Hi. I read a post on google that said that it was possible to do
brass brazing with a large propane torch. The typical Home Depot
variety don't have enough heat output to get the metal up to
temperature. So, I bought some Bernzomatic brass brazing rods, and
looked up a simple design (www.backyardmetalcasting.com). There is a
design called "upwind burner" which I thought would be big enough.

The burner is made out of 3/4" steel tubing with a 1:12 flare at the
end. There is a crosswise 1/4" copper tube (the original prototype by
L. Oliver used steel pipe). One end of this tube is sealed, and a
0.04" orifice is drilled in the tubing. This sprays gas down the
tube. Six 3/8" holes are drilled downwind of the orifice, three on
the top and three on the bottom; and two were drilled on the sides,
even though the text said that they are not necessary. The site also
said that there was no need to leave the main burner tube open on the
back end, but it was left open anyway, since that is how the prototype
was made.

When it was done, it lit OK, but it did not work. The main problem
was that it did not seem to get hot enough. It produced a huge long
flame, which was yellowish at the extremeties, indicating that the
mixture was too rich. It was barely able to raise the target (about
3"x1/2" of 18 ga steel tubing) up to red heat, and this was
insufficient to more than soften the brass rod. It was enough to burn
most of the flux off, due to the large flame. Contrary to the
original designer's experience, the torch was very sensitive to
plugging the tube in the back. The flame became even richer. From
some more investigations with google, it seemed that this kind of
burner requires a venturi. It is odd that the one on
www.backyardmetalcasting.com did not. A venturi was fabricated with
an inlet taper down to about 3/8" within 1/2" and out to full diameter
within 3 1/2". This venturi did not work well at all. It made the
flame very rich, looking like it had almost no air. Furthermore,
propane leaked out of the
holes which were supplied to draw in air, and was easily ignited.
This created an unpleasant odor, as well as a safety hazard.

Several posts recommended the use of a tweco contact tip as an air
orifice. This was difficult to retrofit, due to the design of the
upwind burner, since the rear of the burner tube is not really
accessible. Being a little wiser from previous experiences, I did not
want to do anything really permanent without more careful
investigation, so the tip was just clamped in the propane hose with
some twisted steel wire, and stuffed in the back of the burner tube.
This worked a little better, but the miserable makeshift venturi was
really interfering with the airflow. The venturi was removed, and the
flame looked more reasonable with a shorter inner blue cone, but it
still had some yellow indicating richness.

There are alternate burner designs, perhaps more well tried, which use
venturi's made out of pipe reducers. Would these designs be more
recommended? The lionel Oliver design is appealing due to its
simplicity, but if it is difficult to get it to work, perhaps some
investigation should be made into the EZ-burner type of design, which
has the air inlet in the back. The tweco tip can still be used.
Although www.backyardmetalcasting.com has an e-mail button, it is
discouraged to send e-mail to Lionel Oliver, since he is
understandably very busy. Has anyone noted any success with these
large torches for brazing? They certainly do have the potential do
generate a lot of heat, since it only took several minutes to empty a
partially filled disposable cooking propane cylinder, although to no
real use.

Thanks,
Eric