A couple Lapping Questions

I read many lapping articles and didn't really find the answer to these questions. I plan on lapping my heatsink soon, to achieve some better temps, maybe 4c-6c cooler would be very nice. I never really checked my heatsink for smoothness, but in reinstalling my heatsink I put some AS3 on the heatsink and noticed many little lines running parallel where the AS3 was applied. Also, my temps for a slk-900 are not as good as they should be. So anyways, back to lapping. I believe I'm going to go with the one way method. Starting from one spot, moving it in one direction and then picking it up and putting it back to start and doing the same thing over. Well, when doing this should you ever rotate your heatsink 180 degrees? I heard people say not to rotate 90, but I thought rotating 180 might get good results to keep things even, so its not always the one side on the recieving end. Also, since I have a beastly heatsink, would it be ok not to really apply pressure, and just let the heatsink apply the pressure for me. Just moving it back and forth and keeping it even and center, but not really applying pressure. If this is possible, that would be good because I want to play it safe, and not totally screw up my heatsink. Also, I believe the SLK-900's are copper, so does this lap a lot quicker, I think i heard that somewhere. And how do you feel about using the marker for indication? Ok thanks a lot for the help.

theres too many opinions on lapping methods. I am planning on doing the rotating 90 degrees method... just picking it up and putting it in the same spot seems like you might get an uneven base, but thats just me.

Any other input. I think I might be lapping my heatsink today.

lapping

Ive lapped a few heatsinks now, latest was an sk-7. I use a figure '8' pattern. It seems to work well for me, it made about a 4°C diff on this machine(xp2000-stock). I cant comment on the method your thinking of cause I have always used the figure '8'.
HTH
Shane

Depends

If a sink is really horrible I will turn it occasionally until it is halfway decent.

If a sink isn't bad to start with or once I have it close, then I go in one direction only.

Here is why: the base does NOT actually have to be perpendicular to the heatsink or anything- mounting clips are designed to account for variation along that dimension. what it DOES need to be is F-L-A-T, flat. Rotating the sink will slightly round the edges- the leading edge does get more sanding done than the other areas- so each time you pick it up and rotate a sink you are rounding it just a bit more.

The reason I do it with bad sinks is because when taking off a lot of material the sink may get far to much removed from just one side. Finishing it just the one direction seems to straighten things up again.

Remember: FLAT is the goal, shiny doesn't count for anything

right, but the rounded corners of an slk won't have that much of an effect becuase its so long that it goes past the end of the actually processor anyway right?

When I first started lapping heatsinks, I moved the heatsink in a circular pattern on the sandpaper. While I did see positive results, I have since changed my lapping methods.

I did a little research on lapping myself and I found that "lapping" in a circular motion was actually a pretty bad idea. The method that I found most popular among people who claimed to have a fair amount of experience in lapping was the 'lapp-in-one-direction-and-lift-the-object-off-of-the-abbrasive-at-the-end-of-each-stroke' method. Also, most of the articles and guides I read recommended rotating the object 90° after every 10-15 strokes in one direction.

I just finished re-lapping my heatsink three days ago using this method and it lowered my load temperature by 2°C (as reported by the temp. sensor diode in my P4).

- That's 2°C lower than when I lapped my heatsink in a circular motion.

As for pressure... I applied very little pressure to the heatsink while lapping it, allowing for the weight of the HS to do most of the work. It takes longer to lapp this way, but then you don't have to worry too much about pressure being applied to the heatsink's base in an overly-uneaven manner.

stan03 said:

right, but the rounded corners of an slk won't have that much of an effect because its so long that it goes past the end of the actually processor anyway right?

Click to expand...

Yes, but it depends on whether he is using a P4 or and AMD chip. If I remember correctly, my friend's SLK-900 did not quite cover the entire surface of his P4's Integrated Heat Spreader. If this is the case, then having a rounded edges on the SLK-900 would be detrimental to the heatsink's cooling capability if used on a Pentium 4.

So if you're using a P4, you might not want to rotate the HS every few stokes while lapping, as RD pointed out.