Recommendation? DIY Heat Treat Ovens - Specific Design Questions

[Cushing H.]

I am starting this thread so as not to hijack JT's thread on his new build. That discussion has renewed my interest in a HT oven (for basic HT needs), and am interested in a DIY approach. So - I have a series of specific design questions. Here is the first one:

Several DIY videos out there call for using a series of 9"Lx4.5"W bricks stacked four width-wise on the bottom, and two on each side with the 9" dimension running from front to back. With a brick thickness of 2.5", this gives a chamber width of 4". Is this size chamber sufficient for giving even heating throughout (I would likely run elements in the ceiling)? I will really only be doing a single blade at a time.

Will the outsides of the bricks be too hot? If so, I could go to 3" thick bricks ... but that will then make the chamber width only 3" wide - this feels too small to me (both for getting things in and out, and for uniformly running the elements in the ceiling) - what do you think?

 

[mooniesdl3]

I've just ordered bricks (24) to build my own heat treat oven. If you prefer width to height you can put the side bricks outside of the bottom bricks (9" wide), like you said 4"/3" or you can do something in between by cutting a shelf on the wall bricks anywhere in between. I'm move interested in width to an extent and will be putting my heating coil around the sides as I plan to make the channel angled to help prevent it from falling out. The issue with the element in the top is keeping the element from sagging when hot, from what I've read.

This video shows the notched bricks:

 

[Hubert S.]

I built an oven last fall and went with a small chamber and 110V. It heats up relatively quickly and as far as I can tell, the temperature is even enough. I added some additional insulation I had left over from building a pizza oven and the outside stays relatively cool, you can touch it even at 1,950F. I can fit two blades in it.

I really wish I had made it bigger. Not so much to fit more blades at the same time, but to make it more convenient. Getting a foil package in and out is a bit of a hassle. It works ok, but I plan to build a bigger one in the future.

 

[Cushing H.]

I really wish I had made it bigger. Not so much to fit more blades at the same time, but to make it more convenient. Getting a foil package in and out is a bit of a hassle.

That experience might be the clincher for me - I would worry about the same thing. Guess I need to go wider... From your experience - How wide do you think would be "enough"?

If you prefer width to height you can put the side bricks outside of the bottom bricks (9" wide), like you said 4"/3" or you can do something in between by cutting a shelf on the wall bricks anywhere in between. I'm move interested in width to an extent and will be putting my heating coil around the sides as I plan to make the channel angled to help prevent it from falling out. The issue with the element in the top is keeping the element from sagging when hot, from what I've read.

Lots here. I would prefer to minimize cutting bricks (messy!).

If you put the side bricks on the outside, how would you support that 9" span of bricks on the top?? Just how long a span of those ceiling bricks can you have before they are at risk of cracking in the middle and falling into the kiln (if the side walls are thin)?

Others have spoken about using the nichrome wire to make "staples" to hold the element in place. Does that not work if the element is in the ceiling?

I am lucky in that I have a supplier of firebrick 8 miles from me that carries all the sizes I would need. One option is something like 1" or 1.5" thick bricks on the sides of the chamber - but I add another layer outside of that to increase total thickness. but like I said - I wonder about the max acceptable span of those ceiling bricks (which can be pretty thick if needed....... (I also need to be a little careful about total surface area of the inner chamber from a heat loss perspective. I ran the calculations, and I think I will be ok with a slightly bigger chamber - but I still only have 15Amps available in my garage (the builder cut corners in a way that now frustrate me.......)

 

[Cushing H.]

oh - I am also wondering about JT's comment about using ceramic rods to support the wire across the ceiling - but just how long a stretch of rod is at risk of cracking? Would they make the full 9" span if the blocks are on the outside? (looks like his new drawing has a 13.5" span - and he is worried about using ceramic rods). For a lot of reasons it would be nice to take the ceramic rod approach.....

 

[Hubert S.]

I would want an extra inch for height, so maybe 7" wide by 5.5" tall or so. I have not heat treated a whole lot of blades yet, and I want to use this one a lot more before I decide what size to make the next one, though. For me, the height is the bigger issue with the foil packets. I have to get them past the little fixture I put in there to keep the blades upright and they have a tendency to catch the bricks on the ceiling.

Do you have 15A at 220V or at 110V? I think my oven takes a little over an hour to get to 1,950F. It runs on 110V but I did not max out the amperage, probably around 12A. I would not go too much larger on 110V and 15A.

If you want to wind your own coils, you can make a really simple jig out of a couple of pieces of plywood and conveniently wind the coil with a drill. Works really well and makes a professional looking coil. I think I might have kept the jig, let me know if you want to see a picture of it and I'll try to find it.

