boxed in chasis rails

[oldenholden64]

ok have a car here with boxed in chasis rails done by the previous owner. The rails are stitch welded in. I want to neaten it all up and was going to make it a continuous weld, but remembered back to when seam welding cars that it is best to stitch weld rather than run continuous weld. So would this be the same and I would be best to leave it stitch welded and just grind and fill the rest to smooth it all out?

[Billzilla]

Yep stitch welding is the go, for a few reasons.
Firstly it stops crack propogation - If you use one long weld then a crack can just keep on moving along the weld.
Secondly in a crash the welds will gradually let go, dissipating energy far more effectively that a solid welded section.
Thirdly, the metalwork will buckle less with a series of smaller welds rather than one long one.

[oldenholden64]

thanks for that bill, knew about the first and third point but not the second.. and it's a very valid one.

[Nathan Tinkler]

Also it is nearly as strong and only half the weight to use a 50% weld!

Just don't go bananas grinding it back once finished.

And mig does not equal good welds- unless you are running it hot enough to melt the parent material. A good mig will blow holes in the material which are then filled with weld. Truly. Use the highest setting you can on the welder, and adjust your technique to weave and fill in the hole.

If that doesn't make sense I will clarify later.

Muz