Heat Treat Oven Build

Big Smitty

Big Smitty

Joined
Aug 30, 2007
Messages
509
I want to build a heat treat oven and checked out a couple of tutorials on the net. I am looking for some help from some of the experts here.

Most of the ovens that I see are 240VAC and then I reviewed the paragon oven that is 120VAC and have seen some good reviews on its performance. I would like to build a 120VAC oven so I do not have to upgrade my electric.

Can anyone give some specific direction on how to design and where to purchase the heating elements, PID, SSR, thermocouple, ect... I have a good handle on building the oven with the soft fire brick and just need some good, specific direction on the heating element and controls. I am thinking the size will be 4"X5"X18. Thanks!
 
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The PID, SSR, and thermocouple can be easily purchased online. If you have a real good refractory supplier in your area, you may be able to find some things locally, but expect to pay a good bit more.

The following links come from the site where I purchased my TC and they also have the PID similar to mine for a good price.

Here's pretty much what you need:

K-type high temp thermocouple

Good looking PID with programable ramp/soak

And they also have SSR's. You could go for a cheaper PID if necessary. My PID doesn't have ramp/soak programming, but has worked so far. Just have to set it manually.

Hope this helps.

--nathan
 
Oh, and HERE is a great place to buy the Kanthal element that you need if you don't want to coil your own (#7101). One coil will run on 120VAC and deliver 1550 watts.

I've not heard of many building a 120VAC kiln. I know there are some out there to buy, but I'm not sure how a custom built oven will do. I can tell you that 220VAC will get you to temperature (especially for stainless where you're in the 1900* range) much much faster.

--nathan
 
I have an Evenheat now but used to use a 110v Satellite heat treat oven with manual control. I just purchased a PID new thermocouple and SSR and heat sink from Auber. It took me about a hour to retrofit the oven and I will be using it on heat treat days for my spring and blade tempering.

The cost to convert was a total of $84 dollars including shipping for the parts from Auber.

If I knew then what I know now I would have been inclined to build my own furnace.

I think I would opt also for the more expensive pid and get programmable ramp and soak times.

Good luck on building your 110v furnace. My Satellite would get up to 1450(O1 1095 etc) in about 20 minutes, but to get to 1950 took almost an hour.

Ken
 
Thanks guys. I know the 240VAC is the better way to go, but I am in elcheapo mode for now. I suppose I could upgrade a 120VAC to 240VAC later if need be by changing a few of the components. if anyone else ahs info or comments please post.
 
Get an SSR that will handle 30 amps at least. To get 20 amps from 110 you need 5.5 ohms of resistance. To last very long at 20 amps your wire needs to be at least 16 gauge kanthal A1. You would need about 17 ft of 16 gauge for 20 amps at 110v or 26 ft of 14 gauge to stay under 20 amps. Later you could upgrade by going to 50' of 14 gauge wire. and 220v That would use a bit over 20 amps and be smoking fast. I use 50' 14 gauge (.213 ohms per ft)and 220v and hit 1500 in under 10 minutes. It runs a bit over 20 amps. My oven is 22" deep and 5"x5" You could use 20 amps of 110 and get 2200 watts. I would keep the oven small say 4x4 x 12 for 110 or it will be very slow. The better you insulate it the better it will work. I used soft fire bricks and then an inch of Kaowool in a steel housing I fabbed to size. I can remove my top if I need ever to work on the interior. I used smaller wire first shot and it burned up after a while when I started going to 1850 and holding it for D2. Don't scrimp on the wire.

I get my wire from

Pelican
http://www.ec-securehost.com/PelicanWireCo.Inc./Miscellaneous_Requests.html

Thermocouple, SSR and PID from
http://auberins.com/
 
Thanks 1b2

Where did you get the math for figuring the amps, watts, volts ...? I would like to learn if possible. You mention 2200 watts at 20 amps and 110VAC, how many watts are you getting on your 240VAC oven? Sounds to me like I need to go to a larger guage wire to increase resistance at the low 110VAC which pushes up the amps.
 
You can take the long road to learning the formula's and applying them or if you want a quicker way to the answer, try this calculator out that I found online.

http://www.opamplabs.com/eirp.htm

If I remember the formula's correctly from trade school... which was some time ago....

E
-----
I x R

where E= voltage
I= amperage
R= resistance

You need to know 2 inputs to get the 3rd. So when using the formula, if you were looking to find the current flow (amperage) through the circuit, the formula would be E/R=I. If you were looking for the voltage required, the formula would be IxR=E. If you were looking for resistance in the circuit the formula would be E/I=R.

To figure out wattage the formula looks like this

W
-----
E x I

Where W= wattage
E= voltage
I= amperage

The formula works the same way as the last one. So, if you are looking for wattage of the circuit the formula would be ExI=W.

My brain hurts now :D .....I think you will find the calculator a much easier way unless you are going to be using electrical math regularly.

Brad,
www.AndersonKnives.ca
 
Smaller wire has more resistance than larger. Think of larger wire as a bigger pipe. !4 gauge kanthal A1 has .213 ohms per ft, 16 has .339, 17 has .427 per ft, 19 has .679 per ft. Amps times volt is your watts. To figure out what you need. do this. Watts divided by voltage gives you amps. Voltage divided by amps gives you ohms need to run that many amps. Ohms divided by ohms per ft gives you number of ft of wire need. The heavier the wire the less resistance so the more feet of it you need to have the nesssary ohms to keep your amperage down. But this is how it goes

26 ft of 14 will get you 20 amps at 110 50' will get you about 20 at 220v
17 ft of 16 will get you 20 amps at 110 34' will get you about 20 at 220v
8 ft of 19 gauge will get you 20 amps of 110 and burn up in a couple firings

double the voltage and double the length my 50 ft of 14 gauge is .213 ohms per ft for 10.65 ohms 220volts divided by 10.65 is 20.66 amps 20.66 amps times 220 volts is 4544 watts.
If the wire is 2 small in diameter it will burn up with amperage. Wire really doesn't care about the voltage. It cares about the amperage. A piece of 16 gauge wire will take 10,000,000,000,000 volts at 10 amps it will burn up at 1 volt it is carrying 40 amps. In a heat element they work together because the voltage determines the amperage, but the amperage can be lowered by using a longer wire and increasing the resistance. So remember the diameter of the wire is what determines the amps it ill carry and not burn up. The diameter also controls the ohms per ft. The length is how you regulate the total ohms and therefore the amperage.

Clear or really confused/ LOL


I=amps
E=volts
P=watts
O=ohms or resistance
P=IxE
I=P/E
E=P/I
E=OxI
I=E/O
O=E/I
to get correct O (ohms)figure out how many Ohms you need and divide by the Ohms per ft for that gauge wire.
14= .213 per ft
15= .269 per ft
16= .339 per ft
17= .427 per ft
19= .679 per ft
 
The thing to remember is that watts are what heats the chamber not volts. It doesn't matter what voltage you use to get to the wattage that you are using to heat the chamber 2200 watts will heat a 2 cubic foot chamber in y amount of time and it doesn't matter whether you are using 20 amps at 110 volts or 10 amps at 220 volts. the only way that 220/240 volts will heat this same size of chamber any faster is by increasing the wattage through increasing the amperage. if you use the same heating element for 220 volts that you used for the 110 volt then you will double the wattage of the oven and decrease the heating time though not by half.

The biggest reason to use 220 volts in making an oven imo. is that for a given wattage you will draw half the amperage through your shop wiring ie.. 10 amps @ 220 volts vs. 20 amps @ 110 volts this creates less heat and stress on the wiring and service panel in your shop.
 
