How to Build a Heat Treat Oven Control Box

Murat | Posted on April 3, 2021 |

This guide about how to build the control box for a heat treat oven is part of the Knife Material Matters column by Keith from knifematerial.at. You find Keith’s guide below—I’ll explain the very basics of heat treatment before so everyone gets an idea what this is. 🙂

Read Keith’s previous post An Abrasive Discussion or visit his website at https://www.knifematerial.at/ .

What is heat treatment?

Knife making consists of taking a piece of steel, hammering or grinding it into a blade form, adding a handle, and finally sharpening it. In between, there is one super important step: Heat treatment. In movies you see this when an often bare-chested and muscular blacksmith pulls a glowing blade out of an oven (yes, the heat treatment oven!) and descends it into a bucket of liquid, blowing fumes all over the place. Sounds fun, right, but why do it?

Heat treatment allows the skilled bladesmith to harden the steel (stays sharp longer) and toughen it (no chipping). And since you never get your cake and eat it, too, you as bladesmith decide how much you prefer hardness over toughness—or the other way. Because of that, heat treatment is important for the final performance of your knife.

That’s amazing, right? How on earth does heat treatment do that? We know that steel is iron with up to 2% of carbon—no carbon, no steel. By default, carbon is all over the place and bound up, a bit like cookie dough in Ben & Jerries. Heat treatment allows you to smoothen out the cookie dough, err, create a uniform structure, which removes stresses and makes the carbon actually improve the steel properties. As usual, Knife steel nerds has an excellent on the topic that I encourage you to dig in. (Beware, KSN is a rabbit hole—I’ve gotten lost reading there for hours haha)

What about the heat treat oven?

The heat treatment oven is the heating technology you use to heat your knife steel. The ovens are usually a composition of a thick brick chamber big enough to treat any blade including chisels and plane blades. The inner brick compartment is snuggled inside a metal outer case to provide adequate insulation. These ovens have a door with hinges to easily open and close for convenience.

The heating coil wire installed within the bricks is long enough to spread through the oven to provide even heating. The ovens have a thick brick placed in the center for proper placement of the metal.

What you should look for in an oven?

Safety: heat treat ovens deal with plenty of heat and electricity. You want to be safe from both.
Heat distribution: you want the heat to be applied evenly along the length of the blade
Ramp up speed: how long you have to wait until the oven is at the target temperature
Temp control: if your oven allows to target a specific temperature, then it should be able to get there somewhat precisely and maintain that temperature, too.
Energy usage: you want to spend little, obviously, and maybe also consider the environment

Buy or build your own

There are plenty of options to buy a fully working heat treat oven—a popular option is for example evenheat.

If you build your own, then you’ll need something that controls the heat source so that you get to the temperature your blade needs. That’s what the control box is for.

Keith from knifematerial.at was nice enough to share his guide & control diagram on how to build this box—this follows below. We do assume that you know what you’re doing—constructing or using a heat treat oven can cause serious harm & damage. Be careful and use this information at your own risk.

Keith’s How To Guide for the Control Box

I’m going to skip right over the oven build itself and get into the control box. This is the part where a lot of people are unsure of how it works. It’s actually much easier than you might think!

If you need any help building the oven let’s discuss it on Instagram!

Disclaimer

This is only a guide. Neither IndieKnives nor Keith give you any warranty. Use this guide at your own risk. If you are at all unsure please ask a professional for help with the oven!

This guide is based on a supplied power of 220 volts.

⚠️ Do not attempt to run this on 115 volts!!

Wiring Diagram

I’m including an easy to follow wiring diagram to show you how each component is connected.

Here is what you will need

➡️ I put all the parts you will need in a list on Amazon.

One “PID” This is what controls the oven temperature. For our oven we want a PID that can handle temperatures up to 1200°c ( 2200°F ) or more. I recommend the Inkbird itc 100VH. If you buy a different PID make sure it is 110-240 volts input and has a relay output in DC volts (3 – 32 volts DC) .
One heating coil rated for 3000 watts. I recommend buying a finished coil, they are inexpensive and much easier than making your own.
One solid state relay or SSR for short. This relay allows for constant on and off switching of the heating coil needed for your oven.
One thermocouple that can measure up to 1200°C ( 2200°F ) I recommend option #2 from my list it will last longer than the standard ceramic Thermocouple.
One DPDT ( double pole double throw ) power switch. The one I listed is easy to turn off with gloves on but you can use whatever switch you like.
One fuse holder with a 1 amp fuze. This isn’t a must but it will protect your PID if something goes wrong.
One Porcelain screw terminal. To make the electrical connections from the heating coil to your PID. Plastic connectors will not work!
One project box to put all the electronics in. A metal or aluminum box is ideal for this but a plastic box will work if you dont mount it directly to the oven.
Two wire connectors of your choice. Plastic is ok here.
Miscellaneous wires. Silicone insulated wire would be best for this application because it doesn’t dry out and get brittle over time. I recommend using 2mm wire on all line voltage ( 220 volt ) connections inside the control box!

With this, you get your control box working!

Want a fancy alarm light, too? Or a buzzer?

11. OPTIONAL Signal lights or buzzers. These can be wired to show when the heating coil has power or to alert you of a high or low temperature alarm. To use them as an alarm signal you will have to set a maximum and minimum operating temperature on your PID.

The following wiring diagram shows the setup with the optional lights/ buzzers.

I would be happy to answer any questions you might have and hope to see some home made ovens from all of you real soon! Reach me on Instagram at @knifematerial.at!

Cheers,

Keith

Thanks, Keith!

Hope that helps you bladesmiths create the best possible heat treat oven—for the best knives you can make.