Redbaird
Well-Known Member
This was an interesting thread to me. I was needing a way to temper knives after hardening and heard good things about the small toaster ovens. After a few days following the thread, I was more confused than ever. So..... I went to Wal-Mart and bought a $40 toaster oven to see for myself. I used a temp gun that reads up to 2500F , is high quality and very accurate to read the actual temps. The toaster had a max temp of 450 and an hour shut off timer. I started off at 400F setting, put a 6"X 2" 1/8" thick piece of steel in and let it warm up.
After 15 minutes I checked the steel temp. It read 415F. At 20 minutes I checked again and the steel was 417F. I turned the oven down to 380F and checked 10 minutes later reading 402F. I left it there and set the timer to 60 minutes. Every 5 minutes, I checked the temperature of the steel and the thin pan that came with the oven. It ranged from 380F to 412F (+-32) on the pan. The range on the steel was 397F to 404F (+-7). It is my understanding this is acceptable for tempering. I do think the thinner the material the larger the temperature range will get.
On another note, I don't believe adding insulation will decrease the range of temperature variance. I think it will only lower the frequency of the variance. This is not a total guess. I have a lot of experience doing heat treatment on heavy wall alloy piping and insulation does not effect range but insulation will cause the heating pads to cut on less often at the same range . But, I have been wrong before.
After 15 minutes I checked the steel temp. It read 415F. At 20 minutes I checked again and the steel was 417F. I turned the oven down to 380F and checked 10 minutes later reading 402F. I left it there and set the timer to 60 minutes. Every 5 minutes, I checked the temperature of the steel and the thin pan that came with the oven. It ranged from 380F to 412F (+-32) on the pan. The range on the steel was 397F to 404F (+-7). It is my understanding this is acceptable for tempering. I do think the thinner the material the larger the temperature range will get.
On another note, I don't believe adding insulation will decrease the range of temperature variance. I think it will only lower the frequency of the variance. This is not a total guess. I have a lot of experience doing heat treatment on heavy wall alloy piping and insulation does not effect range but insulation will cause the heating pads to cut on less often at the same range . But, I have been wrong before.