Getting More First Minutes Out of A Flap Disc

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.
Reply to
Bob La Londe
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I know what you're experiencing with flap discs and have used this type of disc to good effect
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. I've seen many of this type for sale on ebay and most don't have a high enough speed rating for use on a 4.5" grinder so check what you get if you try one.
Reply to
David Billington
[boring crap trimmed]
So OP wants help finding a better type of flap disc, but never mentions the type they're using now.
Reply to
Cydrome Leader
You know I filtered the sub threads where you went off on your own little childish temper tantrums, but I didn't filter you entirely. I figured once you got over your nasty little snit you would start to act like an adult again. I can see I was wrong. Best of luck to you. I do honestly hope you grow up someday and eventually have a happy life.
To be clear I do honestly hope at some point you begin to have a happy life that does not need to be validated by acting nasty and demeaning to others instead of just being happy with yourself.
Reply to
Bob La Londe
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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I cleaned the paint and rust from the 4" channels for the gantry hoist track with an HF "2 in. Mini Orbital Air Sander" and a 2" coarse scouring pad, the only power sander I own that fit flat inside the channels. It was fast enough on the outside to satisfy my laid-back retiree working rate. After stripping the four 8' channels it seemed clogged with paint but still cut well enough to remove the leak-causing corrosion from the rims of the aluminum motorcycle wheels the sawmill blade runs on. I don't remember if there was mill scale under the paint on the channels. The pad left shiny metal.
The HF tool was meant to be double action but it cut faster with the rubber disk mounted to seat on the outer bearing race and spin instead of oscillating.
The sander and the 2" and 3" pad kits don't work well together as received. I made a stub arbor of 1/4-20 threaded rod and used nuts and washers to control whether the pad spun or oscillated.
It seemed that a 3" pad on a 2" backing conformed to inside curves better and may have been better on edge for shallow rust pits. Although the used pallet rack channels had been stored outdoors they weren't pitted enough to require my needle scaler or sandblaster.
My faster hand held metal flattening tool is a 7" angle grinder with a saucer wheel. Unlike with the usual disk I can see and feel when it makes contact around the arc and is cutting flat. I use it where welds will be bolted together or support something, like the warped engine mount plate on my second-hand log splitter.
Cleaning square tubing seems like a belt sander task.
Reply to
Jim Wilkins
I know what you're experiencing with flap discs and have used this type of disc to good effect
formatting link
. I've seen many of this type for sale on ebay and most don't have a high enough speed rating for use on a 4.5" grinder so check what you get if you try one.
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Good stuff, though to me they are over-priced and too short-lived, perhaps from being sheared down by rust-through holes they uncovered. I don't get 10-20 year paint durability on auto body work unless I sand-blast, which also cleans out the rust pits better than they do.
Reply to
Jim Wilkins
I had not thought of that. I have one around somewhere, but have not used it since my last cabinet building project a few years ago.
Reply to
Bob La Londe
If it has a dust bag , remove it and tape over the outlet . I learned the exciting way ...
Reply to
Snag
Did you ignite a bag of sawdust or shoot sparks down your shirt? Either way it sounds exciting. Did you by any chance get video?
Reply to
Bob La Londe
I had not thought of that. I have one around somewhere, but have not used it since my last cabinet building project a few years ago.
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When I was young I read of a college psychology experiment in which the task was moving muddy water without utensils. There was a pitcher of water and tumblers within sight, but no one either thought to or dared dirty them.
That inspired me to see what things -could- do rather than what they were meant for, "outside the box."
For example I'm watching broadcast (not cable) news and weather on a laptop I turned into a portable battery-powered HDTV that also records.
Reply to
Jim Wilkins
If it has a dust bag , remove it and tape over the outlet . I learned the exciting way ...
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I burn sawdust from the sawmill as part of the kindling in the wood stove. Lying still it chars and goes out, but when picked up in an air stream it roars like a jet engine and fills the stove with flame.
