52100 Question

Agreed, if you are just using a file to guess the hardness the temperature difference is moot. Test coupons are by far the best way to dial in your HT.
 
Seedy Lot said:
If you are a sticker for perfection get a Rockewell tester...
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I'll be the first to admit that I have some serious OCD tendencies, but the fundage will not allow me to buy a Rockwell tester at the moment. Sigh. Maybe I'll have to sell a rifle or two. 😓
 
HPD said:
I'll be the first to admit that I have some serious OCD tendencies, but the fundage will not allow me to buy a Rockwell tester at the moment. Sigh. Maybe I'll have to sell a rifle or two. 😓
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IDK where you are located, but I just picked up a used Wilson 3JR Rockwell tester from a local machinery/equipment liquidator for $200. Only needed a good cleaning & a replacement Brale for under $30. I used files like you before, but just wanted to share that stuff is out there for to find if you are diligent & patient.
 
HPD HPD with current firearm prices parting with a surplus rifle or two to buy a new Rockwell tester might be a wise decision.
 
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HPD said:
I might also use magnesium sulfate to check my Magnacut temp. It melts at 2055 F. [Edit: bad idea because the anhydrous form, which is what melts at 2055 F, readily absorbs water from the atmosphere and Epsom salt melts at just 150C.] [Second edit: pure copper melts at 1984 F. Copper wire is about as pure as you'll get. I wonder if melting some wire is a good test for stainless temps?]
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Tried the copper wire thing. I didnt have much luck with that because of oxidation.

And the melting salt thing does kinda work. But also if it is right at melting temps, and not over at all then be aware it should take a while to melt it.
 
HPD said:
I'll be the first to admit that I have some serious OCD tendencies, but the fundage will not allow me to buy a Rockwell tester at the moment. Sigh. Maybe I'll have to sell a rifle or two. 😓
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Get the secondary thermocouple. Its not that expensive. And it will do better for double checking temps. Than most other things.

Then of course you have to question if you trust the second thermocouple. But getting a good quality one isn't too much.
 
Thermocouples are typically either good or dead. They are very simply two dissimilar wires twisted or wedled together. One or both wires has a different resistance at a given temp. The reader or handheld unit, is programmed to read that difference as a voltage and convert to the corresponding temp. It would be far more likely the reader is displaying the wrong temp that the thermocouple. In that case the reader needs to be calibrated.
 
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Blankblank said:
Tried the copper wire thing. I didnt have much luck with that because of oxidation.

And the melting salt thing does kinda work. But also if it is right at melting temps, and not over at all then be aware it should take a while to melt it.
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Stacy gave a great explanation on why using metal isn't an effective way to determine oven temperature. When I used the salt I let it soak 20-30 minutes at each setting so it would have time to melt. I'm pretty sure my oven is running a bit cool. The only thing is I have a mechanical relay and the temp swing was roughly +/- 10F at each setting. I increased the temps in 10 degree increments. The salt did not melt on the 1480 setting, though the salt layer (roughly 1/16 inch) did look slightly thinner at the end of that soak. It melted completely on the 1490 setting. So I'm GUESSING it melted at roughly 1490, maybe 1495. So if I increase my Austenitizing temp 15 degrees (at least when Austenitizing high carbon steels) I will be close enough. I have ordered a k-type meter and a k-type thermocouple. The meter isn't top of the line, but it seems accurate enough: Amprobe TMD-50. It's supposed to work from -328 to 2,498 degrees. The thermocouple I purchased works up to 2012F, and the business end is flexible and 12 inches long, long enough to reach the center of where I rest the cutting edges of my blade. At 1.6 mm thick, I can sneak the probe through the lower corner of the hinge side of the door: PerfectPrime TL1916SL K-Type Inconel 600 Flexible Thermocouple Temperature Sensor Probes -40~2012°F, 1.6mm / 300mm. These aren't the best tools, but I'm on a budget. I can use these tools for other projects so no big deal if they don't confirm the salt test, but I think they will. If they do then I can confirm my AEB-L temp. That should be good enough for now. However, a Rockwell tester is a must if I ever sell knives. I don't like taking people's money unless I'm confident I'm giving them something of value.

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In my opinion, if you are using a type K TC you want it to be around 3mm (8-10 gauge or 1/8"). A Pt thermocouple can be smaller, and is more accurate.

On eBay you can get an high accuracy S-type Pt-Rh thermocouple for around $60. It will handle around 1650C/3000F.
 
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Stacy E. Apelt - Bladesmith said:
In my opinion, if you are using a type K TC you want it to be around 3mm (8-10 gauge or 1/8"). A Pt thermocouple can be smaller, and is more accurate.

On eBay you can get an high accuracy S-type Pt-Rh thermocouple for around $60. It will handle around 1650C/3000F.
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Thanks. I'll report back on my findings once I get the thermocouple. I will try to confirm the salt test. If I'm not within +/- 5 or so degrees of that number I will consider buying one like you've specified and use the one I ordered for fermentation and distillation.
 
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The thermocouple actually showed that my oven is running pretty close to the stated temperatures. Maybe the +/-10 temperature swings threw off my salt test a bit. I greatly reduced the temperature swing this time by performing a test at 1950 first and then slowly ramping down to 1475F at 600F/hour. My oven readout stayed between 1473F and 1477F. The thermocouple stayed between 1470F and 1476F. At 1950 the temperature swung a little bit more, but not too bad, and the thermocouple read a little bit low but mostly in the 1940's F. So I'm going to say the oven wasn't the issue. It might be running a little cool but not enough to matter. If I want to get more detailed I'll need access to a good Rockwell tester.
 
This is what I've been working on, the 52100 blade. It was my first hidden tang knife. I've put a lot of time and thought into this one. I credit most of what I've learned from reading posts on Bladeforums.
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Blankblank said:
Get the secondary thermocouple. Its not that expensive. And it will do better for double checking temps. Than most other things.

Then of course you have to question if you trust the second thermocouple. But getting a good quality one isn't too much.
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Good job helping folks out 👍
 
HPD said:
The thermocouple actually showed that my oven is running pretty close to the stated temperatures. Maybe the +/-10 temperature swings threw off my salt test a bit. I greatly reduced the temperature swing this time by performing a test at 1950 first and then slowly ramping down to 1475F at 600F/hour. My oven readout stayed between 1473F and 1477F. The thermocouple stayed between 1470F and 1476F. At 1950 the temperature swung a little bit more, but not too bad, and the thermocouple read a little bit low but mostly in the 1940's F. So I'm going to say the oven wasn't the issue. It might be running a little cool but not enough to matter. If I want to get more detailed I'll need access to a good Rockwell tester.
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Its likely what i described without going into the real reasons behind it.

If you are actually at the salts theoretical melting point. It will need to hold there a very long time.

If you are slightly above it should melt fairly reasonably fast in comparison. (Like the 30 minute hold)
 
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