How to make things shine; a lapping tutorial.

[Technohydra]

Welcome to Technohydra's Lapping Tutorial!

Ok, finally ready to begin the lapping tutorial! This tutorial is a little different, as I'll be handling it in 3 separate parts, a 101, 201 and 301 session. Each is beneficial on its own as a mini-course, so to speak, but as a whole, it'll get you to being able to identify, lap and polish damned near anything, with a lot less hassle than you'd think.

 

Session 101

Intro to Lapping Terminology and Nomenclature

 

So, you wanna take something dull and make it shine. What does it take? What process are you really using to get to your end result, and what do you need to get there? These are a few of the things we'll be covering in this 101. So, let's start with some terms.

 

Machining: Any process which by repetition and combination of motion, force, and energy, causes a piece of material to be altered from it's original state and shape to a desired state and shape. Examples include milling grinding, sanding, lapping, turning, cutting, electro-chemical, and CNC(computer-numeric-controlled) processes.

 

Grinding: Grinding is the process of machining a part by friction of a rapidly rotating abrasive surface against a moving or stationary base material. Typically, this is done by hand, and involves a machine having either a wheel of some form of abrasive, or a belt with a resin-bonded abrasive. The process generally involves removing large amounts of material in a semi-precise fashion.

 

 

Sanding: The process of machining a part by friction of a moving abrasive against a stationary part. The abrasive takes the form of hard oxide crystals and composites adhered to a paper or cloth surface. The process removes a moderate amount of material in a semi-precise fashion by applying force to the surface of the material being sanded.

 

 

Lapping: The process of machining a part by the movement of said part against a stationary abrasive surface. Almost always performed by hand, except in the case of lapping wheels. The process removes very small amounts of material in a precise fashion, and is achieved by applying force at a 90-degree angle to the abrasive surface. The only downward force is that of the weight of the part resting on the abrasive. This process is used to produce both flatness and surface finish.

 

 

Polishing: The process of machining a part by the friction of a non-abrasive surface against a part, either moving or stationary. The actual amount of material removed is almost none, and is representative of a very precise process. Removal of the material is facilitated by coating, or loading, the non-abrasive surface with a mild abrasive compound, such as diamond paste or pumice. All force applied in this process is rotational, performed parallel to the part surface. The only force on the part surface is that of the weight of the non-abrasive surface resting on the part. When performed along with lapping, the total process is referred to as finishing.

 

 

Hardness: A rating of the resistance of a substance to being physically machined or altered. This property is reflected in two ways, by trade rating(i.e.; hardened, half-hard, quarter-hard, normal, annealed) and by ASTM scales such as the Rockwell hardness scale(which is beyond the scope of our interest hear). Generally speaking, the harder a material is, the more difficult it will be to machine.

 

Abrasiveness: The rating of the level of abrasiveness of a given machining substance or surface. The scale is general, and ranges from extra-mild to extra-aggressive. The more aggressive the surface, the more material removed in one pass of the material over the part. The more aggressive the material or surface, the more material removed in a single pass.

 

Grit: The frequency of repetition of abrasive particles on a machining surface. The rating is expressed as grits per square inch. Also classified from very course to ultra-fine. The lower the grit rating, the coarser the surface is, and the more material that will be removed in a single pass. Generally speaking, the process of grinding uses extra-coarse materials of high aggressiveness, sanding uses from coarse to fine in aggressive to normal, and lapping uses semi-coarse to extra-fine in semi-aggressive to extra-mild materials. Polishing uses only ultra-fine materials of ultra mild abrasiveness.

 

Finish: The degree of light refraction off of a parts surface, expressed in grits. The rating refers to the last grit of abrasive used to machine the part. Thus, a part properly sanded with 220 grit abrasive will be said to have a 220 grit finish, and a part polished with a 3000 grit compound will have a 3000 grit finish. The higher the finish rating, the more shiny and reflective the part will be

 

Flatness: The degree of deviation of a surface from that of a perfect plane, expressed as amount of deviation over a given distance(i.e. deviation in inches divided by the distance of one inch) Thus if a part deviates from a plane by .10" over a distance of 1", the flatness of the part is .10". The lower this rating, the closer the surface is to being a perfect plane.

