Lapping guide

[Factorxfiles]

I've read a few lapping guides for IHS/HSF, but they seem to have contradictory information. Some say to lap in circles on sandpaper, others say to sand back/forth/back/forth, rotate, repeat. Is there one definitive lapping guide?

I've never lapped anything before, and I want to do it right. I know I'll need a piece of glass, several grits of sandpaper, and patience. The specifics are still a bit unclear though.

 

[zombiebeat]

I'm afraid not, it's down to personal preference and what works for you, much like applying thermal paste.

My preferred method is go in one direction for about 60 times turn the item 90 Degrees and repeat till flat.

What I haven't heard is go in a circle for a looong time, I though this lead to a greater chance of making the surface convex?

 

[spine]

Hand lapping will always make a heatsink base slightly convex. It's unavoidable and inherent to the dragging and pushing of hand lapping.

That said, circles is best. Doing it in a straight motion will produce a bevel across the base and that's the last thing you want. You should lap as minimally as possible since the manufactured base is likely to be pretty flat, just not very smooth.

Lapped to mirror finished bases are just for posting pictures of in forums.
It doesn't add any benefit over a good 600 grit base. Flatness is greater than smoothness.

 

[Factorxfiles]

Thanks for the responses. I'm going go try the circle method first, with a sharpie X on the IHS and HSF (both probably could use it) to see how bad they are before I go crazy.

 

[spine]

You'll see the best improvement from lapping your IHS since althon64 IHSs are blatantly concave. This is partly why people see such massive temp reductions when removing the lid entirely.

Only drawback is that you'll lose all warranty/RMA potential/2nd hand 'sellability'.

 

[Michael Daly]

Hand lapping will always make a heatsink base slightly convex. It's unavoidable and inherent to the dragging and pushing of hand lapping.

It's not unavoidable or inherent to the process. It is easy to generate a spherical surface, though. If you know what you're doing, you can create a surface that's flat to a few tens of nanometers by hand. Optical flats are done this way routinely.

I wouldn't recommend circular or straight motion. Use quasi-random "orbital" motions. Don't press hard either; use more strokes rather than forcing the surface to be cut.

 

[spine]

By circular I meant orbital. And it will make it slightly convex by hand. The way you hold it with your hand means that you can't realistically apply force to the dead centre of the heatsink base 100% of the time. Often you'll put more force on the front most edge of the motion, or sometimes on the back or where ever depending on your technique. Only a machine can properly apply the force at the dead centre 100% of the time. Plus the sandpaper will ripple ever so slightly (invisibly to the naked eye) against the incoming base edge causing a bias in abrasion.

Granted, this level of precision probably isn't significant for adequate lapping, but if you were to lap your heatsink base excessively it'd become a problem.

 

[Michael Daly]

Either you're putting too much force on the thing or your surface is too flexible. Another possibility is the thing is grossly out-of-flat at the start, I suppose. If you have sandpaper that;s loose and not stuck down to the flat surface, you could also get some edge rounding.

BTW - if you want it flat to nanometer precision, you have to have two flat surfaces to work from. But that's taking lapping to an extreme.

 

[conghelach]

I've read a few lapping guides for IHS/HSF, but they seem to have contradictory information. Some say to lap in circles on sandpaper, others say to sand back/forth/back/forth, rotate, repeat. Is there one definitive lapping guide?

I've never lapped anything before, and I want to do it right. I know I'll need a piece of glass, several grits of sandpaper, and patience. The specifics are still a bit unclear though.

I know it can be very hard indeed to resist the evil tweaking bug, that incessant need to tweak, lap, overclock, push etc. it's like a fever I know have had it before too HOWEVER one must also remember the phrase "if it aint broke dont fix it". Why do you feel a need to lap your IHS or HS? are they damaged in some way? not flat? I think most people read tweaking guides and then become "OVERCOME" with the feeling that lapping is something they must do in order to get top performance...............THIS IS NOT TRUE, while in some cases someone may have a bad IHS or cheapo HS then yes lapping to make the contact surfaces flatter would be beneficial but this is not mainstream by any stretch. Most high quality heat sinks are well machined ( thermalright comest to mind here) lapping them is not necessary. I have lapped IHS and HS on some systems I built and compared to the exact same system builds with tall the same cases, cooling, processors and heat sinks, I found no difference on two, worse temps on one compared to the three non lapped systems. Lapping a cpu IHS will void the warranty, you run the risk of damaging it, bending pins etc and when you go to sell it at some point when you want to upgrade you wont find many takers for a lapped processor on ebay.

Why not try using a high quality heat sink, like thermalrights for example, applying a THIN and I mean THIN layer of arctic ceramique or other good paste and see how things go, ALOT of people screw up a HS installation because they cannot overcome the urge to goop alot of paste between the heatsink and the IHS on the processor. Besides that it doesnt sound like you have any lapping skills, you could easily end up making things worse instead of flat.

If your tweak fever is THAT BAD......hand sanding will never do, use some powertools, I imagine these days in shop class the boys are putting their heatsinks on a lathe lol.