Any tips for grinding down welds

[dwa]

It should be kind of straightforward you might think, but after welding some patches into the nosecone of my mates Fordson Major tractor I found it difficult to actually lose the welds and found the grinder was taking too much of the surrounding metal away leaving it quite thin. If I say so myself the patches looked nice and tidy after butt welding them into place, I didn't weld all the way around just gradually welded in between each spot weld until it was almost but not quite a continuous weld around the patch. The patch itself was level with the original metal and I used a 4" angle grinder with a flap wheel attached, not sure about the grit. Maybe grinding is as much an art as the welding itself and I need to perfect that too. It was just a bit frustrating after carefully making nice fitting patches and getting the welding part looking nice, to go and leave the metal thinner than it should be. I know the answer is obvious, take more care, but can anyone offer a bit of advice or a good technique to follow before I set about repairing the front of his other tractor.
Thanks in advance.

 

[madkayaker]

Flap disks or sanding disks are what I use

 

[Robotstar5]

Flap discs and care...

 

[KICKSY]

Let the weight of the grinder do the work, don't push down to hard and
only grind the weld

 

[Hitch]

On old boy I used to work with had a saying-

"You need to learn to grind before you can learn to weld"

True words!

Pretty difficult shapes can be hard work to flush off, a very light touch is normally the order of the day.

On rounded surfaces i find removing the majority with a flap disc then the standard fibre discs and a backing pad work well. They don't tend to dig in as easily as flap discs.
Finishing off with a DA sander and coarse disc helps to smooth out any final marks.


For rounded surfaces, a backing pad, and a single fibre disc, for getting flat surfaces, put 2 or 3 disc and the backing pad to stiffen it up.

 

[KICKSY]

Let the weight of the grinder do the work, don't push down to hard and
only grind the weld

Using flap disk's.

 

[dwa]

I meant to sat flap disc, not flap wheels are what I use. Maybe I am using too coarse a disc.

 

[mike 109444]

dwa you might find that your "fit up " of the patch was to good! If the patch is to snug/tight then when you weld and the metal expands it has to go somewhere. It may rise and so when you grind down the weld you will take some of the ori metal away. If it sinks then in trying to grind the weld flush with suround you will again start taking away the ori metal but still not get the weld to blend. ps the snug/tight fit it what I keep doing (old engineering habits are hard to kick). Try creating a small gap all way round, but will req more effort (lower power) to avoid blow through. Any ho I thought we had all the tractors down this part of the world : )

 

[dwa]

You have a good point there Mike. I will take into account everyones suggestions on my next attempt, many thanks.
We are bordering Northumberland which is a huge farming area, there must be loads of old tractors tucked away. My mate keeps turning them up anyway. I have to say for something that is about 50 years old the metal was really good and a good gauge for welding to.

 

[200T]

Grinding welds on sheet metal IS a high art! Flap discs work well - what also works well if not better is a rubber thingy with sticky sanding discs. Don't know the correct term. This sort of thing: http://www.bosch-do-it.de/accdiyocs...e=Bosch-Akku-Schrauber IXO&filename=44767.jpg

Practice, practice, practice. I find coarse discs are actually easyer to use, as there's less 'polishing' of the harder weld; the flatdiscs dosn't tend to eat the soft surrounding metal rather than the hard weld. If that makes sense!? But you have to be a lot more carefull with a verycoarse discs to not 'drift' off the weld and grind the surrounding metal...

As soon as I have adecent air compressor, I'll try an air file & very coarse belt. Should work well - in theory...

 

[pedrobedro]

I use 60 or 80 grit fibre discs on a flexible backing pad, they work well and work out cheap.

 

[Punx0r]

Great tip Mike. I'll remember that one!

I take down the bulk of the weld with a grinding disc and finish with a flap disc. I'm bucking the trend here, but the flapwheel takes longer and wears down quicker. I see it as for finishing

 

[Dave3066]

I'm in the "start with a grinding disk" camp too. Grind across the weld not along it then flap disk and finish with 120 grit disk on flexi pad.

Don't rush it!

There's a good panel making thread on the Retro Rides forum which demonstrates grinding back welds. Some neat panel making skills too.

Dave