How Do You "Lap" A CPU Heatsink?

[Yggdrasil]

...and what are the benefits. I realize that all temperature programs for Intel CPUs are inaccurate, but my current HSF, an ASUS Amazing 79, does not seem to be getting the job done. I have reseated it twice...and that doesn't ssem to be the issue. I have even thought of replacing it with a Rosewill 775 HSF that I have laying around. I am open to working with this problem, but I really would like to know if lapping works and is worth the effort.

Thanks
Jareyn: Yeah, I have tried AS5, Ceramique, and Tuniq TX-2...no real help on any of them. I have tried smoothing it with a credit card, just putting a thin line of it on the centerline, and using a pea-shaped blob in the middle. No dice on any of 'em. It is becoming a Royal PITA. This HSF is huge and everyone else reports good results, but WTF? Man, I really wish Intel would release Tj max numbers on its CPUs. I have a Q9450 and the 45s are supposed to run cooler, but it doesn't seem to be working. My reported temps are about 48C at idle (using Tj max of 100C)...and they barely pop through 62 when I run small PRIME 95. This was a limited edition HSF, so I could get my dinero back, but it was discontinued at 3,000 units, so no exchange. Grrr!
This is really a great cooler...and it cost up around $80 from NewEgg. Man, I could've bought a Zalman for less than that. I am really displeased. I mean, I'll try the Rosewill just for laughs (a knock off of the Arctic Coller 7), but I just can't do crap because of the Tj max being one of life's great mysteries. The distance to Tj max stays constant regardless of what value you put in for Tj max, so... Anyway...I don'
t get close to 40 short of Tj max, so I am pretty sure I am not damaging the chip. BTW, it is not currently overclocked.
I just know that Rosewill is going to slice my hands up...it is like installing 30 razor blades on the mobo. :-(
This is the url for the cooler:

http://www.asus.com/products.aspx?modelmenu=1&model=2042&l1=16&l2=65&l 3=0&l4=0

[roderick_young]

I suspect the heat sink metal is flat enough that it wouldn't make a significant difference if you lapped it, that is, machined it to greater flatness.

There is typically a flexible pad or something that goes between the heat sink and the chip, to insure good thermal contact. Is that part worn out or missing? Another choice is just to put a dab of thermal compound between the heat sink and CPU.

[jareyn2002]

Due to the machining process, just about every heat sink will have a rough surface. To the naked eye it may look flat or even feel smooth, but there are microscopic groves in the surface. These groves will trap air between the heat sink and the CPU, and cause a poor transfer of heat.

Thermal compound (Artic Silver, Nanotherm, etc.) is used to fill these groves and help transfer the heat from the CPU to the heat sink. Just like air, thermal compound is something else that the heat has to pass through to get from the CPU to the heat sink.

We lap the heat sink to make it smooth, allowing us to get the best possible contact between the CPU and heat sink. Even after lapping, there will still be grooves for the air to be trapped in, but the grooves will be much smaller, and cause less of a problem.

Lapping can be done on any heat sink, pelt, or water block, regardless of its material. Just keep in mind that a softer metal will sand away faster than a hard metal.

[Jeffery H K]

Lapping means making it smooth and flat for the best possible contact with the chip.
You start by putting sandpaper face up on a smooth surface and rubbing the face of the heat sink on it until smooth. Then using fine sandpaper on smoother surfaces up to 1600 wet on glass if you are picky enough

I don't know how much it helps, my cheap heat sinks had visible machining marks in them so it helped a lot