 

[Natlek]

I am starting this thread so as not to hijack JT's thread on his new build. That discussion has renewed my interest in a HT oven (for basic HT needs), and am interested in a DIY approach. So - I have a series of specific design questions. Here is the first one:

Several DIY videos out there call for using a series of 9"Lx4.5"W bricks stacked four width-wise on the bottom, and two on each side with the 9" dimension running from front to back. With a brick thickness of 2.5", this gives a chamber width of 4". Is this size chamber sufficient for giving even heating throughout (I would likely run elements in the ceiling)? I will really only be doing a single blade at a time.

Will the outsides of the bricks be too hot? If so, I could go to 3" thick bricks ... but that will then make the chamber width only 3" wide - this feels too small to me (both for getting things in and out, and for uniformly running the elements in the ceiling) - what do you think?

Probably this is my last post on topics like this one .................Don t copy what you see here .Make real HT furnace .I don t know why everybody copy that Evenheat oven ? It is about money , easy to build or what ??? I never see here Furnace build only with bricks,never ! I will not explain why , BUT real HT furnace are build like on this drawing..
red is brick
blue is kaowool
orange is silica board

 

[Cushing H.]

I would want an extra inch for height, so maybe 7" wide by 5.5" tall or so. I have not heat treated a whole lot of blades yet, and I want to use this one a lot more before I decide what size to make the next one, though. For me, the height is the bigger issue with the foil packets. I have to get them past the little fixture I put in there to keep the blades upright and they have a tendency to catch the bricks on the ceiling.

Do you have 15A at 220V or at 110V? I think my oven takes a little over an hour to get to 1,950F. It runs on 110V but I did not max out the amperage, probably around 12A. I would not go too much larger on 110V and 15A.

If you want to wind your own coils, you can make a really simple jig out of a couple of pieces of plywood and conveniently wind the coil with a drill. Works really well and makes a professional looking coil. I think I might have kept the jig, let me know if you want to see a picture of it and I'll try to find it.

It would be more challenging to get the 5.5" height, as the bricks are 4.5" wide (ulness I went to 6.75" - which might be too high for the chamber). Is 4.5" what you have now ... and you find it not high enough? (to get 5.5 I would need to start cutting bricks - which is doable, but messy....)

I am stuck with 110V, 15Amp. I was planning on emulating Evenheat and going with 13A draw on the elements. I have checked carefully whether I can convert that circuit to 20A, but just can not .... end the basement is totally closed up, so running new wiring is ..... not wise.

 

[Cushing H.]

BUT real HT furnace are build like on this drawing..

Natlek - I am not ruling out anything like that at all. If I go with 1" bricks on the side of the chamber, then using Kaowool as a second layer would make a lot of sense. I was not aware of the use of silica board - but now that you mention it, using it makes a lot of sense to help keep the kaowool in place. My only concern is keeping the integrity of the bricks on the inside layer. Many people have reported that if cement is used to bond the bricks to each other that the bricks crack. the advantage of a single layer of brick, as I see it, is that you can tension them, or hold them tightly in place with an angle iron frame. That is harder to do if kaowool is a second layer, since it has a lot of give.

Question - could you just wire around the inner layer of bricks to hold the things in place, then put the kaowool over that wire?

 

[Hubert S.]

It would be more challenging to get the 5.5" height, as the bricks are 4.5" wide (ulness I went to 6.75" - which might be too high for the chamber). Is 4.5" what you have now ... and you find it not high enough? (to get 5.5 I would need to start cutting bricks - which is doable, but messy....)

I am stuck with 110V, 15Amp. I was planning on emulating Evenheat and going with 13A draw on the elements. I have checked carefully whether I can convert that circuit to 20A, but just can not .... end the basement is totally closed up, so running new wiring is ..... not wise.

Yes, 4.5" is what I have now. For a 2" wide blade, my foil packets end up close to 3". That could probably be reduced with a bit more care and a smaller crimp. With the little support fixture, that only leaves about 1/2" top and bottom, so you have to put the blade in fairly level. It is workable, just inconvenient. I have been meaning to make a lower profile blade holder, maybe that will help.

 

[Natlek]

Natlek - I am not ruling out anything like that at all. If I go with 1" bricks on the side of the chamber, then using Kaowool as a second layer would make a lot of sense. I was not aware of the use of silica board - but now that you mention it, using it makes a lot of sense to help keep the kaowool in place. My only concern is keeping the integrity of the bricks on the inside layer. Many people have reported that if cement is used to bond the bricks to each other that the bricks crack. the advantage of a single layer of brick, as I see it, is that you can tension them, or hold them tightly in place with an angle iron frame. That is harder to do if kaowool is a second layer, since it has a lot of give.

