A useful tip from another hobby is that with three surfaces one can grind a pretty flat surface, such as an optical flat. A more useful aspect for sharpening knives is that with three benchstone surfaces one can always keep all three flat, by grinding them against one another. A useful approach might be to use one coarse carborundum stone which offers two surfaces with a coarse/fine combination stone to keep the three coarse surfaces flat. The coarse surfaces can be used to keep the fine carborundum surface flat, which can be used to keep the different Arkansas surfaces flat. An alternative to the coarse and coarse/fine is to just use three combination stones. A perceived advantage with using carborundum or India stones is that one can always have a consistent grit available, unlike with the much more expensive diamond stones which wear with use, and with carborundum stones being cheap, 6in to 7in models for between $5 and $10 each, it's even cheaper than wet/dry paper over the long run.
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3 Stones = Flat Stones
- Thread starter johno
- Start date
Cougar Allen
Buccaneer (ret.)
- Joined
- Oct 9, 1998
- Messages
- 76,852
I think I understand why you're suggesting using three surfaces -- because when you use only two it's easy to get them to fit together but unless you keep changing which one is on top one gets convex and the other concave. I think that's an unnecessary refinement, though; I used to grind two Hard Arkansas hones together to flatten them and although I didn't try to get them optically flat, I had no trouble getting them flat enough for the purpose.
It was time-consuming, though. Next time I'm going to try an idea I've seen posted: lay a sheet of sandpaper on a glass plate and grind the stone on that. I figure I'll use coarse silicon carbide paper to flatten it fast and then I can polish with successively finer grits. It won't be optically flat, of course.
Optical flats are not easy to make, but a flat with only slightly greater variance is easy to make; it's that last 1/8 wavelength that's the hard part. There's no advantage to getting a hone that perfect.
On the hand, fanaticism can be fun! Just like wasting your time polishing an edge long past the point that it makes any noticeable difference in how it cuts, why not waste your time making optical flats out of your hones??? I think I'll go grind mine right now....
I guess this means I'll have to stop using my diamond hones, so I'll have new errors in my optical flats to grind out. That could be an advantage -- honing will take longer so I'll get to have more fun doing that, too....
-Cougar Allen :{)
P.S. If for some reason you don't want to waste your time (why not???) get coarse silicon carbide bench stones and a fine diamond hone. Then you can bear down hard on the coarse stones without any fear of damaging them and grind fast, and the diamond hone will polish fast with less pressure. Diamond hones stay flat and it's the flatness of your fine hone that's most important, and fine diamond hones are relatively cheap; it's the coarse ones that are expensive.
-Cougar :{)
It was time-consuming, though. Next time I'm going to try an idea I've seen posted: lay a sheet of sandpaper on a glass plate and grind the stone on that. I figure I'll use coarse silicon carbide paper to flatten it fast and then I can polish with successively finer grits. It won't be optically flat, of course.
Optical flats are not easy to make, but a flat with only slightly greater variance is easy to make; it's that last 1/8 wavelength that's the hard part. There's no advantage to getting a hone that perfect.
On the hand, fanaticism can be fun! Just like wasting your time polishing an edge long past the point that it makes any noticeable difference in how it cuts, why not waste your time making optical flats out of your hones??? I think I'll go grind mine right now....
I guess this means I'll have to stop using my diamond hones, so I'll have new errors in my optical flats to grind out. That could be an advantage -- honing will take longer so I'll get to have more fun doing that, too....
-Cougar Allen :{)
P.S. If for some reason you don't want to waste your time (why not???) get coarse silicon carbide bench stones and a fine diamond hone. Then you can bear down hard on the coarse stones without any fear of damaging them and grind fast, and the diamond hone will polish fast with less pressure. Diamond hones stay flat and it's the flatness of your fine hone that's most important, and fine diamond hones are relatively cheap; it's the coarse ones that are expensive.
-Cougar :{)
Cougar Allen
Buccaneer (ret.)
- Joined
- Oct 9, 1998
- Messages
- 76,852
A straightedge is a good idea, but you realize, of course, it will no longer be a straightedge after you use it to check a stone once.
It's been many years since my fit of fanaticism about keeping my hones flat. (I've been using diamond lately.) I seem to recall folding a sheet of paper to make a straightedge and checking it against my steel rule.
Hard Arkansas hones can be flattened quickly if you don't let them get far from flat.
When I first started that fit of conscientiousness about it, I'd been abusing my hones for a long time and they were far from flat. That was what made it time-consuming.
-Cougar Allen :{)
It's been many years since my fit of fanaticism about keeping my hones flat. (I've been using diamond lately.) I seem to recall folding a sheet of paper to make a straightedge and checking it against my steel rule.
Hard Arkansas hones can be flattened quickly if you don't let them get far from flat.
When I first started that fit of conscientiousness about it, I'd been abusing my hones for a long time and they were far from flat. That was what made it time-consuming.
-Cougar Allen :{)
The same concept used in obtaining flat bench stones can be used to check straight edges, by comparison with others. I have lots of straight edges laying aound, some of my favorites being a couple of old squares that my wife picked up at a garage sale for something $5. They look like they have mahogany and brass handles, needed a bit of polishing with steel wool and oil as there was some rust, and seemed to have held well over the years. She also found a Starret protracter/square for $5, it doesn't have a vernier though, which looked little used.
In summary one can easily check and tune stones so that they're flat, without throwing too much money at the problem or taking too much time. Sears has 2in x 7in carborundum stones for about $6. As far as how flat one wants to keep the stones that's a personal matter, just like how sharp one wants to keep a knife. I'll touch my stones up when they start showing lots of light thru a straightedge, which is probably 1/64 to 1/32 of inch.
In summary one can easily check and tune stones so that they're flat, without throwing too much money at the problem or taking too much time. Sears has 2in x 7in carborundum stones for about $6. As far as how flat one wants to keep the stones that's a personal matter, just like how sharp one wants to keep a knife. I'll touch my stones up when they start showing lots of light thru a straightedge, which is probably 1/64 to 1/32 of inch.