Getting More First Minutes Out of A Flap Disc

Bob La Londe · 2022-05-11T15:41:15+00:00

Yesterday I found myself cleaning up a bit of square tube in preparation for welding and later paint. It was outside, but in SW Arizona, that just means it has developed a small amount of protective rust over the mill scale.I started with an angle grinder and a flap disc. It made short work of the light loose rust, but would hardly touch the mill scale. It also showed some rust down "in the" the mill scale. I probably could have stopped there, but I got carried away with myself. This stuff welds really nice if you have bright shiny metal and takes a good paint coat as well with an etching primer, and proper cure times.I probably I could have just used extend or some other rust neutralizing primer after knocking off the loose rust, but this construct will be going into a humid environment.I noticed a fresh flap disc stripped rust, and mill scale amazingly fast. It did more work with less effort in the first minute or two than it did in the next ten. Now the flap disc was still nearly new, but it was performing like one that was half worn away. There was still plenty of grit, but the edge was mostly the flaps rather than the grit, and the face was the same, but also gummed up with mill scale.I am NOT trying to get longer life out of a flap disc. I am trying to get more time performing like the first minute or two of a new disc. I don't care if the total life of the disc is less. Is there a practical way to dress these so that you can expose more grit quickly. I tried spinning it against a wire wheel on a bench grinder. The result was less than amazing.Sans the solution I am looking for is there a better disc for stripping metal than an abbrasive flap disc? I can do the work with a grinding wheel, but its much more skilled to avoid gouging the base metal and doing damage. I tend to only use a grinding wheel to make the bevels before welding.

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David Billington 4 years ago

The Osborn Dronco 4.5" (115mm) ones I have use the standard 7/8" (22.23mm) angle grinder mounting and are rated at 11,000 RPM max so suitable for use on my 4.5" Bosch grinder. The only minor issue I find is due to the depth of the fleece when new it makes it harder to get the pin spanner on the nut but I can live with that. The Dronco part number is 6700 001 100. None of the other discs of this type I've seen advertised had a max speed anywhere near 11k RPM so would have been unsafe in use.

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Jim Wilkins 4 years ago

The Osborn Dronco 4.5" (115mm) ones I have use the standard 7/8" (22.23mm) angle grinder mounting and are rated at 11,000 RPM max so suitable for use on my 4.5" Bosch grinder. The only minor issue I find is due to the depth of the fleece when new it makes it harder to get the pin spanner on the nut but I can live with that. The Dronco part number is 6700 001 100. None of the other discs of this type I've seen advertised had a max speed anywhere near 11k RPM so would have been unsafe in use.

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What I called 2" scouring pads appear to be a denser, fine-textured variant on fleece abrasive wheels.

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Bob La Londe 4 years ago

I tried a couple methods of dressing the flap disc. It would improve slightly but not for very long. 5 seconds of work maybe. I already have the flap disc so I figured I'd see if I could improve their usefulness first before trying anything else.

These are 60 grit Zirconia discs, but results were similar with Aluminum oxide flap discs as well.

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Clare Snyder 4 years ago

On body work I pickle after either blasting OR grinding/sanding Either process can "pean" metal over rust - and the rust ALWAYS wins. Phosphoric acid "metal prep" kills any tiny rust remnants allowing the primer to fully seal the surface and the top coat to last and LAST.

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Jim Wilkins 4 years ago

But I haven't seen them as angle grinder wheels.

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You have to know the right incantation to invoke Internet magic. "Deburring disc" returns this:

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Getting More First Minutes Out of A Flap Disc

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