Bowed Blocks and Lapped CPU's

Heya guys, I was considering lapping my CPU while Im doing tests on the components on the testbed before my case and final WC parts arrive in 2-3 weeks.

Would this be bad if I intend to use a bowed CPU block? Im unsure if the Bowed blocks was to try to put all the pressure on the center of the IHS where the cores are while also giving you the ability to adjust the pressure across the IHS by loosening/tightening the mounting screws on the various sides.

But ive read a few times that Lapping a CPU is bad for bowed blocks, is this true? Is the bow on blocks just meant to counteract imperfections in the IHS on the CPU, and lapping it somehow counteracts this?

Was thinking of lapping it due to having a decently uneven heat across the cores (Core 3 is 10-12c higher under load then core 1+2, and like 15-16c higher then core 4) even after multiple mounts in different orientations with the Thermalright Ultra-120, figure it has to be something to do with an uneven IHS, can a bowed block be mounted in a way to counter that?

Lapped cpus are very good. I encourage you to lap your cpu.

A bowed block will triumph a flat block. A bowed block, when tightened down, will place increased mounting pressure on top of the core. You shouldn't ever lap a bowed block flat. You'll destroy it.

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Originally Posted by IanY

Lapped cpus are very good. I encourage you to lap your cpu.

A bowed block will triumph a flat block. A bowed block, when tightened down, will place increased mounting pressure on top of the core. You shouldn't ever lap a bowed block flat. You'll destroy it.

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^^Agreed.

Pity my illustration skills are non-existent. Otherwise, I would draw you something.

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Originally Posted by IanY

Pity my illustration skills are non-existent. Otherwise, I would draw you something.

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I'd do so, but mine are worse :p:

It's a good idea to lap it, but it will probably be bad for when you sell the cpu. That said, I lapped mine and when I mounted my apogee GT NON-bowed on it, there was no contact with the centre part of the ihs. And i mean NONE. After I bowed the block I got amazing contact with the whole surface..

I suggest you lap the IHS, and bow your block at the same time.

Besides your warranty, I've never heard or experienced anything bad about lapping an IHS.

A stock IHS could be flat, or convex, or concave, or wavy, and likely rough compared to what you get after lapping. A concaved IHS will benefit the most from a bowed block.

But lapping an IHS if wavy or concaved will give you similar gains to using a bowed block.

If you don't mind throwing your warranty out the window, lapping is really a pretty easy performance gain.

And you can lap a bowed block, but you need to first take it apart to allow the bow to be removed. I don't really see the need though, most block bases are pretty good from what I've seen and anything beyond 1000 grit is a wasted effort.

so then is it better to bow the block AND lap the CPU or is it better to either bow the block OR lap the CPU?

Leave the block as it is and lap the cpu

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Originally Posted by WhiteFireDragon

so then is it better to bow the block AND lap the CPU or is it better to either bow the block OR lap the CPU?

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Bow the block and lap the CPU.

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Originally Posted by adpr_02

It's a good idea to lap it, but it will probably be bad for when you sell the cpu. That said, I lapped mine and when I mounted my apogee GT NON-bowed on it, there was no contact with the centre part of the ihs. And i mean NONE. After I bowed the block I got amazing contact with the whole surface..

I suggest you lap the IHS, and bow your block at the same time.

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I had the same issue with my apogee GT. With a concave block and IHS, had absolutely no contact in the middle, could still see the (by then semi dry) brush strokes from when i applied the TIM!
End up lapping both then bowing the apogee.
Lapping the block was a real pain...

Cool thanks guys. Dunno why but from the search I did hear some people seeemed to think it was bad to Lap the CPU with a bowed block (I understand why you dont lap the bowed Block, it compleatly negates the point of it)

I think my IHS must just be wavy since with multiple mounts the core temps differ by such an abnormally high amount (the same core 3 is 11-16c hotter every time)

Lapping it is.

One last question, I use the Thermalright Ultra-120 for my testbed, is that bowed at all or would it benefit from lapping also? (once im doing it, If the heatsink would benefit I figure might as well while im at it)

I saw a guide of someone lapping one before and it seemed a band down the center longways sanded to the copper first, which reminded me of a method of bowing. If it is bowed like that on purpose ill just leave it.

lap the cpu and heatsink or block for a few seconds with high grit paper to find out what they are (concave, convex, wavy, etc). It wont hurt them.5

Lap AND Bow.

Like it was mentioned before, if you care about the warranty of the cpu, don't Lap.

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Originally Posted by adpr_02

Lap AND Bow.

Like it was mentioned before, if you care about the warranty of the cpu, don't Lap.

