Question about tempering

That's VERY interesting Ken. I tried that very PID in you pic on a kitchen oven.....wired it with relays, and the moment the power of switched on. the PID went up in a cloud of smoke. I may have done something dumb in the wiring, and caused it, but after contacting the guy I buy PIDs from, he laughed at me and told me that even though the PID I'd tried to use was labeled for 220V, the amps fried it. Honestly, I never revisited trying to wire another kitchen oven with a PID...... didn't really have any need to once I got my hands on the digital kitchen oven.

I guess the take away is.....if it works for ya....by golly use it!! :)

Ed, it is just a guess, but it sounds to me like you had the oven's coils running directly off the PID controller output contacts. Typically, the PID controller's output feeds the coil of a relay, and the high current for the heating element then passes through the relay's contacts instead of the ones on the PID controller.
 
I had it running through relays....but there's certainly the possibility that I wired something wrong..... sometimes I think Mr Murphy lives at our place! :)
 
Ed, it does sound like there were some wiring issues with your PID. With the stove oven wired thru relays there should have been no amps to speak of on the PID, only the voltage source to power the PID which would have been in mA range. For your use as many blades as goes thru your shop in a week, the digital stove is by far the best choice. I've been impressed how well a digital stove will hold the oven. With my couple of knives per month the toaster oven is plenty large enough.
 
Mr. Murphy is alive and well! You haven't lived until you've wired 480 to a 230 device and then thrown the switch. It's even better when the customer is standing there.
Yeah , it lets the smoke outta them com-ponets and they quit workin for some reason. I think it has something to do with magic.
 
Well...my oven after an hr warm up seems to stay within 10 degrees total. I think adding firebrick and leaving well enough alone will be my next step. Mine is a digital oven and seems to stay fairly consistent.

I bought a hood for my restaurant area in the old mercantile building and it came with chalky panels of fire insulation. I never installed it so I still have the insulation...2" thick. Might do a lower and upper insulation?
 
I've been following this thread and I'm curious about convection ovens. Has anyone tried a small convection toaster oven? Since air is constantly circulating I would think they would keep a fairly even temperature, but I really don't know.

After reading this thread I'm ready to ditch my current toaster oven for something better.
 
I've been following this thread and I'm curious about convection ovens. Has anyone tried a small convection toaster oven? Since air is constantly circulating I would think they would keep a fairly even temperature, but I really don't know.

After reading this thread I'm ready to ditch my current toaster oven for something better.

It would be the best was to go for a small oven for the reasons you mentioned. Topped off with a PID. I found this write up.



For those who have the space there is this!
 

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Here's my tempering oven....it's been there for a number of years, so it's dirty from use. It's a Frigidaire brand. I picked it up from a yard sale, new in the box, for $150. Seems the husband remodeled the kitchen while his wife was on vacation.....and when she got home....she did like the colors and made him change out all the appliances! (wish I had that kinda money to throw away) :)

Tempering-Oven.jpg


Personally, I would recommend this type of oven FAR above a toaster oven. If you've got an electric kitchen oven, you've likely already got a usable tempering oven.
I had to laugh when I looked at that Instructables article about toaster ovens. I know some of you folks use believe different, but I know that just putting a PID in a toaster oven doesn't make it accurate. If you leave it like the pic in the article......you're just wasting your money on a PID, and your time installing it.
 
I have to give him credit for putting wool in it. This is mine for now. It works well. I check them at work. I can hit 58/60 all day long.
 

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For a bunch of years I used the oven in our kitchen. I remember the last time we purchased a new one.....we were at Sears looking around. Cindy was with one salesman, looking at colors and how nice they looked. I was with another, whispering in his ear.... "Hey, which one of these ovens holds the tightest temp tolerance?"...... "Steer her towards that one!" :)

We actually ended up getting the one I wanted.....got it loading in the truck, and as were leaving the parking lots.....Cindy leaned over and very gently said "YOU, are not putting knives in MY new oven." OK.....but you go to work, and I go to the shop! She'll never know! It worked, until one day I got lazy and didn't clean the quench oil off as well as I should have. She came home, and the whole house smelled of burnt oil! OOOPPS! Hence, the reason why that oven resides in the Hot shop. :) The moral to the story is..... IF you're using the oven in your kitchen.....clean the quench oil COMPLETELY from blades BEFORE putting them in the "kitchen" oven!
 