 

 

 

So, what does all this boring stuff mean to you? First off, since we are lapping parts to achieve flatness, we need to be sure not to press the part into the sand paper. That's not lapping, it's sanding and it does not produce either flatness or finish, which is what we are after.

 

Secondly, this should help you a bit in selecting your sandpaper. There is a big difference between the types out there, and getting the right one makes your job a lot easier. Trying to lap through hard nickel-plating on an IHS is a ball-breaking process unless you have the right paper.

 

Third, I can now deliver the rest of the guide as I would normally speak, and you'll totally understand what I'm saying about the processes and materials, so you can concentrate on the how to, not the what.

 

That's all for the 101 session! Boring, I realize, but it's important stuff that's good to know anyways. Coming up next is the 201 session, which will cover material selection, what you need, and how to do the actual finishing operation from beginning to end. Stay tuned, we'll be back!

[Technohydra]

Session 201

Lapping Procedure, Materials, and Effects

 

Okay, so we should all be on the same page as far as what the terms are and most of the basic processes work. Now it's time to take a look at the nuts and bolts of a lap job(not dance). Let's start with your lapping materials.

 

Materials

 

Sandpaper: Sandpaper is the basis for the entire process. Without it, there would be no effective way to lap a part in a uniform manner. So what make some sandpaper work for lapping and others not? The first thing you need to look at are the materials a given paper is rated for and the hardness of the sanding grits.

 

Most general use papers are a semi-hard composite or oxide. The usual ones are silicon carbide and aluminum oxide. Either one of these will work just fine for our purposes. Crocus and emery should be avoided. These abrasives aren't rated for metal when used in sandpaper, and will powder or fracture, resulting in masses of scratches on the part.

 

It's easy to tell the types apart just by looking at them. The silicon carbide and aluminum oxide types are a medium gray color, while crocus is a reddish brown and emery is either green or charcoal black. Most of the time, paper lists the abrasive material on the back as well as the grit rating. Also, this stuff is cheap enough that you can afford to pay a few extra cents(literally) for the good stuff. Cheap paper uses cheap resin to hold the abrasives on, and it tends to crack and release grits, which also cause deep scratches.

 

Polishing supplies: This is the area of lapping that has the least amount of time spent on it. A good polish should take about 3-5minutes. Any more is pointless, as is any less. I have two recommendations here, and they are both extremely good ones.

 

 

First off, this is a polish done on a linen or fine cotton cloth. Because you are using a chemical compound for the polish and don't want to corrode/leave residue on the base material, you need to have a few cloths that are used for polishing only. The first solution: go to an auto parts store and get a decent 3 or 4 pack of polishing cloths. They cost between $2-10 dollars a package, and you get plenty of them. Just go with what looks and feels the smoothest.

 

But wait! While you're there, pick up the second thing you'll need: Mother's Billet Polish. I think the regular Mother's Metal Polish will do a decent job too, but I love the Billet formula. It just shines like a champ. I dare say it could take the hairs off a brass apes butt. A regular sized tin is the size of a shoe polish can, and three times taller. It costs about $15-20 a can, but it's well worth it.

 

Other things: A few little odds and ends to have on hand. First is a bottle of rubbing alcohol, at least 70%. This is used to remove the powdered metal that builds up during the lap, and also to aid in removing the metal polishing compound. Just seems to bring out the final shine.

 

The last thing is a flat, rigid surface to sand on. A small mirror or piece of plate glass works very well, as due laminate table and counter tops. I recommend the mirror/glass because it's portable. Sometimes I lap while grilling/smoking the hookah, sometimes while watching a movie(Aliens seems to work well), or where ever is most comfortable. Just slid a phone book under your plate of mirror/glass, and it's all disco from there. You can get a remnant from a glass shop, or go to Wal-Mart or the local equivalent and get a mirror for $5-15.

