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Heat Treat Oven build.


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Like many others who started out, I started out with the basic gear, A cheap Harbor Freight ASO, some crappy files, and a 1x30 Grinder, Did all of my heat treat by eye in my Charcoal forge. 

I have upgraded a lot of my tools since starting out, But the one process I have not been able to upgrade was the heat treatment process. Sure I went from Charcoal to Propane, but I still lacked the temp control and stability of an electric oven. 

Till now.... 

Short of taking up knifemaking as a whole, this is the most ambitious project I have ever attempted. I am by no means an electrical specialist, but I am pretty good at " put that wire there dummy " and I can do some basic maths.  I am working off the plan and design of another maker ( D. Comeau ) who has a blog page detailing out his build which was very helpful.  

Final dimensions on this will be about 4inch by 4 inch by 18 inches internal space, Since I currently live in my sisters basement and lack the ability to rewire her garage to accept a 20A circuit I had to build it smaller to work with the existing 15A setup.  I dont plan to make anything too big to fit in it any time soon and if I do I can always use my propane forge for that. 

But the first step of the build process is complete, I have the sidewalls together and the mortar cured. Today I will be adding the grooves to hold the elements in, its going to be dual element. 

I will add more pics as the build progresses. 

HT01.jpg 

 

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Forgot to snap a pic of the other side. 

But element channels are in, each brick in my shipment came individually bubble wrapped with a card taped on top warning of the dangers of the dust from these things, So I finally used my Employee discount and grabbed myself a 6300 half mask and multiple pairs of P100 multigas/vapor carts. Working for 3M has more benefits then just abrasives. 

Going to get started on my elements shortly, Gotta cut my round stock down so I can make a jig for that next. 

HT02.jpg

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Using 3/16th round rod to wind my elements, ground a flat spot into the end of it and then drilled a hole so I can chuck it up in my hand drill for the winding process. 

Using 18g Kanthal A1 wire, According to my ( I cheated, The blog post has a xls calc worksheet ) calculations I need 33.29 feet per coil to get a functional oven.  Streched length will be just under 3 feet long which is just a hair over the length of the channel I have in my sidewalls. 

Just waiting for my trusty cordless drill to charge now to do the Elements. 

HT03.jpg

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So I meant to update this, but then real life got in the way as I made progress on it during the week.

 

Winding the coils was a pain ( I screwed two up before I got two that were good ) and I didnt get any pics of that process. 

 

But here are the coils in the channels before final assembly ( I dont have a welder, so its all mortared together ) 

 

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And then mortaring the base and ceiling in place on one side. 

 

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And fully mortared. It sat like this for about 3 days because my IRL job got in the way.

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But I decided come hell or highwater I was getting some progress done tonight. Wiring it all up was actually a lot faster then I thought it would be, so I was able to fire it up. 

 

 

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even with both ends open it heated to 200c ( Default setting, need to configure it still for Murican ) and held it within 2deg for 5 minutes just fine. So i kicked it up to 300 just to see how fast it would go up and it only took about 20 seconds to go from 200c to 250c. 

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Just to give an idea, its only about 60-70% complete, still need to do the back and the door, put the shell on and build a box for my wiring. Even at these low temps the SSR got VERY warm so my next step is to figure out which computer I have in storage is donating its hardcore massive overclocker heatsink to keep my SSR cool. 

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This as been fun, sitting on a stack of blades right now that are going to get used as tests, some O1, W2 and a big ole 80crv2 chopper. 

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Update.

 

Got the back mortared up and the elements and thermocouple run. 

 

put a couple bricks in as a door, and took it up to 500 for the hour the mortar vendor recommends, then took it up to 750f because why not.

 

 

 

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Edited by Robert D.
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Decided to do a stainless temp test run. I plan to move to CPM154 for a lot of my blades so the intended temp target of this oven is 1950-1975 f.

 

But I was able to hit that temp no problem. I did get some cracking along some mortar joints but I already have a plan in mind to resolve those. 

