Lapping my heatsink.

[jimmyw404]

Okay, so I have this heatsink that came stock with my AMD 3000+ and I was considering lapping it, but I have a concern...

Unlike the heatsinks that I see on websites and guides, this one doesn't have a flat surface, it has a threaded kind of circular surface, like a lay's potator chip, only the threads are very very small. This seems kind of odd, so I'm wondering what people think of it...

Should I just leave it be? Or should I sand down the threads?

 

[jimmyw404]

I was just thinking, the closest thing to the surface of my heatsink that I can think of is a metal file... it's weird.

 

[lobadobadingdong]

I personally can't stand the stock retail heatsinks, you'd be better off getting a replacement., but yes the circular lines you see are from the aluminum machining process and (IMO) they should be polished down if you want to use the stock hsf.

 

[akira34]

If you're using it as it came, it should be fine for 'normal' conditions. If you've removed the thermal pad, you might as well lapp it. I've seen the stock coolers on the 3200 and 3400 Athlon64's and they've been very very smooth. Granted they're not the same level as a $50-$60 heatsink.

 

[jimmyw404]

Update: I sandpapered off the threads with 150 grit sandpaper. Now the heatsink looks like a zamboni needing ice-rink.

Tomorrow I'll drop by the hardware store and pick up some finer grit sandpaper. I'm hoping to get a nice finish on it, if not, that's okay. I was intending on getting a nice heatsink sometime when it's more necessary to O/C.

 

[akira34]

You'll want to progress through to the finest grit you can get your hands on.. If you don't do a proper job of it, you risk doing more harm than good in the attempt.

 

[jimmyw404]

Yeah. I'll get whatever I can in 200 increments I guess.

Really I can't imagine it being any worse than when it was threaded, unless I somehow make it concave or convex, which I doubt(and everything points to it being quite straight)

If I rub my finger against it or my fingernail, I can't tell it's anything but smooth as glass... Hopefully tomorrow I can get it looking that smooth.

 

[Tiamat]

yeah, lapping is very time consuming and takes a very long time. I managed to use a grinder to grind the surface to within 0.003". It has a mirror like finish now, but still with some scratches. Guess Im off to find some 1800+ grit paper...

 

[stevennoland]

Originally posted by: Tiamat
yeah, lapping is very time consuming and takes a very long time. I managed to use a grinder to grind the surface to within 0.003". It has a mirror like finish now, but still with some scratches. Guess Im off to find some 1800+ grit paper...

I'm a machinist by trade, and most grinders I use can get surfaces flat to within +/-.00005 of an inch. Obviously, how flat you can get is determined by your ability.

A mirror finish doesn't indicate flatness.

A flat finish is one of two conditions: first, depending on what was used to lap (lapping block and lapping compound) and second, the purity (denseness if you will) of the material being lapped.

Since most heatsinks are of the 6061 aluminum variety (or worse: 2000 or 4000 series) the density of the material isn't great. The grade of the aluminum will determine (somewhat) the spaces between the aluminum. If you could magnify (x100) the surface of an unlapped aluminum sink (only machined), you would see gaps and holes (they would appear as valleys).

Now lap and clean (not just wipe off but remove the lapping compund completely) the sink and then magnify (x100) you would notice the surface is flatter, but the gaps and holes would still be present.

To fill the gaps and holes requires a better (purer) grade of aluminum. The 7075 series is one example.

Obviously, a lot of sinks are made with copper. Copper too comes in different grades, and the same would apply here.

The goal of lapping is to get the sink flatter, or have a greater surface contact between the sink and the heatspreader on the cpu.

Have you considered the flatness of the heat spreader on the cpu?

Many have lapped their cpu's in order to achieve better surface contact.

All of this would be needed if we didn't have thermal pastes and adhesives. These are needed in order to fill the gaps and holes we can't see.

If you want to lap your cpu and sink, be my guest. I'm all for the search for perfection (aka Borg), but you have to justify the cost.