 

Total supplies needed: Sandpaper(2 sheets of 150 and 220 grit, 1 of 400, 600, 800, and 1500), 3-4 polishing cloths, 1 tin of Mother's Billet/Metal Polish, 1 bottle of rubbing alcohol, and a mirror(12" x 10" is way plenty big) or similarly sized glass plate. Final cost is about $33, and the mirror, polishing cloths, alcohol and metal polish will be re-usable, due to quantity or otherwise. Future laps will cost about $8-10, that cost being sandpaper.

 

The grits of sandpaper can be substituted if need be, but I wouldn't get anything lower than 150 grit or finer than 2000 grit. The lower grits are too harsh and cause deep scratching, and the finest grits are ineffective compared to polishing compound.

 

Metals

 

There are differences in the metals you might choose to lap. I could write a volume on this, but I'll keep it brief.

 

Heat sink copper is usually half-hardened, and as such is mildly difficult to lap. It takes about 50% longer than the copper of an IHS to lap flat and smooth. The only trick to mention here is try moving the part faster, but DO NOT press down to get it done quicker. Doing this is not going to give you the results you want.

 

IHS copper is normalized, meaning it is not hardened at all. It is very easy to lap, both for flatness and shine, and takes very little time to get from the 220-grit level to a finished polish. I did mine in about 15 minutes, once I got the nickel off. Also, because of the softness, this copper is very forgiving of deep scratches, as they lap out easily. When lapping this stuff, make sure there is NO downward force being exerted by your hand, as it will make a mess of the soft surface in a hurry.

 

Nickel plating is not hardened, but is very hard by nature. Normalized nickel is harder than half-hard copper. It's used for corrosion resistance. However it has a property that we don't want, that being heat resistance. Nickel plating makes it hard to transfer heat effectively. Nickel is not lapped. Instead, we sand it off. This is done just like a lap, but you are allowed to push down and sand it very hard. There's no other way to get rid of it.

 

Aluminum is usually quarter to half-hard, but is easier to lap than half-hard copper. It also looks cleaner when polished, as it tends to hide scratches. The one difference between this and normalized IHS copper is that it tends to be a little more likely to scratch deeply, and a little harder to remove those scratches. Otherwise, treat them the same way.

 

Procedure

 

*We will not be using water in this process. This is called wet sanding, and as the name implies, it is a form of sanding, not lapping. This guide, if followed, will negate the need to use water to carry away the dust.*

 

Now we're going to get started! First, place the mirror on a hard surface to support it. Now take the first sheet of 150 grit and cut it down the center the long way. Take each of the resulting pieces and cut them into thirds, as illustrated below. You'll do this to each sheet of paper you have.

 

 

Now, take one of the small rectangles you just made(we'll call them "squares" from here on out) and put it on the mirror so that it's straight. Now place the finger and thumb of your off hand on the two corners of that side(see diagram) and place the part you're lapping in the middle of the paper.

 

 

Now, grip the part with the fingertips of your other hand on the top and bottom edges, and begin to slide the part across the sandpaper. Again, don't put any force or weight on the part, at all. All that will do is make the scratches harder to lap out in the next grit. Just let the part slide over the paper, top to bottom. I usually try for two 'up and downs' a second, which isn't terribly fast. If your hands get tired, you're either gripping too hard or hold the paper down with too much force. This isn't at all about strength.

 

Now, after about 5 minutes, look at the bottom of the part you were lapping. It will have some scratches on it going in the same direction, and if it's not flat, some areas that aren't scratched very evenly or at all. If the part looks perfectly evenly scratched, you're most likely ready for the next step. Otherwise, keep at it. The first grit you use will take anywhere from 10 minutes to an hour to achieve flatness, just be patient and keep moving the part. If the part seems to be moving too easily, replace the paper with a new square. If you hear a brittle 'scritching' noise, stop right away. Turn the paper on its edge and tap it a few times, not on the sanding mirror. Then wipe off the bottom of the part. This sound means that a small piece of abrasive grit has come loose and is making a nasty scratch in the parts surface. The sooner you catch this, the less you'll have to polish out later. Tapping the paper out every minute or so is helpful to remove metal dust as well.

