On 2008-08-14, Joseph Gwinn wrote:
In article ,
"DoN. Nichols" wrote:

On 2008-08-13, Joseph Gwinn wrote:
In early June 2008 I bought an old Vigor Burnout Furnace (model CA 1065)
for $95 from a seller on Craigslist. The furnace appears to have been
built in 1979, but does work.

O.K. I picked up a small one at a tool flea market at a
collector's gathering. The heated area was about 4" wide, by 3" high,
by about 6" deep, with a counterbalanced raising door with a mica window
for viewing the interior when hot.

On my Vigor, the heater volume is 13" wide by 6.5" high by 7" deep. The
door swings to one side on vertical-axis hinges.

A lot more space.

Hmm. 4*3*6= 72 cubic inches, versus 13*6.5*7= 591.5 cubic inches, a
volume ratio of 8.2 to one. Did you get a burnout furnace, or a melter?

I have no idea. There were no labels -- manufacturer or model
number -- remaining on this one.

But there were no provisions for runoff of wax, and the
orientation is similar to a brick on its flat side, with the smallest
area towards the door.

If the original controller were still present I might have a
clue from the range it was intended to cover. But all there was was a
pair of stiff wires insulated in asbestos coming out the back to connect
to my controller. It works nicely for heat treating small workpieces at
least.


But it came with *no* controller.

I have a Robertshaw "infinite" controller for sale cheap...

No thank you. :-)

[ ... ]

Since I already had one of the Omega controllers and a stainless
steel enclosed thermocouple, all I had to do was to make a housing for
the controller and the SSR (a 20A 240V one which I also already had).
While I was at it, I added a locking miniature toggle switch (the kind
where you pull the handle to enable switching) between the output of the
controller and the input of the SSR, so I could use the controller to
track the cooldown temperature without having to reset it to cool down.

OK. I didn't do that.

An easy thing to add after the fact -- as long as you have some
extra front panel space available.

The oven was on legs about as tall as the aluminum box which I
selected for the housing, so I put that box on standoffs on the
right-hand side legs to minimize conducted heat from them (and not much
heat there anyway).

The box was sufficient heat sink for the 20A SSR, since I could
expect no more than 15A load from the wall anyway. I did use white heat
sink goop when I mounted it to the chassis, of course.

This would *not* work on my furnace - the box is steel (poor heat
conductor) and itself gets quite warm at max temperature.

O.K. Make an aluminum box to mount on the side, with standoffs
and perhaps an intermediate sheet of aluminum between two sets of
standoffs. Use the original controller box for storing accessories
which won't be harmed by the heat. :-)

[ ... ]

So, for the SSR I got a large heatsink from Omega, which dropped the
temperature to 36 degrees C.

The controller was a bit more difficult. I ended up making a set of
spacers from 0.5" diameter gummy aluminum rod on the lathe, and cutting
two aluminum plates with clearance holes, all to space the control box
away from the body of the furnace, with two parallel plates between,
thermally isolating control box from furnace body. Now, the PID
controller temperature is 35 degrees C max.

No tall legs on yours, I presume?

None whatsoever. There is a ventilated skirt which is an extension of
the vertical walls of the furnace. I have it setting on a wood bench,
which does not get all that warm.

O.K. How tall is the skirt? Not tall enough to use it as the
mounting point for the controller, I presume.

Overall, it sounds like a
Blue-M muffle furnace which I had a work with the same duty-cycle type
controller. That one had the controller in a box to the right as part
of the overall oven housing. It did have a heavy-duty thermocouple
connected to an analog meter for readouts of the temperature.

No doubt this has long since gone to a surplus sale. :-)

Sounds like the Vigor for sure.

Proably made by the same company -- whether that it Vigor or
Blue-M -- just for different markets. The Blue-M came from a lab supply
catalog.

At this point, I have declared victory, as 35 or 36 degrees C is low
enough that reliability won't be much reduced.

Agreed. I was quite amazed at the Omega controller. About two
thirds of the way up to set-point it shut off and measured the coast of
the heat on up, so when it reached near the set-point it had a total
overshoot of 1 degree F.

That's a self-tuning PID (Proportional Integral Derivative) controller
for you. These used to be expensive, top-drawer industrial controls,
and now they are jellybeans. Mine cost $99 new.

Hmm ... I think that they were $200.00 when I got mine, and
since I got mine at half price, I got it for the same that you did. :-)

There was someone on this newsgroup who had several left over
unused after a project closed down, and who was offering them here. I'm
glad that I got one. I wonder whether we even have the same model? It
would take me a bit of work to verify the model now. Mine has the
plug-in strip along the top which says that it is displaying in degrees
C, but I've switched mine over to display in degrees F, since that
matches the information in _Machinery's Handbook_ more closely.

I got the controller for half price from someone in this
newsgroup in advance of need -- just knowing that I would eventually
need it. As it turns out, I was right. :-) Same for the SSRs -- I tend
to stock a few for future needs.

I've so far taken mine up to 1850F (1010C) and that took about
an hour, so I don't expect it to get much hotter. :-)

I don't think my Vigor will get quite that hot at present, although if I
do some more repairs it probably will manage. One fine day the heater
element will fail, and they are still available for about $60, long
after Vigor went bust. Vigor must have sold a lot of these furnaces.

I did have to make a bushing to go around the thermocouple probe
to minimize airflow through it. The original hole was something like 1"
diameter -- way too much for the skinny probe which I had, so I turned
up a bushing of lava, and then cooked it in the oven itself (which turns
it from whiteish-gray as machined to pink. :-)

It may be time to do another one, with a larger hole for an
alternative thermocouple which I found out in /dev/barn/01 a couple of
weeks ago with an analog meter. That would give me a totally power-free
way to monitor the temperatures.

Good Luck,
DoN.

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