CPU Lapping

As I understand it lapping a heaksink is pretty common, but how come I see so little CPU lapping? Most HSFs aren't bad in the way of flatness, but the CPU is anothner story. An Athlon XP has its core "rounded" in that black goo and has identification on the core right where the HSF goes on. When I took my 8045 off my CPU I noticed the CPU numbers had been embeded into my HSF with the help of some ASII. Flatness on almost any good HSF cannot be over one thousandth of an inch, while the CPU core can be off as much as 5 thousandths. Thses kind of deviances make AS3 seem like a waste because most of us aren't even starting with flat surfaces.

If you were going to do it I would use REALLY fine sandpaper, like over 1000 grit. but you alreaqdy knew that, cuz you seem to know what you are doing :) I remember reading here that someone did it, but he lapped it too much and went straight through the core. I was going to do it to my new P4, but it looks so flast anyway I figured I'd just leave it be.

I don't know about your comment on the flatness of HSF. The last one I lapped was done on a piece of glass. After a few passes on the roughest grit I took a look at the bottom. Right where the die would be was an area the size of a dime that was untouched by the sandpaper.

After we finished lapping the HSF, added some ASII, and a single 80mm intake fan, we dropped the CPU load temps by 26C. Now you tell me that was worth it.

But you are right in that some HSF are much better machined than others. This HSF was a decent copper one, but it only cost like $20. Now take something like the SK-6, where you might pay 50% just for the HS, and you have to buy your own fan, it had damn well better machined so fine that lapping isn't necessary.

I got the flatness measure from my 8045, so it probably was on the higher end of workmanship, but I have been using 1000 grit with water for most of my lapping. It makes the surface really flat, and with water doesn't leave many embeded particles.

It was FaTs who lapped his CPU. Afterwards, the contact was so good, he'd get higher temps with any thermal paste! I'm also going to attempt lapping the processor. I'm going to first use 800 grit, then finish off with 1600 grit. Hoping to drop my temps because I get 45 load with the alpha at 18C ambient...something's not right there. Anyways, i'll report back after the weekend on this one :)

or you could just buy a CPU that doesn't need lapping... hmm maybe A P4!!!!!

GO INTEL :p

sorry, just had to say that :)

I have lapped a few Athlons with success but I don’t recommend it. You are better off buying a better HS, switching to watercooling or using pelts. Due to AMD’s quality control, you never know how much material you have on the die to work with.

The first thing to do is check the core’s flatness with a razor blade and a 20 power loop. If you have a convex core, don’t bother lapping as it will only get worse. Lap the core with 2000 grit and water as the lube, checking the progress every 20 seconds with a 20 power loop. You will only need two to three minutes total lapping time before the etching is gone. If you see copper, you loose. Note I have seen Athlons with copper exposed from the factory, hence my comment on quality control.

Do your final lap with a fresh sheet of 2000 grit and your choice of premium thermal grease as the lube.

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Originally posted by !shira!
or you could just buy a CPU that doesn't need lapping... hmm maybe A P4!!!!!

GO INTEL :p

sorry, just had to say that :)

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No core lapping, just the IHS.

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Originally posted by Un4given


No core lapping, just the IHS.

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just what i was gonna say...Those things are not 100% flat, lapping will always help. I'll see if my core is concave or convex, if concave, i will definitely lap it.

Talldude – You’re a wild man. You definitely have my respect for your testicular fortitude. :D I wish you luck.

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Originally posted by MrThompson
I have lapped a few Athlons with success but I don’t recommend it. You are better off buying a better HS, switching to watercooling or using pelts.

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I understand what you are saying in terms of thinking logically, but obviously I could care less about wrecking my processor after making a homeade watercooling system, and doing my HDD window.

My emphasis is on absolute performance, not what you would be safest doing. If that was the case I'd say "Dude..you getting a Dell":D

Oh yeah !shira!, just one more thing. If I could get and knew about the 1.6 northwoods when I got my 1700+, I would have gone Intel. I am in no way biased toward Intel or AMD, its just whatever I can have the most fun with.

