I'm working on a set of tables, and using 1 inch square tubing. I've cleaned the oil off of the metal, but it's still left with a sort of smoke grey color. I've used a heavy wire-brush on my 7" grinder to remove this finish, but it is real difficult. I heard a lot of comments about mill scale, and was wondering if this is this smoke grey color on the metal, or if it's just a different chemical sprayed on the tube to prevent rusting.
Any good suggestions for removal? Other than the tedious wire brushing - it sticks real well!
I'll submit the finished pictures in the projects section. I'm going to remove the color, as I want the shiny silver color, that I'm spraying with clear finish to keep from tarnishing/rusting. However, I've seen some nice metal colorings now. Might post that as a separate question under projects.
Some mill scale can be quite difficult to remove. I've found that wire brushes sometimes only burnish the scale.
You may want to try a flap disc (careful, they can be aggressive) or a non woven abrasive like a 3-M type scotch brite discs. If a polished steel look is what you want the scotch-brite discs work good. For a tough clear finish try 'PERMALAC'.
I believe he is just talking about the regular grey Mill Finish. If you haven't welded it up yet, be sure you pay attention to the seams on the square tubing, so you can position the seam to the rear. The seams usually have somewhat of an indentation along them, which you will discover when you start cleaning and polishing them.
I've used a flap disk on the metal, with mixed results. The disk has a hard time getting into the center of the dimple on the tube (especially on the welded side), unless you really grind quite a bit of the edges away. Also, even the 120 grit leaves quite a few scratches.
Even the wire brush on the big grinder leaves scratches, but not as severe.
The one thing I found that is really nice if you want a real smooth finish is a polishing/grinding disk at my LWS, which really polishes the metal after being wire brushed. It almost makes the metal look like it's been chromed - however, it does wear away fairly quick - I need to get another couple for the second piece of my project, and take a picture show everyone. They have 2 levels, one is a orange color, and the other is green - but they aren't Scotch Brite pads. These are fairly smooth - but firm, with just a little abrasiveness. I haven't seen these grinder disks anywhere else.