The air stream is from blowing into a 3/8" vinyl tube that ends in a 1/8" nozzle, tapered inside and out to amplify airflow like an aspirator or steam injector. Maybe someday I'll try dribbling sawdust into the forge blower.
Reply to
Jim Wilkins
I can't recommend a product, but my experience suggests that the rapid deterioration has more to do with the quality of the adhesives used to attach the grit than it does with the grit itself. The bigger sharper particles of grit simply get ripped away, leaving you sad.
Find a product that uses a better quality adhesive. Maybe rated for higher temperature or loads, or to be installed in large sanding machines where it's tedious to change the abrasives.
Clifford Heath
Reply to
Clifford Heath
Except it doesn't. You need chemical treatment as well, as I'm sure you know. Metal is crystalline, and some rust will always penetrate into pores finer than any blasting sand.
Clifford Heath.
Reply to
Clifford Heath
I thought that flap discs worked by having the used-up edges wear away and expose new grit. But that never happens for me. The various things that I've tried to expose new grit have never worked. So either I'm missing something or they just don't work that way. If I'm missing something, I would really appreciate being clued in. If they don't work that way, what is the point of having flaps?
Reply to
Bob Engelhardt
I've been using these for many years, first noticed when B&D started selling a consumer version in the 70s, later same product from 3M and Germany. They're the only thing that will remove mill scale without gouging the metal.
But I haven't seen them as angle grinder wheels. I use them on a high-speed end grinder, ones meant for that use. Just the edge of the wheel hits the metal. Any steel in otherwise forged ornamental work that is going to be left unworked can be stripped of mill scale leaving only faint linear striations, no overlapping partial-circualar grinder marks. Among other things, I've made 16 ga. panels stripped this way and blued with Oxpho-Blue(tm). Blueing would take poorly/unevenly if the mill scale were not stripped and angle grinder marks would look really bad.
You have to have supporting widgets -- collars with spurs -- to hold them because they -- at least all the ones I've bought -- come without any hub.
Yeah, you do have to be careful to avoid sharp (or any) edges, holes, protrusions which eat them away very quickly. Where you can do that, they last pretty well.
I've used bead blasting for forged ornamental work but, where possible, I prefer phosphoric acid pickle. Probably overkill for typical structuraal welding work and it does NOT work all that well on mill scale.
Reply to
Mike Spencer
I think I know what you and Bob are saying.
Answer is - sorry - don't know.
With a "hard" side-grinding disk - an angle-grinder "carborundum" disk - if it gets blunt and clogged from lightly skimming over big-area flat surfaces, you can sharpen it by crudely "wiping" the disk along the edge of some chunky iron. Small area and big force = rip at the disk surface. Have a heavy offcut of piece of scrap to-hand to re-sharpen your grinding disk on.
I don't know of the same with a flap disk. I've known them never clogging due to the flap construction and never getting blunt through wearing-away and progressively exposing new grit. Do try the same trick of "wiping" harshly along a narrow edge on some scrap?
Reply to
Richard Smith
I've used bead blasting for forged ornamental work but, where possible, I prefer phosphoric acid pickle. Probably overkill for typical structuraal welding work and it does NOT work all that well on mill scale.
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20,30,40 years ago I wasn't taking notes and photos of rust repairs. As best I remember Naval Jelly didn't guarantee a lasting repair, maybe because I didn't wash it off properly or dry it fast enough. Etching primer didn't hold up well either. Sandblasting and a wipe with lacquer thinner did, so I stopped experimenting. It's difficult to separate the effects of the several variables involved.
The 20+ year old paint job on my truck's pitted rear bumper is only now starting to deteriorate. SEMS paint appears to last longer than other spray can paints I've tried, Duplicolor and PPG needed rework after 2-3 years. Road salt is a serious problem here but driving can become extremely difficult without it.
Reply to
Jim Wilkins

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