Damascus for two days, then measured the temperature of the forge using a type S (Platinum) thermocouple. It was doing 1280-1310 degC (2336-2390 degF).

 

As is the way of such things, there followed a brief discussion on achievable temperatures, some burner adjustment and a melted forge lining. Peak temperature measured was 1470 degC (2678 degF).

 

The thing I had wanted to achieve by the exercise, was a realistic value for a welding forge temperature for knifemaking. Several of the guys using the forge were very good smiths. A couple of them had guessed the temperature within 30 degC but one was 30 degC high and the other 30 degC low. Most were happy to admit they had no idea what the temperature was. Nobody had said it was too hot. Nobody had said it wasn't hot enough. If it had needed to be hotter, it could readily have been adjusted to make it hotter.

 

Based on that experience, I'd say that for welding what the type K can do is tell you whether the forge temperature is in the right ball-park and give some indication of the temperature distribution. It'll be close to its limit though.

 

Based on my limited understanding of metallurgy and welding, a base-metal thermocouple isn't going to be much use for measuring the higher welding temperatures needed for mild steel or wrought iron.

 

My feeling is that continuous measurement in a welding forge is only likely to be helpful if you are sure the temperature distribution is even and that the thermocouple itself is measuring at a point that is at the same temperature as the working area, since the thermocouple is fragile and can't encroach on the working area itself. Effectively, it's only useful in a really well-designed and well-executed forge. I've not seen a forge that I feel is sufficiently well-designed and -executed to convince me that the continuous measurement would be useful, but I've seen plenty where a check measurement in the working zone would certainly be useful to some people.

 

For HT, leaving the thermocouple in will not be a problem. For forging, it may not be a problem either, but a lot depends on your setup and how you work. For welding, I'd say you are better off taking it out. Personally, I'd take it out for forging too.

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Wow Tim, great info! Your knowledge in this far exceeds my own, and I cannot thank you enough for sharing it.

Thanks!

 

John

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I sort of agree. Heat treating is where I really need to know how hot my forge is. Forging or welding, my hammer will tell me if I'm hot enough. It is nice to know though if the adjustments to the air and/or gas flow is moving the temperature in the right direction.

 

Doug

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I was doing some more research on pyrometers last night and one thing that I noticed, even on units that were rated at around 2400 degrees, was that the thermocouples that come with them are rated to a lower temperature, maybe only to around 700 degrees. At least on Amazon, you need to look up the equivalent thermocouple as a replacement unit to find out. What you really need is a ceramic shielded probe. The best source for them that I found is actually Ebay, though some assembly may be required. I only noticed one ceramic shielded probe on Amazon and it was 60" long.

 

Doug

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That's a bit longer than I could use :o And that is a very useful observation. The thermocouple I got from amazon was not rated nearly to the temps I needed, which is where the Omega one came in. As I learned, K-type (mini or standard) does not inherently mean it will be able to handle the temps of the forge.

Another thing I noticed is that the higher the operating range, the greater the uncertainty. The Omega thermocouples are fairly good in this regard, according to tests done by someone with carious brands of thermocouples.

OmegacladXL_Chart.gif

Once they reach the upper end of the operating range, the deviation increases exponentially. So, I suppose the point I am making is, they are more reliable in the rated operating ranges. (makes sense, but I thought I'd say it anyway..)

 

John

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  • 4 months later...

As the OP appreciates, there are 2 things needed for temperature measurement.

 

One is the thermocouple, the other is the display.

 

Realistically, you only need a simple handheld readout for checking temperatures. I use a TM902C bought off ebay. It's dirt cheap and accuracy seems good; the readings compare well with much more expensive big-name instruments. Downside is a Celsius-only readout. I'm in the UK and don't think in Farenheit, so it's not a problem for me, but it may be for some. It reads to 1300 degC, which is 2372 degF.

 

If you need Farenheit, it's a safe bet that even the cheapest readouts will be at least as accurate as the thermocouple itself. It's worth spending on a good thermocouple, though.

 

I'd recommend an Omega KHXL-14G-RSC-18 thermocouple. It is a type K, mineral insulated thermocouple with an Super Omegaclad XL sheath, able to stand a working temperature of 1335 degC, 2440 degF. It has a handle and a connection cable. The diameter is 6mm, 1/4", making it rigid enough to put the tip where you want it without sagging. It has a grounded junction for fast response and is 18" long. The fast response and 18" length are a real hand-saver. In one of the old paper catalogs, there was an option of additional length. I'd suggest another 6" would be worthwhile, if it's available, to give 24".

 

http://www.omega.com/ppt/pptsc.asp?ref=KHXL_NHXL&Nav=tema06

 

as original poster John points out, most of the economy pyrometers seem to use a mini-K output. so, using the omega XL with the "utility handle" with the regular K input isn't really going to work. i can find omega probes that have a "quick disconnect" that can be spliced as John describes, but doesn't omega sell any XL probes with a connection cable that ends in a mini-K plug?

Edited by joe pierre
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Omega sells round K female to flat k male connectors here (part number TAS-(*)-2 Female standard to male mini), but either I messed up the order or I spliced it before it came and cancelled it.

 

If you were so inclined, you can get the K-type (regular) female end and use that as your 'disconnect' where the other end is the k-mini male end that would go into the pyrometer. This would give you a longer wire, which may or may not be useful.

The Female end that attaches to the probe:

K-round female end (part number OSTW-CC-K-F)

The flat pin k-mini male end that inserts into the pyrometer:

K-mini male end (part number SMPW-CC-K-M)

 

Hope this helps

 

 

John

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Omega sells round K female to flat k male connectors here (part number TAS-(*)-2 Female standard to male mini), but either I messed up the order or I spliced it before it came and cancelled it.

 

If you were so inclined, you can get the K-type (regular) female end and use that as your 'disconnect' where the other end is the k-mini male end that would go into the pyrometer. This would give you a longer wire, which may or may not be useful.

The Female end that attaches to the probe:

K-round female end (part number OSTW-CC-K-F)

The flat pin k-mini male end that inserts into the pyrometer:

K-mini male end (part number SMPW-CC-K-M)

 

Hope this helps

 

 

John

 

ah hah! i knew they must have something like this, but i couldn't find it. thanks a lot.

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  • 3 weeks later...

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