 

OK, so you have the part to the point that it's scratching evenly across the bottom? This one time, we are going to do something different. Turn the part a quarter turn to the right, so that the corner that was on the left is now on the right. Now, we'll lap with the same grit for about 3-5 minutes. This is called cross-hatching and we're doing it to make sure that the part if actually flat, not just grooved in the contour of the paper being used. *If you're working on an IHS, the nickel plating will take a lot of work to get through. You have to get rid of it all before you can proceed to the cross-hatch.* Do this until the scratches from the previous direction are gone, and all you see are the ones from this round of lapping.

 

Once the crosshatch is done, again turn the part to the right a quarter turn. Get a square of the 220 grit and repeat the process of lapping. This grit should take about 10-15 minutes. Now, there are a few scratches that just won't seem to go away. This is normal, and you can ignore them, as they have no realistic effect on the finished product. You'll find that while they may look deep, if you run a fingertip over the part once polished, you can't even feel them.

 

Continue this pattern with every grit up through the 800. Rotate a quarter turn, lap till the scratches from the previous grit are gone, repeat. Each new grit should take less time than the previous one. By the time you get to the 800 grit, it'll take about 3-5 minutes to get done with it.

 

When you are ready for the 1500 grit, take one of the polishing cloths and apply rubbing alcohol to it. Use this to wipe down the surface of the part, as it will remove the dust and grit from the previous steps. Now, lap on the 1500 grit as normal, and then do a crosshatch, like with the 150 grit. This will help achieve a better base for the polishing step. When the results of the crosshatch look nice and shiny, again wipe the part with alcohol and allow to dry.

 

Polishing

 

This is an easy step, but it's what produces the mirror finish that looks so nice. Take a new polishing cloth and get a small amount of the Billet Polish on it(about 1 cm square, and a millimeter or so thick). Beginning in the center of the lapped surface, rub the polish in small circles so that every 1.5-2 seconds, the polishing cloth has traveled over the entire surface of the part. The polish will turn a grayish color. This is both desired and expected. About once a minute, apply about half the original amount of polish to the cloth, and reverse the direction of the circles. Do this for about 5 minutes.

 

Now, take a third cloth, and gently wipe off all the polish from the part. Again, get out your alcohol cloth, and wipe down the part using the same circular motions that you used in polishing. What you should have now is a copper hand mirror. You should be able to see your reflection in it from any angle, and the metal should almost glow. As I said before, there will be a handful of residual scratches left over, but they can't even be felt with the fingertip. They look deep, because with a surface that is so highly polished, any scratch will look deep. Again, ignore them, they don't hurt a thing.

 

Now place the part, polished side down, on a Kleenex or something equally soft. This will protect the surface until you are ready to install and use it.

 

Congrats, you just polished a part to a 3000 grit finish.

 

This concludes session 201. Session 301 will be a pictorial walk-through of the process, and will have some tips and tricks to make things easier. It will also include a few tests, such as a rudimentary flatness test. Keep with me, and check back often. I'll try to finish up this weekend, if I can find something that needs shining up.

[Technohydra]

Session 301

Practical Application, Pictorial, and Testing

 

Welcome to the last session of the lapping tutorial. I'm mostly going to be posting and explaining some pictures here to better describe things that are hard to explain. First off, let's look at our sandpaper squares:

 

 

This is one of each grit I'll be using, from coarse to fine, left to right.

 

So, next, I'll place the 150 grit paper on a flat surface, in this case, a laminate topped table at work. Remember the diagram of how to hold the papers down?

 

 

Notice the POS heat sink there? This is what happens to parts that piss me off:

 

 

So, now I'm going to grab the part by the sides facing the top and bottom edges of the paper.

 

 

Now, I gently slide the part top to bottom. All the force is in making the part move up and down. None is directed into the sandpaper. Let the weight of the part do the work, while you provide the motion.

 

So, after a while, you check the progress of the lap. At some point, it'll look very evenly scratched.

 

 

Now rotate the part to the right, and do the crosshatch. You know what to look for, so go until the scratches are even again. This is the only time you'll do a crosshatch until the 1500 grit step.

