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Possibly the simplest oven a noob can build?

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  • Possibly the simplest oven a noob can build?

    Hey folks. My name is Anthony Park. I'm a swordsmith and I'm looking to build what i hope to be a very simple oven.

    It just has to be long enough to temper a sword, not heat treat it.

    So basically I have to bake a 4 foot long by up to 6 inches wide(in case a wide sword curves) piece of metal. Up to 600 degrees.

    I would like this to be inexpensive. it's basically a 5 or 6-foot tube as i envision it. A large tube with insulation and some kanthal wire.

    I figure kanthal because it seems difficult to find inexpensive heating elements of 4-foot length.

    It's an 9 inch duct tube with 2 inches of insulation and kanthal heating elements.

    it stands vertically so the springs hang.



    Questions: So if the inside dimension of a tube is about 6 inches wide by 4 ft long. How many kanthal springs will I need?

    How do they hook up to the PID

    How do I know which PID to buy? I don't know how many watts or amps or any of that stuff. I'm sure there is a formula for that but I don't have any of the variables..

    I hope you can lead me by the nose a bit to a successful oven build with inexpensive parts.

    Thanks in advance!!!

    Anthony Park


  • #2
    I have no experience with Kanthal but I can suggest and ask a couple questions. First, most pid's can only directly support a small amperage load so you're most likely going to need a relay, either an ssr or contactor. To keep everything in a safe manner I would strongly recommend that all electrical components be enclosed in some sort of metal box. The pid would control the relay based on feedback received from a tc(thermocouple) mounted inside the tube.

    As for the Kanthal wire I'll also assume it cannot touch any metal so if you're looking to use a metal tube which I assume if you're going upwards of 600 degrees the wire would somehow need to be isolated from the tube. If it can operate on 120vac then the hot side of the wire would connect to the relay while the neutral would connect directly to the source. If I get an opportunity I'll search the wire. I would guess the resistance per foot would be in the specs. With that you can easily calculate the load using ohms law.
    Last edited by ed_denu; 02-12-2021, 11:48 AM.

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    • #3
      I did a quick search on Kanthal and found that each coil of wire is supplied with a resistance number per foot but I didn't see specifics. I guess you might need to inquire or order a specific product. I also didn't see standard lengths, etc. so I'm not sure what or how much product you would need to buy.
      Last edited by ed_denu; 02-12-2021, 11:50 AM.

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      • #4
        hi ed, thank you for responding. do you think you can do a little shopping for me and find some links? It may involve some remedial math. or maybe you could take the time to walk me thru it as you understand it. then i can do the shopping.

        The inner side of the tube will be insulated with kaowool (I don't yet know how to get the kaowool to stick per se, so help with that also would be much obliged. )

        I suspect there is an outer bound for how many amps or watts or whatever will operate on 120 from the wall. But thats all I really know.

        Lastly, i also cannot see in my minds eye what the not hot end of the kanthal spring connects to.

        I can build guitars, I can make swords, and I can do investment calculus, but remedial physics and how that affects what I purchase could use some help.

        Comment


        • #5
          You don't state where you're located but if in the US wall receptacles are typically either on 15 or 20 amp circuits. This obviously will limit you to around 1500 watts.

          The Kanthal website lists some calculations for resistance but honestly I don't understand their numbers. If you had a product in hand it would be very simple to measure resistance with a mm. You could then determine the maximum length of the heating wire that could be supported via a 15-20A receptacle. Their site does show a chat option so you might try to get a simple answer from them via a chat.

          I'll post a simple wiring diagram later that will show you how the wire would connect to the relay. It would be no different than an ordinary oven element. A simple explanation would be that the wire just connects between the hot and neutral feeds of the circuit. The resistance internal to the wire determines how hot the wire will get. Since it's not a dead short the circuit breaker will not trip.
          Last edited by ed_denu; 02-13-2021, 07:50 AM.

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          • #6
            Here is a simple 120vac wiring diagram using an ssr and two elements. Drop one element and this would be useable with your setup.
            120 Volt Service SSR.pdf
            Last edited by ed_denu; 02-13-2021, 11:27 AM.

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            • #7
              I live in Arizona. Will one element be enough to heat a sword in a tube roughly 6 inches in diameter by 4 feet? Thank you so much for trying to help. I really, realy appreciate it.

              Comment


              • #8
                Theoretically 1500 watts, the approximate maximum wattage capable with a 15-20A service, can easily heat 4 cu ft in around 10 minutes, so yes one element of that capacity would be sufficient. However I'm still not sure you've determined what the Kanthal wire is capable of producing. The plan of using a wire to produce heat eliminates the obvious problem of even heat distribution as it would run the entire length of the enclosure. Any other solution and you're dealing with the need to circulate air.

