Luke Dupont
12-05-2021, 8:00 PM
I wanted to share a quick tip for flattening the backs of chisels and plane irons.
I use a lot of vintage tools, and I've never owned any really high end chisels that come precision ground either.
In both cases, the backs of the chisels can be seriously out of whack, such that it can take many hours of grinding on even coarse diamond stones or sandpaper to bring them to a sharpenable state.
In any case, here's a simple trick that I use which reduces hours of work:
If the back of your chisel or plane iron has a hump, such that you're only contacting the middle of the back and not the edges, which is so often the problem, hollow it out with sandpaper!
I can spend hours on a stone getting nowhere, but as soon as I sand the middle bit down, the process goes extremely quickly.
Be careful as you don't want to cut yourself or damage the edge, but I generally find cutting a small piece of sandpaper off and just rubbing the high parts with my finger works. You can use another object in place of your finger, or some other method besides sandpaper if you have one (I'd love to hear!) but the principle is the same. Just work on the high parts off the stone. You will not think that you are removing much metal, and you won't be, but the next time you take it to your stone and check, you will be able to quickly achieve flatness.
I did this just earlier with a stubborn chisel, and afterwards all I needed to bring the back into flatness was a Washita. It's now dead flat.
My theory is that we can waste a lot of time not correcting this problem even on a coarse stone, because when there's a hump in the middle, the chisel will continue to rock back and forth (even if by immeasurably tiny fractions of a millimeter, which we can't notice) which just retains the "bump" in the middle, rather than working it down. So special attention to that hump in the middle may be necessary, or in any case is very benefitial, to achieve a flat registration as well as reducing the surface area in contact with the stone.
Anyway, I just don't see this talked about much, which is why I mention it.
Most people seem to really skip over the "flattening the back" step, or make it look very easy with high end tools (some folks just very lighly polishing the back of some LN chisel on a relatively fine stone which would take decades to flatten most tools I've touched!), and I think this is a disservice to beginners who can easily find themselves grinding for hours and still unable to get a serviceably flat (ie, sharpenable, such that the edge makes contact with the stone) back. And so they use an unflat tool for weeks or months, struggling to sharpen it the whole time. A very coarse flat stone and some attention to high areas will save a ton of trouble and time!
I use a lot of vintage tools, and I've never owned any really high end chisels that come precision ground either.
In both cases, the backs of the chisels can be seriously out of whack, such that it can take many hours of grinding on even coarse diamond stones or sandpaper to bring them to a sharpenable state.
In any case, here's a simple trick that I use which reduces hours of work:
If the back of your chisel or plane iron has a hump, such that you're only contacting the middle of the back and not the edges, which is so often the problem, hollow it out with sandpaper!
I can spend hours on a stone getting nowhere, but as soon as I sand the middle bit down, the process goes extremely quickly.
Be careful as you don't want to cut yourself or damage the edge, but I generally find cutting a small piece of sandpaper off and just rubbing the high parts with my finger works. You can use another object in place of your finger, or some other method besides sandpaper if you have one (I'd love to hear!) but the principle is the same. Just work on the high parts off the stone. You will not think that you are removing much metal, and you won't be, but the next time you take it to your stone and check, you will be able to quickly achieve flatness.
I did this just earlier with a stubborn chisel, and afterwards all I needed to bring the back into flatness was a Washita. It's now dead flat.
My theory is that we can waste a lot of time not correcting this problem even on a coarse stone, because when there's a hump in the middle, the chisel will continue to rock back and forth (even if by immeasurably tiny fractions of a millimeter, which we can't notice) which just retains the "bump" in the middle, rather than working it down. So special attention to that hump in the middle may be necessary, or in any case is very benefitial, to achieve a flat registration as well as reducing the surface area in contact with the stone.
Anyway, I just don't see this talked about much, which is why I mention it.
Most people seem to really skip over the "flattening the back" step, or make it look very easy with high end tools (some folks just very lighly polishing the back of some LN chisel on a relatively fine stone which would take decades to flatten most tools I've touched!), and I think this is a disservice to beginners who can easily find themselves grinding for hours and still unable to get a serviceably flat (ie, sharpenable, such that the edge makes contact with the stone) back. And so they use an unflat tool for weeks or months, struggling to sharpen it the whole time. A very coarse flat stone and some attention to high areas will save a ton of trouble and time!