Dedicated Tempering Oven

Mark Andrews

Mark Andrews

Well-Known Member
Just throwing out some thoughts on what I feel has helped me get more consistent results tempering.

Since I started making knives I moved up from a homemade tin can forge to a little atlas forge and then got a used box kiln and then finally a Evenheat oven.

When I tempered I always used a toaster oven with thermometers inside and also a thermocouple inside for even more accurate readings. I was never truly satisfied with the toaster oven. I loaded them with mass to keep it constant as I could but still not really happy with it.

Last fall I got a Rockwell tester and I started testing my blades. They would come out of the quench spot on as far as hardness was concerned. Then I would temper. I like to do the first temper and try and get my first temper reading 61-62 and adjust from there. Well everything I tempered in the toaster oven was coming out lower than I wanted. Always very useable RC numbers but I just wasn't satisfied. I wanted exactly what number I was shooting for. The toaster oven just jumped all over the place even with the mass in it and I really never knew how much until I got my tester.

So finally I dug out my old box kiln that I mentioned earlier and got it set up as a perfect tempering oven. It is so consistent with the temperature it puts me in a good position to get the numbers that I wanted. And I can repeat this every time . My toaster over was just so inconsistent it was pissing me off.
Now even though I have a Evenheat it takes so long to cool down it was extending my day. So in closing I get consistent results with this. So I figured I may pass this on to somebody who felt the same way as me. So keep your eye on Craigslist (that is where I got mine) and you can score a great way to keep things consistent and save time.
 
Mark Andrews said:
Just throwing out some thoughts on what I feel has helped me get more consistent results tempering.

Since I started making knives I moved up from a homemade tin can forge to a little atlas forge and then got a used box kiln and then finally a Evenheat oven.

When I tempered I always used a toaster oven with thermometers inside and also a thermocouple inside for even more accurate readings. I was never truly satisfied with the toaster oven. I loaded them with mass to keep it constant as I could but still not really happy with it.

Last fall I got a Rockwell tester and I started testing my blades. They would come out of the quench spot on as far as hardness was concerned. Then I would temper. I like to do the first temper and try and get my first temper reading 61-62 and adjust from there. Well everything I tempered in the toaster oven was coming out lower than I wanted. Always very useable RC numbers but I just wasn't satisfied. I wanted exactly what number I was shooting for. The toaster oven just jumped all over the place even with the mass in it and I really never knew how much until I got my tester.

So finally I dug out my old box kiln that I mentioned earlier and got it set up as a perfect tempering oven. It is so consistent with the temperature it puts me in a good position to get the numbers that I wanted. And I can repeat this every time . My toaster over was just so inconsistent it was pissing me off.
Now even though I have a Evenheat it takes so long to cool down it was extending my day. So in closing I get consistent results with this. So I figured I may pass this on to somebody who felt the same way as me. So keep your eye on Craigslist (that is where I got mine) and you can score a great way to keep things consistent and save time.
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Mark, you have joined the ranks of those who have seen the light. In one of my talks at the Ashokan seminar in Sept. I listed several of the least efficient things that guys getting started do in hopes to save (space, money, time) etc... ironically enough some of the most popular that is see in shops of all levels, are some of the lease efficient. Needless to say the ubiquitous toaster oven made my list. I did the toaster oven thing as well and then found how much better my life could be, but I still have to fight with those bagel warmers too often when I teach at other shops. The temperature swings you observed are practically synonymous with toaster ovens. I just had to do a quick temper on a part last night and so I pulled my low temp salt tube out of my Evenheat and fired it up. I liked it every bit as much, if not better, than my low temp salts for tempering, because it held a very tight temperature and only took 10-15 minutes to get there. If I could have a single wish for the knifemaking community it would be that we would all be able to see tips on ways to improve as just that, somebody trying to help folks make better knives with less hassle, and not a personal criticism of what we are doing.
 
