Oven temp verification.

Final comments:
It is just as easy to purchase a digital temperature readout and a type K thermocouple and check the accuracy of any kiln. It may cost around $100, but it will tell you a second (and likely more accurate) reading to compare the PID with. Such a device will always come in handy for checking the kitchen oven, the quench oil temp, the accuracy of your home thermostat, etc. Omega is a good place to get a readout of known value and high grade TCs.

While we all love to give our HT numbers in very tight ranges like 1478°F, those are just the numbers on out readout. A good type K thermocouple is accurate to about .75%, so at 1500° it is +/- 11.25 degrees. So, that 1478° could really be 1467° or 1489°. Your readout may only have a +/- .3% accuracy. so that can make the readout another 5° off the target.
 
there is a relatively cheap multimeter that has a thermocouple add on feature. Model DT33c. Atlas forge sells them. Also pottery supply houses sell temperature cones that bend at specific temperatures.
 
I thought the pottery cones was based on temp PLUS time. I may be wrong.

I've bought the temp crayons. I just checked tonight. I bought a couple, one for example I bought for 1475 said it had a +/- 1% accuracy. So I'm horrible at math but I'm going to assume that's a 28 degree variance. As far as taking coupons or samples for the steel you use are you doing this for every order of steel you ever buy? Can you assume all the different sizes you bought from the supplier are from the same batch of steel? Bottom line to me I can't imagine not having a hardness tester. IF your HT isn't proving your meeting your goals with a hardness test then your just guessing.
 
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Everything in a HT oven has a range of accuracy around +/- 1%. Some cheap PIDs and pyrometers are +/- 3%.
That is why you test several basic steel blades at different temps over a 20° range and find the best results. From there you know what to do on other HT regimes.
 
BUT my point is ONLY with a hardness tester you KNOW your reaching your goal or not! Yes your knives may be incredible to factory knives but you ONLY know if your getting the most from your steel, your knives with a hardness tester based on research from knowledgeable folks that say a knife steel preforms it's best at this hardness. With a accurate hardness tester you can verify you are in fact producing a knife that will preform to yours and your customers expectations . Not that I sale knives at this point for the record.
 
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I am actually surprised at how many makers on this forum do not have a Rockwell tester. To me if one actually cares about their heat treat then they should also care what results they are achieving and testing hardness seems like one of the basic tests.
 
LCoop said:
I thought the pottery cones was based on temp PLUS time. I may be wrong.

I've bought the temp crayons. I just checked tonight. I bought a couple, one for example I bought for 1475 said it had a +/- 1% accuracy. So I'm horrible at math but I'm going to assume that's a 28 degree variance. As far as taking coupons or samples for the steel you use are you doing this for every order of steel you ever buy? Can you assume all the different sizes you bought from the supplier are from the same batch of steel? Bottom line to me I can't imagine not having a hardness tester. IF your HT isn't proving your meeting your goals with a hardness test then your just guessing.
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I know alpha for sure does this. And likely others. They will have a 3 letter code on the billet you can type in on their site and see the elemental values of the steel in that batch.

Different batches will have different codes
 
Seedy Lot said:
I am actually surprised at how many makers on this forum do not have a Rockwell tester. To me if one actually cares about their heat treat then they should also care what results they are achieving and testing hardness seems like one of the basic tests.
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Yeah. But hrc testers arent cheap. And you need test blocks, and all that.

Thats going to be the next big thing i get. Im slowly making my way there.
 
Seedy Lot said:
To me if one actually cares about their heat treat then they should also care what results they are achieving
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I think a lot of makers on this forum, like me, are hobbyists, and can't really justify the expense of a Rockwell tester. That doesn't mean we don't care about the quality of our product! However, I did spring for a HT oven for two reasons - I like "doing it all" myself, and I got tired of sending blades out. So, by following established/recommended HT procedures for each steel (for me that's mostly AEB-L and 440c) and using hardness test files as a rudimentary check of each blade, I am confident I am getting good results. Now, to be clear, I don't sell my knives, I give them away, so I'm not obligated to provide any guarantee. I'm not trying to start any argument, just commenting as to why some makers on this forum don't own a Rockwell tester.
 
Maybe I am just spoiled and have had access to Rockwell tester since I started making knives under the guidance of a mentor who heat treated my blades for years.

When I finally decided it was time to get my own oven I also made sure I could get my own hardness tester because I have seen a few issues in the past that were only caught by checking hardness.

From a selling standpoint I gained a bunch of respect among clients becuase I actually own a Rockwell tester.

From an investment standpoint the tester is expensive and only occasionally gets used but I do feel it was worth every penny.
 
As a long time garage shop time and money burner, the Rockwell tester is one of my favorite tools.
Not that expensive for the satisfaction it gives. Heat treating and working my test and temper to put out a 60.5 Rc knife is my favorite day.
James
 
I agree, if you are selling knives you have an obligation to your customer that I don't feel I have with a gifted knife. But still, I'd love to have a tester. Just for grins, is there a "not that expensive" tester y'all would recommend?
 
I took my knives to a local highly respected local machine shop to have my knife blades tested for RH. They drug it off a high shelve that it had set on for years. Then they placed it on a table and tested my knife blade. I couldn't believe it failed! I had no clue how important it was to use a ACCURATE RW tester.
 
LCoop said:
I took my knives to a local highly respected local machine shop to have my knife blades tested for RH. They drug it off a high shelve that it had set on for years. Then they placed it on a table and tested my knife blade. I couldn't believe it failed! I had no clue how important it was to use a ACCURATE RW tester.
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Failed?
 
Skinner79 said:
I agree, if you are selling knives you have an obligation to your customer that I don't feel I have with a gifted knife. But still, I'd love to have a tester. Just for grins, is there a "not that expensive" tester y'all would recommend?
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I was not having any luck finding a used one so I bought the Grizzly tester when it was on sale, Its very accurate when set up right.
Its a few hundred more now (1295.00) and comes with everything you need. Used machines are out there but vary wildly on price and completeness.
 
LCoop said:
I took my knives to a local highly respected local machine shop to have my knife blades tested for RH. They drug it off a high shelve that it had set on for years. Then they placed it on a table and tested my knife blade. I couldn't believe it failed! I had no clue how important it was to use a ACCURATE RW tester.
Click to expand...

I can't imagine ever putting a good tester on a "High Shelf" as they weigh close to 150 pounds. They need to be permanently installed on a heavy and solid bench. If it had been up on a shelf in a shop for years, it was also likely both dirty and out of adjustment. I would not consider any test done under the circumstance you described as accurate.

Some things you didn't tell us are:
What was the metal in your blade?
Where was the metal purchased?
Was the blade forged or stock removal?
Did you normalize the blade before HT?
What was your HT method and temps?
What as your hardness target?
What was the result they gave?
 
I did the salt test a little bit ago. It melted at about 1490F, so reading ~15 deg high. Close enough that I'm happy with it.

Also changing to an unsheathed TC was a huge improvement on how well the oven controls.
 
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