Lapping

[DukeChestnut]

wut exactly is lapping? i know it refers to cleaning the bottom of a hsf but wut do u use?

 

[DT4K]

I didn't know this until a couple of weeks ago, then I lapped my heatsink. Basically it's sanding your heatsink to make it as flat and smooth as possible so it will have better contact with your cpu core. You use a piece of glass, or some other very flat surface. you then lay down wet/dry automotive sandpaper and sand your heatsink with water on the paper. Start with 400 or 600 grit, and move up to 1500 or 2000. The higher the better. After using the 1500 or 2000, the bottom of your heatsink will look like a mirror and should make better contact with your cpu. I can't tell how much lapping helped me, because I also added a case fan and switched from radio shack thermal paste to Arctic Silver 3 at the same time. But with those those 3 changes, my cpu temps under full load dropped from 56C to 46C.

 

[DukeChestnut]

sweet! i think i'll lap it this weekend. if i can get any temp drop it'll put me in the low 30's high 20's.

thanx 4 the info shanti

 

[Crucial]

depending on the condition of your hsf you might want to start with 240grit and work up to 400 then 600. then finish up with a quick rub with 1500. 2000 is unecessary IMHO. It is more cosmetic then anything. make sure you keep the paper clean. it will help it to cut faster. good luck!

 

[Shaorinor]

Where would yah buy the sand paper?

And while I'm asking this...where do you buy goof off?

 

[FlowerMan]

http://www.virtual-hideout.net/articles/sk6_lapping/index.shtml

You can get high grit sand papers at a well stocked hardware store such as most OSHes. Goof Off (xylene) can be found at these hardware stores too Go figure

 

[Shaorinor]

I dunno if I'm seeing this right, but looking at the visual graphs on that link you provided show that lapping the heatsink added a degree or 2 to the temperature instead of subtracting from it.

Was just like 1 case where it got a degree cooler, sucking instead of blowing and only with the delta.

Again, I'm not sure if I'm reading this right...but that's what I'm seeing.

 

[DT4K]

You're right, for most of the results in those graphs, it looks like lapping made no difference or actually made the temps higher. I don't know why they seem to conclude by saying it helped temps to lap. In my personal case, I have no idea if lapping helped or not. I have a feeling adding a case fan and switching to Arctic Silver probably helped lower my temps much more than the lapping.

 

[Fireman]

I must say it doesn't look very impressive to me either. I'm not trying to crap or anything, I just don't see a big advantage.
There was one 6 degree drop with the Duron@950 sucking on the SK-6 but that doesn't seem consistant with all the other tests results. Many actually went up in temp. I'm confused.

 

[DukeChestnut]

yeah i don't think lapping is highly advantageous. it might help a little but as long as u have a clean surface i think thats more important.

 

[treemonkey]

I read an article (sorry I cant remember the link) that said that you really don't need to go over 800-1000 grit and it is not necessary to have a mirror finish. It is much, much more important that the surface is flat than shiny.

 

[grrl]

Here's the link.

Why Heatsink Polishing Might Be A Bad Idea

 

[FenrisUlf]

Lapping used to be important with older CPUs like the Celeron 300a. Back then, CPUs only put out about 25 watts and had about a full square inch of metal slug for the heatsink to mount to, so contact between the CPU and heatsink wasn't critical. Most of these CPU slugs had a nice bowl shape to them (although it was only a few thousandths of an inch deep, it was noticable with a good straightedge or razor blade). Also, most people were using extruded aluminum heatsinks which also had a curve due to manufacturing processes. What this meant was that only the outer edges of the CPU were touching the heatsink. People started lapping heatsinks and CPUs in order to make the two surfaces match better and provide better thermal transfer. I did this on several CPUs and noticed very good results. Newer Intel and AMD chips come pretty much as flat as can be resonably done in a factory and I wouldn't even think about trying to lap one. Any quality heatsink will come machined flat - probably flatter than you can make it at home. If you bought a good heatsink (and this isn't a place to try to save a buck by going for a POS) it should be fine as-is, don't mess with it unless you really know what you're doing. Learning how to properly apply thermal paste will probably give the best temperature improvements. There is still a use for lapping though. This week I lapped down a GeForce2 core and its heasink - Nvidia chips are notorious for not being flat. The end result was that the back side of the video card dropped about 20 degrees (F) in temperature because the heatsink is now able to effectively pull the heat from the GPU. I didn't measure it scientifically, just used the ol' finger test, but it was quite a difference.