Grinding a weld flat

[WotEver]

All the recent talk of sanding discs and angle grinders has led me to ask something that I've been wondering about for a while.

 

I don't know much about metalworking - wood is my material of choice.

 

A chap did some maintenance on Wot Ever a couple of years back and suggested at the time that he enlarge the steel engine flap in the counter. He did a neat job, and it's now far easier to gain access to the engine and ancilliary equipment. However, when he welded the 'extension' to the flap he left the (very neat) weld standing proud. Assuming that he's a decent welder and achieved good penetration (which it appears he did) can I simply grind the weld back down flush with the surrounding metal?

 

If I can, what would be the best tool to use? I have an angle grinder, various grinding disks plus a flap wheel.

 

TIA,

 

Tony

[gazza]

is the weld bead that much of a problem? i think a nice MMA bead looks best left alone.

 

i hate grinding welds back, sometimes it is necessary for clearence etc but the joint will have been designed with this is mind. is the extension a butt joint? if so what thickness is the steel? its almost impossible to guess the standard of prep that was used. has it been welded both sides of the joint? if so you may get away with it. there are not too many cheap ways of testing root penetration with out usind destructive tests or finding out the hard way (joint failure!!)

 

a 6mm butt weld correctly prepared and welded can be bent thru 90 degrees to carry out root and face bend tests with out failure of the joint. prep for this test is to grind the root and face of the weld flush with the parent metal. before welding the joint will have been prepared with an inclusive angle of around 65 degrees, the root gap should be 1.6mm. correct welding technique will ensure a weld with good root penetration and sidewall fusion. the specimen is bent with a former which as has a diameter 4 x the thickness of the specimen.

 

hope this helps

 

gaz

 

edited to add description of a butt weld root and face bend test

Edited July 28, 2009 by gazza

[paulcatchpole]

If I can, what would be the best tool to use? I have an angle grinder, various grinding disks plus a flap wheel.

 

If you do decide to smooth it out, then a flap disc is ideal...

 

There's some good info on it here: http://www.mig-welding.co.uk/finishing-welds.htm

 

HTH, PC

[WotEver]

Thanks Gaz and Paul

 

It's a butt weld across the width of the engine 'ole flap and it's exactly where I stand. Steel's 6mm. I know he (Baz, the welder in question) didn't do any fancy bending of the joint edges - just plenty of hefty whacks with a lump hammer to straighten it back out after it 'moved' following the welding

 

If you think it's a bad idea I shan't bother - I've lived with it for over a year after all.

 

Cheers,

Tony

[gazza]

the bending is to test a weld specimen, usually to prove the welders competence in a given process, joint and material. non destructive testing is a whole different and expensive field.

 

the key, as with most things is prep. if he ground the edges of the plate to 30 odd degrees, set the correct root gap 1.6 mm for mma or 2mm for mig/mag and achieved good root and sidewall penetration then you should be ok.

 

personally i would leave a decent looking bead profile for all to see.

[DHutch]

Yeah, as said, it all depends on what was done.

- If preped with a V and the like you shoudl well be fine, but if not you may weaked the joint. It also depends how important the weld is stuctually. If the worse that will happen is it will need rewelding you might as well flat it off it its a pain, but if the whole of the back of the boat would fall off without it, then it might be wise to enquire as to what was done before removing what might be a decent amount of the strenght of the weld.

 

I flatted off a weld i did on my trailer, in a rush, with a freinds mig, in the rain, without any prep, on 4mm inch angle. And a week later it all came apart! It might have done anyway (it was a crap weld) but there we go. Penitration? Not very much!

[DHutch]

If you want some photos of poor weld penatration, have a butchers and this:

http://img166.imageshack.us/img166/5566/dscn5100l.jpg

http://img259.imageshack.us/img259/9859/dscn5098l.jpg

[WotEver]

personally i would leave a decent looking bead profile for all to see.

 

I shall do just that, thanks

 

It ain't broke, so....

[Yamanx]

The other problem with grinding, or linishing, is the swarf goes red rusty very quickly, and penetrates any good paintwork it lands on, a, because its hot and b, because it goes rusty. Even with lots of sheets you will get some land on the boat somewhere where you will not get to But you will find it too late.

[WotEver]

The other problem with grinding, or linishing, is the swarf goes red rusty very quickly, and penetrates any good paintwork it lands on, a, because its hot and b, because it goes rusty. Even with lots of sheets you will get some land on the boat somewhere where you will not get to But you will find it too late.

 

Very good point, and one which I was kind of aware of (because I've had it happen) but had forgotten. So thank you very much for confirming that I really should save myself the job

[PhilR]

Very good point, and one which I was kind of aware of (because I've had it happen) but had forgotten. So thank you very much for confirming that I really should save myself the job

 

If the weld joins two plates along a flat surface it is worth checking first that both plates are perfectly lined up. Once the weld has been ground off any slight miss-alignment will be more noticeable and might need surface filling if you want a smooth paint job.