DIY Tempering Oven Completed

S

StuNY

Joined
Feb 16, 2014
Messages
152
Well, my DIY heat treating oven worked out great, but of course I get a little impatient waiting for the thing to cool from 1900 degrees to 400 for tempering. Found myself shooting through the door with compressed air and figured that was probably not so good for the life of the oven!

So after taking readings from my toaster oven and finding them all over the place, I decided to make a cheap DIY tempering oven that would hopefully be more accurate. Also decided that this would not be another multi-weekend project and I wouldn't spend time designing and drawing up this one. Just an early trip to Home Depot looking for whatever parts I could find then make it all up in a day. Ended up using 4" and 6" ducting pipe and end caps with insulation stuffed between. A little furnace cement to seal all up. Picked up a cheapie PID controller that came with SSR and heat sink, Thermocouple, 600w heating element from Amazon and a project box from Radio Shack.

Turns out that not all PID controllers are the same, and I had nothing but frustration trying to autotune then manually tune the cheapie. Ended up pitching it and getting one from Auber Instruments the same as the one that worked so well for my HT oven, but without the ramp soak option. That tuned up nicely and is nailing temperature +/- 1 degree.

So in the end $100 in parts total- until I got the new PID for $40 more- but it works great and has lots of room for big knives- about 20" inside. Not intended to hit more than 600 degrees. Not pretty but it does the job!

Here it is with original PID:
i-4FPV7z4-M.jpg


Wire mesh shelf inside:
i-RGphjSc-M.jpg


Top View:
i-xmCJG9F-M.jpg


New PID controller swapped in:
i-v3zPMR8-M.jpg
 
Very well done and clean. I have studied your heat treat oven build and eventualy built one myself. Ever since I have been considering a tempering oven as well for the same reason you mentioned, but would not have thought about using pipe like this. Could I ask what kind of element you are using and where the placement is inside.
 
Thanks!
I got this 600w element on Amazon. I have it extending from the back/bottom of the oven 12 inches into the oven. I make sure to place the blades all the way back when I load it. In hindsight, this may not be the best heating element. Since it is installed in a stainless tube there is a bit of lag time between when it gets the current and when it heats the oven, and more importantly increases in heat output after current stops flowing. Causes a bit of trouble for the PID but I was able to tune it out pretty well, and ended up telling the PID to only supply 35% power to it to avoid the extremes so you could easily get away with 300 watts or so. Good Luck!
 
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People under estimate the value of a good stable tempering oven. Not a lot of mass there but as long as it holds temp that's all that matters. Using a toaster oven drives me crazy with the temp swings.
 
thats actually a pretty good looking oven, compact as well. I use a toaster oven if Im only doing one blade but if Im doing more, I use my kitchen one on a pizza stone. I make sure my thermometer is in the same spot though. This would definitely come in handy. Do you have a copy of the plans?
 
tattooedfreak said:
thats actually a pretty good looking oven, compact as well. I use a toaster oven if Im only doing one blade but if Im doing more, I use my kitchen one on a pizza stone. I make sure my thermometer is in the same spot though. This would definitely come in handy. Do you have a copy of the plans?
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Thanks! No plans though, just built this in a day trimming things to size and fit as I went.
 
zhyla said:
That's actually really nice looking.

What kind of insulation did you use?
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Thanks! I just used regular fiberglass insulation from HD. Tore off chunks (no paper!) and stuffed them down between the two cylinders.
 
Adding PID control to a toaster oven makes the toaster oven work really good. My toaster oven with a firebrick for a tad extra mass inside normally holds ±1ºF, at max I might have a ±2ºF swing, but once it's stabilized it seldom swings more than ±1ºF. PID controllers are pretty cheap, I got one off ebay (from China) for $15 shipped, but it only displayed ºC, so I wound up with a $40 Auber.

Ken
 
I want to ask how to add a PID to a taoster oven but I feel if I have to ask, I shouldnt do it :-)
 
Good idea to add the firebrick for mass. Just happen to have a couple left over so will slide em in under the shelf!
 
tattooedfreak said:
I want to ask how to add a PID to a taoster oven but I feel if I have to ask, I shouldnt do it :-)
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It's really not that hard to add a PID controller to a toaster oven - It's wired exactly the same as a PID controller is wired in on a homemade oven. Your level of electrical knowledge has a lot to do with how easy it is. I wired a SSR (Solid State Relay) to the output of PID to control a recept in a box - just plug toaster oven to PID controller box with recept and good to go. No rewiring at all involved with toaster oven.

Ken H>
 
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