What Bill says is true. But here is a couple things, you also need to consider. The more watts the faster it will heat ant the bigger chamber it will heat. You are pretty much limited to 20 amps with 110. So 2200 watts is your limit. With that many watts you have a choice between a small oven that heats with in a decent amount of time or a very slow bigger oven. That's why I said a 4"x4" x 12" or 14" for a 110 unit. You don't want your oven to take an hour or more to hit say 1850 for D2. Even if you only do say 5160 you don't want to take a long time to get to 1525. An ovens temperature goes up slower the hotter it gets. The time from 1300 to 1500 will be a lot more than the time from 300 to 500. You don't need your steel to be cooking and decarbonizing for no reason. If I was to built a 110 oven I would keep it small and well insulated and built it in such a way as to be able to make it longer in the future when 220 was available. One coil made from 26 ft of 14 gauge wire would be best, one of 17' of 16 would be ok in my opinion. I coiled my wire by putting a long piece of all thread in my lathe and turning the lathe as slow as possible I fed the wire onto the threads. When I ran out of length on the all thread I simply removed the coils and started again from the other end of my 50' of wire. Good luck and let us know how it goes or if you have more questions. Jim

PS I know Bill just threw out the 2 cubic ft number as an example, but, that would be huge and take a lot of time of watts to heat.
 
I have a couple of questions about building a HT oven. I have been wondering why someone could not build a gas ht oven. This may be a stupid idea, but we have gas ovens so why couldn't you build a gas ht oven. Just curious if someone has ever thought this out or even tried it.

The other questions is where is there some plans to build an electric oven? Thanks.
 
You can HT with gas. Basically a modified forge. One way is to make a chamber (muffle) inside the forge for your pieces. You can control the gas with a pid, thermocouple, SSR and a solenoid valve. Some use a similarly controlled gas setup to heat and melt salt and then place their piece in the salt to heat to quench temps. I like my electric because it is simple, save and keeps a very close temp. It can hold within 1 degree at 1850. I am sure that a good gas oven or a salt pot can do the same.
 
Thanks for all the info guys! I need to play with the math a bit, but the general message is recieved. At this point I am now interested in a gas forge with a PID controller as 240VAC is not an option for me at this time. I need to do some learning on the gas forge as this might be a good way to go for my circumstances.
 
Smitty, I didn't mean to scare you completely away from a 110v oven. I think you could built one to the dimensions you started with. It would just be a bit slow. A controlled gas forge with a good muffle setup would be more versatile than just an oven though. I saw in another thread where Bladsmth is going to post a how to on a controlled forge soon.
 
I just read that too. If I had just need to be alittle more patient before jumping into the middle of a thread. :) Thanks for the info.
 
I built a PID controlled forge that I was planning to use as a salt tank/forge combo.

http://andersonknives.ca/Digitally Controlled Forge.html

It is PID controlled and runs a SSR to actuate a gas solenoid. What I found from building this particular unit is that it's a bit on the large side for a forge but if used as a salt pot it would cut down on the area inside and I think it would be an acceptable size.

It does reach forging temps but takes a while to get there and is a propane pig. When I designed the forge I used 2 venturi burners and it relies on the heat of the forge for auto ignition. Auto ignition is a hit and miss situation on it (self ignites 99% of the time) and a pilot circuit of some sort would certainly help.

If you end up deciding to go with a gas forge setup for heat treating, ( personally I would recommend an electric oven), you should do the research required to make a blown burner rig. It is a much more complicated design but has the advantage of using much less gas. When using a blown burner you have to make a timed circuit for the blower that coincides with the gas valve on/off cycle. I recommend you seek out some of the knifemakers that are using gas salt pots for advice, as they are most certainly using that exact setup.

If you plan to use the forge for tempering as well, a venturi burner/ auto ignition setup wont work, it will have to have a pilot.

For the time, effort, and money you would sink into making a gas heat treating setup, you could probably run 220 volts out to your shop. If you plan on making more than a few knives, eventually you will most likely end up wanting 220 volts out there anyway to power all the other tools you will aquire like a belt grinder, compressor, milling machine, etc.

Brad,
www.AndersonKnives.ca
 
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