How do you properly grind welds in sheet metal? What type of discs or tools to use?

[Kern Dog]

I have tinkered around with all sorts of things with these cars.
Even here in California, we deal with rust.
My welding skills are fair, depending on what I'm welding. The thicker the metal, the better my welds.
I have to smooth over every weld in sheet metal though. For me, it is always a moving target to have the welds hot enough to penetrate but not too hot where they burn through. In short, I have to grind everything to get it smooth.
Therein lies the point. I have used traditional grinder discs, flapper wheels and cutting discs to knock down welds. I'm always nervous about the areas around the welds getting ground thinner and having weak areas. I've seen welds addressed by some guys where it looks so good, you cannot see where the welds were. I know that is a testament to skill but I'm guessing that those guys are using better tools than I have.
What tools are those? What techniques do you use to make the seams invisible?
It is fair to guess that it starts with better welding. It is easier to clean up a good weld than to cut off popcorn welds.

 

[451Mopar]

I like the flapper wheels, but I'm not an auto body guy. They likely have other tricks?
I have seen taking the bulk off with a disc and finish with a file. Sounds pretty time consuming?

 

[icetech]

I have tinkered around with all sorts of things with these cars.
Even here in California, we deal with rust.
My welding skills are fair, depending on what I'm welding. The thicker the metal, the better my welds.
I have to smooth over every weld in sheet metal though. For me, it is always a moving target to have the welds hot enough to penetrate but not too hot where they burn through. In short, I have to grind everything to get it smooth.
Therein lies the point. I have used traditional grinder discs, flapper wheels and cutting discs to knock down welds. I'm always nervous about the areas around the welds getting ground thinner and having weak areas. I've seen welds addressed by some guys where it looks so good, you cannot see where the welds were. I know that is a testament to skill but I'm guessing that those guys are using better tools than I have.
What tools are those? What techniques do you use to make the seams invisible?
It is fair to guess that it starts with better welding. It is easier to clean up a good weld than to cut off popcorn welds.

I did a bunch of research when i started working on mine and i'm glad i did.. I found a video of a fabrication place testing different grinding methods and this is what i ended up using and it works very well
I use these discs Starting with 36grit to knock down the bead and ending with 80 or 120 to make it pretty
Sanding Disks...

On these backing plates.... buy 2 as you will catch and edge and destroy them eventually
backing plate

That saved me a ton of time..

P.S. i tried flapper wheels and didn't like them as much and the cost was higher..

 

[493 Mike]

If you can spare the time, check out the MP&C thread on Garage Journal. The man is a wizard at all phases of body and paint work. He shares all his techniques in the thread.
Mike

 

[Donakey]

I Like 3m cubitron 2” rolloc, they come in bigger sizes , the twistloc backing pad is how they mount. The 3m purple cubitron lasts the longest in my option and doesn’t fly apart. I bent the shank on the mounting pad once but it was a cheap one. 3m is more money but it lasts longer. With a good pad it’s flat not dished. I found the the 3m pads last way longer. If anybody is using different pads that cut well for a long period this would be great information. The 3m stuff is pricy!

 

[Donakey]

Another technique when using air angle die grinder is keeping the backing pad flat. It will dish the sheet metal if used.

 

[mopar4don]

If you can spare the time, check out the MP&C thread on Garage Journal. The man is a wizard at all phases of body and paint work. He shares all his techniques in the thread.
Mike

I agree with Mike. MP&C or Robert is excellent!
Here are 2 links to his threads.

