Some insight from others. Heat Treat/IDK

[Kevin McGovern]

Strange , rest of the edge is like new ? I can t see even smallest chip , like blade was never used if I can say that ? Anyway , looks like it is are very , very thin behind edge ............

are you sure you are looking at his blade and not mine? His does look like it's seen use. Mine, not so much, since it was a brand new test blade.

 

[Randy3000]

I had a hard to track down heat treating problem. Oven thermomemeters are too insensitive to detect temp swings. Also, if it is a thermometer with a base, that base absorbs the radiant heat and the thermometer may not be accurate. For example, in my old toaster oven an exposed thermocouple read 600 degrees whereas with a sheet metal blocking radiant heat it measured air temp at 400 something degrees. Modifying the toaster oven to pid controlled still experienced +/-20 degree temp swings when auto tuned and a heat shield in place. I dont really have anything to add, just wanted to mention my numbers. You hear a lot about oven inaccuracies but i used to dismiss them because i thought they would be small.

 

[Matt-D]

I had a hard to track down heat treating problem. Oven thermomemeters are too insensitive to detect temp swings. Also, if it is a thermometer with a base, that base absorbs the radiant heat and the thermometer may not be accurate. For example, in my old toaster oven an exposed thermocouple read 600 degrees whereas with a sheet metal blocking radiant heat it measured air temp at 400 something degrees. Modifying the toaster oven to pid controlled still experienced +/-20 degree temp swings when auto tuned and a heat shield in place. I dont really have anything to add, just wanted to mention my numbers. You hear a lot about oven inaccuracies but i used to dismiss them because i thought they would be small.

Thanks for sharing. I definitely want to convert a toaster oven to pid in the the future if I don't just build some tempering oven of my own first. Got my thermometer (pyrometer) and still have to test my oven. See how it goes. I can now more "accurately" do forge temps too since I bought some thermocouples for that too.

 

[Matt-D]

I had a hard to track down heat treating problem. Oven thermomemeters are too insensitive to detect temp swings. Also, if it is a thermometer with a base, that base absorbs the radiant heat and the thermometer may not be accurate. For example, in my old toaster oven an exposed thermocouple read 600 degrees whereas with a sheet metal blocking radiant heat it measured air temp at 400 something degrees. Modifying the toaster oven to pid controlled still experienced +/-20 degree temp swings when auto tuned and a heat shield in place. I dont really have anything to add, just wanted to mention my numbers. You hear a lot about oven inaccuracies but i used to dismiss them because i thought they would be small.

I used to not worry about tempering temp swings either, but since I've had two issues (though I think this one is different than the first which was probably related to my method more so -to a degree anyway-) I really want to check it out and make sure it's more perfect. Honestly I'm not sure if it really matters as much (having things "perfect" in every way shape or form) if customers don't abuse or use extreme use knives, it's always nice to be sure of ones methods though.
Anyway,

Thanks to everyone so far for sharing!

 

[Randy3000]

Thanks for sharing. I definitely want to convert a toaster oven to pid in the the future if I don't just build some tempering oven of my own first. Got my thermometer (pyrometer) and still have to test my oven. See how it goes. I can now more "accurately" do forge temps too since I bought some thermocouples for that too.

I dont really like my toaster oven converted to pid control. The pid just isnt able to maintain steady temp. This is with a thin sheet metal in center of rack, with a WW shaped bent piece of sheet metal with thermocouple sticking inside one of the V and the blades in the other V's.

 

[javand]

I dont really like my toaster oven converted to pid control. The pid just isnt able to maintain steady temp. This is with a thin sheet metal in center of rack, with a WW shaped bent piece of sheet metal with thermocouple sticking inside one of the V and the blades in the other V's.

Randy, it should be?

I did insulate mine in between the inner and outer sheet metal housing.

I will say this, I originally had an Auberin's ramp/soak controller in mine, it worked great. I needed the ramp/soak controller for an industrial HT oven I was converting from manual controls, and didn't want to buy another, figured I didn't need those features on a tempering oven, so I bought a cheap ebay PID to stick back in the tempering oven. It's a total POS. I've tried re-tuning it, it'll hit and nail some temp fine, but every once in a while, whenever I open the oven to put something in, or check something, when the temp swings down, it'll run the element full bore, and skyrocket the temp a couple hundred degrees and then show me an error message, typically, with the SSR still pushing power.

Gonna definitely have to replace it, and I've learned my lesson trying to cheap out. However, when it works right, or when I start it cold, it'll hit, and nail exact temp within 1 degree, and with the previous controller it was always right, without any significant overshoot.