Question - could you just wire around the inner layer of bricks to hold the things in place, then put the kaowool over that wire?

They crack because they have not place to expand ....tighten up with angle iron Kaowool would give them place to move little , think about that .
This is how I would build one if I ever make one .Outside is sheet metal ...............
Maybe two layer kaowool on bottom and on top is better ..........

 

[Hubert S.]

Probably this is my last post on topics like this one .................Don t copy what you see here .Make real HT furnace .I don t know why everybody copy that Evenheat oven ? It is about money , easy to build or what ??? I never see here Furnace build only with bricks,never ! I will not explain why , BUT real HT furnace are build like on this drawing..
red is brick
blue is kaowool
orange is silica board

The reason I built mine from IFB is that I had a whole bunch that I bought for $0.50 a piece a few years ago sitting on a shelf...

Can you clarify which side is the inside in your drawing? I had assumed the silica board, Cushing seems to think the brick.

 

[Natlek]

The reason I built mine from IFB is that I had a whole bunch that I bought for $0.50 a piece a few years ago sitting on a shelf...

Can you clarify which side is the inside in your drawing? I had assumed the silica board, Cushing seems to think the brick.

Bricks ................silica board are outside

 

[Hubert S.]

They crack because they have not place to expand ....Kaowool would give them place to move little , think about that .
This is how I would build one if I ever make one .Outside is sheet metal ...............
Maybe two layer kaowool on bottom and on top is better ..........

Never mind my previous post. This is similar to how I built mine. It has extra board and blanket insulation I had left over from a pizza oven build. I would probably not go out and buy the board for this, it is pretty expensive and I think the temperatures are already pretty low. Maybe you are thinking about a different kind of board, though.

 

[Cushing H.]

Natlek - angle iron on the outside of the silica board - or around the bricks but inside of the kaowool?

 

[Natlek]

Natlek - angle iron on the outside of the silica board - or around the bricks but inside of the kaowool?

You don t need angle iron .Make calculation of exact dimension and find shop which can bend thin sheet metal ........it is simple process i don t think that they will charge you lot of money for bending ,sorry i don t remember how you call that kind of press ??Sheet metal box will hold everything in line inside ..
Something like this box maybe will be more easy in DIY .............

 

[Cushing H.]

Ok ... but my question is: done your way, everything inside of the outer box “floats” ... no cement, everything is held in place by friction (and a tight fit)????

 

[LCoop]

Maybe because so many follow Even heat ovens is BECAUSE they work and have worked for years. With that said I made my home built oven using a burnt out ceramic kiln. It used standard kiln bricks which I had to turn around 180 degrees to have a flat "new" surface. Plus it had a 2" insulated super soft almost wool like outside that I re purposed. I carefully figured out the size I needed and bought a furnace plenum kit of sheet metal that you basically cut to size of what you need to make a sheet metal box it all laid in. It works AWESOME. I probably have $200 in it complete with the heating elements, PID and solid state relay.

 

[Cushing H.]

Maybe because so many follow Even heat ovens is BECAUSE they work and have worked for years.

LOL. good point. probably, the answer is that there is not only one way to solve a problem. But I am curious as to what natlek says about mechanical support for the structure. I do defnitely want to listen to HubertS about minimum dimensions of the chamber....... (that is IMPORTANT)....

 

[Hubert S.]

Ok ... but my question is: done your way, everything inside of the outer box “floats” ... no cement, everything is held in place by friction (and a tight fit)????

That's how I built mine, no cement. Mine is held together mostly by gravity. If I had to transport it, I would put bracing on the inside and would probably have to rearrange bricks after transport. The fit is not very tight and the blanket insulation compresses, so you could dislodge bricks without too much force. I heated it up a couple of times without the additional insulation and could feel a good bit of heat escaping from some of the seams. I have two inches of board top and bottom and about 1-2" of blanket on the sides, then thin aluminum sheet in an angle iron frame. Like I mentioned, you can touch the outside when heat treating stainless. If I had not had the left over insulation material, I would probably have used a mix of vermiculite or perlite and a little cement as a binder between the bricks and the sheet metal. Lot's of people have used this with good success insulating pizza ovens.

Putting the bricks together and making the elements was quick, but the frame and everything else took some time. I think making it bigger would not have taken much more time. When the elements burn out in this one, I will probably make a bigger one. I still have a lot of bricks left over and can reuse the ones in the current oven.