First off a big thanks to David Brown, the manufacturer of these kits, for arranging the sample and to Graeme from KustomPCs for his help in getting it to me.

So what the hell is a lapping kit? In fact, what the hell does lapping mean? Are we going to a nudey bar? Lapping, very different to lapdancing (as I soon found out, I don't think I'll be allowed back there) is the art of smoothing a metal surface - in this case, the surface of a cpu cooling heatsink. But why would we want to do something like that? Well, in theory, the best heat transfer between cpu core and heatsink will be made when the two surfaces are perfectly flat. Common sense would dictate that two perfectly flat surfaces will touch in more places than two raggedy ones. Using my amazing artistic skills, here is a little image based explanation I knocked up.

In this hugely zoomed in (and exaggerated) representation of a cpu cooler setup we see the heatsink (yellow) has a very ridged surface. Pressing this against the cpu core (green) means there is only decent contact in very few places. For optimum heat transfer between the two materials there should be as much surface in contact as possible. Here we can see heat transfer is likely not to be too amazing.

Lapping will wear the surface down the the grey line, giving this scenario:

Here the two surfaces are perfectly smooth, and make perfect contact with one another. This may be fairly unlikely, as there will probably be minor imperfections still, but it shows the principles involved. With the two surfaces entirely contacting one another, heat transfer is at its optimum level. And that's good! Yay!

So simple stuff, but can it really make a difference? Well yes says David Brown (who produces these kits) and a lot of computer enthusiasts (those crazy overclocker types) seem to agree.

Lapping a surface is done through several stages of wearing down the surface, to remove all the sticky-outy bits that are damaging your heatsinks chances of performing to its upmost ability. Several different grades of sandpaper (my DT teacher always used to call this stuff 'wet and dry' which I think is the correct term, but we'll stick to sandpaper for now) are used to gradually get the surface smoother and smoother until the desired level. Theoretically the surface isn't perfectly smooth until we get down to ridiculous atomic levels, but for all intents and purposes some very fine grade sandpaper will give a pretty darn smooth surface.

Right then, what's in the pack?

Quarter sheets of grade 600, 800, 1000, 1200, 1500 and 2000 sandpaper are provided, along with an equal sized sheet of glass and a set of simple yet useful instructions. The main jist of the instructions is to use a figure 8 motion, with plenty of water as lubricant, progressively sanding the heatsink base with finer and finer grit paper. It's simple enough, and probably common sense to most people. The figure 8 motion means the base won't have an overall grain (like wood, you know) at the end. If a figure 8 is beyond you (it's kinda tricky at first but ya get used to it) then changing direction often will achieve the same desured effect. I spent about 5 or 6 minutes at each level, since each paper seemed to do it's work in about that time and (more importantly) I'm not patient enough to spend any more time than that on a single task. It seemed to work pretty well, I got the base of my Swiftech looking shiny and beatiful by the time I got up to the 1500 grit paper. When I used the 2000 grit, though, the shiny surface turned to a matt appearance. I've found from several sources that shininess is not the be all and end all key to smoothness so, if you do use one of these and you go through shiny to matt, don't worry.

Following the instructions:

I'd never done this before, so I followed the instruction sheet down to a t. The instructions are really good, written with clueless schmoes like me in mind so don't worry if you think it will be tricky. Step 1 says prepare a work area, preferably near a sink.

I had to do a lot of cleaning to get that area free to work in. This is a student house so there were about 30 dirty plates and glasses in various states of disgustingness, meaning I actually had to do some washing up. After quickly learning how to do that, I could get on with the next step - preparing the heatsink for lapping.

The sheet suggests giving a slight bevel to the edges of the heatsink base. This means removing a bit of material so that the edges are sloped off, to stop them snagging on the paper. It was surprisingly easy to carve away at the copper base - a normal cutlery knife shaved a nice bevel fairly quickly. Now it was time to start the lapping process. The victim? A Swiftech MCX462 (I think... the model numbers confuse me).

Onto step 3.

3) Obviously start with coarser grits first (lower numbers) and progressively use finer sandpaper...

The first couple of sheets removed quite a lot of copper, there was a lovely orangey residue on them!

4) Use plenty of water for lubrication...

Follow this advice, without plenty (and I mean plenty) of water sloshing around you'll be stuffed.

5) Vary the motion as you lap, and try to rotate the heat sink in your hand on occasion...

Forwards and sideways strokes work, but figure eight motion is supposedly the best way to do things.
Also, just to re-iterate, continually refreshing everything with water is a must - it really makes things a lot easier. In emails, Dave enthused to me that water, water and more water is the way forward. Make sure to rinse everything thoroughly whenever changing grits - stray grains of metal could ruin the job.

After using the 1500 grit paper (pretty fine) I took a picture of the surface. I could tell whilst getting up to this point that the surface was getting smoother - you get a real feel for it after not very long, the surface acts quite differently on the paper. Here it is after 1500.

Taking a photograph of a reflective surface is no mean feat. I took loads, and I think these show of the surface the best. It's really quite shiny, certainly a long way from the horrible tarnished surface I started with. In the second picture you can compare the shine of the lapped surface to the raised area adjacent. I was quite impressed.

In the time since I lapped my swiftech, the copper base had returned to a lacklustre tarnished looking finish. Not overly happy with my previous results, and to see if the kit could be used again, I gave it another go. Here are the results:

Still not enough to blind an assailant or attract a sniper - not as pleasing a result as I had hoped for. My housemates did however comment that it looked nice, which made me feel warm and fuzzy inside.

In conclusion:

So what do I think about this whole lapping kit thing? Well there's no disputing that it does what it sets out to do. I started with a horrible murky rough surfaced heatsink and ended with a sexy smooth one. If you're expecting the ability to overclock to amazing new heights you're asking a bit too much of this simple procedure. You might shave 2 or 3 degrees off your temperatures, but not a whole lot more. To get the best possible performance out of whatever cooling product it is you use, lapping is an essential procedure. If you asked me whether it is truly necessary I would have to say probably not, but in our eternal quest for better performance it is another weapon against the enemy that is heat.

But I digress - debates about the benefits of lapping aside, this kit is certainly well put together and contains everything you need. At £8 (or £6 without the glass pane) it's not cheap.. I feel a fiver would have been closer to the mark for a product like this. But you pay for service, and this kit takes all the hard work out of finding the individual pieces. Plus, if you wanted all the individual grits of paper you would probably get roped into buying a pack of each. I'd certainly recommend this kit to anyone wanting to lap their heatsink, it's just a shame it costs a little bit more than a price I think might attract more buyers.

Does what it says on the tin
Well designed kit
Good quality 'parts'
Easy to follow instructions
Slightly pricey
Requires elbow grease* (not included)

* cue "where can I get elbow grease" emails.

Related:
Basic kit
Basic kit with glass
Premium kit (you flash git you)