Thread: high grit then paste

Originally Posted by onimaru55

A large fin can be achieved by excess honing or stropping with pastes.
Sounds like a short convexed fin would be a durable long lasting edge. Is this what you are saying ?

Not entirely. The big issue with pastes, is not that they are pastes, but that we hone in the other direction.

When you hone into the edge, the main thing that happens, is that steel is abraded away. This exposes hard steel, that has always been there since the creation of the razor. The hardness of the edge is equal to the original hardness of the steel.

When you hone away from the edge, apart from the abrasive action, there's also plastic deformation at work near the very edge. This affects the sturdiness of the steel.

To a certain extent this is good, as long as the affected part of the cutting edge does not grow too large. It is the main reason for stropping on leather.
It all comes down to the amount of work done with an away from edge action.

These principles are well know in the industrial world. They are in search of (post-finishing) heat treatment methods to improve wear resistance of important machine parts, such as rolling bearings and cogwheels.
Here's a quote of a paper that sheds some light on the topic.
"In today’s production of engineering components, after the soft forming and heat
treating processes hard surface finishing, e.g. by grinding, honing (i.e. fine grinding),
polishing, or lapping, represents the last manufacturing step. Besides final dimensional
shaping by the mechanical removal of material, its obvious main goal is the
fabrication of functional areas with appropriately low roughness for good wear resistance
in operation. Compressive macro-residual stresses, which can also be formed this
way near the surface, impede particularly the propagation of cracks. During grinding
of hardened steel, a narrow edge zone of maximum 10 μm in thickness experiences
severe plastic deformation."
http://www.ariel.ac.il/management/re...2/2-066_po.pdf

Imho, stropping on pastes is a good thing to push the edge just a tad further, or to put it differently, to give the development of a good fin a head start. But if a not so keen edge needs to be heavily stropped on pastes, this will introduce severe durability problems. I have experienced this first hand, during the period I relied on 30 laps CrO to achieve good sharpness.

I think more in terms of 5 light laps now, but I have yet to try it.

Bart.

Originally Posted by Bart

Not entirely. The big issue with pastes, is not that they are pastes, but that we hone in the other direction.

Imho, stropping on pastes is a good thing to push the edge just a tad further, or to put it differently, to give the development of a good fin a head start. But if a not so keen edge needs to be heavily stropped on pastes, this will introduce severe durability problems. I have experienced this first hand, during the period I relied on 30 laps CrO to achieve good sharpness.

I think more in terms of 5 light laps now, but I have yet to try it.

Bart.

I see your point & agree, especially on overuse of CrO. So have you found the same issues when using a progression of pastes ? I'm wondering if the coarser pastes contribute as much to plastic deformation.

Originally Posted by onimaru55

I see your point & agree, especially on overuse of CrO. So have you found the same issues when using a progression of pastes ? I'm wondering if the coarser pastes contribute as much to plastic deformation.

I don't know. I only had these issues with CrO and with red Dovo paste (2-4 micron). I never progressed between the two. I never gave it much thought, since I started getting better results off the hones, without the longevity issues. It was not until I recently reread professor Verhoeven's sharpening experiments that the differences between honing into the edge and away from the edge caught my attention. I have been reading a bit more about it, and found a plausible theory for the durability problems of my once heavily pasted edges.
I'm sure it all depends on which particles, how much pressure, how many laps, how coarse the whiskers, how demanding on the edge one's thechnique is. But I am pretty convinced that under the right conditions, pastes can introduce a significant decrease of edge durability.
If someone uses them, and he has no problems, who cares?
But if someone relies seriously on pastes and he has longevity issues, then, for me, the pastes are the first (but not the only) suspect.

Bart.

Thanx for the info Bart.
I guess like most things the trick is knowing how much is enough.

Bart you mentioned plasticD, but it sounded too stropping specific. Don't it happen both push and pull?

I haven't really followed up near enough: I've been doing some backstrokes over dried slurry paste; a "pasted" N.Asagi for stropping... I have a fear of backhoning too much from Verhoeven's semi-negative view of it.// It was debris eddying back on the edge that concerned him wasn't it? While the momentum of push stroke directs swarf away from the edge. ??

Originally Posted by kevint

Bart you mentioned plasticD, but it sounded too stropping specific. Don't it happen both push and pull?

Yes, it happens at either direction, but the in the push direction the plastic movement is away form the edge, while in the pull direction, the bur (fin) that forms the last bit of the edge actually grows.

Originally Posted by kevint

I haven't really followed up near enough: I've been doing some backstrokes over dried slurry paste; a "pasted" N.Asagi for stropping... I have a fear of backhoning too much from Verhoeven's semi-negative view of it.// It was debris eddying back on the edge that concerned him wasn't it? While the momentum of push stroke directs swarf away from the edge. ??

The other contributing component to bur growth. The same principles apply.

In the end, I believe it all comes down to the notion that the very last bit of the edge is formed by exposed hard steel and also by piled up honing debris and dislocated steel. ("in the small
influenced rim region due to the induced microscopic gliding processes", if I may quote my source in the other post again) The ratio between those three influences the longevity of the edge.

Much simpler put, edges honed in the pull direction have a larger portion of bur-like material at their very tip. That part lacks sturdiness, and that's why we have to realign it on the strop before each shave. But the strop can only successfully maintain a small fin. (to avoid confusion with folded-over burs from knife sharpening, I like to use the term "fin", but basicly both are the same). If the fin-part of the edge is too large, it will crumble away beyond repair, within a few shaves.

That's why I believe pastes must be used with moderation.

Bart.

Hmm. I need to think about that. I need a new thread