Strange lapping results

ancalime · Jun 28, 2007

So my friend tried his hand at lapping a heatsink for the first time but came up with very strange results. The base of the heatsink changed from an even copper color to an unevenly colored oily looking base. I was not with him when he was doing the lapping but he told me he used a dish washing solution on the heatsink. I am not very experienced with lapping but I never heard of doing this. Could this be what caused the dark oily looking base? Here are some pictures he provided me with:

Before lapping

After lapping

The pictures aren't great but they clearly show a drastic change in color. Any explanations? Thanks for the help.

juane414 · Jun 28, 2007

Well I used a small drop of dish soap to help lubricate the sandpaper... but my arcticlean got rid of any discoloring. If you don't have any arcticlean try some rubbing alcohol.

Soja · Jun 28, 2007

How long did he leave it out (oxidation)? Try letting some ketchup or lemon juice sit on it for a couple minutes then cleaning it off.

juane414 · Jun 28, 2007

"pure" copper will be lighter and shinier, so the darker areas could might not be sanded down completely to the copper layer.

ancalime · Jun 28, 2007

Ok thanks, I will tell him to try and clean it off following those procedures.

He says he is pretty sure he had proper technique as he saw it done before. Therefore, taking his word for it, I don't see how some parts wouldn't be sanded while others were. He did leave it out for a while. If it was just some oxidation kicking in instead of improper sanding, it wouldn't hurt performance would it? I don't know chemistry btw.

Soja · Jun 28, 2007

Not greatly but it really takes no effort to clean it off.

ancalime · Jun 28, 2007

Ok thanks for the advice.

IKIKUINTHENUTZ · Jun 28, 2007

It looks like the sandpaper quality on higher grits seem 'bad'

This happened to me long time ago and the simple solution was to switch to a different brand of sand paper

I cant really tell for sure if this is the cause, I still need a better picture to see

Susquehannock · Jun 29, 2007

Why do people insist on using dish soap?

ancalime · Jun 29, 2007

IKIKUINTHENUTZ said:
It looks like the sandpaper quality on higher grits seem 'bad'

This happened to me long time ago and the simple solution was to switch to a different brand of sand paper

I cant really tell for sure if this is the cause, I still need a better picture to see

That is what I was thinking. He got the sandpaper from SVC. He said it was fine until towards the end (which is when he would be sanding on the higher grits). I'm gonna try my hand on some SVC paper and see if the results are the same.

He couldn't get his hand on any ketchup yet by the way.

Susquehannock · Jun 29, 2007

Some brands of sandpaper are better than others. I have been using "3M" for years with good results.

And for pete's sake - forget about the soap! That is very likely the reason you are having trouble with the finer grits.

Lots of clean water, especially when changing grits, is all you should need.

http://img329.imageshack.us/img329/6242/dc25we.jpg

ancalime · Jun 29, 2007

Hey I never used soap. :attn:

Do you just soak the whole piece of sand paper with tap water? That's what I do but I'm not sure thats the correct way.

Moto7451 · Jun 30, 2007

Soap has always worked well for me but I don't use very much. Really it only helps in the beginning, adding soap isn't helpful.

Hazaro · Jun 30, 2007

I used soap (a finger wipe on the bottle) on the HS, didn't get what I wanted for shine (2500 grit), but that's long over. I don't think it really helped. How'd the temp drop go though?

Susquehannock · Jul 2, 2007

ancalime said:
Hey I never used soap.

Do you just soak the whole piece of sand paper with tap water? That's what I do but I'm not sure thats the correct way.

What I do is set up my lapping station next to the sink with the faucet set on trickle.
That way I can rinse the particles off both the sandpaper & heatsink often.

They key to getting a good finish with the extra smooth grits is to be CLEAN of grit. Soap makes that next
to impossible. Which is why those who use it run into a brick wall at a certain point.

IKIKUINTHENUTZ · Jul 3, 2007

ancalime said:
That is what I was thinking. He got the sandpaper from SVC. He said it was fine until towards the end (which is when he would be sanding on the higher grits). I'm gonna try my hand on some SVC paper and see if the results are the same.

He couldn't get his hand on any ketchup yet by the way.

Ive had the problem with EasyPckits 2000 grit sandpaper

Susquehannock is right though, I use 3M 1500,2000,2500 grit sandpaper and never ran into this problem again

Blazing fire · Dec 22, 2007

IKIKUINTHENUTZ said:
It looks like the sandpaper quality on higher grits seem 'bad'

This happened to me long time ago and the simple solution was to switch to a different brand of sand paper

I cant really tell for sure if this is the cause, I still need a better picture to see

What's the best sand paper I can get hold of? 3M?

EchoTheDolphin · Dec 22, 2007

Some soaps and detergents can accelerate oxidization or ionization of the copper. It'll make it look that funny color. I'm not sure how it will affect it's ability to transfer heat though.

Blazing fire · Jan 4, 2008

What's the best sand paper for lapping?

Spawn-Inc · Jan 4, 2008

Blazing fire said:
What's the best sand paper for lapping?

one that works

i use 3m only and have very good results all of the time. i can get a mirror shine at 2000 grit.

Strange lapping results

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