Thread: Dulling blades on a strop

Over the last 2 months I've been experimenting. Although I doubt anyone will find much interest in this post I thought I would discuss it anyway (its a forum afterall, right?)

I've been experimenting to discover two things:

1) What is the best way to dull an edge with a strop; and

2) What are the best corrective actions afterward

Now you might be thinking, why such a stupid experiment? I can only say that once your past the whole "whats the best way to sharpen, strop, shave" type of stuff you kinda run out of experiments pretty quick, but if you read on you might find some interesting points.

I have to start by saying I limited my tools to a standard lightweight/thin high end Dovo strop, about 2 1/2 inches wide and a barber hone. I did this mostly because I completely misinterpreted the amount of damage that occurs to an edge when it gets dulled on a strop. I might have broken out a 4K had I known better.

What I have concluded is that the best way to dull an edge with a strop is by allowing sag to occur during the stropping action. This is by far more likely to cause dulling than the application of pressure while stropping on a taut strop.

Before the experiment I used to feel that too much pressure and too much sag were probably about equal culprits in the dulling of an edge.

Next, I discoved that the best corrective action is 70-90 strokes on a barber hone.

I was really shocked at the amount of work required to get the razor back up to speed. I thought, before the experiment, that I could correct the problem with better stropping, different stropping, or even say 10-20 strokes on a barber hone.

Even with light pressure and a sagging strop I created enough edge dulling to require a lot of work on the hone, more than I had ever expected.

I agree with you Alan.
The "best" way to dull a razor is light pressure on a sagging strop.
It is interesting to discover what happens with a lot of pressure (on the spine) on a sagging strop.

Originally Posted by Yannis

I agree with you Alan.
The "best" way to dull a razor is light pressure on a sagging strop.
It is interesting to discover what happens with a lot of pressure (on the spine) on a sagging strop.

Just visualizing this, without actually testing it, increasing the pressure on the spine using a sagging strop would stretch the strop in both directions creating, essentially a taut strop. Therefore, why not start with a taut strop to begin with?


Scott

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

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!

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.

That's quite the study! Definitely going to have to really watch the tautness of the strop in future.

Thanks for this useful post!

Attention to detail like this saves me a lot of time on occasion, and I have suspected my early stropping to have dulled one of my razors. I do believe I will go at it on my fine stone longer than I was previously willing.