Originally Posted by justanoldman
In order for new people to not make mistakes in this area I feel compelled to post despite my disappointment with a couple members. Regulars please feel free to ignore the following.
Do not lap your IHS, I will say this again, do not lap your IHS. Having obtained information directly from the designer of a current cold plate for a cooler, it is illogical to lap your IHS without significant testing before doing so.
Most cold plate manufactures assume, and rightly so, that your IHS is slightly concave. They therefore make their cold plates slightly convex in order to match better. After careful testing I have confirmed that the information I previously posted here is correct. The clamping mechanism of your mobo slightly changes the shape of your IHS when installed.
Unless you plan on lapping your IHS while it is installed in your mobo, you have a reasonably high probability of make it fit worse, not better with your cold plate. This is easy to confirm if you want to take the time. Take you mobo out of the case, get a perfectly flat edged piece of metal or razor and a flashlight. Measure the shape of your IHS both in and out of the mobo. Normally these will be slightly different.
Furthermore, if you did manage to somehow make your IHS perfectly flat while installed in the mobo, you would then have to lap your cold plate as well because it is most likely not flat. You immediately void your warranty on most coolers by doing so.
Now before some of you throw your normal hissy fits, remember that I wrote that you should not lap before testing, I did not write no one should lap ever. If you measure your IHS while clamped down in the mobo and it turns out to be convex or noticeably twisted in some way, then lapping may help. This would be an unusual circumstance though.
I spent an entire day installing and reinstalling my H100i with a lapped IHS. It took longer than it should have but I finally found the optimal way to install it, and it was in direct contradiction to the standard instructions. From all my testing I determined that I would have been better off not lapping the IHS, but I did not know this information when I did. I posted it all in here awhile back. You can look and see that I commented at the time how surprised I was that lapping did not help my temps. That led me to do some research into why.
Furthermore, my testing showed that despite my best efforts it is impossible to place the delidded IHS in exactly the same position on the die/pcb every time. These slight variations in the positioning of an IHS can further affect the fit with your cooler because of the force exerted by the clamping mechanism.
Please note that I have a lapped IHS and I have made it work, so this is not a huge deal. However I would have been slightly better off never doing so, and I would hate to see anyone new make the same mistake without directly testing if lapping will help. Hope that helps any new people here.