 

The SSR got VERY WARM during this test fire. And that was with it sitting on about half an inch of 6x6 copper plates. 

 

the external surfaces of the oven got very warm as well, but not so warm you couldnt touch the oven. I only left it at this temp for about 30 minutes but even without a good seal on the door area it was able to hold it very consistently.

 

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Nice!  I just fired some AEB-L in my Evenheat, and after sitting at 1500 for ten minutes, ramping to 1925 and holding for ten more, it's still cool to the touch outside.  It is wrapped in a stainless jacket, of course, but is otherwise not much different from yours.  I did time it on the warmup. 37 F to 1000F in 8.5 minutes, 1000 to 1500 in 7 minutes, 1500 to 1925 in another ten.  

 

I don't know what kind of SSR it uses, but there is a massive heat sink on the back of the control box that gets warm to the touch.  Not too hot, but definitely warm.  I have the Rampmaster 3 with solid state relays, if you want to see about technical specs.

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ill have to look into it, I have the Fotek SSR ( i think thats what its named, Bought it a year ago and sat on it ) but I have a couple VERY large CPU heatsinks sitting in storage that I plan to use to cool this, Benefits of your main IRL job being IT and performance PC building being your primary passion is that you have old hardware laying about that is perfect for your new attempts. 

I bought a roll of roofing flashing ( basically a roll of thin stainless steel ) that is long enough to wrap the whole thing, which is my next step once I fix the cracking on the mortar joints. It all happened on the right side of the oven, Right side wall basically pulled away from the roof/floor of the oven. But I was already planning on drilling a couple holes in the thing all the way around and seating steel pins in place using some high temp epoxy putty I have used in the past ( had to fix a shifter cable on my Beretta, which basically rests on the exhaust manifold ) and should be fine for the temps I will be pushing this thing too. 

but now that I know I can hit the right temps, I wont be doing any more firings of it till I get it completed, I am building it in the same area that my computers are all in and I had to kill power to all three of my desktops and my server in order to run the test ( I am typing this on my mini Inspiron 11 pocket sized laptop ) because any temp over 400 caused it to trip the breaker if the computers were on. 

Considering I have 10 bricks left I am considering building a smaller one to set on top of the current one, with the goal being just Mokume, I could just buy another thermocouple, and then put the elements on plugs and swap the control box between the two, my teenage passion of RC cars and planes is coming back with a score to settle it would seem. As thats how I handled having multiple toys but only one controller for each type. 

 

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If you could get 240V service (I know...)  it should keep the electronics cooler, or at least draw half the amps.  But it looks great so far!

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Glad you came back around to this one.  I don't have 240V access in my shop either, but want to do a similar build one of these days.  I've been too lazy to try to calculate the temperature a 120v fired oven can get to, so it's nice to have an example.

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  • 2 weeks later...

I actually got stuck on it for a bit ( IRL stuffs ) so its still sitting, but I should have it done completely this weekend, Door is built and just needs to be attached and then the whole thing wrapped in sheet steel and its done. 

doing it in 110v is not hard Brian, its just a matter of figuring out what your final amp numbers are and the building the coil to fit inside that amp restriction. 

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When I built my first HT oven, I made an angle-iron frame, put everything together and test-ran it. I was intending to clad the outside in sheet metal, but had no idea how hot it would get until I tested it. The available choices seemed to be plastic-coated steel, Aluminium or Stainless Steel, in increasing order of cost. 

 

In the event, I found the surface temperature reached about 135 degC, 275 degF, but that the IFB provided such poor heat transfer to human skin that it seemed safer without a metal cladding. 

 

I am aware that knifemakers in general tend to cluster towards the obsessive end of the scale and that the unfinished look would be completely unacceptable to some (many, most?).

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I am going with a steel sheet clading just to satisfy my kid sister, whos basement and garage I currently reside in ( TLDR: I ended a relationship and am in the rebuild process ) so regardless of the reasons, that is why mine will have a stainless steel exterior. 

 

 

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