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Aluminum Anomaly / buffing haze
Hi all,
I was hoping someone could help me with my first buffing project. I have experience in body and paint as well as detailing but this is my first metal finishing project. I've worked with some small pieces to practice on prior to this including gold plate, copper, stainless steel and plastic.
I've been charged with repairing and polishing the front grill from a 1969 Chev half ton. Big first project! Too big! This item has all kinds of angles and creases but the total surface area isn't huge. It was coated (painted), pitted (stone chips) and even welded in one place.
First, does anyone have any info on this part? It appeared to have been painted so I have to assume that maybe it isn't a great grade of aluminum or maybe it was never meant to be polished.
I've wound up hand sanding most of it but I stopped to do a test on a section before I proceed. I sanded one section(rail) of the grill from 120 (to remove deep pits) up to 2000 grit and used wet sanding from 320 - 2000. I wanted to buff it to completion so I knew what to expect on the rest of the part before making a mistake that would affect the entire piece.
I spun a spiral wheel (6") on my 3800RPM grinder (with caswell adapter) with black emery. To my joy most of the sanding scratches were gone but I was left with the white haze. I was real happy with this pass though because I was able to dig into the part hard with a lot of pressure and it brought it up to a real nice shine, even with the haze.
Trying to clean the part with mineral spirits left a little more haze from the rag I was using too. Does anyone have a recommendation for cleaning rag and solution between compounds?
I moved on to the white compound on a 6" loose cotton and to my horror it was worse. I had two problems here. The first is more white haze. Not sure what that is. The second problem was having a buildup of spots which I may be able to elaborate on below.
Thinking that maybe I missed a step I moved backward to brown tripoli on a 6" loose cotton wheel - which was the only wheel I had left. It was used for red rouge but I figured there probably wouldn't be any harm moving to a coarser grit as long as I never intended to use it for rouge again.
Here's where the fun began....big gouges. I thought it was just compound residue but nope, the surface had been scarred. It looked like a meteorite streaking through the sky....something like a pit with a tail on it. The compound wiped off but the pit and tail remained. From what I understand this may occur on soft, poor grade aluminum, is that correct? Maybe too much compound or too much pressure causing the metal to roll up. The surface looked terrible and even black emery wouldn't bring it back.
I had to sand those marks out again and this time I went back to white but I still got some of those pitting marks. Same when I backtracked to brown. I was real careful to rake every 30 seconds or so too.
So I am wondering, 1) is my assumption correct that this is a soft grade of aluminum never meant to be polished, 2) do spiral sewn wheels work better than loose on these softer grades, 3) do I need to stop at black emery, and 4) how to get rid of that darn white haze....
Thanks!
I was hoping someone could help me with my first buffing project. I have experience in body and paint as well as detailing but this is my first metal finishing project. I've worked with some small pieces to practice on prior to this including gold plate, copper, stainless steel and plastic.
I've been charged with repairing and polishing the front grill from a 1969 Chev half ton. Big first project! Too big! This item has all kinds of angles and creases but the total surface area isn't huge. It was coated (painted), pitted (stone chips) and even welded in one place.
First, does anyone have any info on this part? It appeared to have been painted so I have to assume that maybe it isn't a great grade of aluminum or maybe it was never meant to be polished.
I've wound up hand sanding most of it but I stopped to do a test on a section before I proceed. I sanded one section(rail) of the grill from 120 (to remove deep pits) up to 2000 grit and used wet sanding from 320 - 2000. I wanted to buff it to completion so I knew what to expect on the rest of the part before making a mistake that would affect the entire piece.
I spun a spiral wheel (6") on my 3800RPM grinder (with caswell adapter) with black emery. To my joy most of the sanding scratches were gone but I was left with the white haze. I was real happy with this pass though because I was able to dig into the part hard with a lot of pressure and it brought it up to a real nice shine, even with the haze.
Trying to clean the part with mineral spirits left a little more haze from the rag I was using too. Does anyone have a recommendation for cleaning rag and solution between compounds?
I moved on to the white compound on a 6" loose cotton and to my horror it was worse. I had two problems here. The first is more white haze. Not sure what that is. The second problem was having a buildup of spots which I may be able to elaborate on below.
Thinking that maybe I missed a step I moved backward to brown tripoli on a 6" loose cotton wheel - which was the only wheel I had left. It was used for red rouge but I figured there probably wouldn't be any harm moving to a coarser grit as long as I never intended to use it for rouge again.
Here's where the fun began....big gouges. I thought it was just compound residue but nope, the surface had been scarred. It looked like a meteorite streaking through the sky....something like a pit with a tail on it. The compound wiped off but the pit and tail remained. From what I understand this may occur on soft, poor grade aluminum, is that correct? Maybe too much compound or too much pressure causing the metal to roll up. The surface looked terrible and even black emery wouldn't bring it back.
I had to sand those marks out again and this time I went back to white but I still got some of those pitting marks. Same when I backtracked to brown. I was real careful to rake every 30 seconds or so too.
So I am wondering, 1) is my assumption correct that this is a soft grade of aluminum never meant to be polished, 2) do spiral sewn wheels work better than loose on these softer grades, 3) do I need to stop at black emery, and 4) how to get rid of that darn white haze....
Thanks!
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