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question about lapping

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Jan 8, 2002
Boulder CO
when you lap, everybody says to use circular motions on wet sandpaper right? well do you mean to tape the paper down on a flat surface, apply water, and then put pressure on the hs and rotate it 360degreese, or tape the paper down, and move the hs with your arm in a circle...

i know this is hard to describe by typing, but i was under the impression that you hold the heatsink steady, and drag the hs around the paper in a circle....

i just read http://www.virtual-hideout.net/articles/sk6_lapping/index2.shtml and it looked like they were not moving the heatsink around the paper, rather spinning it in a 360degree motion with pressure on the paper.

i have never successfully lapped a heatsink. do you do it the way that it looks like they are doing in that article?
re-read the article again.

to cut into the block fast, push down and twist it, keeping it in one place. to slowly work it hold it lightly and run it in little circles.
so essentially i have been doing it wrong the whole time and that is why i have been getting sh*tty results?
Myself, I just use steady force (not alot) and go in small circles. I also wet down the sand paper about once every 30secs. When you see a shine (you'll know what I'm talking about when you see it) on top of the water you are useing to lap with, rinse the paper throughly. Continue this using higher and higher (finer gits) of sand paper and in between each paper change, clean the hs with rubbing acohol to clean away the metal particles left on it so they don't hurt on the next grit. After you have it to a very faintly hazed mirror finish, clean it again with acohol. Use mothers metal polish on it, because it will really bring out the mirror finish and because it is a very high grit sanding paste as well. After sdone with that use acohol again and you're ready to go.
The way that the article describes lapping is a faster way to get rid of the uneven or rough base of the HS. After making it level or semi smooth, proceed to the finer grit sandpaper and use the circular motion or figure 8 that you were talking about in your first post in this thread. Make sure that you dont press down with a lot of pressure as this will cause the base to not be as smooth as you can get it, instead, let the weight of the HS itself act as the pressure applied to the HS. Good luck.
OMFG... this is driving me up a wall... i have tried EVERYTHING. Different brands of sand paper, different surfaces, read tons of different articles, and these scratches are not going away. On my sk6, i just tried lapping, following the guide perfectly, up to 2000grit and i still see tons of scratches. i have tried wet sanding, dry snading, twisting the heatsink on the paper for 1 hour, moving in small circles with not much pressure, a lot of pressure, and no pressure for hours on various grits... the point is I CAN NOT LAP! I HAVE TRIED EVERYTHING AND IT IS NOT WORKING...

my last attempt i used 3m wet dry strips, taped it down so it was 100% flat on a slab of glass, started at 400 grit and made it flat, then moved up to 600, 800, 1000, 1200, 1500, and finally 2000 grit paper doing small circles with no pressure... i still get scratches galore on the bottom of my heatsink... the one thing i have not tried is polish but everybody says not to use it. This is driving me insane cause it seems like i am the only one who can not lap and i am following all of the instructions i have read on various sites perfectly (well obviously i am doing something wrong... but i am doing exactly what the instructions tell me to do)....

AGHHH.. somebody give me some advice to what i am doing wrong... maybe i could go later on post a .asf (yes a movie) of me attempting to lap a heatsink and then somebody telling me wtf i need to do correctly.... unless i can find a good guide or get some good advice, i will do that tomorrow.
here... this was after lapping with 1000grit for 1 hour on a piece of glass. wet sanding, small circles with little to no pressure (as everybody said i let the heatsink do the work?)... as you can see, from this side it looks fine and there is a mirror reflection (yes i know this is not what you are aiming for, you are aiming for a flat heatsink... it is flat also tho).. from the side you can not see any imperfections
however... this is the SAME EXACT lapping job but takin from the top looking down at it.. you can see all of the scratches
I just did one for the first time, a Thermaltake 6cu+. It was pretty easy you just have to make sure you don't get anything between the sandpaper and HS like dirt or it will scratch the hell out of it.

I Tried wetsanding at first but it seemed like I would get a piece of dirt in there every time and scratch the surface, so I started over just with dry 1500.
Lapped until smooth (all machining marks gone) put some 3m rubbing compound (1500 grit )on the sandpaper and went at it some more. Wiped clean with alchohol, went at it with 2000 grit paper and finished with a soft cloth and 3m clearcoat polish(about 2500 grit). Make sure you clean with alchohol before installing.

