Evenheat off by 20* I was right

B

Black cat

Well-Known Member
Title pretty much sums it up.
I suspected the temperature on my evenheat was off by quite a few degrees.
I set up and calibrated my Auberins PID controller and K type thermocouple to exactly 32.0* in an ice slurry.

I drilled a hole in the centre of the front door of my heat treat oven and screwed the thermocouple into it.

I set the oven for 500* half hour soak and allowed it to come to temperature.

I watched the PID reading race to catch up to the oven temp. Around 500* the oven would hover up and down by 3-4 degrees. Reading 497-500* after about 15 minutes it settled on 499-500*

At this point the PID had settled for quite some time at 477* so roughly 23 degrees off.

So with that in mind... I'd love to hear some thoughts. I dont think the oven can be calibrated. I cant return it.
I will just run it and make the adjustments manually unless there is a reason not too.
 
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23 degrees is outstanding accuracy for a knifemaking heat treat oven.

I think I mentioned it before, but if you're not aware, heat treat ovens are rated to be +/- a given percentage, at a certain temp. That's the reason you see such varying prices for similar sized ovens. One company will have a 2-3% accuracy rating at a given temp (generally somewhere between 1000-2000 degrees) while some of the ovens sold at cheaper prices are rated at 5-7% accuracy. In other words lets say you have a 2% rated oven. When set at 2000 degrees, to fall within specifications the temp could be as low as 1960F, or as high as 2040F (2% of 2000= 40).

Generally Paragon ovens have the lowest percentage variance standard (which is why they generally cost more for the same size oven then other brands) Other brands usually fall behind a Paragon in the percentage of accuracy line up.

Your title says the oven is an Evenheat, which means you're likely well within their specifications at the temp you tested (approx 4%). When dealing with temps above 1000F, you can't expect a commercially made knifemaking heat treat oven to be "dead on"....that's just not going to happen.

For "dead on" accuracy, you'd have to go to "Lab Grade" equipment/heat treat oven.....those usually start at $2-3K for a tiny oven (one you couldn't fit a folder blade into). I've seen a couple of the "Lab Grade" heat treat ovens being sold on the used market, that where big enough for knife blades, but they started at $10K+.
 
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Oh! Ok interesting. So then... I'm prepping it to HT 1095 for a clay temper and hamon line aiming for around 62-64 rockwell. Will that range be accurate enough for that and should I go by the reading on the PID I just installed for greater accuracy?

I just tested at 1500 degrees and the PID was steady at 1455 degrees.

I'm starting to wonder if I should leave the PID hooked up and just go by that from now on.

Perhaps 59rc lol ... The more I read about HT 1095... Inconsistent, cracks, temper at 400, temper at 375, temper for one hour, temper for three hours, quench in oil, quench in hot water. Now I remember why I have a pile of 1095 that I never touch lol.
 
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I think you'll be fine, either way you go... with the PID or the oven's controller. Personally there is no way I would want a 1095 blade at a 62-64Rc.... that's just too hard in my opinion. Don't get caught up in the Rc numbers thing.... experiment and test.... I think you'll find that more often then not, those "unimpressive", lower Rc numbers will give you a much more serviceable blade then "top end" Rc numbers.
 
Thanks Ed! In the end with the hardness numbers i've been noticing the same, with practice and getting a "feel" for it you can usually find a sweet spot. When you read all day about HT and and hardness it's easy to get caught up in the numbers.
 
EdCaffreyMS said:
23 degrees is outstanding accuracy for a knifemaking heat treat oven.



For "dead on" accuracy, you'd have to go to "Lab Grade" equipment/heat treat oven.....those usually start at $2-3K for a tiny oven (one you couldn't fit a folder blade into). I've seen a couple of the "Lab Grade" heat treat ovens being sold on the used market, that where big enough for knife blades, but they started at $10K+.
Click to expand...

i agree, even lab grade are +/- 1%, a really good ones come with a "map", if dead center is 1000F, the upper right corner is 995F and so on. Main thing is SHOP, I got my Lindberg/Blue 51442 1200C furnace and controller for $80 on eBay. interior is 14x7.5x5. no one wanted to bid because they wanted $300 for freight, the shop was on my route, so i picked it up.
for the question at hand, run this test several times with the thermocouple in the same spot each time. use real world temperatures, 1475F or 800C if you do a lot of high carbon steel, 1950F for stainless. some pid controllers allow you a correction factor. if your's doesn't, write down the deviation, 1475F when furnace says 1525F.
 
There will be temperature variations in your furnace, top to bottom, front to back and so on! Comparing thermocouplers would only work if they are side bye side ?? Best place is close to where your knives are at in the furnace.
Clint
 
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