problems polishing aluminium alloy with white compound

[rotorman]

hi all,

I think i've achieved a pretty good standard for alloys now up to the tripoli stage. when I get to white compound things go wrong - I'll fill you in on my technique in detail, and hppefullly this will reveal my mistake.

I go the tripoli compound on a loose leaf calico mop. I find the stitched cotton mop removes material too quickly on this particular alloy.

Then I use white compound on loose leaf calico mop. I just bought a new mop, as I didn't want to cross contaminate my compounds.

I am using a 3000rpm bench grinder. The mop are 6"x1".

Now, here's the problem. With the tripoli stage almost mirror with some light buff marks, I move to the white compound.

I have found that with larger flat surfaces, like radiator tops, and in this case, a throttle body, the white compound breaks down (?) on the surface and leaves hazing. the hazing sometimes also has small pit marks where spots of compound have stuck to the surface. the hazing is strong enough that going back to tripoli takes a while to get it out...i don't think the talc trick will be enough to remove the marks?

small areas do not appear to have this problem and are chrome like in finish.

I use a fine hacksaw blade to clean the buff. I try not to overload the buff with compound. I try to apply load to the buff when applying compound so that it has some heat and is applied evenly.

the buildup seems to happen whether i am using a colour stroke or a cut stroke, but appears to be worse with the colour stroke?

What could I be doing wrong?

is it...
(1) the brand of the compound?
(2) technique?
(3) contamination on the surface of the piece (I use mineral turpentine to clean followed by warm water after each polishing stage)
(4) insufficient heat?

Is white compound meant to be used with a colour stroke only, or cut only, or both?

Please advise...any help is much appreciated. I'm getting very close to results I'll be happy with.

[rotorman]

I've had reasonable success since posting this question.

I found that the following worked wonders....

wet the part with mineral turps prior to buffing. IE buff the part wet with turps.

Every time a bit of compound appears to be left behind, wet again.

this has produced zero haze but there has still be some minor compound residue build up.

I figure the turps is preventing the compound to stick to the piece. the cutting particles are lubed and appear to be able to work more efficiently. I might even try this when using other compounds.

I need to be some kero and I'll try that.

Unfortunately my bench grinder just died so I can't try anything.

for clean up simple green and hot woter works well .. every compound after black is more less a color motion .. i use the cut motion 2-3 passes at first black/sisal ... then i go color motion : black/sprial ( i get a nice shine) then green/sprial then to white on a losse cotton... after that i toss on a new loose and hit it with red .. each buff has's it own bag to be stored in and i clean up before putting a new buff on .. the compound's i keed in plastic bag's to ... as for the bench grinder .. caswell got a few nice buffer's .. i lost count of how many machines i tossed out due to locking up .. i keep a spare on hand for when that happens

[rotorman]

Thanks for those tips.

I just picked up an 8" 1HP bench grinder - much better at maintaining speed when pressure is applied. Nevertheless I still need to use a medium on the surface of the part to prevent compound build up (regardless of how much compound is on the wheel)...I'm currently spraying on kero. After each step, I clean with kero, then liquid degreaser and warm-hot water, allowing to airdry.

I will try to go to an 8" buffing wheel. I'm currently using 6x0.5" on a 2850rpm buff. I will go to an 8" wheel which should increase the surface speed and therefore the heat.

Kero while buffing eliminates the haze. The small pits remain. It seems like the pits are being caused by the white compound 'globbing' on the surface. I can't prevent the globbing by altering pressure on the wheel, or cleaning the buff better - it is weird. Kero seems to reduce the problem though.

[rotorman]

globs were actually from TOO much pressure

I'm only using very light pressure now on the new buff while regularly spraying kerosene on the part. Using colour stroke only, gently and slowly going side to side as i push the part through.

working very well I must say...not perfect, but very well.

here is the result (a three barrel, two stage throttle body from a 95 model Mazda RX-7):

Excuse the grainy picture quality - I've compressed these images a lot to reduce them in size

you use only kero ?

[rotorman]

nah kero and the usual white compound on loose leaf mop.

I found the kero eliminates hazing, while reduced pressure seems to get rid of globs forming (which generally leaves pit marks in the metal)