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View Full Version : Got my Heat treat oven now for tempering oven



A.W.Stovall
04-08-2011, 10:15 PM
I know guy's use toaster ovens I bought one but it will not hold a steady temp, Is there a specific one that works well? or a different oven for that?
Thanks Anthony

Rudy Joly
04-09-2011, 06:13 AM
After having 3 over the last few years, I found that they fluctuate up to as much as 15 degrees +/- of your target temp due to cycling. Try wraping the oven in ceramic blanket and keep a tray of playsand on the lowest shelf. Use a seperate themometer inside and turn the oven on over the target temp a good hour before anything goes in it. Ok, you probably know all this.

To specifically answer your question.....
There's a commercial counter top pizza/snack oven (Bunn ?) without glass doors that I can't seem to get the person to part with. The door latches shut firmly and the digital pyrometer fluctuates 3-4 degrees. This one I know holds steady temps. A new one is big $$$$ if you can find it. Maybe fleabay or a used appliance dealer ?

Rudy

ARCustomKnives
04-09-2011, 09:13 AM
I use a black and decker brand that I got from walmart for about 30 bucks, and it seems to hold pretty steady.
Just make sure you get one with 4 elements (2 on top and 2 on bottom) as this will help hold temperature more quickly and consistently than a single element on top and bottom.

Doug Lester
04-09-2011, 01:16 PM
Another thing you can do is to put a try of sand in the toaster oven to use as a thermal mass to buffer the cycling of temperatures. Just be sure to heat the sand up before tempering your blades.

Doug Lester

A.W.Stovall
04-10-2011, 07:34 PM
The oven I have has 1 burner and the temp fluctuates at least 25-30 degrees. I will try to find a heavy duty one.

GerryRandall
04-11-2011, 09:36 AM
I bought a couple of toaster ovens and also found they fluctuated 25-30 degrees. Didn't like that.

So I reconnected my toaster oven to a pid controller and stuck a thermocoupler through one end of the unit. It holds temps +/- 1 degree

jdn181
04-12-2011, 10:21 PM
Cheap heaters (like toaster ovens) use a simple thermostat control mechanism because anything you toast (like bread) won't care if it sees an accuracy of +/-25 degrees. There are a couple of means of gleaning a higher accuracy of control. First being to use a large thermal mass to act like a thermal "shock absober". A tray of sand would suffice. If the sand is brought up to temp and then the blade inserted into it the sand won't cool and heat as fast as the inside of the toaster, thereby keeping your blade at a more constant temper temperature. This is the cheapest solution but requires a higher cost to operate since you're heating a larger mass and thereby requires more energy. More thermal energy = more electrical energy = higher cost, but the cost to operate a toaster oven is pretty negligable to be worried about.

The other option is to wire the elements to a solid-state relay which in turn is wired to a PID controller (assuming the PID controller can't handle the amperage of the elements, but if it can then a solid-state relay isn't required). PID controllers have predictive algorithms in them (and in the case of Watlow Series 96 or SD controllers can actually auto-tune their algorithms) that allow a high degree of accuracy. (It's 11:30pm and I'm halfway through a bottle of wine, so I won't go into Engineering-speak mode to describe these algorithms beyond the fact that they do indeed work). For example, I have a Watlow Series 96 PID controller wired into my propane forge (a left-over of when I was an engineer for Watlow way back when) that allows me to control the heat of the forge to within +/- 7 to 10 degrees F. It wasn't made for this purpose (controlling a solenoid that turns the gas supply on/off) but it seems to work OK. It was really meant to control resistive heating elements which is what is found in almost every electric heater from your stove top to multi-megawatt circulation heaters for refineries - any heater that incorporates nichrome wire...like a toaster oven.

My advice would be to use sand first since it's the cheapest. If you're not happy with the results then look into buying a PID controller off Ebay (can be had for ~$100 or so), spend a couple days reading the manual to truly understand how it works, mount it in a small electrical box, and wire it to your toaster oven. I'd imagine it's accuracy of control for the toaster oven will be +/-1 degree or less.

Wolfe
04-15-2011, 01:59 PM
I bought a couple of toaster ovens and also found they fluctuated 25-30 degrees. Didn't like that.

So I reconnected my toaster oven to a pid controller and stuck a thermocoupler through one end of the unit. It holds temps +/- 1 degreeI need to do this also. Are you switching the 110ac on and off or the elements?

GerryRandall
04-21-2011, 11:57 AM
Switching the elements on and off.