I'm with zackbass on this one...if the processor goes, Damn! just have to get an XP1900+ that OC's more :D

I'm pretty skilled when it comes to working with metals etc. so i've done my fair share of sanding. Chances of screwing up aren't too high albeit it'll be an expensive messup. But i say, if you don't take a risk, life is boring and we don't want that :p.

Life sure isn't boring after trying to get my waterblock airtight at 100psi! I had it hooked up to my air compressor overnight and a miniscule leak popped up that water probably couldn't get through anyway and definetly not at less than 80psi, but, trying to do a perfect job, spent four hours trying to resolder everything. I had already put the whole thing together and lapped it, but I took everything apart. The leak is smaller, but still not fixed. I am sure it won't be a problem, especailly at less than 1psi in the system. Nope, life sure isn't boring for me. :D

i used a whetstone to lap my heatsink

Using a whetstone can be a good idea if you do it right. You really should sand it pretty good first becasue you wouldn't want to use anything rougher than a hard arkansas stone. Also using oil on the stone is a bad idea because oil is a very bad thermal conductor. Because oil doesn't evaporate it would get left in the tiny nooks and crannys (mmmm..English Muffins) that the thermal grease is supposed to fill in for better conductivity.

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Originally posted by zackbass
Using a whetstone can be a good idea if you do it right. You really should sand it pretty good first becasue you wouldn't want to use anything rougher than a hard arkansas stone. Also using oil on the stone is a bad idea because oil is a very bad thermal conductor. Because oil doesn't evaporate it would get left in the tiny nooks and crannys (mmmm..English Muffins) that the thermal grease is supposed to fill in for better conductivity.

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i did use oil but i used my parts washer at work to clean it then used AS2 for reassembly

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Originally posted by zackbass


I understand what you are saying in terms of thinking logically, but obviously I could care less about wrecking my processor after making a homeade watercooling system, and doing my HDD window.

My emphasis is on absolute performance, not what you would be safest doing. If that was the case I'd say "Dude..you getting a Dell":D

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Hey, we're on the same page here! :D

meat322 - Unfortunately your parts washer will not be able to remove all the traces of oil from the microscopic surface imperfections.

i haven't had a problem with the oil residueits cooling great!!!
but since were on the subject of lapping wouldnt a surface that looked like this (VVVVVVVVVVV) have more contact area than a surface that was perfectly smooth when using a thermal compound such as AS2/3.trust me I'm no expert on this just sitting here saying HMMMM ;) :confused:

But core-HS touching directly still gives the best heat transfer :) AS3 doesn't hold a candle to 2 perfectly flat mating surfaces.

Lapping not only makes the surface smoother but also much flatter, which is more important than a pretty shine.

I have lapped many a Blue Orb chipset cooler, and they would have to be the worst examples of heatsinks I have come accross for flatness, sit one on a flat surface and see how much light comes through the gap, pretty poor really as they are not cheap and the average user does not expect to have to lap it to get a finnish that SHOULD come from the manufacturer.

Check this technique out-you won't believe it.

http://www.overclockers.com/tips217/

Think I'll skip that one.

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Originally posted by clh61
Check this technique out-you won't believe it.

http://www.overclockers.com/tips217/

Think I'll skip that one.

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even though i have valve grinding compound I'm not going to do that!! (me not brave enough):rolleyes: what we need is a surfacing machine

A surface grinder is what made those funny little marks on the heatsink material in the first place. Lets not go in circles here thats the marks your trying to get rid of.

It really depends on what the qualtiy of the grinder is. Some machinists have griders that can get a surface flat to a few hundred-thousandths of an inch. Often they use these grinders for a "rough" cut and then use some special means for lapping the surface. I have plans and instructions for everything in a book somewhee around here...