1.40. To restart, tap the warmed rod tip at point X. Keeping a long arc, move it to the crater’s front edge (dotted line), then close the arc to welding length and make a very deliberate pass round the crater. As you come back to the entry point, move on down the joint line.
1.41. Waving the rod tip around or rushing during a restart produces a mess (arrow)…
1.42. …But if you’re slow and deliberate, the restart will be hard to see and will not snag a fingernail run over the area (arrow).
Starts at the beginning of a joint can be pesky. Common is a ‘snail trail’ of weld and a slag trap before a decent weld establishes (1.43). Initially the rod and plates are relatively cold, so metal is slow to fuse. Moving off too briskly (or with a long arc) produces the fault. The trick is to start the arc just off, rather than directly on, the joint edge. Pause for a while before moving off, watching to see that molten metal fuses with both plates. A small sideways weave usually helps: try it and see.
1.43. Recognize this? A slag trap at the beginning of a weld (arrow) springs from two things; cold plates and an arc that’s too long. Pause before moving off or use a run-on plate.
1.44. This nasty finish comes from a combination of bad technique and too much current. The hollow crater (arrow) will be a launch pad for cracks.
1.45. Two in one here. While a flat finish is needed for clean restarts (2), the crater must be filled when a joint is closed (1).
Where an ultra-solid start is important, use a run-on plate. That is, establish the arc on a piece of scrap alongside the joint then move into the work.
End-of-joint finishes matter too. An untidy, hollow finale is a launch pad for cracks (1.44). While a flat stop pad paves the way for a clean restart (1.45, 2), the crater at the end of a joint must be filled to maintain strength (1.45, 1). Producing a good finish takes slow, deliberate action. Rush and you’ll spoil it. Weld up to the end of the joint as normal. Then move back a little from the edge and pause, keeping arc length constant to pile metal into the crater. Circle the rod tip slightly, but not too wide or weld metal spreads too much. Finish the job by travelling forward a touch and breaking the arc with a quick sideways flick of the rod. Concentrate on keeping arc length steady throughout. Don’t pull the rod upwards to break the arc, as this may leave a crack-propagating hole in the finish area.
Tacks are the daily bread of welding. But if a tack weld is to lock plates into the right position (and hold them there under contraction stress, or while things are re-aligned with a big hammer), it needs to be a quality mini-weld rather than a quick blob. Worthwhile tacks in thick material are 3/8"-15/32" (10-12mm) long and fused properly into the joint material (1.46). Where you can, tack on the reverse side of a joint to leave the weld area uncluttered. If this can’t be done and you’re after a clean surface appearance, grind away the tack’s bulk before welding the joint.
On long work, tack as often as you need to hold parts in alignment. Don’t skimp on tack numbers, as it takes less time to weld them than to put things right after joint components have bowed or shifted through lack of anchoring.
Here are two hints for quality tacking:
• Save part-used 3/32" (2.5mm) rods for the job. A short rod is easier to control, and its small diameter means good penetration in a Vee.
• Use more current than normal to give an easy start and quick fusion. Either shift down one rod size (e.g. from 1/8" to 3/32" [3.25 to 2.5mm.) while leaving current setting unchanged, or use a 3/32" (2.5mm) rod on 1/8" (3.25mm) settings.
Slag traps are a fact of life. Good preparation, sound basic technique and lots of practice keeps the little burglars at bay — but what can you do when they show up? There are two options. Either grind out the joint and re-weld it (which won’t be possible if you can’t get a grinder into the area), or use arc heat to melt out the slag and re-fuse the trap area (which is not always 100% successful).
Where possible go for option one. But the second approach will do in a crisis. First winkle out all the slag you can, using anything pointy. Re-welding aims to float the remaining slag to the surface and fuse fresh metal into the joint, so violent measures are called for. Put mega-heat into a limited area by using a lot of current on a small electrode – say 130A on a 3/32" (2.5mm) rod. Then strike up just short of the trap, get the arc running nicely and move slowly over the dodgy area, holding a short arc so it digs out all the crud and the void is filled with fresh metal. Picture 1.47 has details.
1.46. Tacks need to be good-quality ‘mini-welds’, not blobs.
1.47. If you can’t grind out slag traps, use a small diameter rod and high current to re-fuse them. Here, A has been given the treatment while horrors B and C wait their turn.
MAKING THE WELD 6
Up, down and overhead
Now for the bit that brings some operators out in a cold sweat – working straight up, straight down or overhead. If there’s no chance of taking the chicken’s option – which is rotating a vertical job so it’s flat – you’ll have to decide whether to weld uphill or down.
Vertical down work is usually favorite as most people find this easiest. But penetration, and hence joint strength, will be poor in all but thin sheet. Welding vertically down is only good for sheet, for cheering up surface appearance, or for filling awkward gaps where burn-through would otherwise be a problem. Never rely on it where strength matters.