Lapping intervals?

I'm learning the ancient dark art of honing. I've got myself a King 800, a Norton 4k/8k and a Chinese 12k. I've been told that the King and the Norton are soft hones that require frequent lapping but I honestly have no point of reference to measure what that means. Does it mean I should lap after honing each razor? Two? Three?

I've been lapping on sandpaper and glass, seems to work OK. I've only done each stone the once when they were new and I used the pencil mark trick as an indicator. I could do that again, I just don't want to be wasting lots of sandpaper unnecessarily. I've only completely honed one razor on them so far but I had to go back and revisit each stone a couple of times before I got the razor right. (Hey, it was my first try. I did get it there in the end.:p)

What do you guys think? I know I could buy a lapping plate and just use it all the time but I'm only on a sandpaper budget at the moment. One thing at a time.

I tend to lap before each honing session, but I tend to do multiple razors in a session. If the hone loads with swarf then I rub it with my hand under running water to clean it off, and then I'll only lap it once rubbing it with my hand doesnt really bring it back and the cutting performance has dropped off.

If I'm just touching up a single razor I wont bother with lapping, I just wet the hone, touch the razor up then dry the hone off and stow it again.

A DMT 325 plate is a good start for lapping or building a slurry.. Every time you use the stone to build a slurry you are virtually lapping it as well. Hope this helps,
Sincerely;
MIke

With waterstones, you will find that lapping does more than keep the hone flat. It also refreshes the surface, allowing the hone to cut much faster. The occasional refreshing serves to help keep the hone flat.

How often you should refresh the surface is dictated by how loaded with swarf the hone is. You can remove a lot of it by rubbing the wet hone with your hand but over time that starts to have limited effect. That's when you will want to refresh the surface. You will know how far from flat the hone is because as you lap it because the swarf will be removed in the same manner as the gridlines. You will find some regions have the swarf removed quickly, indicating high spots, and some areas will take longer, indicating the low spots.

With wet-dry paper, you essentially can lap a lot without going through a lot of sandpaper. However, I like the speed and storage ease of the diamond stones with the mesh-type surface a lot better :) Since I only have a 1"x4" diamond stone, but lot's of sandpaper, I use sandpaper...

Here's the details on what I do:

I use norton 320 grit wet-dry sandpaper on a piece glass to lap. I've also used regular 80, 120 and 240 grit sandpaper on glass when I wanted something faster for hones I used to sharpen some chisels, and 400 grit regular sandpaper when I was out of 320 wet-dry paper. I tried open and closed coat papers, and garnet and aluminum oxide papers (because I had them all already, and they didn't last very long).

The regular sandpaper lasted about 10-15 minutes worth of lapping time before big, very bald zones rendered it completely unusable - irregardless of type. The wetdry paper lasts about 50-60 minutes before it becomes so dull it's impractically slow (but even then, it only has a few small balding spots).

With the wet-dry paper, I lap before each razor until the pencil grid comes off (about 1-3 minutes depending on the stones grit (coarser stones get unflat faster) and how much I used it last), another time just to make sure (about 15-30 seconds), and then again before the "last set" of passes on each stone (about 10 seconds) just to make sure everythings still perfect, and maybe once or twice more in the middle of bevel setting with stones around 800 to 1200 grit. Afterwards, I rinse off the paper and lay it on the foam "mesh" shelf paper I use under the glass to dry overnight so it's ready for the next honing session.

I've also heard the plastic mesh drywall sanding screen works well for lapping waterstones, but I haven't tried it personally. You can get coarse wet-dry paper and drywall sanding mesh at Walmart or any major hardware store.

ps: Some people use really fine wet-dry paper instead of 800 to 4000 grit hones. I find hones work quite a bit better. For really fine (2000-4000 grit) wet-dry paper, you need to go to NAPA or an autobody store (and pay quite a bit more).