Home made heat treat oven controller help

[jethro]

I am building a grinder and a heat treat oven. I have found a couple of digital controllers on ebay and am looking for advice. What do I need to get other than the controller. I ASSUME I need a relay and a thermocouple, but what else might I need?

I was planning on getting a programmable, but don't know how important it is.

All help and input would be greatly appreciated.

[Ed Tipton]

Jethro...You really haven't told us much about what type of knives you are making, or what the steel is that you will be using. I see you are in your eighth year on this forum, so I ASSUME you have been at least somewhat active during those years.
If you are working with 10xx steels, or some of the less "exotic" steels, then building your own heat treating oven may be overkill. I use 1080 and 5160 steels almost exclusively, and I do all of my HT in either a toaster oven or the kitchen oven. My toaster oven is programmable, and has worked perfectly for those steel types. I paid $5.00 for it at a garage sale. I know I couldn't even begin to make my own HT oven for anything like that cheap.

If in fact you still need to make your own oven, then you will need to decide on whether it is going to be gas or electric, and the obvious things such as what the internal capacity should be, 120 or 220 volts, how much "programmability" you really do need, what type of insulation you will be needing, the correct operating range for your preferred steel type, and how "tightly" the temperature controller needs to maintain the heat, and your ability to construct it properly so that it will function as the design calls for. If you still need to make your own, then you are probably working with one of the more "exotic" steel types, and you could be working with much higher temp ranges than what I work with. Make sure that ALL of your materials are rated to operate under the required conditions,
and that nothing is going to go "tits-up" when in service.

[SIXFOOTER]

I agree with Ed. That said, I started gathering up parts for my HT oven, it still isn't built, but I have most of the parts. Things I learned:
Carefully calculate the current limit for the wire your going to use for the heat element.
Select a control relay with at least 150% of that current limit. (at least 20 amps)
220 works better that 110
Soft fire bricks make an excellent liner
Fit the bricks very closely
put a thin layer of inswool between the bricks anf the oven shell
Put a good heat sink on the relay
Get a PID controller that comes with a thermocouple
YMMV

[jethro]

I knew I was forgetting something important! I have been using mostly A2 and D2. I have the firebrick and was getting ready to start building the frame for it.

[Geno]

I heat treat all carbon steel blades in my forge, and only use the oven on S/S blades.
I have a digitally controlled oven for richer chemestries, but most carbon steel blades work better from the forge to quench rather than trying to rip open envelopes and get it quenched in time.
A2 is air hardening and D2 quenches quickly, both can be done in a forge.
S/S blades require an oven for best results, but carbon steel blades are most often cooked in fire.
Now the grinder is worth every effort...
God bless,
Geno

[ARCustomKnives]

If you plan on building an electric HT oven, you will need several things.

First, as you already stated, you'll need a temperature controller. To use this, you will need the appropriate thermocouple, rated for at least the maximum temperature you forsee yourself needing to use. A lot of places sell TCs specifically designed for HT ovens.
You will also need a relay, the type of which will depend on your controller type. I recommend getting a controller compatible with a Solid State Relay (SSR). The type of SSR you get will depend on the current that your heating element will be drawing.
This of course brings us to the next item you will need: The heating element. Based on price vs. function, ease of installation, etc... I would recommend a pre-coiled Kanthal wire element.
The size/length will depend on how hot you want your oven to get, how fast you want it to get there, and what voltage you will be using. As someone stated before, 220VAC is ideal.j
3000W is pretty standard for a 220V heating element, IIRC. Also get some wire to make staples for holding your element in the grooves of your firebrick.

I would also recommend that you get some firebrick mortar for sealing your firebricks together. This will make your oven a lot more effiecient, as all of your heat won't be excaping through the cracks.
Along with that, I'd recommend some ceramic fiber insulation as well. You can use this to make a seal for your door, as well as to wrap your oven for an extra buffer against heat. (CF insulation is the cheapest route I have found, all things considered, as opposed to say, a ceramic board or paper)

Also, you will need a box for your controller and relay, along with (I forgot to mention) a heat sink for your relay. SSRs generate a lot of heat, and will self destruct unless that heat is dissapated properly.
SSR heat sinks are normally rated by the current draw of the SSR. Make sure you use heat sink compound to attach. (Some guys mount SSRs directly to the metal encloser they are housed it, if using a metal enclosure. I used a plastic box from radio shack for my control unit. Either way, I'd use a heat sink specific to the SSR to be safe.)

Whatever box or enclosure you use, make sure that it will house the controller, the SSR plus its heat sink, a power switch (a normal toggle switch is fine), and I recommend a 2nd switch for cutting power to the coil when putting blades in or out. For example, if you are using a 220V 15A element, you will have 220VAC and 15A running through the coil when it is energized (which it most likely will be when the door is open). Touching this with a blade while energized will equal bad news for you.
The power switch is SPST, and the coil switch will have to be DPST.
Finally, you will need a fuse for the controller (the manual for the controller will specify size and type) and I recommend a fuse for the heating element as well. (size based on current draw of heating element) Also, approprait fuse holders are needed.

Oh, and don't forget the appropriate power cord, based on voltage and current needs.
You will also need some various hook up wires for everything, as well as misc. hardware, such as hinges if mounting a door, a latch to close it.

I think that covers most or all of the major stuff. Obviously you'll figure out what's missing as you go along.
I would advise you to seek professional help for the electrical wiring portions of the project if you have any doubts WHATSOEVER. There are plenty of ways to screw things up, destroy equipment, or even kill yourself.

Sorry for the long post, but there's a lot to this oven building business...

[jethro]

Thank you Bassthumper!

I have ordered my controller, ssr, heat-sink, and thermocouple. I got them all from auber instruments. I also ordered their steel project box. I ordered my element from budget casting supply. It was the 220v. single element that has an operating length of 60" to 120". I still need to get the toggle switches and the fuses and fuse holders.

Thanks again for the information... Btw, I went with the programmable controller also.

[Mike Conner]

I found this link the other day to a video on making your own heat treat oven. It leaves out some details like the wiring schematic but that is easy to figure out. Just thought it might be of some help.
Mike

http://http://www.viddler.com/explor...id11/videos/3/

[PatrickKnives]

Couple of other things to consider, you have to get that red hot wire out of the inside of the oven and attached to your power, this is done with special high temp insulators, a high temp connection, and high temp wires that will connect to your relay. I did not see these at Auber you probably can get them from where you got your element.

I tried to use some clay to seal the bricks but just made a big mess, the brick adsorb the water so quickly I could not get a good fit between the bricks, I just set mine together. I did put kwool behind which seemed to help since the outside does not get hot at all.

Just to clairfy one of bumpers points, if you are going to put a cutoff switch for the element when removing blades, the switch should only be on the low voltage side of the ssr, dont try to switch the power to the element, by cutting the low voltage to the ssr you are doing the same as the controller and dont have to worry about working with a high voltage, high amp line. You can also pause the controller from the front panel and not need to mess with a switch.

[Josh LeGoueff]

I'm a little confused on one part, if I get a pid with ssr, is the relay already a part of the pid controller?

[jtdesigns]

I posted a complete wiring diagram on another forum:

http://www.bladeforums.com/forums/sh...-Future-Sticky

and it utilizes:

Dual SSR
PID w/ ramp and soak
Power on switch
Element switch w/ led light
Door limit switch

[jtdesigns]

No, a PID w/ SSR means SSR output...still requires an SSR