Buying a Heat Treat Oven, Caution: stupid questions follow

Redmeadow Knives

Redmeadow Knives

John Conner
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Knifemaker / Craftsman / Service Provider
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I've been researching heat treat ovens and have a few questions (around a million actually). I'm looking at the Evenheat KF13.5 and the KH 414. I use O1 mostly but would like to try out some 1095 as well.

The Evenheat models in 120v have a .22 Cubic feet chamber, while the 220v models are .51 cubic feet. Will these chamber dimensions "even out" when it comes to heat times? Since the 220 is over twice the volume, will the 120 with the smaller volume be that much slower to reach the same temp? It seems to me that the 220 would still be faster regardless of volume, but if I knew what I was talking about, then I wouldn't be asking questions.

How much does shop temperature affect heating? When we are talking about getting to 1500+ degrees will an indoor shop temperature just above freezing affect things? Will this low air temp affect results when moving between a hot Oven to a warm quench?

I am looking for factors where the 220 model will really outshine the 120. I am leaning towards the 120v but would like to hear opinions from you guys.

Or is this a case of: "think less, grind more"

Thanks in advance
 
I was using a 110v kiln (can't remember brand) for all the stainless HT'ing, but would get EXTREMELY frustrated with the time it would take to heat up. Getting over 1700 was the painfully long part, from what I remember. The temps are @1950 so they are higher than what you would use for HT carbon steels, but why limit yourself if you didn't need to when the $ is similar for a 220v. I know it wasn't a Paragon or an Evenheat, so I am not sure how their 110v units work, but the one I used was marginal at best. And yes, the cold shop would effect the time to heat up on that unit, but more dramatically at the higher temps. I bought a 220v Evenheat kf13.5 about a year and a half ago, and love it. Heats up quickly, even with a cold shop.
 
220VAC will always be a better choice in HT ovens. Faster, hotter, bigger, often better built.
 
My shop gets pretty cold also. The difference of the outside temp doesn't change that much because of the ovens insulation, how ever much time it takes your oven to go from 32 to 85 is about it. Even after running my oven at 1850 for an hour its not that hot on the outside skin. More trouble warming the quench oil if doing carbon blades. I never worry about the cold room temp when moving blade from oven to quench as air is a poor heat conductor and is just starting what you are going to finish with the quench.

I would go with the 220 unit. twice the power and twice the space. I will bet that a 220 oven heats considerably faster even with the increased room. Your not just heating the air but also the inside part of the insulation. Look at it this way. If I had a 6"X6"x6" sq area and it takes 2" of insulation to absorb 90% of the heat. Thats 10"x10" for the top and bottom and 6"x6" for the ends or 272"sq inches and 544 cu in total volume of insulation that is absorbing heat. If I make the chamber 6"x6"x12" I now need 10"x16" top and bottom and the same 6x6" ends so 392sq" and 784 cu in of total insulation. So the large oven only has to heat 44% more insulation with its doubled power. The little bit of air either heats doesn't really take much of the power. These ovens have thicker insulation than 2" and the 90% in 2" is just a guess, but the effect is the same if the 90% occurs in 1" or 4"
 
What you need to look at is the power output or the wattage of the ovens. if they are bothe the same then THERE WILL NOT BE A SIGNIFICANT DIFFERANCE IN THE TIME IT TAKES TO HEAT A CHAMBER OF EQUAL SIZE. If the 220v oven with the large chamber has the same watt/power as the smaller chamber 120 volt oven then the 220 volt oven will heat SLOWER than the 120 volt oven. On the other hand if the 220 volt oven has a higher wattage heat coil in it it will heat faster. How fast depends on the wattage.
 
Man I love this place, articulate responses, exactly what I was looking for. It sounds like 220v is the way to go without question. The wattage on the 220 is twice that of the 110 so it should definitely heat up faster. Thanks for the help gentlemen. From what I gather so far it looks like O1 uses a 10+ minute soak at 1500 degrees, an oil quench, and 2 temper cycles around 400?
 
I have the KF 18 and love it. I would look at getting at least an 18" oven. they are not that much more and you'll have room to do larger blades. Believe me you will kick youself in the future for buying a 13.5" oven when you want to heat treat that compition chopper thats right at 15" long. I would but the 22.5" if were to do it over again. Don't forget to get the blade fixture to keep your blades upright and from just laying them flat on the bottom of the oven floor.
 
Another thing that is often stated is that they don't get all that hot on the outside. That may be so for a short soak at 1475F ... but after the pre-heat soaks, and austenitization at 1925F for an hour THEY GET HOT (enough to burn you bad).
 
I considered the 18" model, but I think it would be very rare for me to make anything over 13". I just finished grinding a request for an OAL of over 10", and I'm not sure that I would ever get into anything over 13". My thought was if I do on rare occasion grind out anything over 13" I could send it out individually. But you make an excellent point, why limit myself? I'll take that into consideration.

I will be ordering the blade fixture as well. Are there any warping issues when leaning the blades against those fixtures? I warned you, stupid questions would follow!

Good point on the heat, at this point I will have lower temps with the O1, but I would like to try other steels at some point.
 
I went ahead and ordered the KF18 240V with Rampmaster from Tru Grit. I don't foresee needing to upgrade from that model.
I'm sure I will have a "what the heck am I doing wrong here? thread" in a couple of weeks when I get to heat treating. Hopefully things will run smooth, but Murphy usually stops by.

Thanks again for the help and opinions.
 
You made the right choice in getting the KF18. I bought the KF14 using the logic that I would rarely need anything larger. Which is true but I would rather have the option of being able to make something larger. I can only heat treat bowies that are about 12" long.
 
lessismore said:
I will be ordering the blade fixture as well. Are there any warping issues when leaning the blades against those fixtures? I warned you, stupid questions would follow!
Click to expand...

I rarely lean them up against the posts. I would rather they stand up on their own on the spine. The posts are there to keep them from falling over in the oven should you bump one while getting another out.
 
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