tempering oven

[JeffreyPrater]

I am trying to make a tempering oven from a toaster oven, I insulated the chamber and put in a good quality thermostat made for a tempering oven, and type k thermocouple to watch the temp.

When I set the thermostat to 300 deg the oven will heat up to about 350 deg then gradually drop to about 250 and the relay kicks on and pull the temp to about 350 again.

Is this about normal, or is it too much variation?

[Bob Warner]

That is really too much variation. You need to try to get at a temp and stay there. Even a 25 degree variation would be too much to me. Insulation is a good idea but it won't make up for bad monitoring equipment. If the thing has to have 50 degrees variation to turn on and off, I would look at another thermocouple.

I just bought a new toaster oven and the temp difference between cycles is only about 7-8 degrees. I'm sure this will get worse with age but it works fine for now. It is a cheap one also.

Is yours new or old?

[Don Cowles]

I use an off-the-shelf toaster over for tempering. The only change I made was the addition of a good oven thermometer. Once the temperature is where I want it (often bearing no resemblance to the setting on the oven dial), it holds within 5 degrees with no trouble.

[Bob Warner]

Welcome back Don. Hope you had a good time and relaxed a little.

I agree that the oven temp and the setting vary greatly. I also bought a good oven thermometer and bring the oven up to the temp I want (ignoring the setting on the dial) then put the blade in. I use a timer to shut it off so I won't forget. I have used the timer to turn the oven on and off three times during the night for tempering 5160 by setting the temp and getting it just right, then turning it off and setting the timer for three cyles to go during the nightime. Come back in the morning and you're done.

[JeffreyPrater]

it was a very old toaster oven and the thermostat was bad, I put a used thermostat from a commerical tempering oven and it must not be very good either, I have a good thermocouple and dial so I can monitor the temp.
I thought that was too much swing, I will look around for another oven or another thermostat.

Thanks for the help.
Jeff

[mike koller]

Jeff,
Try the oven without the extra insulation.....I had added a piece of kaowool to try and help mine but found that it cuased the oven to cycle to much and vary like yours is doing now. I did add a piece of fire brick to mine....pre-heat the oven and the temp shows no variances now.

[JeffreyPrater]

I tried the oven without the extra insulation and it still cycles too much, the thermostat must be bad.

I guess its time for a new oven.
Don what make/model did you buy off the shelf, maybe I can find one similar to start out again?

thanks
Jeff Prater

[Bob Warner]

Have not been to the shop tonight but mine was only $29.95 at the local Walmart.

Be sure to check the temp setting to be sure it goes as high as you want it to. Mine claims to go higher than it really does. I can get 450 out of it but it claims to go to 500. I have not been able to get that much but really don't want that much anyway.

[Don Cowles]

Mine is the cheapest Welbilt toaster oven/broiler. It will reach 500, but it's a bit spotty in that range. I have the hardest time getting it set to warm leather (175-180), but even that is doable with some fiddling and a little time.

[JeffreyPrater]

I will try to find one this weekend, thanks for the help I do have a good thermocouple and guage I can use on the new oven to make sure I catch any problems,

Jeff Prater

[Gene Chapman]

If you stick a large piece in a small oven it may cycle back and forth before it reaches equaliblirum (sprelling), anyway a piece of lets say 1/4 X 3 X whatever size to fit your oven once brought up to temp supplies more thermal mass in the oven and may help the temp controller not to overshoot the set temperature as far.

Once upon a time I made my living maintaining fixing industrial equipment, including heat treat ovens, just my 2 cents worth.

Also wrapping your blade in aluminum foil may reduce the radiant heat from a red/orange element from over heating a blade which the mechanical temperature controller dosen't deal with, it's amazing how close these cheap counter top ovens can control the temperature, hats off to industry.