Building DIY Wax / Burn-Out oven for Casting

[JacksonRobinson]

Hey everyone! I'm building a DIY Kiln that I plan on using for a wax burn-out oven for casting. I will be casting sword/knife parts. I stumbled on a few great DIY heat-treating oven resources here and on youtube (Red Beard Ops and DC Knives)

I would love some "extra eyes" of my plans and calculation, while still in paper form, in hopes to not end up burning my house down.

Basic Oven Specs (I think?)

Interior Oven Space - 15.5" x 9" x 9" = 1395 cubic inches / 0.8062 cubic feet
Watts per Cubic ft - 4339.3



These are my calculation based on the Ohms Calculator Spreadsheet DC Knives provided.

Voltage - 240
Desired - W 3500 (This number is arbitrary for me; I just picked something that gave me the desired length of stretched coil)
Number of Elements - 2
Amperers - 14.583 (I have plenty of room for this number to increase. I'm putting in a new 100amp service panel in my shop and can honestly put in whatever size breaker I want, so if you guys have any better suggestions, I'm all ears.)
Ohms - 32.914
Coil Diameter - 0.375

Length of wire 16awg
Coil length - 6'
Stretched Coil length - 12'

I know this may be very straightforward, but I would rather ask than burn something down.

1. When I input the number of elements being 2, that refers to me using two different heating elements running in parallel, correct?

2. If it says my "stretched coil length" should be 12', does that mean I need to split the 12' in half and have two elements that are 6' long, each with 16.457ohms (32.914/2)? OR Do I need two coils that are both 12' long with ohms of 32.914 each?




I hope that makes sense. I appreciate your help.

 

[Stacy E. Apelt - Bladesmith]

Welcome Jackson.

First - If this is only for wax burnout, 1500 watts and 110VAC will be enough for most size flasks, and 220VAC and 2500 watts would be as big as you would ever want. You can buy a used burnout oven for pretty cheap, so building one may not save a lot. I have one I would give you if you lived near me.

Burnout ovens don't need, or want, rapid heating, nor do they need high temps. Molding wax melts at 700°F and burns at 1300°F. A few hours to 8 hours is required depending on the mold size.

If you will be doing HT on blades, the wattage is fine but the chamber is too small.

 

[JacksonRobinson]

Thank you for the reply. In terms of the size of my chamber, I'm building it to custom fit my 5" x 10" flask. I probably will not use it for heat treating and build one of those later. I will be using wax and also castable resin to burn out.

Should I still be good with those factors?

Also when input that I'm using 2 elements in parallel do I split the required coil length by two or make two coils the required coil length. (Based off DC knives olhms calculator sheet)?

Thanks again.

 

[Stacy E. Apelt - Bladesmith]

Jackson. You have two identical threads running. I am going to lock the old thread you resurrected and link it here.

Old HT oven build thread is here:

DIY Heat Treat Oven Build

Series is additive for the resistance. Parallel is divisive for the resistance. Two 10 ohm coils are 20 ohms in series and 5 ohms in parallel.

www.bladeforums.com

 

[Stacy E. Apelt - Bladesmith]

Jackson,
I don't know how much casting experience you have, or what knifemaking/swordmaking experience you have, but these are things that take a good bit of time and money to learn. Guys like Bill and I have been casting for half a century each. I've been making swords and knives for 60+ years. But neither of us started on big casting projects, complex folders, or Samauri swords.

I'll give you some advice that many experienced makers will back me up on:
You can only do so many things at a time. Building a HT oven takes time, materials, skills, and money.
If you have a good income in your custom playing cards business, I suggest using some of that money to buy a large enough burnout oven and spend the time on learning casting of large objects and making swords and knives.

BTW, a used pottery kiln is often stupid cheap (sometimes free) and will do a burnout quite well. It can be cheaply modified to PID control for exact temperatures.

 

[Hubert S.]

Thank you for the reply. In terms of the size of my chamber, I'm building it to custom fit my 5" x 10" flask. I probably will not use it for heat treating and build one of those later. I will be using wax and also castable resin to burn out.

Should I still be good with those factors?

Also when input that I'm using 2 elements in parallel do I split the required coil length by two or make two coils the required coil length. (Based off DC knives olhms calculator sheet)?

Thanks again.

I'm not an electrician, so take this with a grain of salt. The coils are essentially resistors. If you have two resistors with a resistance R in parallel, the combined resistance is R_total = R/2. To keep the same R_total, you have to use twice as much wire for your parallel coils compared to a single coil. If I remember correctly, Dan's spreadsheet is set up to give you the length of each of the parallel coils, so you don't need to split it in two. You can test this in your spreadsheet by changing between 1 and 2 coils and see what happens to the length. The length for two parallel coils should be twice that of a single coil.

Note that the stretched coil length given by Dan's calculator is an absolute minimum length for a stretch factor of two. I forgot all the details from when I build my oven, but I think I stretched the coil a good bit more, maybe 3x. There is a "Kanthal Handbook" PDF on the web that I found helpful to calculate surface loads. I remember Dan's spreadsheet can produce coils with excessive surface loads, but if you can somehow fit two parallel coils in there, you probably don't have to worry about that.