Oh yeah make sure you use a super flat suface and light even pressure in alternating circles.

1.4 Tb @1596 (9.5 x 168)
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umm... i always get copper in between the heatsink and sandpaper.. there is no way to stop that. I try to wash it out as good as i can... when you do dry sanding, you still get copper on the sandpaper. anywho.. i just did the sk6 at 1500.. here are my crappy results.. .the first one you see here looks fine but it is sideways
now looking straight at it... tomorrow i will try w/ some 2000 grit and i may even buy some 2500grit if it exists
Note, you don't want to use any polish or rubbing compound. You will end up with residue in the microscopic surface imperfections where the thermal grease should be. I prefer to do my final polish with a fresh sheet of 2000 grit and Arctic Silver as the lube. This leaves some Arctic Silver in the microscopic surface imperfections along with the HS and abrasive residue. It’s worth a couple C.
How much pressure are you applying? And what are you lapping on? You should remove the fan if necessary, then pre-soak the heatsink (If the fan can't come off then don't soak it), and the sandpaper in the water for 15mins. Take a towel put it on the floor, put glass on it, take the sandpaper out then the heatsink (If it's soaked. If not then just dip the base in the water), and start lapping. I don't tape my sandpaper. Found it useless as it couldn't stick since the water I apply on there takes the stickyness off. Within 1-2mins I resoak the sandpaper and the base of the heatsink. I take whatever time is needed to do 200grit, the rest is 15mins each except for 1500, which is 30mins. Be sure not to lap too much or it'll lose too much and make no contact.
why water

Can you guys tell me why you guys sand with water? I've tried this method before and all it seemed to do was make it harder for me to do my fluid circles. Every time I tried with water my heatsink would stick to the sand paper and I found that sanding without water made it much easier.

What are the gains with sanding with water over without?

I's there a method to make sanding with water so your hs doesn't stick to the paper?
k yodums i will try your method tonight w/ the 2000 grit.... previously i was getting glass, taping down the sandpaper so it was completley flat, putting watter on the paper, and making little circles... i would then reapply water when things got messy...... i was using hardly any pressure at all.
I think you're done now, by looking at your last set of pictures.

My SK6 did the same thing; lots of scratches or mirror finish depending on what angle you were looking at it from (I only went up to 1000 grit). When I applied the AS2 and rubbed it in, it seemed like it came completely off when I buffed it with the clean cloth. There was no "haze" at all so that tells me those scratches you are seeing are very fine indeed and not of any consequence. My CPU temps are only running 7C above case temps and I've got the 24 CFM Sunon fan on my SK6.

I recommend you install the SK6 with some AS and see how the temps look.
Its better to sand with water because as you sand away more and more of the heatsink, you get large chunks of metal that are sanded of and as you are sanding, these large chunks of metal will scratch the surface of your very smooth heatsink. With wetsanding, you can wash away the larger chunks of metal making sure that you have a clean surface to be sanding on. To prevent the heatsink from sticking to the sandpaper, try Hoots method by adding a drop of dish soap into the water that you will be using to soak the sandpaper, this should hopefully make it easier to slide the darn heatsink around on the grippy sandpaper. As you sand more and more though using the same piece of sandpaper, the heatsink will not stick as much since it has lost a lot if its bite through the sanding process.
i am about to start to attempt to lab using yodums method w/ 2000 grit... just in case it did not work, i got this stuff at auto zone 3m rubbing compound fine cut... this is NOT POLISH. It removes the scratches from the bottom of metal and was designed to be used w/ 3m sandpaper.... does anybody have any comments about wheter or not to use the rubbing compund?
dude, those scratches really dont matter, cuz they cant be felt? so it really wont hirt anything, you can only see them not feel them rite? you hafta lap with some lesser sand paper for a long time and dont bother going over 1000 grit.. just take longer if you really want them scraches out.. 2000 wont take them out

and what order do you go with?
Re: why water

so many choices said:
Can you guys tell me why you guys sand with water? I've tried this method before and all it seemed to do was make it harder for me to do my fluid circles. Every time I tried with water my heatsink would stick to the sand paper and I found that sanding without water made it much easier.

What are the gains with sanding with water over without?

I's there a method to make sanding with water so your hs doesn't stick to the paper?

Easier to lap on, the base of the heatsink won't be scratched as much as dry where the metal on the dry sandpaper will make a huge difference like rivercom mentioned.