Question about weld grinding for best appearance

[digitalwelder]

Hello,
I am building a bumper for my truck and butt welding the joints. when i grind a V joint top and bottom and weld on top and bottom, i get a valley on top of the 2 pieces. When i try to grind the top surface for cosmetic purposes. I end up grinding the surrounding metal because the weld ends up being lower in the valley.
When i grind a V only on the bottom and weld from the bottom, i get penetration through the top but when i grind that small protrusion flat, I find that there is still a bit of a valley and i end up grinding more of a valley to get a smooth appearance.
I have attached hand drawings.
My question is what is the best butt weld/grinding technique to use to get a nice flat appearance on the outside weld.
Using Miller 180 autoset.

Thanks in advance for your help.

[Broccoli1]

What abrasive are you using for the grinding?

A Flap Disc will do the job, you still have to watch how you remove the weld bead though but they sure are a lot better than a Grinding wheel

[tackit]

I use 3" maroon surface conditioning discs and a air powered 3" grinder when I want to get a nice look. I would use a #60 flapper to take off most of the weld and finish with the less aggressive surface conditioning discs.

http://abrasives4sale.com/qc_discs_scd.htm

[digitalwelder]

i'll try the flap disks and the surface conditioning disk. Thanks.

[jfk92]

GREAT timing and question - thanks! So I was just asked today to repair a metal bracket for some family that is about 3/4" thick. The weld is going to be a butt weld - I was planning on grinding a bevel on all "four" edges - top and bottom side and then using my Thunderbolt 225 XL to run a root pass of 6010 in each side then maybe 7018 pass over the top and grind it down (now with a flap disk first) - cosmetically it doesn't really matter- but I do need to make both sides flat/smooth. Does this sound like the proper repair process?

Thanks in advance - and sorry for hijacking your thread - but it's basically the exact same question!

john

[tackit]

A lot has to do with grinder control and technique. I finish some jobs by lightly going over the work in circles so I don't create a groove.

[tackit]

You can get the steel to a mirror finish with the conditiong discs.... but don't try to mig weld over such a polished shiny surface. The weld may not penetrate, just lay on top of the polished steel as though there was proper penitration. I had it happen to me. I think what happens is the heat is either reflected back or the surface becomes so very hard from polishing it effects penetration. Now I always leave what I would call a dull or grained finish when preparing a joint never a polished one..

[MMW]

GREAT timing and question - thanks! So I was just asked today to repair a metal bracket for some family that is about 3/4" thick. The weld is going to be a butt weld - I was planning on grinding a bevel on all "four" edges - top and bottom side and then using my Thunderbolt 225 XL to run a root pass of 6010 in each side then maybe 7018 pass over the top and grind it down (now with a flap disk first) - cosmetically it doesn't really matter- but I do need to make both sides flat/smooth. Does this sound like the proper repair process?

Thanks in advance - and sorry for hijacking your thread - but it's basically the exact same question!

john

I would use a full size grinder with a 7" wheel followed by a 36 grit disc if you need that nice of a finish. I used to do that all the time. A lot of it is grinder control as mentioned. Don't dig with the edge. Smaller grinders are also easier to get a valley with if your not careful.

[jfk92]

I would use a full size grinder with a 7" wheel followed by a 36 grit disc if you need that nice of a finish. I used to do that all the time. A lot of it is grinder control as mentioned. Don't dig with the edge. Smaller grinders are also easier to get a valley with if your not careful.

Understand...kind of what I was thinking too...thx Mic....

[JMK WELDING]

John why are you using 6010? Are you doing an open root then capping it with 7018? Why not just do a 30 degree bevel and butt them and just run 7018. Joe