Have you tuned yours? Is it a cheap-o-china-special from ebay or amazon like the one I'm having issues with?

 

[Randy3000]

Randy, it should be?

I did insulate mine in between the inner and outer sheet metal housing.

I will say this, I originally had an Auberin's ramp/soak controller in mine, it worked great. I needed the ramp/soak controller for an industrial HT oven I was converting from manual controls, and didn't want to buy another, figured I didn't need those features on a tempering oven, so I bought a cheap ebay PID to stick back in the tempering oven. It's a total POS. I've tried re-tuning it, it'll hit and nail some temp fine, but every once in a while, whenever I open the oven to put something in, or check something, when the temp swings down, it'll run the element full bore, and skyrocket the temp a couple hundred degrees and then show me an error message, typically, with the SSR still pushing power.

Gonna definitely have to replace it, and I've learned my lesson trying to cheap out. However, when it works right, or when I start it cold, it'll hit, and nail exact temp within 1 degree, and with the previous controller it was always right, without any significant overshoot.

Have you tuned yours? Is it a cheap-o-china-special from ebay or amazon like the one I'm having issues with?

It is an auber instruments pid. Same one i put in my HT oven that holds exact temp flawless. I insulated 5 sides of the oven with roxul (didnt do the door). I auto tuned by setting At=2 and letting it do its thing. If i remove the sheet metal and let the radiant heat hit it it holds temp fine. Maybe i should do that?

 

[javand]

It is an auber instruments pid. Same one i put in my HT oven that holds exact temp flawless. I insulated 5 sides of the oven with roxul (didnt do the door). I auto tuned by setting At=2 and letting it do its thing. If i remove the sheet metal and let the radiant heat hit it it holds temp fine. Maybe i should do that?

Maybe, not sure why it would be causing a problem unless it's obstructing the TC. The one I have has an element in the top and the bottom, but some only have one. If you only have one, and the TC is separated from the element by the sheet metal, then that may be the issue. Adding some thermal mass to a larger HT oven, on the floor, where it's not blocking anything, can help prevent huge swings, but with a toaster oven, i think it's best to just let it be, what it is. Although I also use some pieces of sheet on the rack for convenience, so I can leave blades spine down, edge up for even heat and less potential warp.

 

[Randy3000]

Maybe, not sure why it would be causing a problem unless it's obstructing the TC. The one I have has an element in the top and the bottom, but some only have one. If you only have one, and the TC is separated from the element by the sheet metal, then that may be the issue. Adding some thermal mass to a larger HT oven, on the floor, where it's not blocking anything, can help prevent huge swings, but with a toaster oven, i think it's best to just let it be, what it is. Although I also use some pieces of sheet on the rack for convenience, so I can leave blades spine down, edge up for even heat and less potential warp.

I have started thinking recently i may be misunderstanding the fear of radiant heat, and i think your post sort of confirms it. I can see in HT ovens where temp can change 100 degrees very fast, temp swings from radiant heat can be a problem. But the toaster oven does take a long time, comparatively, to begin heating the space, so maybe it just isnt a big deal for toaster ovens.

 

[javand]

I have started thinking recently i may be misunderstanding the fear of radiant heat, and i think your post sort of confirms it. I can see in HT ovens where temp can change 100 degrees very fast, temp swings from radiant heat can be a problem. But the toaster oven does take a long time, comparatively, to begin heating the space, so maybe it just isnt a big deal for toaster ovens.

I've read some of what I think has probably helped to contribute to that concern, and while I think it may be a mild factor at austenizing temps in a high powered 220V furnace, with elements very close to the work piece, I still think it's massively overblown. Decarb at those temps is a much more real problem, that possible grain/overheating issues. Most steels can easily survive sustained times at several hundreds of degrees higher or more, during forging or forge welding, and all it takes to bring those concerns back in order, is a bit of care and consideration. Even if the exposed surfaces momentarily peak a few hundred degrees above temp (an extreme example), conduction is mitigating that, otherwise TCs would be evening out to much higher temps. If hypothetically the last few thou on the exposed edges are getting overheated in the steel, it's irrelevant, because you'll already be dealing with decarb that has to be ground away, unless you're austizing out of a salt pot or similar, with controlled, conductive media, where IR heat spikes can't be an issue. Regardless, even further, austenizing temps are "sweet spot" targets, balanced with times at those temps, designed in broad strokes, for general equipment baselines.

Many steels will respond better higher temps with super short soaks, in the case of simpler alloys, like W2, or lower temps with much longer soaks, in the case of many more complex alloys.

All this to say, don't sweat that shit you read. It wasn't invalid information, just blown out of proportion, because of tunnel vision.


