Aluminum question

[mpierich]

I just did a batch of motorcycle fender spacers. They are about 2" wide, 4" long and 1" thick with rounded ends. The 2" wide sides and the rounded ends are exposed in use, and that is what I polished. Sort of.

They had fairly deep machining scratches on them. I worked my way back thru greaseless compound grits, 'til I found that I had to start with 80 grit to get rid of the existing scratches in a reasonable time. It worked fine for this purpose.

BUT, as I finished up with my 320-grit, it became apparent that the surface I had been working on has an orangpeeled-lookng surface. I couldn't get ahold of my customer so I went ahead and polished them, but did not drop back and try to sand them flat to get the ornagepeel out - I had enough time in them already and was not about to completely do them over for the same (small) price I quoted him.

He's disappointed but paid for the work. If I had known this would happen, of course I would have used another tool and sanded them flat before anything else. But, my question is, how could the orangepeel appear after I did all that with the greaseless to remove the heavy scratches?

I'm no metallugist but it almost seems as though the aluminum had areas of lesser and greater density; the greaseless took more out of the softer areas, hence leaving the orangepeel effect. Anybody else ever see this? If my theory is true, then if I had started with a flat sanding (belt or whatever) it probably would not have happened.

Any thoughts?

[sswee]

Seen that a few times. It was usually cast, low grade material, or hot spots from machining too fast with too little coolant. Parts like that I have had to block out to get flat to get looking good. One thing for sure, they are a hassle.

SS

[easleysp]

I've had similar situations with greaseless myself. Not sure what to call it but it looked like you took your thumb and smudged the surface of it. May have been that the compound hadn't dried all the way yet, I dunno. And it wasn't the whole piece either, maybe one or two spots. Sanding it out was a mutha too. Can't really say but I'm sure operator error had more to do with it than anything. Later on.

Steve

[pickleboy]

Originally Posted by mpierich

BUT, as I finished up with my 320-grit, it became apparent that the surface I had been working on has an orangpeeled-lookng surface.
But, my question is, how could the orangepeel appear after I did all that with the greaseless to remove the heavy scratches?

I'm no metallugist but it almost seems as though the aluminum had areas of lesser and greater density; the greaseless took more out of the softer areas, hence leaving the orangepeel effect. Anybody else ever see this? If my theory is true, then if I had started with a flat sanding (belt or whatever) it probably would not have happened.

Any thoughts?

hey mike do you know what the alloy was? if it was 2000 series aluminum bar it is real soft. i would guess that the greaseless got the surface hot and started to "smudge" or "smear" the surface . it probable was not visible due to the fact that the greaseless is not meant to shine but to cut. i would agree on the last point about flat sanding most likely would not have done that. but since i use a different kind of greaseless i cant say for sure.

[sswee]

The regular compounds will do something similar if you keep buffing after the wax residue sticks to the part. It cuts the surrounding area of the spots or streaks leaving the surface high anywhere it had residue on it giving a orange peel appearance.

[mpierich]

Thanks guys. I'm still learning. Probably from now on I will start with something to flatten the surface as well as take out the scratches, then take it a little easier with the 120/240/320 greaseless. I don't mind makin' $3/hour as long as I'm learning, lol!

[mpierich]

Originally Posted by sswee

The regular compounds will do something similar if you keep buffing after the wax residue sticks to the part. It cuts the surrounding area of the spots or streaks leaving the surface high anywhere it had residue on it giving a orange peel appearance.

Yeah, I know what you're talking about - it leaves shadows...this is much worse as far as depth. It literally is nearly as rough as the peel of an orange. But it's a darn shiny orange now, lol...

Originally Posted by mpierich

Thanks guys. I'm still learning. Probably from now on I will start with something to flatten the surface as well as take out the scratches, then take it a little easier with the 120/240/320 greaseless. I don't mind makin' $3/hour as long as I'm learning, lol!

We all learn new things every day...

But with the soft metals stay away from a sisal they are to hard on the metal and it will remove a good bit quick.. I use sprial and black then i hit is with sprial and white