I went from my house oven to a toaster oven then back to my house oven. I really need to get an oven for the shop because in Georgia from April through December it is too dawg on hot to run my house oven at 400-425 degrees for two hours at a time.
 
I had to laugh when I looked at that Instructables article about toaster ovens. I know some of you folks use believe different, but I know that just putting a PID in a toaster oven doesn't make it accurate. If you leave it like the pic in the article......you're just wasting your money on a PID, and your time installing it.
Ed has forgotten more than I will ever know about knifemaking, and I really appreciate Ed sharing his knowledge with us on this forum. I have learned LOTS from watching his videos, reading his posts, and talking with Ed in person at Blade. BUT - we have dis-agreed in the past on epoxy life. I'm not sure if the 3 experts I brought into the discussion were enough to convince Ed on epoxy life or not. I expect this discussion on toaster ovens will have the same result. Ed's mind is made up, he tried it before, didn't work and that's that.
I've been following this thread and I'm curious about convection ovens. Has anyone tried a small convection toaster oven? Since air is constantly circulating I would think they would keep a fairly even temperature, but I really don't know.

After reading this thread I'm ready to ditch my current toaster oven for something better.
Sean, you asked about the convection ovens with air circulating, it's not the lack of circulation that's the problem, it's the type of t'stat used in most of the older kitchen or toaster ovens. The newer type digital controlled kitchen (or toaster) ovens provide better control, not quite up to PID accuracy, but still pretty darn good.

Allow me to explain a VERY simplified version of temperature control: The older style T'stat has a bi-metal coil that moves as it heats or cools opening or closing a contact. This isn't all that accurate and happens at set point. A PID (Proportional–Integral–Derivative controller) controllers "learns" where the contact needs to open or close to to keep temp at setpoint. Ideally the PID would slowly reduce amount of heat as temperature approaches setpoint so there is little overshoot. It seems most of the cheap PIDs used simply open or close a relay rather than reducing heat, it shuts heat OFF or ON. That is why it takes a while to settle down to temperature (as well as heating up the mass in oven). Say setpoint is 300°F, first cycle the PID might open contact at 300, see the temp overshoot to 325. Contact stays open until temp falls to 300, PID thinks might better let it fall a bit more, then at 290 contact closes and temp rises to 298 and contact opens but temp still rises to 310 this time. This cycle continues as the PID learns where to open and close contact to keep temperature right at 300°F setpoint. This is called the "Learning" portion of setup. Once this has cycled thru and the PID has learned the correct parameters, the PID will still overshoot and undershoot during heat up, but it will be less each time.

There is no reason in the world a small enclosure can't be temperature controlled as well as a large enclosure. It's all about the type of controls and heating element, not the cubic volume of enclosure. Check with any process control engineer on that. For anyone who needs to do lots of blades at a time a kitchen stove/oven makes sense. Mydigital kitchen oven will provide ±5°F just fine and that should be all that's needed. A PID controlled toaster oven with an extra fire brick for mass has no problem providing ±1°F control, and certainly ±2°F control is expected.

For the folks here (like me) who seldom do more than a couple of chef blades, or a 4 set of steak knives at a time a toaster oven with PID control makes good sense.

I had no intention of this getting so long, just started typing.

Ken H>
 
You're right about me Ken. :) I made up my mind a long time ago, after trying to get several different toaster type ovens to work.....after all kinds of modifications.... it was just so much simpler, time efficient, and cost effective for me to use a good electric range type oven....so that's what I advocate.

