Topic: Polishing/sanding rear brake panel (tiny compound curves)

[drumstyx]

As I found out in my other thread, I made a mistake using a wire wheel on aluminum, and now I've got to clean up the pitting from that, as well as the awfully rough casting between the ribs.

Thing is, those tiny inner compound curves are a huge pain to remove any significant amount of material from by manually sanding, even with 100 grit. Some corners are even downright impossible, as the sandpaper just won't bend enough to get in there, and screwdrivers tend to rip it!

I have the same issue in some very small areas on the crankcase, near where the sprocket comes out. Naturally I'm turning to dremel and die grinder, but what bits let you do fine sanding? Everything is like 40-80 grit.

So what have people used to sand in tiny areas? The perfect tool would be like, a rounded soft sponge with various grits glued on, ideally available in diameters from 1/4" to 1". Know of anything?


I mean, I can't imagine this guy is sanding and polishing crappy casting marks by hand: https://carpyscaferacers.com/shop/brake-system-parts/drilled-and-polished-rear-brake-assembly/ On closer inspection of those pictures, I guess carpys didn't get it sanded perfectly smooth either, I see some minor blemishes. That makes me feel better, but I still have to start on 1200+ grit tomorrow, and I'm not looking forward to it. I can't believe there aren't tools for this yet...

[edwardmorris]

I used construction styrofoam pieces with paper wrapped around them and had at it. Tighter the space, smaller the piece, got it all nice and even with 400,500,1000,1200 grits in that order, then buffed it up. Came out nice



Rest of the CB750 bits that I did with that same approach

http://forums.sohc4.net/index.php/topic,145462.msg1654695.html#msg1654695

If you can, grab a copy of the current issue of the VJMC magazine, it has my in depth article on how to polish Aluminum (based on the request of many readers and forum members )

[RAFster122s]

Woodworking places like Veritas, Lee Valley have small rubber contour sanders that can get into some grooves but the ends are difficult. It is best that you don't attack aluminum with a wire wheel (unless it is Really a brass wire wheel, not a brass coated steel wheel VERY COMMON, especially if it is inexpensive) The reason you don't want to use steel wheels is because if small pieces of wire break off in the aluminum you will have bits of steel imbedded in the cast part...that leads to rust. 

You may have to resort to small wheels for buffing and use the black emery to cut into those corners...
You will go through a lot of soft spiral sewn soft cotton buffs doing so.  You may need to have them in diameters smaller than 4" and 2" is probably what you will need.

Another alternative is to have the part vapor blasted, or glass bead blasted at low pressure and not polish the part.

Keeping it looking nice will be more work unless you have it powdercoated with a good clear or use something like SprayMax's 2K urethane paint in a spray bomb.  Repaintsupply has good prices on the SprayMax products and can do colors for you in the same spray cans.  Pretty much anything you can have the paint formula for from Autos can be easily mixed, otherwise you will need to send them a good painted part to scan to obtain the color mix formula.

[drumstyx]

I have very, very small buffers for my dremel tool. Under half an inch if I remember correctly, so once I get things level, buffing is no issue at all.

I thought about bead blasting or vapor blasting, but that doesn't remove imperfections from the surface, and probably won't mask anything but the finest of scratches, at which point I might as well be shining it up.

Definitely planning on clearcoating though, I want to bring it back to near-original finish, which was lightly buffed then clearcoated.