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Grinding Weld Beads - Recommendations, please

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What are members' recommendations for tools and abrasives to dress down MIG weld beads?   For reference, I'm talking about stitch welds on sheet metal.

The typical combinations I've seen suggested are:

1) angle grinder/flap disc

2) mini die grinder/2" sanding disc

Abrasive grade recommendations I've seen are 36-grit to start and 60-grit to finish.

I'm curious to hear thoughts on which combination(s) works best.

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I use a die grinder with a 3" cut off wheel to dress welds down most of the way. Then I use die grinders with 2" & 1" rolocs on them 36 grit. Sometimes I finish up with a 4" flap disc, but the flap disc can remove a lot of metal really fast and there is not a lot of metal thickness to start with.

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52 minutes ago, grannyknot said:

A 4" grinding disc followed by 60 grit disc and if it is visible 120 disc. If what needs grinding is in a tight spot then the die grinding bits.

 

IMG_0234.JPG

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I have a selection of carbide bits like that, but those little metal splinters go everywhere!!!

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Yes they do,  Charles, do know if they make a bit for aluminum?  I've tried the carbide bits on aluminum and spent the next couple of hours picking out of the cutting bit teeth with a dental pick.

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50 minutes ago, grannyknot said:

Yes they do,  Charles, do know if they make a bit for aluminum?  I've tried the carbide bits on aluminum and spent the next couple of hours picking out of the cutting bit teeth with a dental pick.

I have some for aluminum and they have a different tooth pattern. I have seen a tip on how to prevent this but can't remember what it was. :blush:

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Lye will evidently clean the burrs of aluminum and beeswax is said to prevent build up but not contaiminate

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Stay away from the flapper discs as they tend to grind the parent sheet metal more than desirable. A baced sanding disc 2-3" on a 90 degree die grimder, or a 4-5" backed disc on a grinder, and lern to keep it flat-ish, the biggest trap is to grind till the bead is flush, but as the weld cools it shrimks and pops up the attached sheet, leaving a lil valley on edge of the weld. 

The other absolute gun tool is a mini 18-25mm wide belt sander, but best if you have experience in using it, otherwise you can dig worse than with a flapper. 

I see qualified boilermakers and sheet metal guys get it wrong all the time in my lime of work, and many a times need to guide/coach them, which they hate, but love when they get it right, and i dont have to reject their work..... 

It does pay to get better at the welding, and this will come with time and experience. 

Nat0 

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On 8/3/2019 at 10:00 PM, Patcon said:

Lye will evidently clean the burrs of aluminum and beeswax is said to prevent build up but not contaiminate

I didn't have any beeswax on hand so used an old candle, works great!

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20 hours ago, grannyknot said:

I didn't have any beeswax on hand so used an old candle, works great!

I think toilet sealing rings are beeswax. Cheap and plentiful.

Sorry I had to stoop to a potty reference...

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I’ve had one for a while. Work great but hard to get a good selection of the sanding belts. They don’t last long when you catch an edge.

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Lots of useful info.  Thanks very much.

Now to the next question:

What processes and/or chemicals do you recommend to prepare the welded area for primer and paint?

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 After grinding and sanding, I normally I use a wire brush, lacquer thinner, and Zinc rich primer.

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I use the 3M  Corps weld grinding wheel with a small die grinder. You can really knock off the high spots with precision then I use the angle grinder with the sandpaper to finish it off. 

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@SledZ  Can you be a little more specific about the '3M weld grinding wheel' that you use?  They have dozens of products that fall into the weld-grinding category.  Do you have the 3M product number or name?

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@240dkw  That wire sounds intriguing.  Unfortunately, it looks like the manufacturer only offers it in 11-lb spools (Cdn $130 plus tax & shipping from KTS Tools).  That's good for commercial shops, I'm sure, but it represents a lot more welding than I need to do (or at least a lot more than I'm hoping I need to do :unsure:).  Other members with more ambitious build programs may want to try it out, though, so thanks for the tip.

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That is what I bought. I have some left over of course, would you like me to put some on a smaller spool and send it to you? Price sure has gone up, l think I paid around 80 cdn  about 5 years ago. 

Edited by 240dkw
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45 minutes ago, SledZ said:

Yep its here on Amazon. I used only one wheel for dozens of long welds. It's a really good grinding wheel.

https://www.amazon.com/3M-1991-Reinforced-Grinding-Wheels/dp/B0002SRLF2

 

Interesting.  It's promoted by 3M as a cut-off wheel, although they say in the spec sheet that it's suitable for cutting and grinding.  There are 4 sizes (diameters) offered, each with its own centre hole size.  The 3" disc you're apparently using has a 3/8" centre hole.  Does your die grinder have a 3/8" chuck, or do you use a step-down mandrel to adapt to a 1/4" chuck? 

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