Welding in patch panels

I've got an upcoming project,I have a 1968 Chevy truck that I bought a few years back,my 14 year old son has had a fit for it ever since I got it,and I plan to restore it for his first ride. I have rebuilt the engine,and now I have to take care of some cancer spots here and there. I have a good...

www.garagejournal.com

MP&C Shop Projects

This thread, while it may show quite a bit of work on vehicles that come in the shop, is primarily going to focus on providing metalworking/metal shaping tutorials, where ever possible using simple hand tools, in hopes that it may inspire others to learn the craft. While I am no expert, in many...

www.garagejournal.com

 

[Rich H.]

rigid tools everywhere possible, except where they won't work or fit. "Stones" (grinding wheel on the angle grinder), cutoff wheels/"zip wheels" on
any kind of grinder that will fit and work. the secret weapon is, by far, the miniature belt sander. For me it was the belt sander that made me appear to suddenly be much more skilled than I think I really am. Google "13 inch belt sander" to see the small, hand held devices I'm mentioning if you are not already familiar.

Flap discs seem like a good idea and seem user friendly, but their flexibility usually leads to thinning and damage of the surrounding metal.
I will use them where they make sense and where i can avoid doing any harm with them, but it's less and less over time.

 

[Daves69]

........It is fair to guess that it starts with better welding. It is easier to clean up a good weld than to cut off popcorn welds.

I've never been a body person and welding in even a small patch for me is trying let alone the grinding the excess. I use a backer wherever possible anymore.

A gimmick or worth a look at?

 

[BeepBeepRR]

Dont know if you ever watched Puddins Fab shop on youtube he shows how to grind down welds and tells you what to use.

 

[zyzzyx]

What I use to knock down weld beads is a hard wheel on my die grinder. 3" X 1/8". Heat is your enemy and by
using the edge of the wheel you can knock down the high spots efficiently and you have alot of control. Anything
else just wears out fast and makes heat.

 

[4mulas]

Hey Kern, round sanding disc’s or Roloc’s and a steady hand!

 

[j-c-c-62]

The main issue when working on sheet metal and grinding, etc, we know heat is your enemy, so go slow, bounce around in your work area, resist getting aggressive.

 

[eldubb440]

3 inch x 1/8 wheel on a die grinder; followed up with 24 grit 3 inch roloc disc

don't assume a thicker wheel cuts faster, it doesn't

thicker wheel also gets wobbly and out of balance

 

[halfafish]

I used a regular angle grinder abrasive wheel that was somewhat worn from previous use. The working edge was fairly well beveled and rounded so as mentioned above, I slowly and gently used just the rounded edge of the wheel to knock down the bead. When I got fairly close to flush I switched to a flapper disc to get it close enough for bondo and seal sealer to finish the job. I'm just a hacker at body work but it came out OK.

 

[493 Mike]

One of Robert's (MP&C) recommendations was to use a cutoff wheel edge to grind welds. It imparts very little heat to the weld and cuts fast.
Mike

 

[Dodge33]

What I use to knock down weld beads is a hard wheel on my die grinder. 3" X 1/8". Heat is your enemy and by
using the edge of the wheel you can knock down the high spots efficiently and you have alot of control. Anything
else just wears out fast and makes heat. View attachment 1706507View attachment 1706520

Here is my winner! The only thing I do a little
different is use a 3 inch air cutoff saw with a
3/16"- 1/4" thick 3" diameter 3M hard wheel.
You have variable speed doing it this way.

 

[Kern Dog]

I have done that.

I have no immediate plans to cut and weld anything. I’m just trying to improve my skills to make things easier later.
I bought these things…

The thin and flat plates allow a small gap that gets filled by the welds.

To use these things, you’d need access to the back side of the panels.

I’ve done lap welds for patch panels but it seems that butt welds reduce the risk of corrosion forming.

 

[zyzzyx]

Yes, Yes, And Yes!

And whatever you do,
don't forget the Cleco's!

 

[khryslerkid]

I'd generally start with a 4-1/2" sanding disk, I like to stack two together to make them more rigid, and you have a spare to change to when the top one starts to get dull. Then when close to having the weld flush change over to a 2" sanding disk on my angle grinder to complete.

The trick to any grinding is to watch the grinding marks (scratches). They will tell you exactly where you're making contact.