Lapping Help

[SkItZo]

Not really too sure where i should be putting this.... Mods, please feel free to move to appropriate section if this isnt the correct area.

I need some assistance with my lapping attempt of my TRUE (In other words Big friggin heatsink) I have tried several different methods (Up and down 30 strokes, rotate 90 degrees, repeat, ive tried pullin towards me only, pushing away from me only,) but for some reason i am lapping the corners more than the middle. What am i doing wrong?

http://img341.imageshack.us/img341/7518/27022008114dh3.th.jpg (http://img341.imageshack.us/my.php?image=27022008114dh3.jpg)
http://img184.imageshack.us/img184/6263/27022008115ru6.th.jpg (http://img184.imageshack.us/my.php?image=27022008115ru6.jpg)

[Nanometer]

I though we had a guide floating around how to lappe. Maybe look around you might find it. But, I use a piece of glass and wet sand paper, starting at 500 grit and i usually stop at about 1000. I don't do fancy stuff. I start with 500, then move to 800 then to 1000. Sometimes I'll polish, but majority of the time I don't. I only do it if it's discolored and I want it to look pretty. I also turn 90 degrees every 10 strokes or so.

[SkItZo]

I've looked at several guides on here, (mainly for cpu's but the same theory applies) as well as a demo that was upped on youtube for the same heatsink. I am lapping on a peice of glass that i got in a kit, i started on 240, went up to 400, then 600, then 1200 (Thats all my auto store stocked) but as you can see the corners are ground down more than the middle, it is still extremely flat (checked with the blade of a stanley knife) its just that the corners are ground down more. I know this wont make a difference because of the size of the heatsink but i plan on lapping my CPU soon enough and i dont want the same thing to happen with it.

[GunterFalstaff]

i dont know much about method, but as far as lapping sandpaper/kits i would recommend this one... easypckits(Premium) (http://www.easypckits.com/products/premiumlk/) i looked in every store in the whole city of Edmond and didnt find anything higher than 800 grit >.< but then i stumbled on this lapping kit... ordered it today and it looks promising =P. Goes to 10 micron (equivalent of 2,500 -3,000 grit!)

[-= rtz =-]

Weird...it shouldnt happen if u used glass,maybe your sand paper isnt laying perfectly flat on the glass...are u sure it is taped well? U dont need to use wet on all grits,just for the final touch with 1200/2000 grit u can use wet paper.

[SkItZo]

i dont know much about method, but as far as lapping sandpaper/kits i would recommend this one... easypckits(Premium) (http://www.easypckits.com/products/premiumlk/) i looked in every store in the whole city of Edmond and didnt find anything higher than 800 grit >.< but then i stumbled on this lapping kit... ordered it today and it looks promising =P. Goes to 10 micron (equivalent of 2,500 -3,000 grit!)

Thats the kit i got my peice of glass from ;) Saving the good paper for my cpu also ordered some polishing compound, but from the way it was looking at P1200 i wont need to bother with it

Thanks

Weird...it shouldnt happen if u used glass,maybe your sand paper isnt laying perfectly flat on the glass...are u sure it is taped well? U dont need to use wet on all grits,just for the final touch with 1200/2000 grit u can use wet paper.

I taped the corners, maybe i should tape the sides as well... Yeah, the water is just to lubricate it, makes the lapping process take longer when trying to flatten it etc

Thanks

[-= rtz =-]

I taped the corners, maybe i should tape the sides as well... Yeah, the water is just to lubricate it, makes the lapping process take longer when trying to flatten it etc

Try taping the paper along the sides,tape every side completely,not just the corners.It should lay perfectly flat on the glass.
AFAIK wet paper is used for polishing/final touches,highest grits,and it indeed slows down the lapping process if used on lower grits.

[Dialtone]

possible try doing figure 8's... i think up to 1200grit 1500 grit is all that is needed..but i use up to 2000grit on my cpu


for lube put a drop of dish soap in the water y ou are using it will help

[little_scrapper]

If your base if flat as you say then your lapping the corners more because the drag of the sandpaper is causing you to lean the HS ever so slightly. period.

Same thing was happening to my ninja. even thougn I held it by slipping my fingers into the base kind of I still could not keep the the thing completely flat againt the paper when I moved it. It had a tendancy to want to lean when I started to move it and thus the edges and corners got ever so slightly rounded off. Was still flat in the middle and the only thing I could do was to move it at a turtles pace. Very slowly.