[How do I?] Brushed Finish On Aluminum

Brushed finish, or "graining" as we used to call it is done with enormous belt sanders and sometimes "Flap" wheels in a production environment. If it's absolutely flat, u might get away with a belt sander, but your fears are warranted. Part of my last job was restoring brushed stainless equipment, and practice and patience with a sanding pad seemed the only reliable method. The brush finish actually consists of short scratches 1/2 to 1 inch long among thousands of others. Difficult to reproduce in a shop because most methods produce long or continuous scratches. I had some success with a "drum" type sander in a cutoff type rotary tool, The drum needed to be slightly soft under the sandpaper tube or roll. U might get away with using the nose of the belt sander rather than the whole surface ...?.....Use of a fairly coarse emery paper seems best. 100 - 180 or so, but that was for stainless. good luck !
 
Thoughts on finishing aluminum.
I have to go with Andre on this. Restoring motorcycle engine covers and making electronic control panels I've found ScotchBrite leaves the nicest bright non-polished surface on aluminum. I particularly like doing engine turning patterns on panels with it, It's very forgiving and never digs in leaving a deep scratches like some sanding can. Wire wheels, unless very fine, can also be variable and leave an orange peel surface when worked too hard. I always use some fluid when surfacing aluminum, I prefer mineral spirits, but denatured alcohol and soap and water work well too. It depends on what happens after.

If I want a very smooth but flat looking surface, like before anodizing for black gun parts, I finish with a scouring powder or pumice slurry. Rougher looking flat finishes I just abrasive blast.

If I have to paint aluminum the absolute best adhesion I've ever obtained is washing down with scouring powder followed by a dip in a mild solution of lye ( 1 tbsp. Red Devil Drain Cleaner/ quart water is pretty mild). Rinse well and let dry thoroughly, but don't touch!
 
If you try a brush, I would use a stainless one. And they make Scotch Brite belts for your belt sander $$$. But to try and get that industrial look, especially on a large surface, is not going to be easy. Keep us posted, I’m wanting to hear how it turned out. Good Luck, Dave.
 
Scotchbrite wheels are around $40. Expensive, but trust me they're worth it.

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I tried the belt sander. It removed the metal quickly but made some gouges as I feared. It would be impossible to keep the surface flat so I quit. I finished the rest with a hand sanding block and was able to sand out some of the gouges. It looks pretty good. Hard to photograph.
R
 
Not a brushed finish, but another option for a matt finish is to submerse the part in a caustic soda (lye) solution - like you would do when preparing the part for anodising. The caustic soda will etch the aluminium surface leaving a dull, micro roughened, surface.
 
Happened to be doing some caustic soda etching today so thought I would show an example.

New lid handle I knocked up today
IMG_1364s.jpg
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Example of identical pieces - one straight off the lathe and one after caustic soda etching
IMG_1362s.jpg
 
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