Excellent purchase. I use my 18" top loader quite regularly for
annealing, tempering, and normalising. I made a controller that connects
in series with the mains lead and fitted a thermocouple in the kiln, I
just set the energy controllers currently on the kiln to full on and let
the temp controller do the work. I used a Cal controls 9400 and solid
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?
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.
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 in a good control box, available on e-bay.
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.
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.
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
The clanking relay does have the advantage in that you might realize you
left the kiln on ;)
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.
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.
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