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What does lapping do?

post #1 of 35
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I saw some people and 'How to' lap your CPU or heatsink with sand paper. What does it do anyways? It makes it easy to contact thermal compound? And cools better?
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post #2 of 35
It makes the surface more even and allows for better transfer of heat.
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post #3 of 35
Quote:
Originally Posted by FearSC549
I saw some people and 'How to' lap your CPU or heatsink with sand paper. What does it do anyways? It makes it easy to contact thermal compound? And cools better?
It makes the heatsink and cpu flatter, which results in more contact area (as opposed to the various imperfect holes left by imperfect IHS and stock heatsinks). With added AS5, the temps drop as much as 15c idle and possibly 12c load (but don't quote me on it).
post #4 of 35
Not 15c, not even close. Maybe 4 or 5.
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post #5 of 35
Quote:
Originally Posted by Retrospekt
Not 15c, not even close. Maybe 4 or 5.
My load temps dropped 10 c while running dual prime and idle 38-25c.
post #6 of 35
At the microscopic level your IHS (Internal Heat Spreader) and the footprint of your HS (Heat Sink) look like a series of mountains and valleys. These gaps cause the heat transfer process to degrade.

Smoothing the surface of matter allows for greater physical contact and therefore more efficient heat transfer. One indicator as to how "smooth" a surface is will be it's reflective properties.

My temp drop averages around 8C... That makes me happy inside!
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post #7 of 35
Quote:
Originally Posted by Retrospekt
Not 15c, not even close. Maybe 4 or 5.

It depends, I've lapped quite a few cpu's and hs's now, and it can vary. It depends how flat they are to begin with, and where the imperfections are. I've had a couple cpu's (and hs's) that were concave or otherwise not flat, some are worse than others. Unfortunately cpu's seem to have a tendency to be concave, so the most important part (the center) is sunken down and not making very good contact.

I've had lapping drop me only a couple or few degrees, sometimes 6-8 or a bit more even, so far it's always helped some. The more un-flat your surfaces are, the more it should help. Flatness is way more important than to be shiney and polished. If you by chance had a perfectly flat cpu and hs, then lapping probably wouldn't help much. But so far, I have yet to see a cpu or hs, which was perfectly flat.

Once I start the sanding and use the sharpie trick, I can always see imperfection of the flatness, on cpu and hs surfaces. I did have one Big Typhoon (out of 4 I've purchased for me and others) that was dam close to flat. But then I had another BT that had a really uneven surface, it varies. Same for cpu's, my p4 prescott was ultra concave, others have been less uneven. Most important is to lap correctly, if you don't do it right and with care, and you're not really getting it flat, then you have nothing.
    
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post #8 of 35
Most heat spreaders are concaved, so lapping them gives a flat surface for more contact, also it removes the microscoptic imperfectsions on the surface of both the heat spreader anfd heat sink. on an average you get 3c to 5c temp drop.
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post #9 of 35
Two flat objects compared to two concaved objects touching...

imagine that...there is like..a big sandwich of AS5 in the middle of the two concaves....

When I lapped my BT, I got a 12C drop in load.

That's without an IHS! I had the IHS off before AND after...so I must say....the combination of the two would have made quite an improvement had I dont them both at once....

I'll never put on a heatsink again before lapping it.
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post #10 of 35
What is an IHS? Does it come with stock AMD cpu coolers? And how do you lap your cpu, sounds fun.

Edit: And is AS5 worth it? I know its not a lot of money so what the hell But does it reduce temps a lot? What % if it does?
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