Essential Tools for DIY Boatbuilding In Steel or Aluminum
Backyard boatbuilding with steel or aluminum requires tools that can cut, grind, drill and weld. Actually, apart from the welder and steel brushes, and a few simple rules what not to do,
you can use with aluminum the same tools that you would use for working with steel.
In DIY boatbuilding, welding is the most demanding metalwork process. To weld successfully, you will have to learn the basics, apply them and build up experience.
Things that you do for love: My son and I, both computer professionals with absolutely no
previous experience in working with metals, actually went through a 6 months, two evenings a week training on
MIG and TIG welding at a local T.A.F.E., where we learned the basics from the real professionals. And then, we burned a few holes while gaining some experience during the process of building the Platypus.
Even now we know that the first (and most important) welds that join the large bottom plates together are among our worst. Yet, they hold very well, tested slamming many times against the choppy seas.
The Welding Gear
Welding Steel: The Stick Welder
For welding mild steel, a regular and most often used stick welder (more formal name Shielded-Metal-Arc-Welding or SMAW welder; also Manual-Metal-Arc or MMA welder), will do an
excellent job. It is the cheapest welder, providing the simplest form of welding.
One output electrode (ground) of a DC (Direct Current) or an AC (Alternating Current)
welding power supply (welder) is connected to the two metal pieces (the base materials) to be
welded together. The other output cable ends with a simple holder carrying a replaceable consumable electrode coated in flux. The welding power supply is capable of producing high amperage
electric current (in the range of 30-250 A (Amperes) and more; the maximum current depends on the power of the welder). The operator, wearing a protective welding helmet and heavy welding gloves,
touches briefly the materials with the electrode, moving it instantly away to produce and maintain an electric arc. The arc heats the two base metal pieces and melts the consumable electrode, its core becoming
the filler in the weld pool. The flux disintegrates in the process, releasing shielding gases and slug that floats to the surface of the weld, both forming a protective layer that prevents contamination
of the weld from the atmosphere while hot. Once the weld has solidified, the slug has to be chipped and cleaned away, which substantially slows down the whole process.
The two graphics above right are for SMAW welding. Yet, the general principles are the same for other types of welding.
As a material, steel is the easiest to weld. When heated, it nicely changes color into bright red, so you get an ample warning when the piece you are welding is overheated and is about to melt. Also,
the weld on steel is very strong, actually stronger than the base metal. The only problem is, if the steel pieces you are welding are not properly secured and cooled off, they will deform from the heat.
By changing the consumable electrode/flux type, the stick welder can be used to weld various steel alloys (including stainless steel), but also aluminum, nickel and copper alloys.
CAUTION: The welding arc emits intense bright light which is very painful and harmful to the naked eye. A special darkened vision glass helmet (see below) is a
basic requirement. The arc also emits very strong UV (Ultra-Violet) radiation that is harmful (carcinogenic) to the skin. For that reason, welding is always done with long sleeves and all skin areas covered.
As the sparks that occasionally fly around could contain substantial pieces of molten metal, it is a good idea to wear heavier clothing (overalls). Also, wearing heavy welding gloves (except for TIG welding, see
below) is a practical must, to protect your hands from high temperatures that develop.
Work in well ventilated area. The welding process, and especially the disintegration of the flux, releases toxic vapors and small particles that represent a high health hazard. Avoid breathing them in.
Welding Aluminum: The MIG Welder
For welding aluminum, the most often used is the MIG (Metal-Inert-Gas) welder. Its ground electrode is just a thick cable capable of carrying hundreds of Amperes of current, with a massive clamp
at the end to attach to the two pieces to be welded together (it is essential that both are in good contact with the ground electrode; if you forget to attach it, or the contact is not good, there
will be lots of black smoke, lots of splatter, but no welding will happen). The other electrode cable ends with a special welding gun with a trigger that, when depressed, starts from its tip
the flow of the inert protective gas (argon) and aluminum filler wire. The wire carries the polarity of the other electrode. The moment it touches the material to be welded, the electrical spark starts the
welding arc that melts the filler wire, creating the melted welding pool that joins the two materials. Both the aluminum wire and argon keep flowing from the tip of the gun for as long as the trigger is depressed.
The speed of the wire flow is regulated by the settings of the welder commands, while the flow of argon is controlled by the flow regulator installed on the valve of the attached argon cylinder.
The picture to the right shows a very powerful, 3-phase MIG welder MIGOMAG 350PF3 that we purchased to build the Platypus. It proved itself to be
an excellent machine, enduring hours after hours of our work with only very rare minor hiccups in the wire feed, mostly because of our wrong initial setup or an unnoticed sharp kink in the gun cable. It consists
from two boxes, the very heavy voltage regulator unit with a stand for the gas cylinder, and the portable wire feeder with current/wire speed controls on it. The portable feeder houses a replaceable spool of
aluminum wire (0.9 - 1.2 mm) and a push-type wire feeder that, when the gun trigger is depressed, forces the wire through the inner lining of the gun cable. The feeder unit has its stand on top of the base
voltage regulator, where it can rotate in all directions. Or, it can be taken off the base (together with a spool of wire it weighs about 18 kg, and has a pair of wheels at the back so it is easy to move around),
remaining permanently attached to it by a wide and massive 10 m long cable that carries gas pressure hose and electrical cables.
The gun cable is 3 m long and attaches to the portable feeder.
Every powerful MIG welder is, by necessity, bulky and heavy. It contains heavy wire gauge transformers and controls that produce and safely regulate currents that go into hundreds of Amperes.
The fact that ours had a much lighter wire feeder unit connected with 10 m cable, plus the 3 m gun cable, meant that we could easily weld up to 13.5 m away from the stationary base. That enabled us to bring
the portable feeder on board the Platypus, as the hull started getting shape, and do our welding there having all required commands at hand. If we had chosen a different, one unit welder, we would have had
a bulky, heavy problem.
MIG welding is fast. It depends on the skills of the operator how fast, but it is several times faster than stick welding. And, as all types of welding do, it develops intense heat (aluminum melts at
660.320C, 1220.580F, but the molten weld pool goes way beyond that). What makes it harder, there is no change in color that might warn you that the weld pool is overheating and you
are just about to burn a nice see-through hole in the material (fortunately, this is not very hard to fix, yet it is a big time waste). Plus, aluminum is hot-short, which means it shrinks when heated and
deforms the area easily, unless previous precautions are taken to ensure an even cooling of the welded pieces. That means you can not just weld continuously. Depending on the skills of the operator and
the thickness of the materials to weld, one would weld in steps of 15-20 cm, clean the new weld with stainless brash and inspect it, let it cool off (do something else in the meantime), and once it has
cooled down, continue for another 15-20 cm. It is a process. But, in welding terms, that is fast.
The MIG welder can be successfully used to weld thick aluminum (or steel, including stainless) materials, but it is limited from the low side to sheets of about 1.5 mm (depending on the skills of the
operator). Actually, anything less than 3 mm requires very careful preparation (remember distortion!) and concentration.
A welded spot on aluminum is weaker then the base material around it. It depends on the actual aluminum alloy how much weaker (the Platypus hull has been built
from the 5083-H321 alloy (all the credit goes to the designer Phil Curran), which retains high strength in the weld area (very important for backyard boatbuilders and
amateur welders).
By changing the filler wire, the MIG welder can successfully weld steel and stainless steel.