Tips for electrode welding for total beginners
(written by a guy who used to be the same total beginner just about two months ago :-) )
- For welding transformers with AC output, use rutile electrodes. Usually you can just walk in a shop and ask for electrodes for a transformer welder and they will give you the right ones (worked for me). Welding inverters with DC output can use both rutile and basic electrodes.
- For 2 mm steel, use 2 mm electrodes (2 mm diameter of the wire, not the coating) and welding current 60..70 A. With 60 A the arc is sometimes difficult to start, but once started, it is stable and easy to control. I've used only 60 A because my welder doesn't support any other usable value (80 is definitely too much), so I can't compare. I don't know how (and if) it works with thinner steel.
- Always keep the electrodes in a dry place (garage without heating is not a good place). Never use hundred-years-old dusty electrodes you have found behind a cabinet on your cellar floor. Bent electrodes with cracked or missing coating don't work right either.
- The return clamps of some cheap welding machines are very weak; they are actually designed for car starter cables, not for welding. If this is your case, it's better to invest some money into a better clamp, the difference is really significant.
- Attach the return clamp somewhere near the welding place, but not so close that it would be exposed to flying sparks. Around 30 cm would be good.
- Before welding, always make sure the parts are very well clamped together. When cooling down, the steel shrinks and can easily distort the assembly. Golden rule: do not remove the clamps until you can touch the welds without getting burnt.
- Always position the assembly so that the intended weld is horizontal. Molten steel is liquid like water and heavier than it, so it always flows down. If "down" means "away from the seam", it is bad. If you tilt the weld a little "uphill" (not much), the weld will be thicker because the steel flows back and builds up. Vertical welding is possible, but not recommended for beginners.
- Electrode coating is a non-conductor. If the electrode developes a cavity on the tip with the wire buried inside, you must carefully knock it off or the arc will never start. But be careful, don't make the wire stick out too much - that's even worse.
- Slag, rust, paint and many other sorts of dirt are non-conductors as well, so be sure to remove all remains of them from the place where you want to weld (some sharp object and a wire brush are suitable combination). If you leave them there, the arc will go around them and you get a bubble or crater.
- Do I have to say that an eye shield is a must?
- To start the arc, briefly and lightly touch tip of the electrode to the welded part (anything more and they stick together), quite as if striking a match. This creates a short circuit which builds up currents in the transformer coils, allowing the arc to develop. If the electrode sticks to the metal, tear it off quickly before it overheats. Don't release the holder, it would damage it. The hardest part is to learn not to fear that sparkling, sizzling little sun. Once you start to enjoy it, everything else is rather easy :-).
- Move the electrode slowly and steadily, with the tip almost touching the molten pool. If you pull it too far, the arc starts to cut the metal instead of joining it.
- The puddle under your electrode is half steel and half slag, so don't stop when it is as thick as the intended bead should be - you must make it twice thicker, because half of it will go away afterwards.
- Don't knock off the slag when the weld is still hot. First, it is easier when it cools down (if the weld is nice and smooth, it falls away almost effortlessly). And second, it helps keep the metal from cooling down too quickly and thus becoming fragile (tempered).
- Forget about bridging gaps wider than 1 mm, the molten steel would just drip through. If you need to do it, put something (a piece of electrode wire with removed coating, a steel plate etc.) into the gap and hope it will not melt before you're done.
- Chromium, zinc or other plating must be removed before welding. If you try to start the arc on such surface, the electrode just sticks to it, sparkles and doesn't weld at all.
- If you can find some welding "guru" to help you at the beginning, everything is much easier. But practice is necessary in every case. Get some scrap steel and keep playing with it until you are confident enough to start serious work on your bike. After all, your life depends on quality of the welds.
- Care for good ventilation, as fumes are quite unhealthy, particularly when eventual coatings haven't been removed completely. Weld outside if possible, else, open windows and doors. Consider directing a cheap fan at the welding spot. I once didn't bother removing the zinc coating from the backside of the square tube I was welding--afterwards a had fever and shivering.
- Consider buying a machine with "anti-stick" function. They prevent the electrode from sticking to the steel when coming too close. They're more expensive but time saving, particularly for beginners.
- Here's a very good instruction video showing electrode welding with AC source. About an hour long.
TIG (GTAW) welding
Proper filler material is important with a 4130CrMo. Common practice is an ER80S-D2 filler wire. ER70S-2 is a more common acceptable alternative yet gives a slightly weaker weld joint. Yet with proper joint design, like a cluster or gusset, the cross sectional area and linear weld length compensate. Best practice is a full penetration weld to eliminate stress risers on the inside of the tubing. When full penetrating, an inert purge gas is recommended to minimize oxidation. Also best practice is a slight pre-heat to drive water out of the system minimizing hydrogen embrittlement.
Post heat treatment
With GTAW (tig welding), a post heat treatment to stress relieve the weld area and heat affected zone is also recommended. This can be accomplished with an oxyacetylene torch, gently heating to dull cherry red and cooling off slowly. More professional parts are heat treated in an oven. When oxyacetylene welding 4130 CrMo tubing, this post heat treatment is not necessary as the system gets so hot it generally stress relieves and normalizes itself. Many light aircraft structures are still welded with this process.