Next to bending tube,
welding is high on the list of interests to anyone wanting to fabricate
motorcycle frames and related parts. Makes sense…after you have the parts bent
up, you need to weld them.
First issue is what welding
process to use? We will limit this article to materials and material thickness
found on custom motorcycles. Metals used in motorcycle can vary widely in
thickness. “Gauge” sheet metal is a thickness less than ¼”. 16 Gauge is about
1/16” thick and higher numbers are thinner. 18 gauge is thinner than 16
gauge. Sheet metal ¼” and thicker is
referred to a “plate”.
Oxy / Acetylene torch rigs
are often used for aircraft frame construction with chromoly steel tubing. A
proper mixture of fuel and oxygen makes a neutral flame that protects the weld
from oxidation. The flame heats the metal until a puddle is formed and filler
rod is hand fed into the puddle forming the weld. Dark goggles are used so the
weld puddle can be seen in the bright light of the torch flame. Other benefits
of an Oxy rig are the ability to heat metal for bending or attaching a cutting
torch for cutting steel.
For the small shop and home shop, arc welding processes are the
usually the best choice for welding. Arc welding includes Stick, MIG and TIG.
Rather than go into a big discussion on how to weld or how each process works,
let’s just try to find out what is best for doing the job. Consider that you
need a welder capable of at least 100-140 amps to fillet weld 1/8” wall tube
(lower amps will be used but this is a good number to start with). This does
not include things like motor mounts, axle plates and steering necks, which are
much thicker and may take more power. Proper joint fitting and multiple passes
will allow a smaller welder to do heavier work (within limits). “Duty cycle” is an important consideration
as this is the amount of time you can weld in a 10-minute period before the
welder needs to cool down. If the welder you are using has a 50 percent duty
cycle at 120 amps, you can weld for 5 minutes and then quit for 5 minutes to
let the welder cool. At 200 amps, this same welder may have a 20 percent duty
cycle allowing 2 minutes welding and 8 minutes cooling.
Stick welding is a low cost
process compared to MIG and TIG. Stick welding for practical motorcycle
fabrication is limited to welding steel. Stick welding is faster than TIG but
slower than MIG. A bit of skill is required in holding the angle of the welding
rod and feeding as the rod is consumed by the weld. Stick welding works well on
less than clean metal but makes a bit of smoke and spatter in use and works
well outdoors since there is no concern for shield gas. A stick welder with 225
amps output makes a good small shop welder capable of doing heavy gauge metals
to thicker plates and shapes. Stick is not good for sheet metal work. There are
small rods for sheet metal but results are not usually good. Stick creates a
slag cover over the weld that needs to be chipped off (can be easy to a real
pain in the butt). There is also spatter to clean off that usually has to be
removed with a chisel or sander.
MIG welding is a higher cost
process. The same machine can weld steel and aluminum by changing wire and
shield gas. Flux core wire eliminates the need for shield gas and functions
similar to stick welding, as it is not sensitive to breezes or less than clean
metal and also smokes and spatters. Using a mix of CO2 and Argon reduces smoke,
spatter and helps improve penetration when shielding solid core wire. Argon
alone is used with aluminum. Switching between different thickness metals and
aluminum may require different wire sizes and type, rollers, contact tips,
torch liners and gas mixtures. Expect to get a machine with at least 210 amps
output for bike fabrication. The smaller MIG welders in home improvement stores
just don’t have enough power to weld even the thinner frame tubing. MIG is good
for sheet metal work especially for making quick tacks. Simply pointing the
wire and pulling the trigger makes a quick spot weld. There does however tend
to be some excess weld buildup with MIG on sheet metal causing a lot of extra
finish work. MIG also produces a bit of
spatter that requires a chisel or sander to remove. Flux core makes a slag
similar to stick that needs to be removed. Shielded gas / solid wire MIG makes
nice clean welds that require little other finishing (other than removing
spatter).
TIG welding is a higher cost
process and usually the highest since the power supplies are complex and there
are a number of accessory items required to start welding. TIG welding is
slower that stick or MIG. There is little or no smoke and spatter with TIG.
Welds are very clean and generally require no finish work. Penetration is not a
strong point of TIG welding and proper joint preparation is very important. For
most metals, straight argon is used for a shield gas. With straight Argon,
welding can jump from most varieties of steel, to aluminum, copper, brass and a
number of other metals will little more than machine adjustments and a
selection of filler rods. Since TIG uses a shield gas, breezes or a fan can
cause issues with the shield gas which will ruin a weld. Stick and MIG welding
are accomplished by holding an arc or wire length, angle of electrode or wire
and travel speed. TIG also involves these elements plus feeding filler wire
with one hand and controlling arc start and amperage with a foot control (or
torch mounted finger control). These extra elements make TIG a bit harder to
master than Stick or MIG.
Welding the thin (about 1/8”)
wall of motorcycle frame tubing is probably best done with TIG. The process is
slow and very controlled. With proper application, the other arc processes will
weld this size material but will require extra special attention to making good
welds and will have somewhat larger bead deposits. A welder should be selected
by capability and not cost. Amperage and duty cycle are two main elements to
consider.
More to come…