Horror show
Typical repair by an untrained welder: a thick, wandering line of filler material surrounding the repair section. Weld dots sit on the repair joint, not fusing into it.
Simple insert repair Start right
1 Here’s a typical repair area on the side of a chassis rail where an outrigger has been cut off. Chassis is usefully thicker than body, but same principles apply.
Cut it out
2 Cut out the localised corrosion. You want to get back to clean, solid steel again, utilising straight edges. Straight edges mean simpler repair panels and simpler welds.
Make it tight
3 Make a repair section, and here’s the first secret: make it as tight fitting as possible. Chamfering edges 45 degrees helps tuck it in and improves weld penetration.
Fit it right
4 James uses the dotting technique with a MIG welder to fix the repair panel in place. The tight fitting helps aid good fusion between weld joints and panels.
Watch it disappear
5 Getting each element right means no weld gaps. James now dresses the weld: removing the raised cap of the weld. Watch the weld become invisible, and the repair, too.
Why it matters
6 Invisible welds aren’t just for cosmetic perfection. Our smoothed repair section now makes fitting the outrigger easy. Once fitted, the whole area should look untouched.
More complex repair Often the case
7 The repair area often increases as you chase back to solid metal. James trims this panel for the top of the chassis in the same manner as before.
Extra tab
9 A small tab, equal in width to the inside of the chassis, is made. Two holes are drilled each side of the joint on the chassis and repair panel.
Fill it
11 The drilled holes are now filled with a puddle weld, fixing the tab to the chassis. This tab gives extra meat for the repair panel to be welded to.
Back-up needed
8 This top section repair has plenty of side rail material to work with, but achieving a strong weld at the butt joint (arrowed) with no blow-out, needs more work.
Tab first
10 The tab is held in position (half width) with a clamp. Notice the tab is visible through the two holes drilled in the chassis near the joint edge.
Panel goes on
12 The repair panel goes on. Here, the first hole is puddle welded and there’s one spot weld on the joint. The butt weld along here will also penetrate the tab.
Mix and match
13 The repair panel top is clamped, then tack welded. Now, inspect the existing surrounding welds which dictate how your finished welds will need to look to blend in.
Get the right profile
14 The original factory welds are proud on the corners, not dressed back. James expertly produces matching welds on the repair. Note the butt joint is also fully welded.
Voila!
15 The right visual weld profile means that dressing the corners to match the adjacent factory finish is easy. The butt weld with backing plate has been dressed flush.
Scale it up
16 For larger repairs, the same idea scales up. Here, two right-angled tabs are used to join a chassis rail. Tabs are perfect for strong box section repairs.