Potters kiln as a heat treating furnace?

Discussion in 'Shop Talk - BladeSmith Questions and Answers' started by Nic., Apr 22, 2016.

  1. Nic.

    Nic.

    814
    Dec 8, 2014
    Hi! I was at our local gun store today (they get all sorts of other tools and stuff too) and saw a kiln in there. I wish I would have got pictures, but it's an octagon and about the size of a big boot box. I talked to the one of the guys there...apparently they tested it and it reaches 1800 degrees. It is electric and variable temp. I've been using steels like 1084 and 1095 where I need temperatures of 1475, so the temperature shouldn't be an issue. Hopefully this isn't a silly question, but would something like this work well as a heat treating furnace? I would probably have to put a rack in it for blades to sit inspired they weren't just laying on the bottom of the kiln, but otherwise I think it would work...but I wanted to ask the people that are more wise than me.
    Thank you!
     
  2. Lieblad

    Lieblad

    Jul 24, 2015
    I think it can work. Be sure you can accurately maintain temperature.
    Might be a bit large unless you run alot of parts.
     
  3. Stacy E. Apelt - Bladesmith

    Stacy E. Apelt - Bladesmith ilmarinen - MODERATOR Moderator Knifemaker / Craftsman / Service Provider

    Aug 20, 2004
    They "can" work, but are not really what you want. What I did with one was make a low temp salt pot for marquenching and heat bluing with nitre salts.
     
  4. Nic.

    Nic.

    814
    Dec 8, 2014
    Ok, thanks guys!
     
  5. stalbot

    stalbot

    315
    Sep 7, 2012
    a guy I work with, Dan Graves, uses one to do his heat treating. No issues. You can see some of his work if you do a search here.
     
  6. deker

    deker

    Nov 14, 2005
    You can use them just fine for HT. They can be a bit big so they'll eat a bit more power and take longer to come to temp, but work just like any other kiln. The key with an older pottery kiln is that the controls tend to be not as nice as we like as bladesmiths. I just recently re-fitted a large kiln that I picked up years ago so that I could HT stuff that won't fit into my Evenheat. It was older and had one of the cone style controllers that was no good to me at all. So, I got a PID controller that could drive some relays and made it digitally controlled. It's not that hard to do if you are comfortable with hooking up electrical stuff and if it's a good enough deal to leave you a couple hundred $$ to put a digital control on it.

    Let me know if you decide to head that route and I can take some pictures of min and describe the electricals.
     
  7. DanGraves

    DanGraves KnifeMaker / Craftsman / Service Provider Knifemaker / Craftsman / Service Provider

    Mar 5, 2006
    I have one that I put a pid controller on and it works great. Have had it about 8 yrs. Love it and if the price is right I would go after it.
     
  8. Nic.

    Nic.

    814
    Dec 8, 2014
    Ok guys, thank you for the feedback! It sounds like putting a different controller on there is the way to go. Just curious, how much would I be looking at for one of those controllers? I'm pretty good with wiring, so that wouldn't be an issue.
    By the way, is that Deker the forged in fire guy? I would love to see pictures of you don't mind, thank you!!
     
  9. Drew Riley

    Drew Riley Riley Knife and Tool Knifemaker / Craftsman / Service Provider

    Oct 17, 2007
    Check out Auberins.com. They have some good products and great customer service. Price will depend on a number of things, especially if you want a programmable PID.
     
  10. Stacy E. Apelt - Bladesmith

    Stacy E. Apelt - Bladesmith ilmarinen - MODERATOR Moderator Knifemaker / Craftsman / Service Provider

    Aug 20, 2004
    I'll explain my comment:

    They will work, but are not designed to be used for HT. They are made to bake slow and long. Big units are more usable than small ones. Many require 40 amps at 220VAC.
    For firing pottery, as I remember 1800F is barely enough for normal clay baking work. It takes a bigger and hotter oven to vitrify glaze and fire earthenware.

    You gave the specs as 110VAC and 1800F max - That isn't a big one. The first of the problems comes from the depth not being sufficient to hang blades. Opening the top to put in and remove blades is not a pleasant (or safe) thing. Most folks make a hole in the top and suspend the blades on 1/8" stainless hanger hooks. They put a fire brick or layer of insulation over the hole.

    Most likely you will need to make a pottery kiln PID controlled, as the temperature control for a knife HT and a pottery firing are far different things. This isn't hard to do, but adds about $100 to the cost.

    Additionally, the last 200-300 degrees on the pyrometer scale dial are like the last 30 MPH on your speedometer. You are unlikely to get there easily. I found most 110 volt devices that have a scale reaching 2000F will go to 1800F max. Ones rated for 1800F usually get to 1600F reliably. Because pottery kilns are designed to take pottery from cold to as high as the fusion point of the glaze ( around 2400F), they are massively insulated, and minimally heated, they heat up slow to allow the clay to slowly change. If you open the oven while hot, the temp will fall, and it takes a while to come back up. The big kilns have sufficient thermal mass in the thick refractory to keep these swings smaller, but the small hobby kilns can take a good while to return even 50 degrees. Knives require a pre-heated oven, so we use faster heating coils. If the temp drops, they rebound fast.

    I say if the price is below $100, get it and play around. Add a PID controller. At the least it can become a small tempering oven.

    I took one and cut a 4" hole in the top. I made an 18" salt tube from heavy walled 4" OD stainless pipe. I have niter salts in it for low temp salt quenching and bluing hardware and damascus. I wrapped two layers of kaowool insulation around the exposed pipe that sticks out the top of the kiln.


    Final comments and summation-
    Pottery kilns are not designed to be opened once hot.
    They are not designed for rapid temperature changes.
    They are made to be sealed up and run through a firing cycle that ends at room temperature a day later.


    And beware ******** They are not usually made with door interlocks. That means the coils are powered when you reach in and pick up a blade. If the blade touches the coils you can receive a serious .. or fatal... shock. Your HT gloves will most likely protect you, but that is a chance I would avoid rather than take.
     
  11. Kevin McGovern

    Kevin McGovern

    Jul 31, 2015
    I have toyed around with the idea, so I appreciate Stacy's input. They are tempting as they are often for sale cheap on craigslist. I keep going back and forth between getting one cheap adding a PID ( and now altering the top per Stacy's comments) and making my own oven from scratch. When i run the numbers, the build costs really add up with bricks, coils, steel, terminals- all things the pottery kiln would not need. Add to that the PID, SSR and heat sink and the pottery kiln can be a pretty attractive option. Jury's still out for me, so I'll keep using the ol' paint can forge for the time being.
     
  12. Nic.

    Nic.

    814
    Dec 8, 2014
    Well when you put it that way Stacey, it isn't as attractive! Thank you very much for all the input and sharing of experience! I might play around with it, but all of your info makes a lot of sense...thank you for taking the time to share your knowledge!!
     
  13. deker

    deker

    Nov 14, 2005
    Ask and ye shall receive! Don't want to derail this thread, so look here.
     

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