Pottery Kiln and metalworking

Gah. How big is it?

Pete

yes. you can still get parts for it at

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Interior is septagonal about 16" across, 20+" high.

Wes

I am sure that it is useful if you can find space for it. For $20 you definitely did OK. I once bought a twice bigger kiln for $50.

i

You did ok but you will come to complain about it!! It certainly gets up to the temp ranges you need. But the pottery kiln tends to be made to take mostly round/cubic objects, the kiln has a roughly spherical work space. Most of the objects you want to heat treat are much longer and thinner, ie shafts, knives, etc. Lots of wasted heat there. top loading is really a lot of fun when you try and pull out a chunk of A-2 at

1750F. Annealing is fine, just fire it up to temp, let it cool in the kiln. May have to give it a jolt of current every 15 minutes or so for the first couple of hours.

Odds are good that the coils will be really heat cooked, if they are even still working. No big deal, the pottery supply places have all the replacement elements. Last time I was doing one they were around $25 per coil, takes several coils for a kiln that size.

You will want to put > Uncle was at an estate sale today and called to ask if I wanted a twenty

Now youve gone and done it! It's gonig to take a hundred post thread to hash over that word. :-) ...lew...

That is the word that came to mind at the time. How was I supposed to know the popular term would heptagonal?

Wes

[snip]

I figured unloading would not be optimal but this is much better than nothing. 6 years ago I could have bought a small side loading oven for 20 bucks but passed on it thinking I didn't need one. (wood dorking days). How I regret that, it had a digital control and I knew its history.

I still have to turn it on. Supposedly it was working but that was 10 miles of driving and some moving around ago.

I was looking over ebay. I have a temperature controller that I repaired, going to need a relay and proper thermocouple.

Wes

I already do something similar with my Lee casting pot for casting lead bullets. I wired up a old omega cn76000, a iron-constantine thermocouple and a cheap mechanical relay attached to a duplex receptical. The pot is plugged into my controller and I set the pots thermostat to a bit above a reasonalable casting temperature so it can act as an overtemperature safety in case something goes wrong with my control setup.

So do you have any tips on how to set things up for easy, safe unloading?

Wes

I would try using zero crossing SCR units. I converted a couple of furnaces to them and have had no problems. One of these days I will do my own, but the banging on and off of the main contactor I can hear in the office so I know the thing is on.

John

I haven't delt much with top loading furnaces but the ones I've seen hang the stuff or have a basket to put the metal into.

John

Nothing I have done so far requires rapid unloading from this furnace as the annealing, tempering and normalising all can be left at a fixed temp or left to cool naturally with or without the lid open AFAIK. For quenching I have a smaller furnace that has done so far but the top loader could be used, the pieces just being removed quickly for quenching.

If you are worried about electrical safety and the problems with electrical conductivity at high temps then my top loader does cutoff the element supply when the lid is opened, I think this is fairly standaard.

Perhaps it would be possible to modify one side to allow long objects to be passed through. In particular, it is often not necessary to treat an entire shaft, but rather an end or a bearing journal, for example. Slight modification to the firebricks would probably permit objects to extend out one or both sides, likely with plugs to block the holes when not in use. ww88

A SSR that interrupts at zero would likely be a lot nicer and not introduce powerline noise. Now I got to find a place to get one cheap along with a heatsink.

The clanking relay does have the advantage in that you might realize you left the kiln on ;)

Wes

I found a similar, though probably somewhat older, kiln in a junk store for $14.00. Looked like a really good buy at first glance and it mostly works ok for what I use if for. The main complaint I have about it is the way the heating element coils tend to sag and droop out of the support grooves in the refractory liner. Right now the elements are trying to form a rats nest on the kiln bottom. The original instruction book came with it and the company advises the user to take out the excess sag by squeezing the coils back together while they are red hot, which presumably means while they are live! And even if you do this, after firing a few times the coils will have stretched again and you are back where you started. Apparently this was designed as a starter kiln for potters on a tight budget, who don't object to working around live circuits. I had thought about maybe forming a ridge of refractory cement along the lower edge of the wire grooves to hold the coils in place, but have not tried it yet.

Mike

You can buy stays, or short wires, that are inserted into the refractory brick and keep the elements from sagging out of their grooves.

Next stop, case hardening!

Damn, I paid 26 bucks for 25 feet of wire to hook it up. I should have put my retirement savings in to copper futures.

Wes