|Auto brakeline tubing||Stainless tubing & piano wire|
As a heat source I use a micro-torch fueled by oxy-acetylene. This provides more
than enough heat to do brazing at the scale I work. I use 1/16" diameter
Harris Safety-Silv 56 brazing
rod. This rod melts at about 1200 deg F. It is a high silver content brazing rod
that flows well on carbon and stainless steels. I buy it at my local welding shop
for about $12 per one ounce canister. I use the matching white Harris flux with the
brazing rod. (Note: Some people have had problems with hardened residual flux left
on their tubing. Make sure you are using a flux that matches the brazing rod you
are using and try to avoid overheating the joint.)
|Micro torch||Safety-Silv 56||1/16" brazing rod||Flux for brazing|
A typical tubing cutter, as shown here, is the cleanest way to make most cuts.
However, you can use a Dremel or die grinder with cut-off blade, hacksaw, etc.
For mating tube joints, it is best to fish-mouth the tube so the two pieces
mate very close. This will also provide the greatest strength at the joint.
This take a little practice, especially when mating at an angle other than
perpendicular. I have cut fish-mouths using a 1/4" rat tail file, Dremel
tool, abrasive cut-off blade in a table saw, and with an end mill bit.
|Tubing cutter||Tube fish-mouth||Dremel bit||Rat tail file||Mill bit|
Bending steel tubing is fairly easy, it just takes a little practice and patience.
I have several automotive hand tubing benders that work very well. Try a few bends
and you'll get the hang of the bending dimensions. I also recommend bending hoops
starting from the centerline and working each direction with the bends. You'll find
that each bend will have a slight directionality and bending from the center out
in each direction will keep the hoop more symmetric. I also occasionally hand bend
tubing around solid round stock, as needed, for oddball shapes or radii. The form
below is made from two pieces of aluminum rod and a piece of steel plate. I use it
to bend stick pack cradles.
|Tubing benders||Round rod form|
Holding pieces in place while brazing is one of the trickiest parts of building
a chassis. I usually work on a piece of sheet steel and use various methods to
hold the tube in place. I use scraps of steel plate, box tube, welding magnets,
small c-clamps, and bailing wire as holding aids. Your ingenuity will help here
as you try different configurations.
As I work and assemble each piece, I usually try to check dimensions with a
tape measure or caliper and also eye-ball the chassis for straightness and
symmetry. An angle finder can be useful as well. Checking often will help
you discover an error before you add more tubing to the assembly.
|Prototype chassis||Fabrication aids||Typical joint||Tubing examples|
I typically use 3/16" size tubing, but have built with 1/4" tubing and one
large chassis with 5/6" tubing. For small braces I sometimes use 1/8" solid
steel rod. I fish-mouth all the tube, but find it unnecessary when using the
smaller rod. I will grind it at an angle for a closer mating fit. Mounts can be
added by brazing sheet steel to the chassis. I have also brazed small nuts
on the tube for holding body panels and such.
Copyright (c) 2003 by Jay Kopycinski, All Rights Reserved.