How I am making an electric furnace

First off, I changed the title. It sounded a bit too much like 'this is how to do it, every other way is wrong'. I also got some helpful, informative feedback on potential future issues. So this is basicly my build log on an experiment to see how well it works. Copy my ideas at your own risk.

Here is the schematic I drew that I used for the forge, and will also use for this oven. The switches are lighted, so when the switch is on, it's lit. That is what pin three is for. If you are not using lit switches, just omit the wires to pins 3. Also, I'm using the 2nd alarm of the pid controller to turn on the fan at about 100*. I did this only so the fan would not be running while I'm messing around with the controller with the heater off. This is completely optional, as I could just use the switch to manually turn the fan on or off. But, the controler has the extra output, so why not use it. I did not put pin numbers in the schematic for the pid, because you may be using a different controller. Also, don't be jealous of my mad bitmap image skills.



The first part I want to make is the bus bar. I got this from lowes. I forget how long it was originally. Just cut it to length, and cut the corners as shown. Band saw, hack saw, teeth, whatever you have. File or grind it smooth. Drill the holes and attach it to something non-conductive. I had this scrap piece of plastic that works well. And is proven (from my previous project) to hold up to heat well. Make sure to sink the head of the screw into the block so it can't touch the metal structure you attach it to later.




That's all for now,
Thanks for watching,

 

Well Kelly, I do believe you are 100% correct. So now I'm left with some choices to make. For as much as I hate doing re-work, I think the best thing for the burnout oven is to add an additional 1-in of wool. So that would give me 1 1/4 in total. No need to remove the 1/4in already there. I am tempted to just press-on and worry about it later, but I know that when 'later' comes, I would be wishing I took care of it now. So before I continue adding the electrics (my new controller will still be a while arriving anyways), I will undo the wired in ceramic rings, add more wool, and rewire them. I'll try it without additional posts and see how loose they feel.

As far as the bread-maker forge, well, that is already done, and given it's design, would be pretty much impossible to fix without a complete rebuild. So for that, I think I will completely redesign the hotbox section. I will design it with the plan of having 2 inches of wool with a stainless shell. Then I will just swap the electric section over to the new hotbox. Hopefully I can get that done before the original one fails. In an attempt to prolong its life, I will try to replace the thin ceramic paper with 1/4 in wool. There isn't enough room between the coils and the wall for anymore than that.

Thanks again for the advice,
Scott

 

Boy am I glad today is done. Just my luck, the part of the build that is the most tedious and least fun is what I had to do twice. Basically I took everything apart, added an inch of wool, and put it all back together. So no pics this time, because it looks pretty much the same as the last pics.

Since this is just the burnout oven, and the temp probably won't get above 1000, I hope 1 1/4in of wool now is enough to protect the steel walls. I would have added 2 inches (2 layers of 1in, I only have 1/4in and 1in), but I am running low on wool, and it was difficult enough as it was refitting the coil. It was almost too long with the extra loss of wall length. I don't think I could have got it to fit if I added any more wool. When I redo the forge, I will build it to accept three inches of wool.

I didn't add any spacers under the ceramic bushings (which I got from my local mom&pop appliance repair shop). I just wired it so that it would not crush into the wool too much. they are a little bit loose, but it works fine.

I hope to get all the electrics done (again, minus the PID) within the next few days, and then work on getting the outer cover installed. I also need to get the door done and installed, and add some wool to the ceiling and floor. Still quite a bit of work left, but I think I got the bulk of it done.

As much as I hated to redo the liner wool, I'm glad I did. I lost a few square inches of space, but hopefully it will work out much better for me. So thanks again Kelly.

Till next time,
Scott

 

6 lb.

 

Not much got done today. I did get the fuses, bus bar, power cord, and SSR installed. Make sure you use thermal compound between the SSR and heat sink. I also wired what was there.
Later,

 

I've been slack'n off a bit the past few days. I did as much wiring as I could. I'm short two switches, so I'm waiting for those. The wiring will be cleaned up later.

I started on the door. The first step is to remove all of the plastic parts of the door. The outside has a recess that's good for laying in 1/2in of ceramic wool. Then I cut and drilled a steel wall to be riveted on top of that. I'm also out of steel rivets, so that's a trip to Lowes tomorrow.

The inside of the door will receive 1in of wool and a fiberglass wood stove door seal.

