Ugh, what did I do wrong when lapping?

[aggressor]

First pass > 600 grit, 800, 1000, 1200, 1500, stop

Started over due to some scratches. Stop at 1500 again. The Heatsink is a mirror finish. I go to the final 2000 grit......Boom, gone. Zero reflection

Did I do something wrong? I don't want to start over again, it's such hell

 

[Mingon]

A mirror reflection is not always the best as long as it is flat and free of most deep scratches dont worry

 

[aggressor]

For me, the only way to tell is how clear the reflection is. Running my finger over it doesnt tell me how smooth it is

 

[Mingon]

You should be able to tell by using your eyes

 

[mechBgon]

Not all mirrors are flat Flatness is the goal. If you want it shiny as well, put a dab of thermal compound on it and polish lightly with a cotton cloth, but be as even as possible so you retain your flatness instead of ending up with a concave surface.

 

[huesmann]

You could use a metal straight edge, like a metal ruler to check for concavity/convexity. Rub some goop on it and squeegee it across with the ruler. If it's thicker in some areas you don't have a flat surface.

 

[Naruto]

Well, did you use wet 2k grit sandpaper? Also, don't force the 2k grit sandpaper, simply glide the heatsink over it gently in 90 degree rotations with the sandpaper on the flat surface.

 

[aggressor]

Yes, all the sandpaper was wet.

 

[Amorphus]

any leftover residue from the 1500 grit when you started on the 2000?

 

[aggressor]

noper.

 

[soja]

Stop at 1500 grit then. The performance differences between 800 grit vs 1000+ are supposively minimal to none. I stop at 1200 when lapping my hsf and waterblocks.

 

[Mday]

as you go up in grits, the actual amount of "lapping" you do decreases. that is, you should spend less time lapping as you increase the grits. use a polishing compound for higher grits, and dont forget to keep your sandpaper clean.

 

[Blooz1]

After reading this thread today, I tried Mech's suggestion about using thermal compound for final polishing after lapping. I had 2 sinks cut down to bridge the MOSFET's on my 8RDA+ which had been lapped and were flat and smooth. They did not, however have a "mirror" finish. (I realize this is not totally necessary to achieve a flat surface)

I first tried AS3, and after about 5-10 minutes of polishing with a small amount on a cotton rag, I had an "acceptable" finish which was much brighter than what I had started out with. Just for the heck of it, I decided to try AS Ceramique on the 2nd sink.

What a difference! After less than 5 minutes, I had a complete "mirror" finish! It's much tougher when you start, but the finish comes up twice as fast. Now there's a reason to buy those large tubes!

Thanks for the hint, mechBgon!

 

[mudboy]

Did you try using some metal polish on the lapped surface? After lapping, I used some Happich Simichrome and it was like buttah, even after 600 grit wet.

Pete

 

[Zepper]

Toothpaste will also do a nice final polish.
.bh.
:sun:

 

[KF]

I have seen the same thing with some fine grit abrasives, where some leave it shiney and some make it dull. As near as I can figure, some have a small amount of anti-oxidizing agent, and some don't. I have heard that abrasives, like the commonly used aluminum oxide, are slightly acidic, which accelerates corrosion. Aluminum especially, but all metals, begin to oxidize immediately on contact with air. Polishes have something in the mixture which dissolves the oxide film, and something that leaves a thin protective coating behind, so it at least looks shiney for a while after you're done.

Almost all aluminum products are anodized, which puts a tough, uniform film on it, to keep it from corroding badly and to make it look good. When you lap it, you remove that protective layer.