Lapping Film, still confused

uilleann · May 25, 2017

I started to use 1, .5, and .1 lapping film on my knives with the WE system. I do it afer diamond stones up to 1500 and choseras 1000-10000. After the 1 micron I get a beautiful mirror finish. But then after the .5 micron there are all of these micro scratchs that will not be removed with the .5 micron. The .3 micron further enhances the non scratched surfaces but does nothing for the scratches. The edge still looks beautiful and you have to have your eye on the blade with light coming from one location to see the scratche. So they are very fine. But I did not see them after the 1 micron.

Today I got some diamond lapping film from another vendor. I got 6,3,1,.5,.1 films. I went back to the knive with the micro scratches. I started with the 6 micon. The finish looked worse as expected but the micro scratches looked to be gone. Then I did the 3 micron and it really started to look go. Then the 1 micron, and it was looking even better. Then the .5 micron and it became amazing... no scratches anywhere and a brilliant shine. Then the .1.......... Lots of micro scratches started to appear all over the place. I had to go back to .5 micon .

So what is going on here..... The only thing that made any sense is that the scratches are always there from a courser grit and had somehow been smeared over. At some point that smear is removed revealing the hidden scratch. That does not make much sense to me. SO I am puzzled. The good news is that I have a hell of a mirror edge at .5 microns. ;-)

Topshot · May 25, 2017

Maybe just stop at .5 ?

uilleann · May 25, 2017

I cannot argue with that.

cbwx34 · May 25, 2017

Maybe the .1m isn't really .1... or it's contaminated? Easiest way to check is to change directions between steps... and see if the scratches that "appear" are the result of the current step.

115Italian · May 25, 2017

The scratches are the low spots. The film is not removing metal, just polishing it. The finer the mirror finish, the more noticeable the low scratches. You need to go back to a fine stone or ceramic and get those high spots even with the low spots. Or just stop at the 1 micron and save yourself the trouble.

miso2 · May 25, 2017

115Italian said:
The scratches are the low spots. The film is not removing metal, just polishing it. The finer the mirror finish, the more noticeable the low scratches. You need to go back to a fine stone or ceramic and get those high spots even with the low spots. Or just stop at the 1 micron and save yourself the trouble.

This makes very sense to me.

Miso

bucketstove · May 25, 2017

115Italian said:
The scratches are the low spots. The film is not removing metal, just polishing it. The finer the mirror finish, the more noticeable the low scratches. You need to go back to a fine stone or ceramic and get those high spots even with the low spots. Or just stop at the 1 micron and save yourself the trouble.

Hi,
yes, high grit abrasives like found on the films remove small amounts of metal,
they not fast enough to remove the deep scratches left from coarser grits a few steps before

Commonly sold diamond polishing paste come in these microns 40 / 28 / 20 / 14 / 10 / 7 / 5 / 3.5 / 2.5 / 1.5 / 1 / 0.5
This progression matches a 33% reduction in grit size for each step that is recommend

Code:

 28  / 40  * 100 = 70 % -30 %
 20  / 28  * 100 = 71 % -28 %
 14  / 20  * 100 = 70 % -30 %
 10  / 14  * 100 = 71 % -28 %
 7   / 10  * 100 = 70 % -30 %
 5   / 7   * 100 = 71 % -28 %
 3.5 / 5   * 100 = 70 % -30 %
 2.5 / 3.5 * 100 = 71 % -28 %
 1.5 / 2.5 * 100 = 60 % -40 %
 1   / 1.5 * 100 = 66 % -33 %
 0.5 / 1   * 100 = 50 % -50 %

REK Knives · May 26, 2017

While there is a high probability that it's coarser scratches being revealed, I have experienced what you are explaining with several different lapping films at 1um and under as well, and I'm 100% confident that they were not lower grit scratches. I think it could either be cross contamination on the films from the factory, or in your case it could be that the glass backing has some nicks out of the corners that need to be sanded out.

uilleann · May 26, 2017

razor-edge-knives said:
While there is a high probability that it's coarser scratches being revealed, I have experienced what you are explaining with several different lapping films at 1um and under as well, and I'm 100% confident that they were not lower grit scratches. I think it could either be cross contamination on the films from the factory, or in your case it could be that the glass backing has some nicks out of the corners that need to be sanded out.

hmmmm, I will check that

Mo2 · May 26, 2017

uilleann said:
I do it afer diamond stones up to 1500 and choseras 1000-10000.

ummm, diamond stones and chosera stones do not have the same grit ratings. i just find it strange to go from 1500 with diamonds and then start with 1000 chosera. isnt that going backwards?

how much pressure are you using with the lapping flims and which type of lapping films are you using? there are 4 different kinds iirc (alum Oxide, diamond and Silicon Carbide and Chromium Oxide).

also clean the blade and the film to verify both are clean.

in any case, before going to the next grit, make sure you remove all the previous scratches from the last grit, if that makes sense. i like to go only one direction with one grit then the other direction with the next grit, but everyone has there own way.

in any case, im not sure why your lapping flims are not working as intended.

uilleann · May 26, 2017

The 1500 grit to 1000 Chosera was actually a habit I developed using the KME. They suggest and I have seen that it helps smooth over some of the courser grind lines of the diamonds and better prepares the edge for the other chosera's.

The lapping film is working great through .5 micron.... its just the .1 micron. So it could be the new tape, or maybe I am contaminating it, or maybe some rough glass is hitting the edge. I have some things to check out on this one