That being said, I say if a toaster oven works for an individual, then by golly use it! That's probably the one thing that keeps our craft interesting and new.....things work different for different people, and in different environments....and Heaven knows differing opinions abound! ;)
 
Ed has forgotten more than I will ever know about knifemaking, and I really appreciate Ed sharing his knowledge with us on this forum. I have learned LOTS from watching his videos, reading his posts, and talking with Ed in person at Blade. BUT - we have dis-agreed in the past on epoxy life. I'm not sure if the 3 experts I brought into the discussion were enough to convince Ed on epoxy life or not. I expect this discussion on toaster ovens will have the same result. Ed's mind is made up, he tried it before, didn't work and that's that.

Sean, you asked about the convection ovens with air circulating, it's not the lack of circulation that's the problem, it's the type of t'stat used in most of the older kitchen or toaster ovens. The newer type digital controlled kitchen (or toaster) ovens provide better control, not quite up to PID accuracy, but still pretty darn good.

Allow me to explain a VERY simplified version of temperature control: The older style T'stat has a bi-metal coil that moves as it heats or cools opening or closing a contact. This isn't all that accurate and happens at set point. A PID (Proportional–Integral–Derivative controller) controllers "learns" where the contact needs to open or close to to keep temp at setpoint. Ideally the PID would slowly reduce amount of heat as temperature approaches setpoint so there is little overshoot. It seems most of the cheap PIDs used simply open or close a relay rather than reducing heat, it shuts heat OFF or ON. That is why it takes a while to settle down to temperature (as well as heating up the mass in oven). Say setpoint is 300°F, first cycle the PID might open contact at 300, see the temp overshoot to 325. Contact stays open until temp falls to 300, PID thinks might better let it fall a bit more, then at 290 contact closes and temp rises to 298 and contact opens but temp still rises to 310 this time. This cycle continues as the PID learns where to open and close contact to keep temperature right at 300°F setpoint. This is called the "Learning" portion of setup. Once this has cycled thru and the PID has learned the correct parameters, the PID will still overshoot and undershoot during heat up, but it will be less each time.

There is no reason in the world a small enclosure can't be temperature controlled as well as a large enclosure. It's all about the type of controls and heating element, not the cubic volume of enclosure. Check with any process control engineer on that. For anyone who needs to do lots of blades at a time a kitchen stove/oven makes sense. Mydigital kitchen oven will provide ±5°F just fine and that should be all that's needed. A PID controlled toaster oven with an extra fire brick for mass has no problem providing ±1°F control, and certainly ±2°F control is expected.

For the folks here (like me) who seldom do more than a couple of chef blades, or a 4 set of steak knives at a time a toaster oven with PID control makes good sense.

I had no intention of this getting so long, just started typing.

Ken H>
That makes sense. I'm familiar with the bi-metal coils that are used in old HVAC systems. It appears that the same setup is used in toaster ovens. I didn't know that.

I put a temperature probe in my toaster oven the last time I heat treated. However it was all over the place. It never did settle down.
I'm going to have to think about my next step.
 
Thanks for all the input gents. Turned out to be an interesting and informative thread.
I am erring on possibly converting my old toaster oven to a PID as I just found out my dad has one in his garage......so I can do it for free.

Or should I wish to get a more up to date PID etc it is cheap as chips. So I might try it but just for my wood stabilising oven as I am fed up of the thing get far to hot or if I turned it down to cold.

Luckily I have not had any stabilised blocks fail yet but knowing my luck there will be a failure in the future with the oven in its present state (bi metal control) which if my blocks failed to cure would be more expensive than the PID
 
Or should I wish to get a more up to date PID etc it is cheap as chips. So I might try it but just for my wood stabilising oven as I am fed up of the thing get far to hot or if I turned it down to cold.
I actually had good experiences using my toaster oven for stabilizing...but NOT for heat treating.

I think the simplest path of everything I've heard here is: A digitally controlled electric with fire brick in it. That because I'm an electronic idiot...and I have the other two...oven/bricks. So when I say simplest...I mean for Ted...lol.

Ken H helped me a BUNCH when making my marking unit (Him and Rick-07) He knows a lot so if you are at all queasy at electronics snap pics as you go and he'll get you squared away in a jiff...
 
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