Designing a HT oven

D

deker

Joined
Nov 14, 2005
Messages
3,496
So, I've made the decision to build a HT oven, and now I'd like to see if you folks might help me answer some questions or think of important things so I don't miss them.

This will be a long post, so turn back now if you don't have a few minutes :)

I've chosen (and bought) a controller. It's the Omron E5AX. I've got one already that is in use as a pyrometer for my gas forge and have manuals for them handy. It's a complete digital process controller and can support lots of types of outputs for heating element control (I figure I'll probably go with solid state relays). It also has a serial port on the back of it so that I can connect it to a computer for configuration, logging, and control. There's even a company who makes reasonably priced ($100/license. You need a license for each controller though :() control software for this controller. I may give a shot at writing my own though (hey, I ain't a computer geek for nothing!). With computer control I can do all the fancy ramping/holding I want.

I think I have a handle on all the math for how much heating element wire I need based on some assumptions made fom the specs on elements at Budget Casting Supply.

Here's where I need your help folks. What would be a good target for interior chamber dimensions? I was thinking I'd like a chamber about 24" long (just in case I decide to make something with a 14" blade or something....it'd leave me a little wiggle room). So something roughly equivalent to an Evenheat 22.5. What I'm not so sure I need is the 10" chamber width. Could some of you folks chime in on this chamber dimension bit? It sure would be helpful to learn from practical experience BEFORE I start cutting up firebrick.

I'm open to any suggestions. I plan to do a thread on some forum or another on the build similar to what I did for my grinder build once I get it all figured out.

-d
 
have you tried to find the software online? being a geek myself i know you can pretty much find any software you want for free if you just look hard enough. what is the software called and i can help you try and find it. if i find it you will be getting an email from me.
 
PimpinSquee said:
have you tried to find the software online? being a geek myself i know you can pretty much find any software you want for free if you just look hard enough. what is the software called and i can help you try and find it. if i find it you will be getting an email from me.
Click to expand...

Being a guy who's had to do that kind of work for a living for a small company before, I'd never take food out of the mouths of the developers. It takes a lot of work to write good software, and these guys are a small company. As close as I'd get in this case is writing my own (and releasing it for free witha BSD style license).

-d
 
deker, do you have Andy Gasciogne's "furnace build" pdf?
 
fitzo said:
deker, do you have Andy Gasciogne's "furnace build" pdf?
Click to expand...

Yup! Been staring at the pics in it trying to get an idea for dimensions and the required firebrick Tetris. I'd like to maximize useable volume while minimizing the number of required bricks. Man, where are my lincoln logs? :)

-d
 
why not CAD up your design to a 1/4 scale and figure it that way. if you dont have a CAD program or access to one just send me all the dimensions and stuff and i will draw it out for you and give you the numers and stuff. no charge of course. would only take me about an hour or less.
 
fitzo said:
Make a pan of brownies! You can eat the model. :)
Click to expand...

I like the way you think fitzo! :)

PimpinSquee said:
why not CAD up your design to a 1/4 scale and figure it that way. if you dont have a CAD program or access to one just send me all the dimensions and stuff and i will draw it out for you and give you the numers and stuff. no charge of course. would only take me about an hour or less.
Click to expand...

I may take you up on that. Dekers don't do graphical things really well ;)

-d
 
:thumbup:

What I discovered with my oven (mark II) is that the largest comfortable
dimension for 20A/220V (~4KVA) is about 18"x4"x4" . As you increase the
dimension past that, it will get progressively slower @ reaching temperatures
you want for stainless/D2 (~1900F). My oven is _very_ fast.

Now, if you can get 30A/220V circuit going, you can probably have 24"x6"x4"
oven, yes. It is a matter of installing proper breaker & having right gage wires
to the oven. SSR will need to be rated to that amperage too.

The spiral _HAS_ to be Kanthal and of proper gage. The larger the gage, the
more surface there is for the wire to emit the heat into the oven. The smaller
the gage, the more likely is the spiral to fail prematurely.

I had a few pretty extensive posts, on the subject, in this very forum and you should be able to find them.
 
deker said:
So, I've made the decision to build a HT oven, and now I'd like to see if you folks might help me answer some questions or think of important things so I don't miss them.

This will be a long post, so turn back now if you don't have a few minutes :)

I've chosen (and bought) a controller. It's the Omron E5AX. I've got one already that is in use as a pyrometer for my gas forge and have manuals for them handy. It's a complete digital process controller and can support lots of types of outputs for heating element control (I figure I'll probably go with solid state relays). It also has a serial port on the back of it so that I can connect it to a computer for configuration, logging, and control. There's even a company who makes reasonably priced ($100/license. You need a license for each controller though :() control software for this controller. I may give a shot at writing my own though (hey, I ain't a computer geek for nothing!). With computer control I can do all the fancy ramping/holding I want.

I think I have a handle on all the math for how much heating element wire I need based on some assumptions made fom the specs on elements at Budget Casting Supply.

Here's where I need your help folks. What would be a good target for interior chamber dimensions? I was thinking I'd like a chamber about 24" long (just in case I decide to make something with a 14" blade or something....it'd leave me a little wiggle room). So something roughly equivalent to an Evenheat 22.5. What I'm not so sure I need is the 10" chamber width. Could some of you folks chime in on this chamber dimension bit? It sure would be helpful to learn from practical experience BEFORE I start cutting up firebrick.

I'm open to any suggestions. I plan to do a thread on some forum or another on the build similar to what I did for my grinder build once I get it all figured out.

-d
Click to expand...


