View Full Version : My new HT oven build WIP

12-01-2011, 10:25 AM
I recently got into cooking knives and my older HT oven was too small, so I did build a bigger one.
Not the prettiest of sorts and still missing the outer shell ,but works excellent.

Some Data: Interior 50cmx12cmx12cm (approx 19,7`x4,7`x4,7` sorry I am a metric guy :)) up to 800C (1475 F) in 15 min, up to 1100C (2000 F) in 35 min. 2300 Watts element from 1,3mm Kanthal A1 resistance wire. Initially I wanted to use a stronger one but I finally settled at 2300W. Regulated with programmable PID+SSR and relais + door contact switch for safety reasons. It was made using a minimum of tools and was fairly easy to construct. Can be used horizontal and vertical for hanging longer or thinner blades to minimize warp.
The oven is easy to disassemble in case of element change or possible repairs. Thats why the friebricks are not mortared together.



I used 16 firebricks, some angle Iron for the frame, ceramic strip between the bricks to prevent any gaps, vermiculite board for element holders pinned to the brick. for ease of construction I did not want to put grooves into the bricks because this is messy and the bricks break easily when the heating coils are tightly spaced and you are not careful. Because the oven is to be used vertically I did also pin the elements with U-shaped pins from smaller Kanthal wire to the bricks so they cannot fall into the chamber when used upright. Vermiculite board is easy to work, cheap and for me readily avaliable, its max temperature rating is 1100C (2000 F) so if you are doing mainly stainless it would be operated constantly at its upper limit, as I do mostly carbon steels and only the occasional SS Blade I think it will hold up fine. This is the first time I did use vermiculite so far no changes detectable but I cannot comment on how it will hold up in the longer run. If you want to stay on the totally safe side put grooves in your bricks. My woodstove uses the same for the firing chamber and the boards have to be replaced after 2 winters. during winter the woodstove is in almost constant use ,so if it lasts anything nearly like this in my HT oven I am good to go.






Because the oven has exposed elements its advisable to be sure no current/voltage is in your elements when you open it. On my former oven I did always pull the plug before opening but I found it to be very annoying and so with the new one I use a door contact switch an a power relais in conjunction with the PID+SSR so the elements are completely separated from the line when the oven is opened. It works perfectly and I found it to be much more convenient in use. power relais and door contact switch are shown in the lower left and middle of the pic.


To connect the elements i used ceramic connectors and thick copper wire cable. Initially I thought it would get very hot at the connectors but it does not.


I recessed the elements a little at the door to have some space to insert a blade holder when hanging blades in the upright position so the door closes without problems.


Just wanted to show you my new toy an so you can see you dont have to spent high dollars or have a fully equipped workshop to make something like this. I used a cordless Drill, a Drill press, a Hacksaw and the cheapest welder avaliable. But the frame could be also screwed or pop riveted together.

On how to properly design the used heating element look at my other thread here: http://knifedogs.com/showthread.php?21072-Heat-treat-oven-How-to-design-and-calculate-the-heating-elements

Thanks for looking.:)

12-01-2011, 11:51 AM
That is super cool! I've been wanting a HT oven but the prices have kept me using my little Paint Can forge. If I could get my head around the electronic calculations and figures, I just might try this.

I see that ebay has quite a few PID + SSR's with thermocouples. Will these plug directly into the heating coil? Are you suing 220v or 110?

12-01-2011, 12:36 PM
Hi Don,
I am from germany and we use 230V here. The calculations use only a few basic formulas and you can calulate th whole thing with 110v w/o problem. just find out how much amps are allowed at your place and with 110V x max amps = max Wattage which is allowed. for a basic controller you need a PID and a SSR Relais and a k-type thermocouple. no safety precautions there,no fuse no door switch etc. please unplug the oven before opening even if the coils are not heating they can be live!
the PID is connected to 3 things :110V, to the thermocouple and has a +/- connection to control the ssr relais.
the SSR is connected with the +/- to the PID and on the other side one port to mains and one to the coil.
Mains is connected both sides to the pid, one to the ssr and one to the coil. Please connect grounds to the shell of the furnace. In the documentation that comes with the pid it should be mentioned what port where to connect. do not confuse the +/- wires in the thermocouple and in the connection from the pid to ssr. Maybe the crude picture will help a little. Sorry, as I am not a native speaker I hope you could follow.


Battle Creek Knives
12-09-2011, 07:29 AM
great job man !!!!!!!!!!!!!!!!!!!!!!!!

my only concern is the way you installed the grooves, I'm assuming they're glued on ?? I cant see them lasting and causing your element to fall down, is there a reason you chose hard fire brick over soft??

very nice build in general , how long did it take?? costs??

excellent first couple posts btw...

12-09-2011, 09:32 AM
Hello Rob,

Thanks a lot!
The grooves are pinned with 3x 3mm SS steel pins to the bricks each. And these bricks are not hard firebricks but insulating soft bricks. As for why I did it this way :I wanted to try the vermiculite board material for this and not to have cutting grooves into the bricks.
If your elements are thightly spaced I knew from former ovens that that the material in between grooves tends to break if you are not careful, just ease of manufacturing, besides the door area where i slightly recessed the bricks they were used as is, no messy cutting. This is the first time I have tried this method to fix the elements to the wall so I cannot comment on performance in the long run. So far the oven has ben used a few times and the Vermiculite board is entirely unchanged.

This Material is widespread here ,easy to work and cheap besides, so I gave it a try. No Idea if something like this is avaliabe in the US. If you want to stay on the safe side use the traditional method and cut some grooves for the elements. As an alternative you could cut strips from ceramic fibre board (something like fiberfrax duraboard) to support the elements. And if you want to spend some money the entire oven could be built from Durabord instead of the firebricks. But for the price of 2 inch duraboard here I could build three ovens with the soft firebrick...

As i did build this in the few hours of spare time here and there I cannot exactly tell how long it did take, all together maybe 1-2 days. As I did have to buy most of the stuff the total costs of material were about 300€ .Depending on what you have at hand or can get cheap on ebay etc. it will maybe less than that but its still a lot less than an Evenheat or paragon of the same size.

12-16-2011, 05:29 PM
Doing a little more research, I came across this WIP. Building a Heat Treat Furnace (http://www.budgetcastingsupply.com/papers/HT-FURNACE.pdf)

I also found most all the materials (except the angle iron) are available in one spot. www.budgetcastingsupply.com (http://budgetcastingsupply.com/)

This is looking more and more doable. The only question I have is if a 110v unit would get hot enough, quick enough, to be practicable. I work out of my Garage and do not have a 220v outlet handy. If I did, I'd probably have a 2x72 hooked up to it! :)

12-19-2011, 03:01 PM
I found that you will need app. 0,8Watts per square cm of chamber surface to get the oven hot enough. the better the insulation and the lower the thermal mass of it (I am thinking of something like fiberfrax duraboard) the quicker it gets up to temperature.

110V limits the oven size somewhat. What you can possibly do is to use two heating coils and plug them into two different cirquits/outlets. You will need to find a pid which can control 2 SSr at once. This will get you at least up to 220V.