Precision lapping (again?!?)
 

An article just posted, by Ian Anderson, at overclockers.

http://www.overclockers.com/articles892/

Comments? (N8, Bill,...)

terrifically good article
of course I like such that present information clearly that is of use to me

wish I could pick his brains for a week or two !

Yes, I like it, although a picture with each of his descriptions would add a lot of useful info.

I also agree with his statement about a human getting a better final product than a machine.

I have several lapping and polishing machines at my disposal, but I can always do a better finishing job than the machines. A human can learn by experience, a machine does not.

Whether 'the reader-or-web writer' can do a good lapping/polishing job depends on their skills and experience, hence the number of horrible statements and lapping/polishing guides I have seen online.

My $0.03

N8
why don't you write a (comprehensive ?) lapping technique article ?

1. Lack of time. I hardly have time to post here.

2. I am working on a visual polishing step-by-step display for researchers and grad-students here at work so they can compare their samples with this visual display to see if they are doing things remotely correct when they do lapping/polishing on their own.

This display will have 1" diameter aluminum and glass circles in a sequence of finishes starting from diamond saw cut at one end to polished with 0.02 micron colloidal silica at the other.

I could try to take really good pictures and post these later, but this will not be as nice as actually holding the display pieces for side-by-side comparisons.

I would like to incorporate the techniques in writing as well, and I could post that online.

This might take me a couple months in my spare time (hmmm, what spare time) at work.

Don't worry about missing out. I will let everyone know when it gets done.

I found it interesting but completly useless actualy. How does one get the base "flat" by hand in order to get to the "polishing" stage? That is the problem I have with my blocks is getting a flat base. I have yet to be able to do it by hand lapping. I can make a nice polished look but it isn't flat. My mill isn't up to fly cutting anymore so I have to start with stock copper from the supplier, which as you probably know, sucks but most DIY'ers are in the same position. I got a decent sanding block and start with 100 grit and then work up to 600grit and that is usually where I start to "polish" it. Even though I get a good print of silver compound it isn't anywhere near flat. I can get it to where the little AMD symbole on top of the die makes an impression in the silver compound though. Best I can do with what I got and it has taken a lot of work to get that good. Not to many of us can or wants to afford a Lap Master. :D

Maybe his next articles will inform us on a decent way to hand lap a block....

Good statement. I do rely on our Lapmaster machines to get things flat and these are not your everyday item. I can and have done this by hand many times, and experience counts, which is hard to get unless you do this a lot. Writing a technique guide won't solve the experience factor problem that usually is the main obstacle to flatness.

I imagine that no amount of experience matters much unless one has a way to evaluate their end results.

Short of spending $100+ for an optical flat and monochrome light source. How could a person gauge their progress?

if one cannot 'see', they're flying blind

$100 eh ?
the flats can be had cheaply enough (to 3" dia), but the lamps are pricey
- I think Fisher sells the pieces for a DIY solution

You can get things very flat with a good high quality set of files, some chalk, and good filing technique. This will get the base very flat, the polishing is done by sandpaper.

and this would be using a 'platter of piss' as a reference standard ?

It's bright idea time again...

Distance between the block and the wall would magnify any distortion in the base.

If eye level was kept on the same plane as the laser between the block and wall, it would eliminate percieved error caused by irregularities in the wall.

Before I put on my nomex suit to brace for the flames, think of this... Why do telescope mirrors have to be so perfect.

Jeeze Bill....

You certianly gave me a good chuckle with that one

On second thought, screw the line that gets traced on the wall, look at the pattern.

Example: Reflect light of a CD you're holding in your hand onto a wall. Flex the CD a little. See how it goes from a round circle of light (flat) to something funky shaped (not flat). That's using non-coherent light at an acute angle. Now imagine using coherent light and an oblique angle. Any deviation from flat would be pretty obvious.

Is the block perpindicular to the wall, or slightly angled towards it.

In the pic, it's slightly angled, not sure if this is intentional or just a mess-up.

** Etacovda picks up shovel and throws dirt back on the thread

No grave robbing! ;)

Halloween comes late this year
:-)

Jeez man... Thread Viagra...

If the reflected beam were to be perpendicular to the wall, the base of the block would have to be slightly tilted toward the wall.

Having ground a couple of telescope mirrors, one mistake most people do when lapping is only lapping with the wb on top of the "tool". Continued lapping in that matter will produce a concave surface. You have to alternate wb on top/tool on top. This will produce a flatter surface. Just my 2cents.

convex on a stationary tool below

My bad! Your absolutely correct.

ok I just read that article and parts of hte articles from stellafane and I have come to the conclusion that, that article is nearly comletely useless for all of us. Laping is all well and good, but the amount of time and effort that it would take to get a surface that perfect as described in the article would take so much time that it would not be worth the small gains gotten from it.

And he even states that this method is only really for test purposes and freaks who want to brag a bout having a surface polished to the quality of a telecope mirror.

Maybe true, but it's all part of the learning curve. Ya' don't learn nuthin, if ya don't try!

i suppose, but i will stick with my amateur lap job and some as5.

But the one thing i would like to try is when lapping to use the liquid abbrasives with the cpu as the tool. That seems like something that would be interesting.. Just have to find the abbrasives and some dispensers for them..

Anyone know where to get them?

The problem is you 'amature' lap job could just make matters worse. Depends how bad your surface is to start with and/or how good your method relly is.

Im convinced alot of peoples lapping only makes things worse.