How far should I grind the welds? Completely flat? Leave a bit for strength?

Also, how much does this weaken the structure? For example, on the sides of the chassis, we grind the bottom for the floor, the side for the body work, the top of the upper tube where the body panel folds over, and the inside of the upper rail where the body panel wraps around for riveting. Does this make things weak?

Thanks,
Shaun

The flatter the weaker so only as flat as you need to.

How weak depends on how good your weld penetration is.

Sorry but I don't know enough about the subject to quantify the exact amount of weakness induced by grinding.

If you have good penetration then grinding all the welds off will weaken it very little. If you had crap penetration then grinding the welds off could weaken them significantly.

How much do you trust your welds?

Get a flexible nylon backing pad for your grinder and some 60 or 80 grit fibre disks to linish the welds down. They don't cut in like grinding wheels and they don't make as much mess. They also last ages.

peteff is right, that's how I smooth off my welds - works a treat

James

Or a flap disc if you are rich enough.

Here's a gratuitous waste of bandwidth.

Thanks for the feedback, gents. I will try the alternate methods of material removal and see how they work.

As far as penetration goes, I think that my welds are solid. I tried many test welds before starting on the chassis, and was unable to separate any of them even by beating them to death with a BFH. The tubing bent, but the welds didn't break.

I am assuming that, given sufficient weld penetration, the normal thing to do is to grind the welds flat and not worry about it? Is this what everyone else has done?

Thanks,
Shaun

That's why it's best to chamfer the joints first.

a good weld will be almost totally unaffected by grinding flat, as the weakest point is still (im led to believe) the edge of the heat affected zone. However if you didnt get total penetration, it will be significantly weaker - there is even a stress raiser on the back there the tubes are still unjoined!

Gazza285,

Thanks for the recommendation of the flap disc. Fantastic control and does a top job.

Cheers,
Shaun

You are very welcome.