homebuilt heat treat oven...

S

SkaerE

Joined
Sep 9, 2001
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not a forge, but an oven. not just a tempering oven, but a kiln-like oven that can be used for annealing, normalizing, and hardening. im sure it would be tricky, but has anyone here done it? i read that some feller at CKD forums did, but no info on how...

so, any info?
 
Moore, could you post some pics of your gas oven and the controls? I would like to make a natural gas oven and am in need of ideas. TIA
Ken (wwjd)
 
Skaer,Try Meta-Machines,P.O. box 2037,Whitefish, Mt 59937.They had plans and infro a few years ago.Tried a web search but did not come up with anyfurther infro.
 
Electric is far better, especially if you plan HT stainless steels.
You can easily attach a computerized control unit to an electric kiln, which can manage precise heat increase and decrease slopes and maintain a correct temp within a few tenths of a degree.
Such control units can be found in glass or ceramic working hobby stores easily, even if they are quite expensive.
 
There is a book "LI'L Bertha a Compact Electric Resistance Shop Furnace" by David J. Gingery. Published by Lindsay Publications. Worth reading the 69 pages of how to. Thinking someday I might build one?
 
I built my own electric HT oven and I am in the process of making it bigger.

I used stacked insulating firebrick held down to a thick sheet metal plate with threaded rod. No fancy doors, just more stacked brick. I cut groves into the IFB with a 3/8 inch dovetail bit and a hand drill.

I used Kanthal elements which are good to 2300 degrees (3100 watts 220V)(Elements)

I got a new Omega digital controller off of eBay for $90 and used stainless steel bolts(through the IFB) to connect the elements to the wiring.

My total for the controller, a box of bricks, solid state relay, the element, and the bolts was less than $200. The controller is good to + or - one degree and the interior oven size is 4 x 4 x 18.

I am going to mak a bigger one to try to do some mokume in the oven instead of in the forge. It will have inside dims of 13 x 9 x 18.

Hope this helps.
 
hey Laredo nice job. thats a good link too. that heating element working well for you?

couple of questions:

is it portable at all? must be heavy as sin

so the door is just a bunch of stacked bricks?

soft fire brick or the hard kind?

have any pictures of your setup?

thanks.

one more thing: how hot does an oven need to get? i only have access to a 110/115 outlet right now. no 220 for me, not yet. seems i can get a 110 element that will go to 1400 deg. too low for hardening anything? suppose i can always build a forge instead :)
 
ok, back to this idea.

found this: Element, Kanthal, 120 Vac, 1550 Watt, 2300 °F Max

runs on 120 (which is what i have) and goes to 2300 degrees, plenty hot.

hey Laredo, have any pictures of your oven? is this the element you used? how long does it take to get up to hardening heat?

thanks again
 
I have some pics that I will post tonight when I get home from work. I am going through and rewiring it for the fourth time this weekend. The biggest problem I am having is getting a good solid connection to the elements. I have six individual elements in the new ht oven, all wired in series. I have ss 8-32 bolts going through the wall of the furnace to make my connections to the elements. The onlything I have to tighten to is the soft fire brick so I cannot get a real good tight connection. So what i did is order some 1/4 in ss tubing with 0.035 wall and will use that as a bushing around the ss bolt and be able to tighten against that.

I used a kanthal element that was 3100W in my little furnace (4x4x18) and that guy got to 2000 deg in about 5 minutes. I now have about 3600W in the big ht oven and have gotten it to 1600 deg, but it took about 2 hours and then the elments burned out because of that bad connection. I have also insulated the outside of the oven with Kaowool stuff to help her get to my target of 2000 deg.

Yup the door is just stacked brick, and it is not very portable. The little one was ok to move around but this big one is heavy.

anyway, I will get you some pics.

More to come later......
 
hey, here are the picks. Since these picks were taken, I have added a couple inches of kaowool to the outside of the oven and a sheet metal "box" for it.


The top bricks are "pinned" with 3/8 inch ss steel rod

furnace1.jpg



The groves for the elements were cut into the bricks with a 1/2 or 3/8 inch (i can't remember which) dovetail router bit using my drill press

furnace2.jpg



furnace3.jpg


Hope these help
 
just to let all the interested know, I just got done putting in the ss tubing as a bushing around the screws. This allowed a solid mechanical connection to the heater elements. She has been running for a while with no problems. I think that did the trick.

Also, I did use a 1/2 inch dovetail router bit to make the grooves. Tomorrow i am going to put the kaowool insulation back on and she what kinda temp it can get to. Keep your fingers crossed for that 2000 deg target.:)
 
so what temps could you reach before?

is the controller a simple "plug in" kinda setup? (doesnt take much electrical know-how to hook up to the elements)

thanks for all the great pictures
 
Hura for you guys making your own kiln/forge/oven. I flurted with making a kiln before I bought my Even Heat. I had enough bucks at the time and wanted to spend my time learning knife making instead. I did make a very small propane forge for HT simple carbon tool steels before buying the kiln.

I really like this thread and will watch for it to fall away and then print it for my records.

Hat is off;

Roger
 
SkaerE, whenever you work with electricity you need to be very carefull! If you don't feel confdent doing it yourself, find a buddy that knows electricity to help you out. That is what i did, for wiring the stuff into the breaker box.

Wiring the elements is not difficult. The element that you described above, will use about 13 amps at the 120V and has about 9.3 ohms of resistance. The max temp will be dependant on the ht oven size and how well it is insultated. If you keep the element in one single piece, you will be fine. If you cut it into multiple pieces, you have to wire them in series so that the resistance is additive. If you wire multiple elements in parallel, the total ohms resistance is less than what you started with and you will melt your elements becuase more amperage will run through them. Go here for the difference between series and parallel wiring.

I think one other thing to take into consideration is the interior size of the oven. At least how far your elements are going to be from what you are heat treating. When my ht oven was 4 x 4 x 18 i was mostly trying to fire blue the furniture for a dagger. Steel is supposed to blue around 550 to 575. I would set my temp on the the oven to 550 and would not get the color I wanted. I tried all different combinations of temp and time. What i finaly found that worked was set the temp to 750, and just checked the piece for color every couple minutes until it was what i wanted.

The only thing I can figure out is that in the 4 x 4 oven, the piece was so close to the elements that the surface of the piece was getting overheated by the radiation from the elements. With the big oven last night, I set the temp to 550, put the steel in, came back an hour later, and it was blue.

Budget casting supply sells rheostat type controllers, and other ceramics places sell the pyrometers. I use an Omega digital controller with a solid state relay to run mine. It is a smple controller, basically on and off, none of that fancy ramp and soak stuff. If i ever get into ss and other complicated alloys, i will probably buy a controller that is programable.

Anyway, let me know what other questions you might have, and hopefully I can answer them.
 
Just an update on this project. I finally got her to 2000 deg last night. It took about 3 hours to get there. After an hour it was at 1350 and then really slowed down after that.

This whole project was not as simple as I thought, I had to do alot of relearning of all the electrical theory that I had forgot from school. Anyway, I am deciding on my final configuration of elements and then I am going to go through and wire it all up, again, but with High temp wire. Normal electrical wire just does not cut it.:)

If you all are thinking of making your own and need some help, shoot me an email and I will help you do some calulations.
 
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