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longjohns · 04-24-2003, 10:03 PM

i fabricate some metal furniture at my work. the think to keep in mind about sanding steel (as mentioned above) is that it's much harder than wood, so requires much more effort to sand. It is definitely smart to use the finest grit you can which will still yield results. Be very diligent about progressing sensibly through the grits - you can waste a lot of time if you skip too many grits and find yourself unable to remove scratches from the last step.

there is also a big difference in the finish you'll get depending on what methods of sanding/grinding you're using. for example, here's how i might go about polishing a piece of steel:

on a disc grinder:
grind any big welds down almost flush with a cutoff disc
grind welds flush to the surface with 120 grit fiber-backed disc
scratch removal with more discs - 65 micron, 45 micron (approx 220 grit, 280 grit, respectively)

then i switch to a dual-action sander with 150 grit sandpaper. i might then use 220 grit on the DA sander, but often i'll just go to the red 3M ScotchBrite pads. much of what we do gets nickel plated, and the nickel can cover some degree of scratching. for chrome plating, the metal must be extremely smooth, almost polished.

that's probably more technical than you're looking for - i guess the point i'm emphasizing is being very deliberate about removing scratches at each step. contrary to a comment above, it is often helpful to alternate sanding directions between steps. two reasons - it is easier to tell when you have successfully removed the last step's scratches, and your piece will stay flatter.

if flatness is a concern, keep in mind that your workpiece will usually be as flat as what you use to sand it. this is why people use thick plate glass or accurate grinding stones to lap precision metal surfaces. if you use nothing but soft-backed pads or sandpaper held in your hands, expect to lose flatness. where it's important, use sanding blocks, belt sanders, files - things with hard, flat reference surfaces.

the higher polish you put on metal, the more you will notice if it's not flat.

i'd better quit babbling!! ;-)

04-24-2003, 10:03 PM	#14 (permalink)
longjohns Insane	i fabricate some metal furniture at my work. the think to keep in mind about sanding steel (as mentioned above) is that it's much harder than wood, so requires much more effort to sand. It is definitely smart to use the finest grit you can which will still yield results. Be very diligent about progressing sensibly through the grits - you can waste a lot of time if you skip too many grits and find yourself unable to remove scratches from the last step. there is also a big difference in the finish you'll get depending on what methods of sanding/grinding you're using. for example, here's how i might go about polishing a piece of steel: on a disc grinder: grind any big welds down almost flush with a cutoff disc grind welds flush to the surface with 120 grit fiber-backed disc scratch removal with more discs - 65 micron, 45 micron (approx 220 grit, 280 grit, respectively) then i switch to a dual-action sander with 150 grit sandpaper. i might then use 220 grit on the DA sander, but often i'll just go to the red 3M ScotchBrite pads. much of what we do gets nickel plated, and the nickel can cover some degree of scratching. for chrome plating, the metal must be extremely smooth, almost polished. that's probably more technical than you're looking for - i guess the point i'm emphasizing is being very deliberate about removing scratches at each step. contrary to a comment above, it is often helpful to alternate sanding directions between steps. two reasons - it is easier to tell when you have successfully removed the last step's scratches, and your piece will stay flatter. if flatness is a concern, keep in mind that your workpiece will usually be as flat as what you use to sand it. this is why people use thick plate glass or accurate grinding stones to lap precision metal surfaces. if you use nothing but soft-backed pads or sandpaper held in your hands, expect to lose flatness. where it's important, use sanding blocks, belt sanders, files - things with hard, flat reference surfaces. the higher polish you put on metal, the more you will notice if it's not flat. i'd better quit babbling!! ;-)