4.5 inch grinder abrasive tech

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Jul 20, 2006
Redwood City, CA
I recently bought the entry level grinder that Milwaukee makes (or has made in China) and I'm beginning to spend some quality time with it grinding welds. :grinpimp:

I used the Milwaukee abrasive wheel that came with the grinder for a while and I've bought a few 4 1/2 - 7/8 inch arbor wheels at various hardware stores, etc. with mixed results as to how well they seem to do at grinding welds. Today I picked up the (now older) wheel that came with the grinder and was surprised to find that it still seems to work better than anything I've bought. A few questions:

1) Does Milwaukee make really good wheels, or is it maybe a coarser grit than the others. The Milwaukee seems to wear away faster but continues to work. The other wheels (Norton, Makita, etc.) seem to plug up really fast.

2) I assume that with a hand-held grinder no one ever uses coolant or wax stick, etc. I also assume there's no way practical way to diamond-dress one of these wheels?

3) What is a good coarse grit for removing lots of weld material (18 ga sheet metal) with minimum heat/wheel plug-up?

4) What is good finer grit (finish-up) for getting closer to the base sheet metal (do those "flapper" things have a place in finish work)?

5) Anyone know where I can order a bunch of Milwaukee wheels online at a good price?

6) What about the 4-1/2" x 1/4" x 7/8" Grinding Wheel A24R Metabo at Lehigh Valley Abrasives (recommended by fj40charles in an earlier thread)? Would this be a good choice for rough grinding welds?

Thanks for any feedback.
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well i have good luck with sait 60 grit 5 inch sanding disc. we use it on 16ga metal . get a firm but flexible backer pad , as you all ready know dont dig with the edge of wheel use the whole pad and heat is your enemy on thin metal . i like to bog the grinder down till rpms drop . then look ,never more than ten sec pressing . to much heat can cause the sanding pad to fail early
Grinding disks get used up too quick to bother doing anything to them other than using them. Keep a few almost worn out ones handy for the tight spots a new one won't fit.

Flap disks beat the snot out of grinding wheels for removing weld material. Faster material removal and much easier to smooth surfaces together. Unfortunately also 2+x as expensive per unit and don't last as long as a grinding wheel.
hey, i guess you really need the right tool for the job , if you have alot to grind , well you need a bonded wheel , to sand or polish a little weld out of 16ga or thinner i prefere the sanding pad
I get grinding wheels at a welding supply store. much better than stuff you get at the hardware store.

there is a difference!
I'd also gotten a few from the local Airgas store before. Just a few days ago the Airgas manager gave me a flap disc to try out. He said the flappers cut faster and cooler but wore out sooner than a hard grinding wheel (as CruisinGA also stated). These were "Weiler - Tiger" flap discs and they seem to work great. I used them on a few weld beads/tacks and couldn't believe it. Even at a 120 grit they cut the welds like butter compared to to the hard wheels I've been using. And they seemed much quieter with less heat build up.

So I got a few more from Airgas and then ordered a bunch (flappers, cut-off, hard wheels) from Lehigh Valley Abrasives. They seem OK (Lehigh brand flappers) - have not tried them yet. Shipping (US postal mail) was kind of weird with all the wheels loose and banging around in a box with a few pieces of paper thrown in for padding. And I ordered 3, 4-1/2" Grinding Wheels (A24R Metabo) and they shipped 3 of some other brand (German I think?) instead.

In future I may just take out a bank loan and get a bunch of those Tiger discs.
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Flapper disc for sure - I "borrow" mine from work cause they are $7.80 CDN each. I am the purchaser at work and first started getting them at $13-15 each until I shopped around. Of course I buy 30 or 40 at a time. I don't know the brand off hand, likely VSM, but to be honest for all the "our product is better" talk I find they are all the same. Except the super, super cheap crap.

Here's a shot of my welded on wheel arch rib before an 80 grit flapper disc on a 5" Walter variable speed grinder set at speed 5 (out of 6). Someone mentioned keeping it flat and not gouging - a must.

This is the end of the floor ribs in my 45 LBP by the tailgate. I made this panel from flat sheet and had to weld the ends of the ribs and then dress them. I used a 2" angle air grinder with an 80 grit sanding disc (because of the tight spaces), then the 80 grit 5" flapper disc to smooth, then a 80 grit 6" random orbital. All the same grit but different effects.
Also, when you think your flapper disc has about had it - keep going. I find they last longer than you think. Another point to consider is that a new disc will remove material faster than you think because you were used to the old one you just changed out.
The ribs before grinding
see the air grinder he has in the above photo, I use one of those for all the small stuff, with everything from a scotbrite pads to 40grit, they are great on small stuff,

I agree with everyone else the flap disc's work great on cleaning up stuff, I keep 3 grinders one with each a flap, grinder and wire wheel when I am welding alot it makes things go faster...
i personally like flapper wheels way better then grinding disc's .

walter makes good disc's .

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