Subject: Gas Forge Building Results & Weekend CBA Class Report

From: "[email-masked] 415.855.5707" <[email-masked]>
Date: Mon, 06 May 1996 09:46:55 -0800 (PST)

Hi All,

Last Friday I finally got around to building the gas forge I've been collecting
parts for.  The besic design is a "rip-off" of the "Cuenca Forge" which is
detailed at: 
http://www.nets.com/bsmithplaza/mrocks.html

Basically, I built an angle-iron frame work to hold some firebricks (the hard
kind).  The burner assembly is all made from welded black pipe and plumbing
fittings.  I made the gas jet froma 1/4" brass pipe plug drilled with a #68
bit.  The forge works well although it doesn't seem to make enough heat to weld
with.  

I am wondering if bricks are a good choice for lining, do they reflect enough
heat?  How do they compare with the soft kind?  With ceramic wool linings?

They *do* get a very purty orange color after five or ten minutes :-)

The forge was simple to build and even simpler to use.  You do need some basic
fabricating equipment like a welder (and a weldor if you aren't one) a metal
cutting saw, a hole saw and a brick chisel.  It took me about four hours to
build it - including taking pictures along the way.

==========

Yesterday was my monthly CBA forge workshop.  Very cool, I made three simple
projects from the COSIRA book which are part of the lesson plan for the CBA
class and in the afternoon I made a set hammer from a 1.25" bar of 1085 steel. 
I drilled a 1/4" pilot hole for the handle and drifted it out to the proper
shape for a wooden handle.  The back side was drawn out slightly and the
corners rounded off.  It was a blast to make something useful!

Joe

---

From: Steve Smith <[email-masked]>
Date: Mon, 6 May 96 11:54:55 MDT

Dear Joe,

Sounds like a fun weekend.

> The forge works well although it doesn't seem to make enough heat to weld
> with.  

Did you try changing the propane pressure? My forge uses a #68 hole
also, and it gets plenty hot at 10psi (but I'm at 5000 feet
elevation-your results will differ). As I increase the pressure to
15psi, the temperature climbs a bit. Above 15psi the temperature
decreases, which I would guess means that 15psi is a neutral
mixture. This may be a peculiarity of my burner, too.

You could also try a different sized chimney (is there a chimney?). If
you have a hole for exhaust, try blocking one quarter of it with brick
and see what the temperature does.

To really figure out what is going on, you need to measure
temperatures. You can do this with a type K thermocouple and meter
which will cost around $100-120 (let me know if you want more info),
or you can take a look at this web site:

	http://tbr.state.tn.us/~wgray/howto/optpyro.html

This site describes building an optical pyrometer. You match the color
of a tiny light bulb filament to the color of an object in your forge.
The current running through the bulb is proportional to temperature. A
pretty cheap way to go. Even if you don't calibrate it, it will give
you a way of saying whether the temperature went up a little or down a
little. I haven't built one of these yet, but it looks like a pretty
useful item.

Measuring this stuff takes careful work due to the long time constant
of the forge. Either measure temperature at several times and plot the
curve, or wait a set period of time (like 10-15 minutes) between
making a change and measuring the result. 

> heat?  How do they compare with the soft kind?  With ceramic wool linings?

I think that bricks aren't quite as good an insulator as the wool
linings in the same thickness, but your bricks are thicker, so I don't
think this is a big deal. The major difference between the bricks and
wool is thermal mass--bricks will take longer to heat up. 

--
Steve Smith
[email-masked]