                I think two questions need to be addressed. First what is the resistance per foot of the Kanthal wire, and second is it capable of existing in an enclosure with no air circulation, reaching 600 degrees without issue. The Kanthal site certainly shows the strips to be capable of high heat applications, but have you inquired about small retail sales?

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                • #9
                  I did a quick search and these elements could possibly work for you. 120V and good to 1700 degrees
                  https://www.mcmaster.com/strip-heate...-and-dryers-7/

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                  • #10
                    hey Ed. I looked at that and saw this one. What do you think?

                    I guess its no different than kanthal in that one end is positive and one is negative. this one will bend in half. It's 60 inches long. Do you think one element stretched to its full 60 inch length would be good enough and also avoid a fan? I'm not opposed to a fan, just that its an extra part.

                    I have to figure out how to terminate both ends outside the oven though correct? I guess that will mean 2 junction box like things to cover any wiring. thoughts? what gauge wiring will i need to wire this element to the various computer parts?

                    Wattage,
                    W
                    Watt Density,
                    W/sq. in.
                    Current,
                    A
                    Lg. Material Max. Heat
                    Output, °F
                    Min. Bend
                    Radius
                    Wire Connection
                    Type
                    Size Type Mount. Fasteners
                    Included
                    Each
                    1,500 30.6 12.5 65" Incoloy 1700° 15/16" Screw Terminals 10-32
                    UNF No 3540K43 42.50

                    Last edited by Tony Park; 02-17-2021, 04:13 AM.

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                    • #11
                      If the element stretches the full length of the tube I don't see why you would need a recirculating fan. Yes, you will need to figure out a way to connect each end to the wiring, incorporating a junction box on each end of the tube would be acceptable. Use hi-temp wire wherever it would be exposed to heat. Thhn type cable is sufficient once routed outside the junction box. 1500 watts wouldn't require any wire above 14 gauge. Wiring within the control box could certainly be smaller gauge but no problem sticking with 14ga.

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                      • #12
                        So, one last question for now. Is it best practice to bend the element so that the terminals are outside of the oven chamber, or is it best to leave the element completely inside the oven chamber and use high temperature wire to hang it inside, and run the high temp wire through the pipe to the junction boxes?

                        I ask because this will be a vertical oven and it had to have a door to get the sword in and out from the top.

                        Relatedly, if I am to bend the element so that the terminals are outside the chamber, that means some hot element will be running thru insulation to the junction boxes. How do I insulate the elements such that the insulation doesn't burn?

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                        • #13
                          Your configuration is unconventional so you're going to need to be resourceful. Typically an element would be mounted(screwed) onto the jb and the connections then made internal to the box. That's going to be harder with a cylindrical shape that requires an opening on one end.

                          I think I would look at an element size that doesn't require bending or at least not a bend that reverses the direction of the element. Adjust your tube size to be slightly larger and fix one end of the element to a jb at the end of the tube, then possibly put a 90 degree bend at the other end going through the side of the tube into a jb mounted outside the tube. An element slightly shorter than the length of the tube isn't going to materially change the heating characteristics. Just a thought. For safety concerns you never want the element ends and connections exposed where someone can come into contact with them.

                          I'm not sure what insulation you're looking to use but mineral wool or similar will not burn.

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                          • #14
                            Thanks for all your help. As I gather materials i will post back to show you how far im getting... Thanks so much for your time and talent. By the by, if you have any questions about investments and tax, asset protection, estate planning... consider any knowledge i have at your disposal, gratis.

                            Just email me at [email protected] and i'll be happy to help. You can also find me on desktop computer at panopticglobal.com... doesn't work on mobile for some reason.

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                            • #15
                              Hi Ed, ok, so I've decided on the element and have a running idea how to build this. What controller and other electronic equipment for this project? Inexpensive but durable is the idea for this part

                              Basically, its a large tube that will sit horizontally and the element is a large staple with short legs that run out of the side of the tube thru ceramic pipe to the junction boxes.


                              its an 8 in diameter pipe with 2 inches of kaowool.... should I use refractory cement to get the kaowool to stick to the side of the tube

                              and foil backed mineral wool for the outside. The wool will be substantive enough to fill a simple 1x1" wood frame with dimensions of 16x16x60 inches. Probably doesnt have to be that substantive but you get the idea.


                              I'm using the same element as above: 3540k43 @ McMaster Carr

                              Is there anything available on Amazon that will work reliably?











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