Thread: Advice on lapping plates

for lapping stones i too like the granite tile with SiC also, low tech and inexpensive solution,
but nobody mentioned checking with decent straight edge both stone and lapping surface, not to mention checking true of straight razor
I rechecked some stones i recently lapped and they have a very slight convex towards center of stone, which i understand is the norm coming off of saw, guessing i have less than .5mm variation. much better than concave. some like the intentional convex but that is a whole different conversation.
worked on one near flat stone yesterday and it is not so easy getting it truly flat, inspite of having the right equipment

So, where are we up to... I found I had to take several millimetres off some of the Chinese stones, to get past imperfections etc, so for the rough work I used a concrete paving slab. Worked ok to take material off, but left big scratches. I then smoothed them out with a lapped 250 grit stone, which also worked well. Although the binder in the 250 stone is quite soft, and the Chinese stones are said to be hard, it seems the abrasive in the 250 stone is much harder than the natural stone, and the material came off the natural stone without obvious wear to the 250.

Experimentally, I then tried one or two of the Chinese stones on wet and dry up to 1200 on the granite worktop, and got a nice flat smooth surface. On giving this a few preliminary tries honing razors, I found that I didn't really feel any improvement over my King 10k stone, which is my current highest stone, and maybe wasn't as good as the edge off my 10k. This is a rough preliminary assessment. It is true that I had one razor which wouldn't seem to come round on the 10k, for reasons I do not know or understand, but on the Chinese stone it came round straight away. So something different is going on, there is something to explore.

For the future, I have a diamond plate on order, and will get some SiC grit if I need it. This batch of stones are basically lapped now, so the question is really finessing them at this point. I have read that the Chinese stones may benefit from a very high level of lapping/polishing. Is this best achieved by burnishing with tool steel? Lapping/polishing on very high grit? polishing two lapped stones against each other? Or some other method?

Thanks in advance

Ed

On hard finishers that you are not going to slurry, burnishing with a knife of hard tool is an option, and it is very effective with some hones. There is also the possibility of changing from water to Smith’s solution, or use soapy water, or glycerine to make for a more refined edge.

Originally Posted by RezDog

On hard finishers that you are not going to slurry, burnishing with a knife of hard tool is an option, and it is very effective with some hones. There is also the possibility of changing from water to Smith’s solution, or use soapy water, or glycerine to make for a more refined edge.

Many thanks. In my preliminary experiments both with lapping and honing, I have found that dish soap stops the hone catching and makes everything much smoother. I did not know it had an effect on the edge.

So, a grit is of a give size. Let’s say 10k, it has at least 2 sides that equal 10k to fall through a 10k mesh, it may be longer on the other end. On Natural stones there is no mesh.

But for the sake of this discussion, let’s say the grit is 10k high and wide. It is held by a binder, at 5k high and still 10k wide. (Yea, we don’t really know how deep)

Any lubricant will lessen the friction and depth of cut, will not cut the full 5k deep but still 10k wide. How much does lubrication limit, not much? Slicker oil limits more, water less.

Burnishing cuts off/crushes the top of the grit, how much? Who knows, say 25-50 percent. A lot depends on the grit, stone, the process used to burnish, hard carbon steel will burnish more than soft stainless, how much pressure and how many laps used.

A burnished stone will polish more than cut.

I use an old Carbon Steel Cleaver that I can put some pressure on to burnish. Short strokes about ½ to one inch overlapping down the length of the stone, then long blending strokes to even out the surface. Keep repeating until the proper finish is achieved.

You can see the surface burnish and get shiny, it will take a shallower cut when use to hone, but the grit is the same as it was made, just not as tall.

Rubbing two stones is slow, and a pain to do, hard carbon steel is faster and more effective.

The problem with Naturals and particularly Chinese Naturals vary wildly in terms of performance.

Originally Posted by Euclid440

Burnishing cuts off/crushes the top of the grit, how much? Who knows, say 25-50 percent. A lot depends on the grit, stone, the process used to burnish, hard carbon steel will burnish more than soft stainless, how much pressure and how many laps used.

A burnished stone will polish more than cut.

Many thanks!

I have burnished one stone in the meantime, with the back of a kitchen knife, possibly not ideal but the best I have to hand. In any case, it has gone from not being as fine as my 10k stone, to not making any (yet) discernible difference to a razor after a good 100 laps. So it makes a massive difference! These are preliminary perceptions, so let's see what further experimentation reveals.

Try more laps. Are you going from the 10k to the natural? I like to start the edge at the same place every time I’m experimenting with a finisher, gives you a base line.

Originally Posted by jfk742

Try more laps. Are you going from the 10k to the natural? I like to start the edge at the same place every time I’m experimenting with a finisher, gives you a base line.

Yes, that was from a 10k, though it was really just a brief trial to check the lay of the land rather than a proper experiment. I also have a bunch of identical razors to experiment with, as well as the five Chinese stones, so I am planning to do some proper comparisons to find out how to get the best out of the hones. I totally agree that the edge should start at the same place every time for research and experiments.

I have one and everything I tried only got me to about 5k-8k equivalent. I’ve heard of some people getting ones that work as finishers though. I like mine for final finish on knives. Mine cuts fairly fast even with a burnished face.

So, a word of caution so you don’t waste a lot of time or drive yourself crazy, those stones either will finish, or they won’t.

Few can improve a 10 or 12k edge. Better than honing identical razors, pick your best shaver and hone it on the 5 stones, to find which stones are finishers. Then experiment with the finishers, the rest are paper weights.

For me, a natural finisher can improve a 12k edge or I am not interested. Learning a Natural stone is a process, you have to learn the stone, to squeak out its potential. Some give it up, some make you work.