Deker

I've built two heat treating ovens. The first was 4 X 4.5 x 18 (cavity) the second, which I still need to put a proper latch on the door, is 6 x 6 x 20 (cavity) Both are capable of about 2200 degrees F. I used Insulation brick for these guys. I have also helped a friend build one using Inswool for insulation. If you are interested in my adventures let me know and I'll throw together my thoughts and some photos. I also work with temperature controllers as part of my day job and can probably answer questions you might have on how to hook them up. I can also give you guidance on heating elements (how to wind them and what wire to use).

Jim Arbuckle
 
DAMNENG said:
Deker

I've built two heat treating ovens. The first was 4 X 4.5 x 18 (cavity) the second, which I still need to put a proper latch on the door, is 6 x 6 x 20 (cavity) Both are capable of about 2200 degrees F. I used Insulation brick for these guys. I have also helped a friend build one using Inswool for insulation. If you are interested in my adventures let me know and I'll throw together my thoughts and some photos. I also work with temperature controllers as part of my day job and can probably answer questions you might have on how to hook them up. I can also give you guidance on heating elements (how to wind them and what wire to use).

Jim Arbuckle
Click to expand...

Well Jim, as far as I'm concerned open up the flood gates and give us all any info you have! :) I'd love to see some other folks' designs so pics are encouraged. If you want to email them to me I can host them and link from this thread.

As for the elements, What I've been offered is 17ga Kanthal A1, listed at .04321 Ohms/ft. Looking at this page at budgetcastingsupply.com gave me the idea for 2 coils in series of about 34" length (coiled). The part I could use a little refresher on is the math to convert ohms of resistance to watts and amps. I want to make certain that I'm in the right ballpark for amperage.

On the controllers, I'm likely to have a few questions as well, I'll make sure I ask you when I get there. :)

Thanks!

-d
 
I have built a 4.5x5x16. I used the 3x6x9 insulating soft firebrick wrapped in inswool. Made a stainless box with a front loading door that swings down. Right now I just use a pair of cheap vice grips for a latch. I used a milling machine with a 1/2 end mill to make a 5/8 inch deep grove. The end mill was not a carbide bit so it decreased in diameter as the brick abrasion wore it down. Use ceramic rods in the back corners to keep your elements in the groves. I also had some left over Kanthal wire that I used to make some retaining clips that were inserted into the firebrick groves to keep the elements from working out. Talk to John the engineer at duralite.com they have been great for designing the elements. Be sure to use a quality K- thermocouple, omega is a good choice. I lost a thermocouple early on and literally melted/incinerated three 440C blades! Must have gone over 2600f....that was not a good day. I can get to 2000f in approx 30 min. I love mine and would defiantly build another as opposed to buying one. Just my 2 cents.

Brent Cramer

Bdcramer@juno.com
here are some links I used

http://www.joppaglass.com/elements/mainelpg.html
http://www.bladeforums.com/forums/showthread.php?t=422519
http://www.duralite.com/
 
Look up the plans by Andy Gasciogne. Very easy oven to build I'm sure you could stretch it a bit to get your length.
Mine has a chamber 4.5 by 6 by 18inches and will hit 1500degrees in under 10 min.
Take Care
TJ Smith
 
I knew DAMNENG couldn't stay out of the fray! Jim, I am just about ready to make my HT oven...LOL!



Craig
 
So from the sound of it a 6x6x22 or so chamber size would do me well. 4x4 seems a wee bit small to me, but that's likely because I'm thinking of a few larger projects I'd like to do eventually such as cleavers, etc Or the occation odd-shaped kerambit or something that might not fit in 4x4.

Let me do some scribbling today and see how I can work this out.

-d
 
Deker -

it will be slow @ that dimension, unless you go 30A @ 240V .

The calculation is very ez: the length of wire (L) in feet, per-foot-resistance (R) in Ohm, desired Amps (A) and voltage (V) are related like this:

A = V/ (R*L) . Solving for L: L = V/(A*R) . To get 20A out of 220V with
.5 Ohm/F wire, L = 220/(20*.5) = 22 feet of wire.

I wind my own spirals out of wire I got from resistancewire.com. It is very
ez to do if you have a lathe.

Kanthal A1 spiral will last you forever, as long as you stretch the spiral so that coils don't touch e.o. The spiral should be stretched evenly and tucked
into the groves w/o stress . After first firing, the spiral will become very brittle and you won't be able to adjust it (bend, strech, compress etc)
 
blades&grace said:
I have built a 4.5x5x16. I used the 3x6x9 insulating soft firebrick wrapped in inswool. Made a stainless box with a front loading door that swings down. Right now I just use a pair of cheap vice grips for a latch. I used a milling machine with a 1/2 end mill to make a 5/8 inch deep grove. The end mill was not a carbide bit so it decreased in diameter as the brick abrasion wore it down. Use ceramic rods in the back corners to keep your elements in the groves. I also had some left over Kanthal wire that I used to make some retaining clips that were inserted into the firebrick groves to keep the elements from working out. Talk to John the engineer at duralite.com they have been great for designing the elements. Be sure to use a quality K- thermocouple, omega is a good choice. I lost a thermocouple early on and literally melted/incinerated three 440C blades! Must have gone over 2600f....that was not a good day. I can get to 2000f in approx 30 min. I love mine and would defiantly build another as opposed to buying one. Just my 2 cents.

Brent Cramer

Bdcramer@juno.com
here are some links I used

http://www.joppaglass.com/elements/mainelpg.html
http://www.bladeforums.com/forums/showthread.php?t=422519
http://www.duralite.com/
Click to expand...

Nice links Brent. Thanks for posting that.

As I read about the work that goes into making one of these, I wondered about how much money you saved rather than buying a decent low end commercially built oven.
 
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