air sander vs. angle grinder

[1930artdeco]

Quick question-I am installing floor pans with my MIG welder, so that means a lot of grinding on my part. I have a 4.5" angle grinder that I can use stones with or I can get a backer pad and use sanding disks with it. The other Option I have is to get a 5" air sander and use the disks with that. My compressor should put out about 7 CFM-when I get it running;(. The third option I have is an air grinder with the 2" fiber disk attachment.

The grinder works but I admit it gets old quickly grinding down the welds. I already know I am not the best welder but I am getting better-albeit slowly. Should I get the disks for the grinder or should I get the 5" air grinder/disk set up? The 2" does a good job but it is made more for spot weld sanding. What are your recommendations?

Thanks,

Mike

 

[rlitman]

You're not doing any significant air grinding on 7CFM. A 2" air angle grinder uses about twice that. Most of the ratings you see that show 4-8 CFM are assuming a 25% duty cycle. If you're ok with 1 minute of grinding and 3 minutes of waiting for your compressor to catch up, then that's fine I guess. It's not fine with me. 50% is more realistic.

What about a 4.5" angle grinder gets old? Because even a cheap one is going to remove material faster than any of the pneumatic options you suggested. Maybe you want a better grinding wheel. You might prefer flap discs, or if you want to see what you're doing, a see-through disc (there are a few options of those, I use Norton AVOS).

 

[Steve from Socal]

The 4.5" angle grinder by far the most effective, get some flap wheels AND 5" discs. The 36-40 grit discs will remove a lot of metal. Sanders run at higher RPM than grinders but the 4.5" grinders work fine with abrasive discs.

 

[K13]

The best way to cut down the bulk of a weld is a pneumatic die grinder. Use a cut off disc held at 90 degrees to the weld and knock the majority of it off with that. Then get a flap disc for your grinder to clean it up.

 

[1930artdeco]

Thanks for the replies. The reason the grinder gets old is the motor and vibration. But if the disks take off material faster then I may just get the backing pad and some disks. There are better stones out there that I need to get I just wasn't sure if one was better than the other.

Mike

 

[CGT80]

You don't need a backing pad. Flap discs have their own backing and come in 24, 36, and 40 grit. Start as course as possible and then finish with something finer like 80 grit. For the final pass, resin discs can work well.

Get rid of the piece of **** grinder and buy a decent one. They should not vibrate. A bad hard disc will also vibrate. I have a 25 year old 5" variable speed milwaukee that has tons of power, but also 3 of the 4" makita grinders with a very small body. They are great for detailed work and would be fine for what you are doing and they are cheap. One of mine has a flap disc for aluminum only, another with a 40 grit for steel, and the third has a cut off disc. Diamond cut off discs **** and I have tried a few of the good ones. Use better tools when possible and composite cutt off discs when they are really needed. 4.5" is more common, but not in a comfortable and light body.

You should use abrasives like they are free, but buy good performing products. When they wear out, it just becomes far harder to do get the job done and you will create more heat. Leigh valley abrasives work fine and were a good price, but name brand stuff from home depot works fine if you want to spend the money or need it right away.

My air die grinders will run non stop, but I have a real 5hp air compressor. Corded grinders will be the best. 2 and 3 inch flap discs are great for small areas and the air grinders are light weight, but it takes a ton of power to run an air compressor that size. I was using die grinders for a lot of blending and after buying one 4" makita, switched to them for most of my work. They are much faster than die grinders.

 

[The Cobbler]

I use both for grinding . I tend to have more control with my Ingersoll rand 317 's than with an angle grinder. It's obviously smaller & lighter weight, and you can use smaller discs as there isn't the nose getting in the way . I use cut off wheels that are too small for an angle grinder on the sanders too . I have 1 sander with a chuck installed so I can use drum sanders on it
bottom line in my opinion, no one tool is perfect for all aspects , no harm in using a variety of tools to get the job done .
I find I'm not using flap wheels much anymore, I am using sanding discs more now.