Kevin R. Cashen said:
I just had to do a quick temper on a part last night and so I pulled my low temp salt tube out of my Evenheat and fired it up.
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Love reading your posts Kevin. I can keep up most of the time, but you threw me a curve on this one. Can you explain your low temp salt tube and how you use it in your Evenheat?

Thanks,

Robert
 
Robert Dark said:
Love reading your posts Kevin. I can keep up most of the time, but you threw me a curve on this one. Can you explain your low temp salt tube and how you use it in your Evenheat?

Thanks,

Robert
Click to expand...

For space savings I have a dual function unit for my low temperature salt bath. It consists of a vertical, stackable (up to 4 feet) Evenheat kiln assembly that I lower a 7" steel tube with a shroud cover attachment into. The kiln provides the heat to bring my salt tube to marquenching and tempering temperatures. But when I want to just use the kiln as an oven I use a chain fall, on a track above, to hoist the tube up out of the way into the rafters, and replace the lid on the kiln.
 
Kevin - I have always read your posts with pleasure and have learned a great deal from them. I thank you for your effort. Now, a question if you please. I am using a toaster oven for tempering - I had added a TC with a PID controller. With extra mass inside, and with PID control - my temperature (probe is settled between blades) of blades is held ±1ºF, with some swings as far as ±2ºF, but not many - most of my temps will be 399-400-401 as max swings (if using 400ºF as target. The toaster oven actually holds closer temps than my evenheat oven.

Now - is there much to be gained with some other means? I'm sure salt baths would be better because that temp is so even all over.

Thanks again for providing the group with your expertise.

Ken H>
 
KenH said:
Kevin - I have always read your posts with pleasure and have learned a great deal from them. I thank you for your effort. Now, a question if you please. I am using a toaster oven for tempering - I had added a TC with a PID controller. With extra mass inside, and with PID control - my temperature (probe is settled between blades) of blades is held ±1ºF, with some swings as far as ±2ºF, but not many - most of my temps will be 399-400-401 as max swings (if using 400ºF as target. The toaster oven actually holds closer temps than my evenheat oven.

Now - is there much to be gained with some other means? I'm sure salt baths would be better because that temp is so even all over.

Thanks again for providing the group with your expertise.

Ken H>
Click to expand...

Sounds like you got a good toaster oven, sometimes we do get lucky. I think a horizontal kiln would actually be nicer than my salts. My vertical kiln setup has a serious thermal gradient (what we could call thermal clines in diving) from bottom to top when I am heating a sword in just the kiln, so the salts help even that out. A long horizontal kiln would eliminate much of this problem and not involve the 2+ hours to come to temp like my salts. There are also some issues with my salt setup that requires some experience and skill to deal with, there are some serious lags to bump up the temperatures because the probe is in the salt but the kilns need to overheat to get the temp to register, thus there is invariably some over shooting to get them to even out, and it takes time. It is one of the things that use to make me really grumpy when friends would send me blades to do and include a huge variety of blade types and steel types, I would be up for almost 24 hours trying to get them all done. Of course there are some tricks that require using multiple thermocouples and special switches but it is still a pain. A straight kiln doesn't have these issues. On the other hand the heating with the salts is fast and absolute. For those who are not ready for a kiln, I always found the volume and mass of a normal kitchen over to be darn near as good as a kiln, and I did many, many blades in mine for years before I went to the more industrial setup.
 
Thanks for the comments Kevin - My toaster oven isn't any great shakes, it had almost a 50F swing originally, it wasn't until I added the PID controller and a couple of fire bricks for mass - then it settled down with good temperature control. I was surprised myself how good the wife's oven was - per a TC I used it has a very small temperature swing - not as good as the toaster oven now, but still adequate.

I can see where a long/tall kiln would have a nice temp gradient - even the Evenheat oven I've got has a temperature gradient from bottom of oven to top of oven. I measure this by putting a TC on bottom, and also monitoring the top TC - they will vary a good bit. Of course, I did confirm that both TCs were reading together by placing them adjacent to each other.

73 de Ken H>
 
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