If you really want to add a baseline of certainty, get a hardness tester. That'll at least tell you if you're hitting max potential RC with your austenizing temps, and the appropriate subsequent RC with the "by the numbers" tempering temps. It won't guarantee grain size or the homogeneity of the steel structure, but there are other ways to test that. Assuming you're leaving enough material to clean up any potential decarb made during that process, you'll have nothing to worry about from any hypothetical IR based or other temp swings that don't show on the instruments, manifesting in the work.

In the case of the source material I suspect you've been reading, I recall they were talking about tempering in a 220V HT furnace, and were seeing momentary spikes when using more sensitive equipment. It's a valid concern, but I still think conduction of the steel takes care of it, assuming you don't have wonky equipment. In that case also, the concern was IR based spikes from direct LOS of the elements, but still, if you're tempering after austenizing, you're going to remove any material that may have theoretically gotten significantly hotter for a fraction of a second, and regardless, it's temperature *and* time, that ultimately determines the temper.

 

[Randy3000]

I guess the very real and clearly measured +/- 20 degree temp swings caused by trying to block radiant heat is worse than the undetected boogey man, and will take out the shield. I have only tempered twice in the toaster oven with the shield so far. Thanks for putting my mind at ease.

 

[javand]

I guess the very real and clearly measured +/- 20 degree temp swings caused by trying to block radiant heat is worse than the undetected boogey man, and will take out the shield. I have only tempered twice in the toaster oven with the shield so far. Thanks for putting my mind at ease.

My toaster oven does actually have tiny inverted V shaped shields covering each element fwiw Randy, without any issues you mention. Maybe try something like that, if you're still concerned, but I don't really think I'd bother.

 

[scott.livesey]

Thanks for sharing. I definitely want to convert a toaster oven to pid in the the future if I don't just build some tempering oven of my own first. Got my thermometer (pyrometer) and still have to test my oven. See how it goes. I can now more "accurately" do forge temps too since I bought some thermocouples for that too.

damage look like abuse. nail or rock. for thermocouples and related wiring stuff best selection is at McMaster/Carr https://www.mcmaster.com/#thermocouples/=1dvsnyl i have several and have had no issues. for displays go to amazon. don't overthink tempering. verify your temperature, run toaster oven in convection mode, protect blade from direct radiation of elements(i just use a tray above and a tray below). pid control will be a nice project if you want to learn wiring and controller programming, but not essential for making a good blade.

 

[MoSmith]

I'm using a toaster oven for tempering as well and couldn't keep the temps from swinging wildly whenever I opened the thing. I finally got a couple of pieces of heavy flat stock (.25") and put them in the oven. I turn the oven on early and use a temp gun to measure the slabs. When the slabs are up to temp I sandwich the blade between them. It's still tough to make an exact temp but the steel slabs keep the swings from messing-up the temper.

 

[Stacy E. Apelt - Bladesmith]

People spend far too much time worrying about temperature swing in ovens. Unless the swing is over 100F and the cycle takes 10 minutes, it probably won't change the final hardness any detectable amount.
Swinging +/- 20 degrees over a five minute cycle won't even be noticed by the steel.

The difference in a two hour 400F temper and a two hour 450F temper is barely over 1 point. I get a chuckle when folks suggest raising the temper 5 or 10 degrees to get a less chippy blade. (To be honest, I used to think that before I learned more metallurgy).

 

[Matt-D]

People spend far too much time worrying about temperature swing in ovens. Unless the swing is over 100F and the cycle takes 10 minutes, it probably won't change the final hardness any detectable amount.
Swinging +/- 20 degrees over a five minute cycle won't even be noticed by the steel.

The difference in a two hour 400F temper and a two hour 450F temper is barely over 1 point. I get a chuckle when folks suggest raising the temper 5 or 10 degrees to get a less chippy blade. (To be honest, I used to think that before I learned more metallurgy).

Thanks for sharing! assuming that's 99% true that would save me a lot of money and headache building a "perfect" tempering oven. Always better to get things more spot on I suppose, but truthfully I don't know. Nice to have a little pyrometer to at least help give me an idea now. My kitchen oven does do the + or - 20 degree swings it seems within a 5 minute cycle. Though if I open the oven, let heat out, close it again and then let it re-stabilize I'm not sure if it ever quite reaches it's set temperature since the little orbs (or what every judges the temperature in an oven) must be a little hotter than the oven itself.

Does two hours vs one hour cycles really make that much of a difference? I could understand how more time is better but just wondering if that's the case with carbon steels and how much it really adds? Even the stickies only recommend 1 hour cycles.