A question about convex edges in relation to stropping.

[SwissHeritageCo]

I think I'm missing something here. When I strop my V edges (maintained with a guided system), they stop responding after a few stroppings and need to be touched up on stones... whereas my convexed edges can be maintained on a strop for the longest of times.

Is this user error? The convex seems to have superior edge retention too. If it's thicker (which I dont think it is, literally ground the shoulders out) then why doesn't it suffer in performance?

In any case, it seems to me that my convex edges can be brought back to keen from just a strop a lot longer than a V edge.

 

[BluntCut MetalWorks]

Physics might be obvious but explanation could be difficult to envision... well, below is a crude sketch of stropping v-edge.
Given steady stropping angle+pressure on a particular v edge.

Notes:

1) force vector on edge shoulder area stay almost steady and abrade very little thickness due to low and lowering psi on subsequence stropping session due to large area of contact

2) force vector near apex area is reduced quickly on each iteration because apex area is receding away from strop surface, also psi on shoulder area is lower which gradually flatten strop surface toward apex, thereby reduce strop spring back pressure to apex area

As for stropping convex edge - basically the strop follow the contour of edge, so psi is low through out until rapidly increase toward apex. Increase rate depends on strop pressure and spring-back of strop surface material. Apex will get shape/sharpen for many more sessions than v-edge.

 

[Obsessed with Edges]

I'm inclined to believe that any strop with much compressible 'give' in the substrate will tend to wrap around the apex more on a V-ground edge than it will on a convexed edge profile. So, if there's any abrasion involved at all, the V-ground apex will fairly quickly round over and become dull, hence needing regrinding on a stone. A compressible substrate is better able to smoothly follow a convexed edge profile without wrapping around the apex, UNLESS too much pressure is exerted.

My observations over the last many years echo yours, in that I've also noticed it's easier to maintain a convex by stropping than it is to maintain a V-ground edge on a strop with any compression in the substrate. For V-ground edges, I firmly believe a VERY FIRM or HARD strop of hardwood is much better suited for those.

Edited to add:
I used to describe an effective stropping technique as one which allows the substrate to just lightly skim the 'cheeks' of the apex at such minimal pressure as to prevent the substrate from wrapping around or over the apex at all. Whether with a V-ground edge or convexed, it can work either way with good technique, i.e., maintaining a conservatively low approach angle and making sure most of the compression of the substrate is exerted in the area behind the apex and not near it.

 

[SwissHeritageCo]

Gentlemen, those are some lovely break downs and exactly what I needed to know - thank you

Consider me enlightened.

 

[Twindog]

Stropping can sharpen an apex, dull it or leave it unaffected. It all depends on your technique.

It doesn't matter if you have a convex edge or a V edge. It doesn't matter if you use a leather substrate or a hard substrate. All can work or fail, depending on your technique.

The thing that matters is how the strop approaches the apex and how it exits the apex.

For every edge, there can be multiple methods that work or fail. For example, more pressure on a leather strop can compensate for a too-shallow angle. For this reason, stropping is both an art and a science. One technique can work on a V edge or a shallow convex, but fail on a more severely convexed edge.

Nonetheless, stropping, done correctly is an awesome tool. There is a reason why old-time barbers stropped their razors on a leather strop before shaving a client. And there is a reason why their razors had a built in angle guide.

 

[derfred]

I strop my V edges on balsa. It takes a light touch and 1 or 2 passes to go back to hair poppin.