PID Controlled Tempering Ovens

[CDHumiston]

Does anyone know of a source to buy a nice PID controlled Tempering Oven?

I know people make these at home and I've watched a lot of YouTube videos.
Bottom line is I don't want to make one as it looks like a lot of trouble.

I have a Paragon heat treat oven and it just takes too long to cool from 1950 to 300 degrees!

I guess I could put my blades in the freezer while I wait...

Has anyone tried out those $500 range 1/2 size ovens? I've been looking at this one.

Thoughts? Experience?

https://www.amazon.com/dp/B01K3L61L...olid=2UFDW4OK99MDQ&psc=1&ref_=lv_ov_lig_dp_it

 

[Stacy E. Apelt - Bladesmith]

According to the listing, that oven only sets the temperature in 50° steps. That would not be suitable.
However, you are on the right track as a convection oven is a good tempering oven.

You can convert a convection oven or toaster oven to PID control with most any PID, a type J TC, and an SSR. Look in the sticky's under "PID Control Forge, ...etc." and you will find plans for converting a toaster oven, which is basically the same thing.

Tempering oven build:
http://www.bladeforums.com/threads/pid-controlled-forge-heat-treat-oven-plans-wip.1385057/
Super clear wiring diagram - perfect for controlling a tempering oven: Postb #4 has the PDF
http://www.bladeforums.com/threads/pid-controlled-tempering-oven-diagram.1002319/

Here is the basic schematic for building a PID controller box to plug in any toaster oven or other electric heater device and control it:



If building electronics isn't your strong suit, you can buy one premade on eBay and Amazon for around $200. This will run a full HT oven. You could build a very simple tempering oven with quartz rod heaters for tempering using much cheaper components than a HT oven needs. A controller like this would run it just fine.

 

[Scaniaman]

I bought a medium price range household oven. It is true to set temp by +/- 2 degrees

 

[Natlek]

According to the listing, that oven only sets the temperature in 50° steps. That would not be suitable.
However, you are on the right track as a convection oven is a good tempering oven.

You can convert a convection oven or toaster oven to PID control with most any PID, a type J TC, and an SSR. Look in the sticky's under "PID Control Forge, ...etc." and you will find plans for converting a toaster oven, which is basically the same thing.

Tempering oven build:
http://www.bladeforums.com/threads/pid-controlled-forge-heat-treat-oven-plans-wip.1385057/
Super clear wiring diagram - perfect for controlling a tempering oven: Postb #4 has the PDF
http://www.bladeforums.com/threads/pid-controlled-tempering-oven-diagram.1002319/

Here is the basic schematic for building a PID controller box to plug in any toaster oven or other electric heater device and control it:

View attachment 2028426

If building electronics isn't your strong suit, you can buy one premade on eBay and Amazon for around $200. This will run a full HT oven. You could build a very simple tempering oven with quartz rod heaters for tempering using much cheaper components than a HT oven needs. A controller like this would run it just fine.
View attachment 2028427

I don t think so, he can set it between numbers on table , you know ? It is sliding button thermostat.
BTW , are you SURE that this thermocouple on picture is RIGHT Type for tempering oven which work with very low temperatures ?
If this is quality oven he don t need PID controller at all .
What I would do on this oven is that I will change position on thermostat . I mean on part which is inside oven not on adjustment button . I will put it /firmly attached to a piece of steel or even better if he drills a hole and pushes that part inside / in place where knife should be placed . That will extend the time between on/off cycles , the temperature inside oven drops much faster than the temperature of the steel inside due to weak insulation, door side and the thin sheet from which it is made. Thermostat will react on temperature on steel not on temperature of that thin sheet of metal where they are usually placed. Then use some other more precise measurement device with thermocouple also fixed to steel inside to determine exactly where the temperature is, let's say 200 C degrees on control button .

 

[Stacy E. Apelt - Bladesmith]

"I don t think so, he can set it between numbers on table , you know ? It is sliding button thermostat.
BTW , are you SURE that this thermocouple on picture is RIGHT Type for tempering oven which work with very low temperatures ?"

What I meant is the only markings are in 50° steps. There is no readout so you would not really know the temperature unless you ran it on a PID and TC. I also doubt it is controlled, so the temperature may vary or climb.

That TC is in the photo for a kiln controller, but would work fine for a tempering oven in the 400-500°F range. I used the photo as an example, not an exact item.

All, you need to do to use any type TC is connect it to the right terminals on the PID and set the PID to type J, K, RTD, B, N, T, E, S, etc.

Type J is most accurate between 200° and 500°F. They are also the lowest price probes. This is a good choice for a home built/modified tempering oven,
I don't have my charts here, but IIRC type K is most accurate between 700° and 1700°. It is still more than accurate enough for our uses at tempering ranges. RThey are more robust than type J.
The best choice if you want the highest accuracy for a tempering oven would be a three wire RTD probe (Pt100). They have a 100 ohm platinum junction and the highest accuracy. They are also more expensive.

TIP:
For many situations you can use a "washer" style TC. It has a round ring on the end instead of just exposed twisted wires, and a shielded metal wire sheath over Teflon covered wires. They are rated up around 480°, so would work for most 400° area tempering ovens. They are usually very low price, and come in grounded and ungrounded tip. You can bolt one to any object to read the temperature (like a platen, forge shell, exhaust pipe, quench tank, etc.). In a tempering oven, bolt it to the plate or rack where the knife will sit. Try and have the least amount of lead wire inside the oven.
Another choice is a sheath style probe in the desired probe length with a screw in sleve. You can tap a hole in the device or weld on a nut and screw the probe in. If you use ones with a standard type J plug on the cable you can take your readout or controller to the device in use and just plug it in.

These are examples of what I am referring to: