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convection oven mods


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Hi,

 

I picked up a convection oven this morning with the intent of using it for tempering blades. The dial goes to 450 but my oven thermometer told me otherwise. With the temp dial maxed I could only get a hair over 400. Are there any tricks for getting a few more degrees out of an oven like this? Thanks!

 

-jeremy

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Off the top of my head, it seems there could be two issues.

 

1) Poor insulation. How is the oven insulated? Perhaps if you increased the efficiency of the insulation by either adding more insulation or using better insulation. Are there any areas of energy loss? Cracks, or seams, where you are loosing heat. Cooking ovens are often vented, on purpose, to allow moisture to escape. Are the vents oversized for your purpose?

 

2) Are the heating elements defective or insufficient? Do you have adequate power for the oven? Most ovens run off 220V and if yours plugs into a 110 outlet, I would say you have a problem!

 

Last of all... Cooking ovens are usually horrible for tempering steel. The controls are simply not set tight enough to handle the task. Yes, you can make them work. Yes, you use what you have and they are affordable. That said, you would be better off building a tempering kiln with a programmable controller than putting more money into a kitchen oven.

 

~Bruce~

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thanks bruce. what i bought is a little convection oven (like this one http://i.ebayimg.com/00/s/MTIwMFgxNTk5/z/3s0AAOSwd4tT6Aai/$_12.JPG?set_id=880000500F), so its somewhere between a kitchen oven and a toaster. its what i can do for the time being, and i know that its not ideal. its what i've got though, and i'm looking to get the most out of it for now. i was just taking a stab to see if there were any tricks, possible electronic mods that would make it possiblty to kick it just a little bit hotter.

 

if i stick with this oven, my next step would be to mod it to work with a PID (like this http://www.bladeforums.com/forums/showthread.php/599423-Pid-Toaster-Oven-Conversion?

 

this one does have an exhaust out of the top, so i can look at that as a source of heat loss. i was thinking about making a box lined with insulation to enclose the oven. also a covering for the door, since it is just glass. i've read elsewhere that people recommend a pan of sand at the bottom to retain some heat and help even things out. i might try this, but really the oven seemed to maintain temperature, it just was not getting as hot as i'd like i to.

 

thanks for the help, bruce!

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The point of the sand is to add thermal mass. A thick plate of steel, set in there, will do the same thing and is a lot less messy than sand! Especially if you have young children and they like to "help" in the shop. Ask me how I know this. I have a very similar, toaster, oven that I use for tempering myself. The trick is too keep an oven thermometer in there and watch it to know where the temperature peaks at. You will probably hit the temperatures you are looking for by simply blocking the exhaust out the top.

 

~Bruce~

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a weird thing happened... i put a large-ish plate of steel on the bottom of the oven. about 3/4" plate by maybe 5x8. its what i had. i then put a sheet of inswool over the top, covering the exhaust fan, and also covered the glass-only front door. i cranked the oven to top temperature and "stay on" mode. it got up to about 300 degrees and stayed there. huh? so thats weird. so then i took the all the insulating layers off and the temperature was then able to reach the 400 range. i put the wool back over the front door, and i managed to get up around 430 or so, and that was after about 1.5 hrs total. i guess if i can get up that high and hold the temperature there consistently i can use this for some steels. i'd still like to push it up to 500 degrees or so, but maybe that is when i can invest in something better. anyway, i always enjoy a little bit of experimentation. thanks for the tips!

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Interesting discussion. I have recently experimented using a convection oven as well.Opposite of your issue, mine seems to run hot. I haven't actually gotten out my digital thermometer to determine the exact temperature, I was just going by color. I set it at 450 , and I was getting dark brown/purple which would indicate temperatures up to 550 F . Strange... certainly not a device I would use for alloys requiring precision tempering cycles. Works good otherwise.

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