[bigben2k]

Here's my take on the lapping issue:

If the block is poorly lapped, then, as we apply the paste, air pockets may remain on the surface of the block, deep into those scratches or crevices.

If the block is polished to a mirror, then the effective surface of the block, within the contact area, is reduced/minimized.

In a properly lapped block, these crevices are not so deep that they cannot be completely filled by the paste, but they are also not so flat so that the effective surface of the block is as small as it can be.

For example, assuming that the surface is very finely scarred to form perfect rows of triangular pyramids, the effective surface area of the block would be tripled, in comparison to a perfectly flat finish.

I believe that a perfect row of pyramids with 45 deg angle sides, or rows of 45 deg "ramps", would be optimal. This would translate in an effective surface area 1.4 times that of a perfectly flat surface.

On the other end, the surface could be formed of very long microscopic points, but the effectiveness there would be reduced, as the tip of such points would not actually improve the thermal transfer much, if at all.

The thermal paste is also a big factor. It needs to be low in density, as least during the application, so that it effectively penetrates the crevices of the surface. It should probably be applied with great care, the same way that plaster is used to patch a wall: use a spatula (razor blade in our case), spread the compound around, from all directions, while applying some pressure, to ensure maximum coverage.

Realisticaly, an imperfect surface (that is relatively level) would have a surface that has been created by the cutting mechanism (saw, mill, etc...) and that may have been smoothed by a variety of processes (sanding, buffing), possibly using different substances (polishing compound, oil, mild acid, etc...).

Also realistically, we do not lap our blocks with electron microscopes. The tools that we have are simple, and limited:
-sandpaper, usually found in 600, 800 and 1000 grit.
-water (or any other lubricant used while sanding, but water should be best)
-buffing wheels, and sometimes buffing compound.

The process is very simple, as long as one understands that the block must remain perfectly flat while being sanded, otherwise, a curved surface (with irregular sanding) will be the result.

This is easily achieved with the use of a flat surface, like a pane of glass (because its flatness can be seen in the reflection). We can lay the sandpaper on the glass (which is in turn laid on a table), add a little water (optional), and run the block over it several times, in circular motions. The result can be "measured" simply by passing one's hand over the sanded surface. The result should also be visually inspected: an earlier attempt at lapping may have created an unusually large or deep scratch that a finer sanding may not be able to get to. All in all though, we have to keep in mind that the only area of interest here is the contact area with the core.

I believe that using buffing wheels, especially with buffing compounds, is a bad idea, for lapping a block. The buffing wheel creates too flat a surface, and some of the buffing compound would surely remain on the surface.

In any case, the resulting surface will be highly irregular, and will not have any form of perfect rows of perfect pyramids.

When I get my block (and the rest of my computer), I will test with 600, 800 and 1000 grit sandpapers, and report my results (unless someone beats me to it!).