Heat Treat Oven Build

[SLC_Blades]

Hey everyone, I've been trying to repress my urge to work with stainless because I have no way to heat treat it and don't want to outsource it but I think it's time. As you can see from the title, I'm looking to build a simple, PID-controlled electric heat treat oven and want to get some input from people that have done it before I go and do it myself.

Questions:
•I'm away of some safety hazards regarding the electrical portion of the project (plan to install a door switch so that I don't kill myself fumbling for the knife) but if there are any other major safety concerns I should watch out for, what would they be?
•What is the purpose of calculating my power usage (in kw)? This is something I see a lot of people talking about so what kind of numbers would be ideal?
•I don't have a welder and am definitely not buying one just for this project so would it be feasible to do a metal frame with entirely mechanical connections?
•Any recommendations for a specific gauge of Kanthal wire I should purchase?
•How should I lock the electric coil into the brick? I've seen two different methods: digging out a channel and dovetailing the inside to retain the coil; digging out a regular channel and using extra pieces of Kanthal wire as staples to hold the coil

Okay I think that's about it (sorry it's a lot)
Any input is greatly appreciated, thanks!

 

[timgunn1962]

I've built 8 so far. I'm in the UK where we have 230V mains power and rather different wiring practices to the US, so I'll leave any advice on the electrical safety side of things to others.

Calculating your power usage is useful insofar as it tells you whether your power input is in the same ballpark as other HT ovens of broadly similar construction that are proven to do the job you want yours to do. I have built ovens from 18" long to 27" long, all using 3kW of elements (the standard UK domestic power outlet is 13A at 230V, so 3 kW is the maximum "use anywhere" power over here, which simplified my choice). Unless you have a particularly unusual requirement in terms of size, I'd regard 3 kW as a pretty good starting point.

I did build one quick-and-dirty 42" oven using 3 kW of elements on each side and running off 2 13A supplies. My latest 27" ovens were built to enable 2 to join together to make a long one, and will take extension spacers to further extend the length to 66".

A no-weld build would be entirely possible with a little thought. The best approach for you will obviously depend on what equipment you have available.

I would not use less than 16 AWG Kanthal A1 or equivalent. I used 16 AWG for the first 5 ovens I built and I think 16 AWG is probably a pretty good choice for hobby use, but a couple of guys who used my ovens professionally suffered element failures and I used 1.6mm wire (1/16",14AWG) for the 3 most recent builds. I think that using Stainless allthread to get through the wall with the elements connected on the hot side by clamping between large washers was a contributing factor in the earlier element failures. I now use twisted, doubled tails.

I use straight-sided grooves and pin the elements in place with U-shaped Kanthal staples. It's the most tedious part of the build now that I cut the grooves with a router. I cut the grooves for the first one with a saw and filed them with a length of allthread, but that got very old very quickly and I used the router from then on.

You have not asked about thermocouples or PID controllers. That may be because you already know enough not to need to ask. On the other hand, it may be because you don't know enough to know what questions to ask. If it's the latter, do some research and ask the appropriate questions when you need to.

 

[SLC_Blades]

I've built 8 so far. I'm in the UK where we have 230V mains power and rather different wiring practices to the US, so I'll leave any advice on the electrical safety side of things to others.

Calculating your power usage is useful insofar as it tells you whether your power input is in the same ballpark as other HT ovens of broadly similar construction that are proven to do the job you want yours to do. I have built ovens from 18" long to 27" long, all using 3kW of elements (the standard UK domestic power outlet is 13A at 230V, so 3 kW is the maximum "use anywhere" power over here, which simplified my choice). Unless you have a particularly unusual requirement in terms of size, I'd regard 3 kW as a pretty good starting point.

I did build one quick-and-dirty 42" oven using 3 kW of elements on each side and running off 2 13A supplies. My latest 27" ovens were built to enable 2 to join together to make a long one, and will take extension spacers to further extend the length to 66".

A no-weld build would be entirely possible with a little thought. The best approach for you will obviously depend on what equipment you have available.

I would not use less than 16 AWG Kanthal A1 or equivalent. I used 16 AWG for the first 5 ovens I built and I think 16 AWG is probably a pretty good choice for hobby use, but a couple of guys who used my ovens professionally suffered element failures and I used 1.6mm wire (1/16",14AWG) for the 3 most recent builds. I think that using Stainless allthread to get through the wall with the elements connected on the hot side by clamping between large washers was a contributing factor in the earlier element failures. I now use twisted, doubled tails.

I use straight-sided grooves and pin the elements in place with U-shaped Kanthal staples. It's the most tedious part of the build now that I cut the grooves with a router. I cut the grooves for the first one with a saw and filed them with a length of allthread, but that got very old very quickly and I used the router from then on.

You have not asked about thermocouples or PID controllers. That may be because you already know enough not to need to ask. On the other hand, it may be because you don't know enough to know what questions to ask. If it's the latter, do some research and ask the appropriate questions when you need to.

Thank you so much, that was incredibly helpful! And yes, I didn’t ask about the PID because I’ve spent a lot of time researching it and can now say that I understand how the wiring works.