 

There isn't a reason to show the results of each grit. If you rotate between each grit and sand until it's even, there will be no doubt when the part is ready for the next grit. The scratches will be going the same direction you were lapping, and you won't see any of the previous grit's scratches.

 

Follow the procedure until you get to the 1500 grit step, and then do another crosshatch. You'll see that the part is already fairly shiny. That's nothing! Get out the polishing cloth and Billet Polish. Remember to alcohol the part off first.

 

 

Get the right amount of polish on the cloth and rub it on the part. Notice how it's white at first.

 

 

 

Now, as you polish the part, you'll notice that the paste turns a gray-black color.

 

 

Keep at it for about 5 minutes, adding more polish as the part seems to be running dry.

 

After you're done polishing, wipe off the paste with a cloth. Then alcohol the part base again. You should end up with something like this:

 

 

Here's a better pic of my lapped e4300.

 

 

You can check the flatness of a polished part by doing this sort of thing, just set it up so that something like a newspaper is below it. Check the reflected image against the surface being reflected. If it's a mirror image, you're flat. The more distortion you see, the more off flat the surface is.

 

Another test is to put a drop of thermal compound on a piece of flat glass, then press the heat sink evenly down overtop of it. Be sure to get the thermal compound as close to centered as you can. Once you've finished pressing down the part, look at the underside of the glass. The thermal compound should be spread evenly over the footprint of the sink. If it's not, you've got an area that's not flat.

 

So, what are the benefits of lapping heat sinks and water blocks? Most of the time, not too much, about 1-3 degrees improvement. Most heat sinks and blocks are pretty close to flat, and the only thing you're doing is sanding out the machining marks.

 

What's the benefit of sanding an IHS? It depends on the CPU, really. Most of the AMD heat spreaders are pretty decent, other than the nickel plating. The C2D's are a case-by-case basis. Some are ok. Mine was fairly out of flat, and lapping it shaved 5 degrees off of my load temps. Some are worse, the best case I've heard of has been a 10-degree change.

 

Well, this has been my lapping tutorial. For now, I'm going to consider it finished, but if there is any other information that you'd like to see covered, or have any suggestions, post em or PM me and I'll be happy to get it done.

[General Septem]

Looking forward to your guide.

[Technohydra]

Thanks for the booster, Septem. I'll definitely try not to disappoint.

 

As an update, session 101 is finished, and has had the diagrams added to further illustrate the difference between the four material removal processes mentioned. Session 201 to follow soon.

[AnUnknownSource]

looks great so far, looking forward to the pics!

[Technohydra]

Another update. The 201 session is now completed, including a few more diagrams and the instructions to get a lap done from rough to mirror shine. If I can find anything that needs to be lapped this weekend, I'll post the 301 session. I'd like to do a cpu IHS, but I don't have any spares at the moment, so I think it'll be a heatsink base.

 

As always, keep checking back, and I'll post updates to keep you...well...updated, hehe.

[General Septem]

Why did you not wet the sandpaper first? Almost everyone else does this, but if there's a reason why not to I'd be interested to know for the next time.

 

Excellent guide by the way.

[Technohydra]

Thanks!

 

The purpose of wetting sandpaper is to reduce the friction of a sand, as well as to carry off the particle that are being machined off the part. Because proper lapping does not use downward force to remove material, the friction caused by the parts weight and gravity is very small, but required. Reducing that friction with water will make the part slide a little easier, but it'll add almost 40% to the time required to complete a lap. If you listen to the sound the paper is making and tap it out once in a while, you'll get the same effect as using water with less time involved.

[General Septem]

That's a good point that I'd never thought of before. I liked the water because it made the paper stick to the glass, but if you're not bearing down on it like I was I can see not needing it. I wish I'd seen this guide earlier though, if nothing else it would have saved me some blisters from putting so much weight on the Tuniq. :tooth:

[Technohydra]

Ooooh, thanks for the idea, I just came up with a lapping method for huge heatsinks. I'll update the guide later and throw you a bone for the inspiration!

[General Septem]

Ooooh, thanks for the idea, I just came up with a lapping method for huge heatsinks. I'll update the guide later and throw you a bone for the inspiration!

 

Who, me? I didn't even realize.