Strange Shapening Experience

[Joe O'Leary]

I started rehabbing some chisels the other day. When flattening the first back I got to 400 SC, then 600 SC. Got a very shiny mirror finish. Then, when I went to an 800 waterstone. The scratches looked deeper and the finish dulled. Kept going up to 8000 and never got the mirror I got with the 600 SC paper (dry).

Any idea what's going on here??:confused:

Joe

[Jerry Palmer]

Could be contaminated stones. 600 CAMI and 800 grit Waterstones are about comaparable in grit size to each other. If the 800 stone was contaminated and created larger scratches, removing them by moving to higher grits will entail a lot more work to remove them.

[Mike Henderson]

Is that an 800 waterstone or an 8,000 waterstone? An 800 stone is fairly coarse and would not provide a mirror finish. An 8000 stone is fairly fine and should produce a mirror like finish, with some light scratches in the finish.

Mike

[edit] I may have misread your post. After you achieved the mirror like finish did you go back to an 800 stone and then take it up to an 8,000 stone? If you did, with no intervening grades of stones, I would expect that it would be difficult to get the scratches from the 800 stone out with the 8,000 stone - it's too big of a jump. If you used a range of stones, such as 800, then 2000, 4000 and then 8000, you should achieve a mirror like finish. But why not go from your 600 paper to the 8,000 stone if the 600 paper was giving you a mirror like finish? Why jump back to the 800 stone?

[Joe O'Leary]

I wasn't very clear. After the 600 paper I went to waterstones as follows:
800, 1200, 4000,6000, 8000.

The scratches after 800 were uniform, so I think the stone was OK. I did get a mirror, as usual, after 6000. What I can't figure out is why I get it with 600 paper. It's pretty old Norton stuff labeled "600-A Tufbak Durite closekote waterproof Silicon Carbide".

Joe

[Mike Henderson]

I would guess that as you used the 600 paper, the grains were being broken down to smaller grains which made it act like a much finer paper. Just a guess.

Mike

[John Schreiber]

I've had the same experience, staying with scary sharp from 220, 400, 600, 1000, 2000 grits. I get a mirror surface at 600 and loose it when doing 1000 and don't get it all the way back at 2000 grit.

My assumption has been that the 600 grit paper is made differently in some way so that it tends to polish better. There is no question that the cutting edge is better after 2000 grit. Since my objective is sharp tools instead of mirror finishes, I have ignored it.

[Wilbur Pan]

I think the problems are twofold. First, as Mike suggested, if you are jumping from an 800 stone to an 8000 stone, that is a BIG jump, and an intermediate step would be really helpful. But it seems that you are taking intermediate steps.

The other problem is that by going from 600 grit SC paper to an 800 grit stone, you are actually taking a step backwards. The problem is that the sharpening world has different standards for paper and stones, and varies depending on what part of the world you are in. 600 grit sandpaper has 16 micron particles, which is finer than even a 1000 grit waterstone, which has 20 micron particles. An 800 grit waterstone has particles that are about 25 microns. If you were using 600 grit paper, the waterstone you should be moving to is a 2000 grit, minimum, which is about the same as 700 grit paper. A 4000 grit waterstone would be even better.

You can find a table with all of the grit equivalents at the end of this Badger Pond article on sharpening (http://www.woodcentral.com/bparticles/sharpening7142.pdf).

Oh, don't worry about the mirror finish. Just worry about the edge that you get. I've found that it is easier to get a mirror finish using the Scary Sharp method, but that overall using Japanese waterstones gives me a slightly sharper edge, even though the bevel seems a bit foggier.

[Joe O'Leary]

Wibur, I think you 've got it. I was reading my grit chart incorrectly and thought the 600 paper was 25µ but that was for a fine diamond 600.

Thanks everyone,

Joe

[Wiley Horne]

Joe,

Building on what Wilbur said, the silicon carbide is friable and will break down into smaller particles. This was Mike Henderson's intuition, and he's right. So you start out with s/c 600g, but by the time you're done, it's a considerably finer grit--you might have been about done when you finished with that paper! The 800g waterstone was a big step backwards for a number of reasons.

Wiley