Sanding Stages

Update: Based on feedback from readers we've updated the process described here.

Because we are using water when lapping, you MAY want to remove the fan from your heatsink before you start if you are worried about getting it wet. You should also be doing your lapping far away from your other components since sanded copper or aluminum getting on your motherboard could cause a short, for instance ;). Also please be aware that you can do such a thing as sanding away TOO much of the heatsink (or CPU if you are lapping your CPU) so be very careful and take this very slowly.

The basics are very simple: the lower the grit of the sand paper the rougher the surface and the more metal it will scrub off of your heatsink. Higher grit sandpaper also leaves deeper scratch marks. If your cooler does not have serious rough patches you can skip the 320 grit and start right off with the 600 grit paper.

The purpose of the first stage is to flatten the surface and remove any imperfections. Start by taping your sandpaper to a flat surface such as a piece of glass, or a flat, smooth table surface. The piece of sandpaper should be large enough that you can rub the heatsink over it without any of the heatsink leaving the paper surface. You want to lubricate the sand paper so dab some water on the paper surface, making sure it all gets wet. To start use 320 grit sand paper. With the sandpaper facing upwards, revert your cooler and place it facedown against the rough side of the paper. Make sure the cooler is level on the sandpaper and that you are applying very little pressure on it... the pressure MUST be even so that you don't create a slanted surface! Now begin rubbing gently in a circular motion; don't press too hard just allow the sand paper to do most of the work. The water acts as a lubricant so if it begins to dry drop some more water on the paper again to prevent any deep scratching. Keep sanding for a minute or two and then dry off any excess water. You may want to rub off the cooler every so often to clean off the grit.

The surface should look dull with some mild scratching; however it there is deeper scratching you should start again with the 320 grit and rub lighter for a few more minutes. The end result should feel flat and even; if you hold a straight edge now you should see uniform light if not try some more sanding until you achieve this.

After the 320 grit

The purpose of the next stage is to remove most of the scratching caused by the 320 grit. Begin with the 600 grit paper, again taping it onto your flat surface and wetting it with water. Rub the cooler lightly and in a circular motion again for 2-3 minutes and repeat if necessary. The end result of this stage should be very smooth and much lighter scratching on the surface. The below picture shows our results after using the 600 grit paper, you can't really see the detail in the picture... when you're doing the sanding just look to make sure there are fewer scratches. Again, during this process you want to keep the paper and surface wet since the water acts as a lubricant... and remember to keep cleaning the surface and the paper so that you're not scarring the surface with the grit that comes off during sanding.

After the 600 grit

Our next two stages are for polishing. Start with 1000 grit. Throughout this process you should rub away the water and sanded grime and keep resoaking your sand paper to clean off the impurities - this should result in less surface scratching and a better polish job. When you are near finished, wipe away the water and check to see if you have a dull shine; you should be able to see a reflection, if not repeat. If you don't have 2000 grit paper you should still be able to get a decent polish on your heatsink. However, we find that a 2000 grit paper gets you that extra gloss. So move to the 2000 grit and keep rubbing in a circular motion until you have achieved a very nice mirror like sheen. Don't be too concerned if the whole sink doesn't shine, just worry about the center when the CPU die will make contact. You might need to hold the heatsink up to the light and angle it several different ways to see the reflection. Don't be concerned if you can't get a mirror like shine like what a polishing machine might do at a factory (some of the newer heatsinks come with this machined shine). You should be able to get a nice, smooth finish that will reflect much better than before, but you might not get a perfect shine.

You should end up with a nice reflection like these two. Ours turned out so well I had to take angle pictures because the glare over exposed our shots.

Cleaning

Finish by cleaning the heatsink with some isopropyl alcohol to remove any residual impurities or oils from your fingers. If you don't have any isopropyl alcohol you might squeeze by with some diluted dish detergent that you rinse off with water. Just make sure that you use a non-lint cloth to wipe off the cooler. You're going to be tempted to run your finger across the dry, smooth surface because it should be quite a bit smoother than what you had when you first started!