Greasless compounds vs sandpaper

[68commando]

Ok Guys,

I got the rotary orbit sander and some papers. I took the breaker cover which I had sanded by hand and polished and it still had some file marks in it. I used the 220 paper with the sander which seemed to take out all the file marks fine and even the rough aluminum casting marks. Of course the pits come and go. Then I sanded with 360, 400 (because I had it), 600, and 1000. Then I polished it with the black compound, brown, and white. The result is below. There are still some fine scratches in it that could come out, but no file marks. There is still a rough appearance to it if you get up real close or look under a magnifying glass, it looks sort of orange peelish. You can see it in the pictures. But from 3-4 feet away, it reflects images pretty good. Doesn't have that blue tint like chrome. I am wondering if I the roughness is just part of aluminum? That cover which is 3" in diameter took me about 3 hours.

Dave

[Rasper]

Dave,

When I sand metal I try to analyze whats happening. If pits come up in places they weren't before, I figure there are pits (porosity?) in the casting and I am exposing them as I grind down into it. But if they are the same old pits, then I know I just haven't gotten them yet.

As for scratches: I look and see what size they are. After some experience I am able to tell an 80 grit scratch from a 150 grit scratch, and so on, and that tells me which sandpaper I didn't use long enough. If I see what I think are 150 grit scratches, then I know I need to go back and use the 220 or 240 some more.

In your photographs I couldn't see the scratches, but I did see the pits.

One thing you can try is using scotch brite (surface conditioning) pads. They seem to move the metal around some, rather than just grinding it off. They seem to fill in scratches and pits with the adjacent metal, kind of like spreading butter on toast. I use them on a die grinder at high speed, (probably take the rest of your life to do it by hand), sometimes with water to keep the metal cool if it is sheet metal. (Heat shrinks metal.)

Richard

[mpierich]

Originally Posted by 68commando

Ok Guys,

I got the rotary orbit sander and some papers. I took the breaker cover which I had sanded by hand and polished and it still had some file marks in it. I used the 220 paper with the sander which seemed to take out all the file marks fine and even the rough aluminum casting marks. Of course the pits come and go. Then I sanded with 360, 400 (because I had it), 600, and 1000. Then I polished it with the black compound, brown, and white. The result is below. There are still some fine scratches in it that could come out, but no file marks. There is still a rough appearance to it if you get up real close or look under a magnifying glass, it looks sort of orange peelish. You can see it in the pictures. But from 3-4 feet away, it reflects images pretty good. Doesn't have that blue tint like chrome. I am wondering if I the roughness is just part of aluminum? That cover which is 3" in diameter took me about 3 hours.

Dave

The orangepeel and pores are just due to the material itself. The deeper you go the more pores will probably appear so don't waste too much time on them. The orangepeel, I've concluded, is from varying densities and also not really fixable (although if you use geaseless compound it will do that to any broad surface). If you want a show bike, get everything plated; but the cover looks just dandy to me if it was on my bike. If you have scratches that only show up at certain angles, you could go back and work on them but no sense in driving yourself nuts over something that no one else will notice.

[68commando]

Thanks Guys,

Yes, I had figured out that the pits come and go with grinding away of material, so I don't worry about them too much. I was unsure of the orange peel, but I was figuring that it was due to the different hardness/softness of the aluminum in different areas. I also noticed that when I go from the 220 to the 360 that the 220 marks come out pretty quick unless there is a low spot. However I also notice that if I am sanding with the 360 one way and then switch the sanding to 90 degrees from that, new low spots seem to come up. If I get them all out in one direction, they show up in different places when I sand in another direction. I guess this is a function of the varying softness of the material. That is what seems to contrubute to the orange peel effect in the end and it is impossible to get it all out in the casting. I agree that the final effect if fine for what I want and it probably would not get much better. Now on to the bigger parts!!

Thanks a lot Fellas, enjoyed the feedback and will post some pictures when I get done.
Dave

[baz]

hi guys , quite new to this forum but been polishing for a long time,just came across this thread.to 68 commando you have received very good advice and tricks from mpierich and rasper ,but d ont expect to get perfect results from norton aluminium castings , those castings are porous and they are very sensible to orange peel effect .but you are on the right track
i started by hand sanding parts 17 years ago, now have my own shop using 3 large stationary buffers (5hp) with up to 3 16 inch buffs stacked together.
one thing i do to minimize orange peel with greaseless is to never use it alone .
always add some green or black compound over my greaseless and when i get to
320 graseless i d ont let it dry on the buff . i apply the graseless and cover with
green compound and use immediety, that should leave you with a very smooth satin finish ready to buff