 

[K13]

Lots of guys posting sound like they are talking about grinding on steel fabrication applications not automotive sheet metal replacement. Grinding wheels and super coarse grit sanding discs have no place in that arena.

 

[whateg01]

... Grinding wheels and super coarse grit sanding discs have no place in that arena.

Grinding wheels absolutely do have a place. A grinding wheel let's a user remove material in one specific spot while not touching the surrounding metal. Used right, they can limit the amount of heat put in the sheetmetal to reduce warpage.

 

[Brianf60]

Flap discs on the angle grinder is the way to go. Try to get a multi pack with assorted grits and you won’t be disappointed.

 

[The Cobbler]

Grinding wheels and super coarse grit sanding discs have no place in that arena

grinding wheels absolutely do have a place. A grinding wheel let's a user remove material in one specific spot while not touching the surrounding metal. Used right, they can limit the amount of heat put in the sheetmetal to reduce warpage.

I agree with "they do have a place " and I often use 24 or 36 grit to take the weld down quickly . I learned it from Fitzees fabrications on You tube.

 

[1930artdeco]

Thank you, for all of the replies. I have ordered a backing pad and disks and will give them a shot. I am just wanting to take the welds down quickly. Holding my angle grinder at different angles waiting for the stones to work gets tiring after a while. I am almost ready to cut out the rear pass. floorpan and weld the new one in!

 

[joe_padavano]

For floor pans, why even bother with knocking down the weld beads? It's going to be covered by sound deadener and carpet.

While I prefer TIG to MIG for automotive sheet metal, the trick to dressing a MIG weld is to remove the proud weld bead without taking off too much of the base metal. As noted above, a cutoff disk in a die grinder, held at 90 degrees to the weld bead, is the way to do this. Get the worst of it off then use the flap disc to smooth the remaining metal.

 

[whateg01]

For floor pans, why even bother with knocking down the weld beads? It's going to be covered by sound deadener and carpet.

Because maybe op doesn't want to be a hack. Some of us care what it looks like under the paint and trim.

 

[joe_padavano]

Because maybe op doesn't want to be a hack. Some of us care what it looks like under the paint and trim.

If I cared what it looked like, I wouldn't be using a MIG for sheet metal.

 

[1930artdeco]

"Because maybe op doesn't want to be a hack. Some of us care what it looks like under the paint and trim."

This. I know I don't have the skills/tools to make the welds look like a professional welded them in. So I am just trying to make it functional and look as good as I can. And right now I don't have the money to get a pedal for my TIG set up, that I will have a hard time using on the pans as the car sits. When I go to do the quarter panels, that is a different story.

Mike

 

[bugzilla46310]

I agree with the flap wheels. Quick removal of material and much nicer finish than the grinder.

 

[csp]

The edge of a cutoff disc is effective at removing beads and it has so little area in contact that heat doesn't become an issue.

 

[CGT80]

There are two different shapes for flap wheels as well and I think the conical ones allow more focused grinding vs flat. Just like the post above, target the high area of the weld first and avoid removing unnecessary material around the weld, to avoid heat and thinned panels.

It takes a conscious effort to do this and it could be done after using a hard wheel or cut off wheel if desired. Floor sections are going to be much more forgiving, but it is good practice in case you work on exposed body areas or other projects.

Tig can be worse for heat build up. It can also be quick and low profile with good fitup and good skill. Some parts are not at all suited for tig welding, such as welding aluminum rod to thin flat angle. The spoolgun was a much better tool for that project. I like tig for tacking thin steel sheet. If you move too slow, it is easy to put too much heat into a weld. Mig forces you to move faster. It depends on your skill and experience as well as the type of job. I switch back and forth between tig and mig on projects.

 

[danielbuck]

The edge of a cutoff disc is effective at removing beads and it has so little area in contact that heat doesn't become an issue.

it's a counterintuitive way to use a cutoff disc, but it does work very well and gives you a surprising amount of control to minimize excess metal removal. I like using a 2 or 3" disc on a diegrinder. I don't do a whole lot of sheet metal, but when I have it has worked great!