 

Hey brother... Do you know about TGGT wire? This is stuff designed to be near heat. I think it's some kind of fiberglass coated wire. A little more found here. http://www.alloyavenue.com/vb/showthread.php?12805-Wheres-the-electricians&highlight=kiln

There is a place in ocala, FL I got it from. It's cheap, the right stuff and they shipped fast. I see they doubled the price... hmmm :-/ http://www.ebay.com/itm/PER-FOOT-10...499941&hash=item3f72345fab:g:t48AAOSw9GhYYWI-

 

That's actually the wire I'm using to connect to the heating element.

 

perfect.

 

Well, the wiring is all done. and tested. One thing I noticed that I'm trying to decide if it bothers me or not: I wired the fan switch between the fan and the PID. Which means, the switch doesn't see any power until the PID turns the fan on, which means the little red LED on the switch only comes on when the fan is on. If I would have wired the switch between power and the PID, then the LED would be on when the switch was on. In other words, the way it is now, the LED is a 'fan on' indicator. The other way would be a 'switch on' indicator. It's not really a big deal either way, but the other two LEDs are 'switch on' indicating. Oh well. I guess I can live with it.

I also try to do a better job with wire management, but I think it's ok.



The door is almost done, So I basically need to put on the cover, make the back panel, install the door, and it should be ready to go.

I do have one question though. I read somewhere that a burnout oven needs a vent so the wax or PLA fumes can escape and not accumulate in the oven. Is this correct? And does anybody know the formula for over size/vent size ratio?

Thanks for any input,
later,

 

So THAT'S why my kiln whistles a little when I lift the lid. No kidding, learned something new today and it's not even 8am. Well I'll be dipped in slurry!

 

The vent has been something that has been in the back of my mind since day one. I did do a search for it, and did find lots of figures and pics on kiln vents. But I didn't find anything that specified how big the vent hole should be compared to the area of the kiln. I'm thinking if it's too big, then you would lose too much heat, and if it's too small, then it wouldn't be as effective.

So, when in doubt, 'eye-ball-it'. I started by buying two 3in dia 90 degree elbow ducts from Lowes. I wanted to take advantage of the hole already there that was once part of the wave guide, but since that was raised up a bit, it put the pipe too high up. So I drilled a 1in dia hole in the top that would allow me to position the duct out the back of the oven. I think a 1in hole should work fine. It doesn't look to big or too small.

And yes, I do realize that the pipes are galvanized. I did a bunch of research on the use of galvanized metal with high temp applications. I found a bunch of contradictory information, but from what I could gather, it will not give off any fumes until it reaches a temperature much higher than I plan on my oven getting. And, even if it does give off fumes, remember it is part of the ventilation system. So the fumes will be vented out and away. And even if, worse case scenario, it does give off fumes, and the vent aspect of it fails, and I breath in the fumes, it will be much less than OSHA sais is an acceptable amount to be exposed to. And even if, worse-worse case scenario, I manage to breath in a huge amount of fumes, the poisoning effect only lasts 24 hours, and it only causes cancer if you live in California, so I'm fine.

The 3in duct sticks out the back about 2in, so I will now need to build a fan box and get some 3in flexible ducting. I already have a fan (from the microwave), so that part should be fairly easy.

I also installed 1in ceramic wool to the inside ceiling, and held that in place with .041" stainless wire. It's sort-of 'sewed' in place.



The next step is to insulate around the hot box liner, install the cover, install the door, make a few panels to seal off some openings left over from removal of the microwaves plastic vents and panels, and it should be about ready.

Thanks for watching,
Later,

 

I think it's looking good. I wouldn't be worried about your galvanized fittings.... if they do get hot enough to smoke, replace them with some black pipe fittings from HD. Eventually, it will all burn off. Ya seem smart enough, you won't be running this thing on the kitchen counter top. lol Is that .041 wire easy to replace? It will be interesting to see how the stainless tolerates high heat cycles. I'm usually the guinea pig, you can carry the torch for bit.

The only thing that scares me with electric kilns is reaching in there. I started to reach in that big pottery kiln of mine once with that sucker on. I caught myself real quick when I remembered I was wearing a metal suit. You could always add a safety switch on the door of your setup??? hint hint

 

Kelly and Jason, thanks for the input.
I have thought about a switch for the door, but as of now I still don't know exactly how I am going to make the door latch, so it hard to think about the switch. I would like to add one, but we'll just have to wait and see how it goes.

And that's a good idea about the vent gate. I'll probably do that. And keep in mind, the duct is 3in, but the hole the duct will suck from us only 1 in. I could always make that bigger.

I did think about the wire replacement. It will all (mostly) be accessible by taking off the outer cover, but hopefully that won't be for a while. I've heard of people using this wire to make heater coils out of, but don't know how long it will last. So I guess I'll find out eventually.

Thanks again,