Arduino, thermocouple, firebricks, and heating elements?

[Kevin Zito]

Thanks guys! All super useful insights and information!!! I have a few electrical engineers and a computer scientist telling me, “man this is gonna be so easy and cheap.” They are also willing to do it all for me for free. So it is a little tempting I can’t lie. HOWEVER, I know how these things can turn out. I have wired a couple houses and big shops so I’m not completely in the dark, but almost. I am also willing to bet that evenheats and paragons cost what they cost for a reason. But remember I have three kids, oldest is 4, so things are a little tight. I have to be smart with my money. I have my shop almost started lol.... I had to demo a lot of stuff. It’s just a slow process mainly because I want to do this once. I know things won’t be perfect, but I hope to get them close. Thanks again for all the advice fellas... don’t know what I’d do without y’all

 

[KenH]

Kevin - With all the good WIPs out there on oven building you're not having to design from scratch, but can follow an existing proven design. I do think the building of the oven is VERY doable at a good cost saving over a commercial oven. The big question is how do you wish to control it? Do you wish to have a few stored programs that are selectable at the touch of a button? OR, would it be a hassle to enter new (or use existing) parameters each time you HT? Since I use 90+% AEB-L I can use the same program I used last time, and the few times I do other alloys it's not a hassle to enter different HT parameters.

My HT program is simple, ramp up at full heat to 1975⁰F and hold. I can hear the relays clicking when it reaches temp, let it stabilize for 20-30 minutes, put blades in oven, soak for 8 minutes and start quenching blades. Once finished with quench, turn oven off. I have a different PID controlled oven for tempering.

Arduino? Better have a VERY good knowledge of programming and PID control. There are some good libraries out there for PID control so it's not something you'd have to write from scratch. It would be a fun project doing all the programming and getting it going. With a bit of work you could even store different HT programs selectable at the touch of a button.

Perhaps the easiest and least expensive would be to purchase one of those cheap PID controllers for $20 or so to start, then with use, you'd have experience to decide how extensive you would need the programming to be.

Good luck and have fun - those Arduino µC are fun. I usually embed the chip on a PCB board rather than use an actual Arduino. Now since the Nano's are less expensive than the µC chip, I use a Nano.

Ken H>

 

[Andre Grobler]

My last comments are these:
1. If you dont have variable output pid and ssr keep elements a boit 6” from the blades.
2. Use the highest insulating capacity bricks or board you can find.
3. Dont skimp on the TC go thick and long enough to touch the blade...
4. Make sure you can dissasemble easily to replace stuff.
5. Make sure your elements will stay put... they swell and shrink a lot
6. A good door is half the battle

 

[Rick Otts]

Not I, this was another maker talking to me! I personally have built a lot of my own equipment but I always try to build it as save as I know how to. Now the fact that the seasoned maker was building his fourth,............ IMO that in its self says a lot!!!

I also had another maker when I was asking details on building something, (can't remember at this moment what it was, but the advice stuck)!
He told me I learned to think about it like this, would you rather be building equipment or building knives!!

That sounds like Ed

 

[emmawilson]

One thing to keep in mind in all this is safety. Those coils are ready source electricity and accidently touching a blade to one is well,............lets say a real bad day! A HT oven must have a safety switch so the power has to be off before the oven opens! The direction the door opens is something to think about as well and having a counter weight is a plus at the door when you have a handful of hot knives! Take a look at this one. View attachment 63334 You have to think where is that hot door when you are reaching into the oven and that door will stay hot for a while! This one the door flips up. View attachment 63335 Which to me sounds a better idea to me about getting it out of the way. This one has a spring system to keep it up while you are in and out of it!!! View attachment 63336 Here is a side mount door with a counter weight, so there is many ways of doing it! You just do not want to accidently come in contact with that hot door!!

Any and all electric connection need to be enclosed to avoid electrocution. Also a little planning ahead on how the power enters your cabinet is good as well. I remember a thread where a fellow had an oven he built and it was up and seemed to be working well. He had penetrated the cabinet with his electrical leads on some home made brass rods reviews. The oven got slid back on the bench accidently and the 220V touched the metal the shed was covered in. He lived the oven fried and he learned a valuable lesson.

Do your planning ahead and it is feasible to do!

It’s feasible! If you can program PID control, you’re already ahead. The main challenges will be insulation, safety, and even heat distribution. You'll need firebrick or ceramic fiber insulation to retain heat efficiently, a solid-state relay (SSR) with a heatsink to switch the heating elements, and a thermocouple (K-type) for accurate temperature measurement. The biggest risks are overheating, electrical hazards, and uneven heating, but with proper failsafes (thermal cutoff, circuit protection, and good airflow), you can make a functional HT oven for much less than a commercial unit.

 

[Taz575]

Yeah, I built a 27" long, 7" wide, 6.5" tall chambered oven with a WiFi Ramp/Soak PID, element kill switch, door shut off switch, etc for around $1200, not including my screw ups!

Here are some pics of my build list. I went with RedBeard's wiring method/schematic and Jarod Todds design using quartz tubing across the top of the oven and used 12ga Kanthal wire for the element.

 

[KenH]

Since you've got that all priced out, and is that a spreadsheet file? What was the total price if you don't mind me asking?

 

[Taz575]

$1200 roughly. I have an excel file somewhere, need to find it!

 

[Coop]

I built my home made heat treat oven probably for less than $400. But pricing now days is crazy. I found a burnt out pottery kiln for free. I reused the kiln bricks by turning them inside out. I used the floor and top for the bottom and top. I made the cabinet enclosure using a plenum kit available from any HVAC supply house. Other than the plenum kit I only had to buy the elements, $30 PID, K thermocouple and SS relay. But I'm a electrician so the wiring wasn't that difficult. It comes up to 1975 degrees in less than 35 minutes. But the kiln I found for free had a additional 2" of insulation plus the fire bricks. So it's like super insulated. After hours of heat treating I can place my hand on the outside with out even worrying about it being hot.