Thread: Dulling blades on a strop

I agree that passing a razor on a sagging strop will ruin an already keen edge. It is simple geometry. If you have a taught strop it is very similar to a leather paddle strop. With the spine and edge of the blade held with uniform pressure against the leather surface the bevel should be essentially flat, in full contact with the leather. If catenary (the fifty cent word for sag) is introduced, the blade (regardless of pressure distribution) will then be describing a chord across the radius of the catenary. This will hold the bevel off the surface of the strop and force the edge to drag tangentially across the leather subsequently rolling and/or breaking the fine edge. You can do exactly the same thing with a taught strop or a paddle by lifting the spine of the razor while stropping.

Originally Posted by icedog

I agree that passing a razor on a sagging strop will ruin an already keen edge. It is simple geometry. If you have a taught strop it is very similar to a leather paddle strop. With the spine and edge of the blade held with uniform pressure against the leather surface the bevel should be essentially flat, in full contact with the leather. If catenary (the fifty cent word for sag) is introduced, the blade (regardless of pressure distribution) will then be describing a chord across the radius of the catenary. This will hold the bevel off the surface of the strop and force the edge to drag tangentially across the leather subsequently rolling and/or breaking the fine edge. You can do exactly the same thing with a taught strop or a paddle by lifting the spine of the razor while stropping.

I think this is incorrect, or at least oversimplified. With even a little bit of pressure the strop loses its parabolic shape and describes more of a very shallow "V", with the strop bending to varying degrees at both the spine and the edge. The bending at the spine doesn't affect the edge at all - if all the pressure is focused on the spine and the blade just wafts behind, then all the bend in the strop is at the spine and the edge will strop normally on the straight trailing edge of the "V" - you're just using the spine to finish tensioning the strop. Similarly, even with a shallow sag you can dull a blade if you apply a torque to the blade so all the bending in the strop occurs at the edge of the blade. Of course it's easier to get everything right if you minimize the variables, which is where the "keep a taught strop and use very little pressure" rule comes from - it's easy to keep the strop taught, and easy to keep the pressure light. Or at least easier than dealing with the changing angle, pressure, and torque as you stroke across a slack strop, stropping against the straight trailing edge of a changing angle as you sweep across. It can be done - we've all seen Lynn shaving off a slack strop in his youtube video But the fact that something *can* be done a certain way is not a reason it *should* be done that way.

I always find that the key is pressure. Very light ........tis the same for honing, stropping and shaving, even though the exercises are different. Less pressure is usually mo bettah

Have fun.

Lynn

A really interesting post and thanks for the experimentation.

I have found that the stiffer the blade, the tauter the hanging strop must be. The full hollow ground razor has enough flex in the blade to accommodate a slightly less taut strop.

Full wedges strop really sweetly on a strop laid on a flat surface.

Originally Posted by mparker762

I think this is incorrect, or at least oversimplified. With even a little bit of pressure the strop loses its parabolic shape and describes more of a very shallow "V", with the strop bending to varying degrees at both the spine and the edge. The bending at the spine doesn't affect the edge at all - if all the pressure is focused on the spine and the blade just wafts behind, then all the bend in the strop is at the spine and the edge will strop normally on the straight trailing edge of the "V" - you're just using the spine to finish tensioning the strop. Similarly, even with a shallow sag you can dull a blade if you apply a torque to the blade so all the bending in the strop occurs at the edge of the blade. Of course it's easier to get everything right if you minimize the variables, which is where the "keep a taught strop and use very little pressure" rule comes from - it's easy to keep the strop taught, and easy to keep the pressure light. .

I totaly agree!

Now let's add another dimention to this stropping thing: the path of the razor over the strop and relation to the angle of the micro-serrations at the edge.

Maybe another thread.


Scott

Interesting experiment, and thanks for taking the time and effort doing this sort of thing, Alan . I think hese kind of experiments can be useful 'cos they come from the opposite direction we usually take. We're all naturally consumed with getting our razors sharp (and the right kind of sharp to boot), but I guess it's also a good idea to sometimes experiment with achieving the opposite results so one can have a more intuitive understanding of how the material behaves - ya know, the whole gestalt.

Leon

Originally Posted by mparker762

I think this is incorrect, or at least oversimplified. With even a little bit of pressure the strop loses its parabolic shape and describes more of a very shallow "V", with the strop bending to varying degrees at both the spine and the edge. The bending at the spine doesn't affect the edge at all - if all the pressure is focused on the spine and the blade just wafts behind, then all the bend in the strop is at the spine and the edge will strop normally on the straight trailing edge of the "V" - you're just using the spine to finish tensioning the strop. Similarly, even with a shallow sag you can dull a blade if you apply a torque to the blade so all the bending in the strop occurs at the edge of the blade. Of course it's easier to get everything right if you minimize the variables, which is where the "keep a taught strop and use very little pressure" rule comes from - it's easy to keep the strop taught, and easy to keep the pressure light. Or at least easier than dealing with the changing angle, pressure, and torque as you stroke across a slack strop, stropping against the straight trailing edge of a changing angle as you sweep across. It can be done - we've all seen Lynn shaving off a slack strop in his youtube video But the fact that something *can* be done a certain way is not a reason it *should* be done that way.

How is what I wrote incorrect? I basically state that if you drag the edge of a razor across a strop with (the bevel lifted but the edge on the leather) you will damage the edge.

Whatever.