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If he's worried about temps, the chance that he has overclocked his CPU is very high, which voids the warranty already.

ok fellas, what we are talking here is heat transfer.....pressing a rounded or as some fellas here call "bowed" surfaces to a flat surface will not have the same surface contact as flat on flat...... even with perfectly flat planes you still lose a percentage of surface area due to the surface finish, or as we call it in the machine trade as "micro inches" its a measurement of the peaks and valleys of a flat plane... this is were the thermal compound comes in filling the mountain range finnish that even 2000grit paper will produce. trying to use pressure to acheve this kind of surface contact, to me is not rite. even if you used alot of pressure, all your doing is bending the crap outta the mobo at best. trying to tweak a flat surface into submission agianst a bowed surface.....man oh man......i what we are trying to do is get perfect contact with two flat planes to draw the heat away from the source. i understand this is just my logical opinion. and people do as they like......peace, randy.

You are assuming that there is no "give" in the IHS surface. niksub's experiments with stepped blocks and the bowed block phenomenon have proved that there can be gainful pressure deformity WITHIN the edges of the IHS, where most conventional flat blocks merely sit on the rim of the IHS and therefore have most contact pressure there, away from the centre where the cores are.

Bowing the block or stepping a flat one so that the contact step is well inside the IHS boundary removes the non-deformable edge of the IHS from being an impediment to good contact IN THE CENTRE. That is why this isn't about the theoretical gain of matching surface-to-surface flatness.

I think we are still waiting to see commercial blocks that use niksub's idea of flat-stepping rather than bowing, as this should be the best of all worlds, combining the advantages of both methods. :yepp:

Well, just lapped the CPU to the copper and the temp difference on the testbed with the Thermalright Ultra-120 is still the same, core 3 is still 10-14c hotter then the others (oddly enough I diddnt really notice a temp difference either)

Watercooling is still about 3 weeks away, can a bowed waterblock correct this?
Or after lapping and proving its not the IHS surface does it mean its something else?

Can 1 core really be that much hotter then the others if the IHS surface is now perfectly flat?

The fans on the Thermalright are 1600rpm ones, and the northbridge fan/heatsink seems positioned so that it hits the heatsink where the orientation of core 3 would be, dont think it could cause that much a temp difference though.

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Originally Posted by IanB

You are assuming that there is no "give" in the IHS surface. niksub's experiments with stepped blocks and the bowed block phenomenon have proved that there can be gainful pressure deformity WITHIN the edges of the IHS, where most conventional flat blocks merely sit on the rim of the IHS and therefore have most contact pressure there, away from the centre where the cores are.

Bowing the block or stepping a flat one so that the contact step is well inside the IHS boundary removes the non-deformable edge of the IHS from being an impediment to good contact IN THE CENTRE. That is why this isn't about the theoretical gain of matching surface-to-surface flatness.

I think we are still waiting to see commercial blocks that use niksub's idea of flat-stepping rather than bowing, as this should be the best of all worlds, combining the advantages of both methods. :yepp:

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the heat shield is very bendable.....the silicon chip isnt.....

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Originally Posted by the monk

the heat shield is very bendable.....the silicon chip isnt.....

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What the heck are you talking about?

Generally speaking most IHS's on a cpu are concave up. That is the center of the IHS is lower than the outside.

As a result of this a perfectly flat block would have trouble making good contact with the center and would have to rely on thermal paste to get the job done.

With a bowed block the center of the block sits deeper than the rim aka (convex down) and thus matches up with the convex IHS.

Heres a nifty little pic I just drew just for you.

http://img88.imageshack.us/img88/2098/blockpq4.png
http://img88.imageshack.us/img88/209...5c7175041b.jpg

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Originally Posted by aspire.comptech

What the heck are you talking about?

Generally speaking most IHS's on a cpu are concave up. That is the center of the IHS is lower than the outside.

As a result of this a perfectly flat block would have trouble making good contact with the center and would have to rely on thermal paste to get the job done.

With a bowed block the center of the block sits deeper than the rim aka (convex down) and thus matches up with the convex IHS.

Heres a nifty little pic I just drew just for you.

http://img88.imageshack.us/img88/2098/blockpq4.png
http://img88.imageshack.us/img88/209...5c7175041b.jpg

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generally speaking isn't what im talkin about......mine was convex.... for good heat transfer, surfaces have to have good contact to each other....thats what the heck im talking about......

Even if yours was convex, a convex block would simply mean there would be increased pressure between the center parts of the ihs and block resulting in a minimally thick layer of thermal paste between the two.

This would result in the best possible heat transfer.

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Originally Posted by aspire.comptech

Even if yours was convex, a convex block would simply mean there would be increased pressure between the center parts of the ihs and block resulting in a minimally thick layer of thermal paste between the two.

This would result in the best possible heat transfer.

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any kind of radius, would equal in non contact, less the heat transfer.....

Who are you... yoda?

lets just say im a man who knows what a flat plane is.......