Thread: Does a Suehiro 20k need to be lapped?

If so, I have a lapping plate I use for my coticule as well as wet/dry sandpaper up to 1200 grit. Will those work ok? Does the stone even need to be lapped? Thanks.

Most stones need lapping, even just in case, when you get them, whether new, used, natural or man made. It depends on its condition. Draw some lines on the stone with a pencil and give it a quick lapping with something fine, since we are talking about the gokumyo. If the pencil marks are not gone after a few laps, you can spend some more time lapping, or use something coarser. If they are removed, then, proceed with the lapping, with something finer.
In your case, and if there are no too obvious signs that the stone needs a lot of lapping, I would use the coticule on my first try, wet lapping. And if the pencil marks are gone, then you're good to go.

I didn't know you could use a coticule to lap another stone. I will try it.

IME the suehiro 20k is a bear to lap. Mine needed lapping from the git-go. YMMV. ..........

Would a regular lapping plate like what I use for my coticule work?

Yes it does and it is hard, very hard. I use a 140 diamond plate and it took some work. I had a small dip in the center of the stone and had to remove a bit of the stone face. The dip left scratches on the bevel until it was flat and smooth.

I then use a 300, 600 and 1200 diamond plates, then a 1k and 4k to smooth.

Grid the stone several times to get it flat, I think you will only have to do it once it is hard and will not be getting that many laps.

If you get scratches on a bevel, lap it again.

Check the other side to see which is flatter to begin with.

Mine had little mill marks in it. It's long gone now, but I do recall that it had little very fine mill marks, and in a hard stone, you want those gone.

Originally Posted by Euclid440

Yes it does and it is hard, very hard. I use a 140 diamond plate and it took some work. I had a small dip in the center of the stone and had to remove a bit of the stone face. The dip left scratches on the bevel until it was flat and smooth.

I then use a 300, 600 and 1200 diamond plates, then a 1k and 4k to smooth.

Grid the stone several times to get it flat, I think you will only have to do it once it is hard and will not be getting that many laps.

If you get scratches on a bevel, lap it again.

Check the other side to see which is flatter to begin with.

+1 - Very hard - mine took forever to lap with SGDLP - but once it's flat it will stay that way...

-john