# Cheap annealing oven



## homebrewed (May 10, 2021)

I recently had a need to stress-relieve some home made springs and learned that a toaster oven can be used as a relatively inexpensive annealing oven.  I also found some info on using a particular model as a reflow "furnace" for making your own surface mount print circuit boards (here).  So I did some browsing and found one on Amazon for a reasonable price -- this one .  But I noticed they had some with cosmetic defects for a much lower price, about half off.  I ordered one for a little less than $29 and got free shipping to boot.  When it arrived I took a close look at it, thinking I might need to repair a broken foot or the like; but I didn't find anything obviously wrong with it!

My wife thinks it's too nice to use as an annealing oven but we've never found the need for one of these things.  While looking good It will anneal hardened steel, stress-relieve springs and reflow circuit boards just fine .


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## Ulma Doctor (May 10, 2021)

Sweet score!
I bought a small oven similar to yours, but it was made by Krups. Works great for small stuff!
(I got it slightly used for $12 at Goodwill)


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## benmychree (May 10, 2021)

I do not think that device has enough temperature capability to do much in the way of drawing temper, much less annealing, a spring temper is around 600 deg. F


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## FOMOGO (May 10, 2021)

I got two for free. Had to repair both, but fairly easy fix. The best one is in the house, and I use it most every day. The other one is destined for the food area in the shop. Haven't checked the actual temp, but they do get hot fast. Might have to check it with the  IR temp gun. Mike


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## Boswell (May 10, 2021)

I have one similar for reflowing surface mount PCBs  but that is all I use it for.


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## homebrewed (May 10, 2021)

Ulma Doctor said:


> Sweet score!
> I bought a small oven similar to yours, but it was made by Krups. Works great for small stuff!
> (I got it slightly used for $12 at Goodwill)


Bettah yet!


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## Hawkeye (May 10, 2021)

I use a toaster oven, but more often my kitchen oven, for tempering, but they won't get anywhere near hot enough for annealing or normalizing. As with hardening, the steel has to get up to critical temperature (actually glowing) in order to anneal it. My gas forge or heat treating oven are required for those treatments.


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## homebrewed (May 10, 2021)

benmychree said:


> I do not think that device has enough temperature capability to do much in the way of drawing temper, much less annealing, a spring temper is around 600 deg. F


I can't report back (yet) on how it works for stress relief and tempering.  At this point just repeating stuff I "heard" on the I-net.  One source indicated 500F for one hour would do, another 450F in a toaster oven.  One thought that occurred to me is that the heating elements emit IR, while the oven's thermostat is listening to air temperature.  So, depending on what a part's emissivity is in the thermal IR band is, it could get much hotter than the air temp in the oven.  

There are some materials that have unusual characteristics in this regard, like silicon.  It strongly absorbs visible light but is transparent in the thermal IR region, so it can't emit IR down there.  As a result, when exposed to (say) sunlight it gets very hot.   This effect has an impact on the efficiency of solar cells, because their internal losses increase as their temperature increases.  It doesn't appear to be a large factor, but it's there.


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## homebrewed (May 10, 2021)

homebrewed said:


> I can't report back (yet) on how it works for stress relief and tempering.  At this point just repeating stuff I "heard" on the I-net.  One source indicated 500F for one hour would do, another 450F in a toaster oven.  One thought that occurred to me is that the heating elements emit IR, while the oven's thermostat is listening to air temperature.  So, depending on what a part's emissivity is in the thermal IR band is, it could get much hotter than the air temp in the oven.
> 
> There are some materials that have unusual characteristics in this regard, like silicon.  It strongly absorbs visible light but is transparent in the thermal IR region, so it can't emit IR down there.  As a result, when exposed to (say) sunlight it gets very hot.   This effect has an impact on the efficiency of solar cells, because their internal losses increase as their temperature increases.  It doesn't appear to be a large factor, but it's there.


Specifically, for stress-relieving springs.....


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## Winegrower (May 11, 2021)

I bought an eBay heat treating oven that was inoperative, for peanuts, and sure enough the fault was in the controls.   I took them out, and used an inexpensive PID controller and solid state relay, works directly on the AC line.    While I didn't use it for heat treating, it made an excellent oven. Temperature stability was OK, maybe +- a half degree C.


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## GunsOfNavarone (May 11, 2021)

I'm working on a project right now that is A2 tool steel. As I am fairly new to CNC, I have seen some obvious signs of work hardening (ironically when I'm being to cautious). If I did work harden an area I was working, are you saying I could use a toaster over to anneal the part and give it another go? If the answer is yes...this would be something I would also be interested in. Would a oven work at well? I have no idea the exact temps but I thought it was something like 450* for a couple hours? I'm not sure if that is dependent on type of steel?
I really want one of those Hot Shot ovens but that's a whole investment, but would open doors that are not available via a toaster oven. Honestly annealing would be more useful to me now that tempering/hardening anyway. Make a Pop Tart and anneal a work piece? Sign me up!


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## COMachinist (May 11, 2021)

GunsOfNavarone said:


> I'm working on a project right now that is A2 tool steel. As I am fairly new to CNC, I have seen some obvious signs of work hardening (ironically when I'm being to cautious). If I did work harden an area I was working, are you saying I could use a toaster over to anneal the part and give it another go? If the answer is yes...this would be something I would also be interested in. Would a oven work at well? I have no idea the exact temps but I thought it was something like 450* for a couple hours? I'm not sure if that is dependent on type of steel?
> I really want one of those Hot Shot ovens but that's a whole investment, but would open doors that are not available via a toaster oven. Honestly annealing would be more useful to me now that tempering/hardening anyway. Make a Pop Tart and anneal a work piece? Sign me up!


You will need about 1550-1600 deg F soak through for A2, then cool at 40 F/ hr to 1000 F and you can cool it by leaving in the oven with door open to cool normally. So no, a toaster oven will not even come close. You can get temper it at 400-500 so it is useful for tooling. If you can find an old garage sale with a ceramic kiln for sale, you can do some fair hobby shop heat treating, of crucible steels.  
CH


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## homebrewed (May 11, 2021)

Winegrower said:


> I bought an eBay heat treating oven that was inoperative, for peanuts, and sure enough the fault was in the controls.   I took them out, and used an inexpensive PID controller and solid state relay, works directly on the AC line.    While I didn't use it for heat treating, it made an excellent oven. Temperature stability was OK, maybe +- a half degree C.


Yes, you can get very affordable PID controllers and SSRs these days.  Makes it easy to build up a temperature controlled system.  I have one hooked up to a slow cooker whose built-in controller failed.  I use it for sous vide cooking, among other things.


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## Winegrower (May 11, 2021)

Off topic a bit, but a bit like homebrewed mentioned, these controllers have a lot of uses.   I put a 60 watt bulb (remember those?) in an ice chest and controlled the temperature precisely for brewing kombucha.


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