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Best way to lap?

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ap673

Member
Joined
May 23, 2004
I've looked at quite a few lapping instructions and most of them are different in little ways. Does anyone know for sure the proper way to lap a heatsink? I've heard do cirles, back and forth, and the straight line then lift and repeat methods. Also what grit sizes are best for a good finish, 800-1500? And last, are you suppose to use soap to ease the friction?
 

tehnull

Member
Joined
Jul 8, 2003
Location
East Flat Rock, NC
I just got done lapping my heatsink. I started at some crap sandpaper looked to be about 100 grit then went up to 400 then 800 then 1500 then 2000 I went all directions except in a circular motion as that promotes roundness which is bad. I put my sandpaper on a clean piece of glass and then put about 4 ounces of water on it. I can now see my reflection perfectly in it after finishing it off with some silver polish. :cool: To me soaps sounds like a bad idea because it may break down the adhesive in the sand paper I could be wrong though. Water was plenty enough for me.
 

icesaber

Member
Joined
May 22, 2004
Location
Michigan
circles can leave a circular groove in which heat can be slowed. even though it might look completely mirrored, it never is, and the metal and the thermal compound have different rates of transfer.
back and forth can leave hook-shaped marks and scratches if you aren't careful. I've experiences things like this, and they're a pain in the axx to remove once they're there.
my best experiences have been with straight and lift. it leaves a straight line, and even if there are still microscopic grooves, they go the whole length of the sink and the heat can transfer in a linear fashion.

as for soap, I've never attempted that. and as for grit, I use 1500 because that's what I had in the garage :) and it seems to do great for me...

I'm no expert, and I don't claim to be. what I've said is from my own experience, and anything anybody out there can add or correct is completely welcome :)
 

nosilverman

Member
Joined
Apr 14, 2003
Location
New York, NY!
tehnull said:
...I can now see my reflection perfectly in it after finishing it off with some silver polish.

I have heard that this may be a bad idea. The polish can leave some stuff in the microscopic groves in the metal that would be bad for your temps. After you get past 1000, you wont get much more by going higher.
 

Sean Lindstrom

Member
Joined
May 8, 2002
I do a final scrub with lots of plain water and a (nylon) toothbrush. This because I think microscopic bits of swarf (copper dust) may be lodged in the surface, though I have no proof of that.

***

One tip all the lapping how-tos miss is to be aware of how the heatsink, when flat, sticks to the abrasive (paper). When a heatsink rather stutters than slides across the wet paper that's a sure sign all is well. At this stage it either moves very stubbornly or, with less pressure, surfs on a thin layer of water. A danger here is that the paper may become so friendly with the heatsink it rather sticks to that than the surface plate. To prevent this the paper must either be backed with water or -better- glued down with spray adhesive.

***

I like to form the final cut by rotating the heatsink. There will be grooves in any case, and I guess concentric rings inhibit excessive loss of compound during operation.
 

Silversinksam

Moderator/ Silver Paste Taster©
Joined
Aug 8, 2001
Location
Sunshine State, USA
ap673 said:
I've looked at quite a few lapping instructions and most of them are different in little ways. Does anyone know for sure the proper way to lap a heatsink? I've heard do cirles, back and forth, and the straight line then lift and repeat methods. Also what grit sizes are best for a good finish, 800-1500? And last, are you suppose to use soap to ease the friction?


If you need lapping supplies, Dave over at EasyPcKits offers great prices and great service