V - Sharpening Convex Edges

[HeavyHanded]

Are you still comparing two blades with equal near-apex angles? (as in your drawing below)
The way I see it, the V-bevel has a larger contact area with the strop than the convex bevel at the terminal sharpening angle. So, in fact, the pressure is higher on the strop for the same downward force on a convex bevel than for a V-bevel.

Here's the principle behind convex and stropping - is the same as if you angle the shoulder back into the leather on a V bevel though it still work more reliably working against a curve, you don't elevate the spine to just hit the apex. The ellipse shows where the pressure spikes. Used with a black/white compound in combination as many convex mfgs recommend, it concentrates stock removal at the hump, where it needs to stay thinned out for overall geometry to remain constant. Over time it will still be necessary to thin this out, but the strop will maintain it for a long time without appreciable rounding at the apex.

 

[HeavyHanded]

Great videos :thumbup:
Have you taken basic physics? You do understand the concept of mechanical advantage, yes? Note where the concavity flairs out on those splitting axes. Is it within the first inch? NO, categorically NO, it is WELL BACK from the edge. WHY?? Because the goal is to maximize penetration first through increased mechanical advantage from the thinner edge (lower bevel angle) that does NOT significantly reduce the tools inertia, and THEN, only after the grain is separating and the blade is sunk deep enough to eliminate the likelihood of a bounce-out, then BLAST the round apart through that quick increase in thickness.

If you put the thick wedge up front, you have a significant loss of mechanical advantage, like using a slug instead of a slimmer bullet, that results in all that inertia being lost almost immediately to impact, to crushing the material instead of splitting through it as intended, there is increased risk of a "glancing blow" as well as binding due to the increased resistance of the wood against such a lack of mechanical advantage in the blade - the thicker the wedge, the greater the resistance to splitting. The ideal geometry is to get 2-3 inches of steel embedded into the round before flaring it apart in order to beat the strength of the round trying to keep the gap closed.

The only reason for a convex edge up front is to provide more strength (thickness) against the edge being bent/deflected inside the round and resulting in failure of the blade.




The concavity increases clearance on each side of the head. Weight-reduction is the bi-product. You want the weight to increase the force of the swing, to aid the inertia. You want the thin edge (and I DO see flat sides with rounded shoulders) to maximize penetration (mechanical advantage) with just sufficient thickness to prevent edge-flex and failure, and you want concave cheeks to prevent the wood on either side from from slowing you down - clearance to prevent binding and also glancing of the blade off the side. When felling, at least the trees that I'm familiar with, the trunk is usually thicker than the height of the entire blade.

Finally, regarding flat-sided splitting mauls, you've seen how those work, haven't you? It isn't a one-man job, the maul has a polished poll for a reason - it takes a second main SLAMMING that poll with a sledge hammer to push that wedge through the round - the inertia comes from the second man with the hammer, the first man with the maul just gets the thing to sit just inside the face of the round.

EDIT to add: try as I might, i couldn't find a video of the two-man splitting teams. As a scout, the Amish trained us to split large oak rounds this way. The mauls are just wedges on top of a long stick. The stick makes it easier and safer for one person (usually the younger/weaker) to hold the wedge in place while the other strikes it with the sledge, then pick up the wedge and place it on the next log without even having to bend over. The maul was reserved for large rounds and two-person teams. If rounds were smaller (<14" diameter) or only one person was present, an axe was used instead. Lifting that maul for a swing was a mad chore, not recommended for splitting... But I do see a lot of youtube videos of folks doing that way, so perhaps I'm wrong, though it seems odd given the design of the handle (straight and round) and the massive weight behind such obtuse geometry that presents a very deliberate pounding surface on the back end... Maybe folk forgot what it was for? *shrug*



I live in the woods in WI, I heat with oak that i cut and split myself, I HAVE tried various profile strategies, I also understand the physics behind which work better than others for different scenarios. What you describe in the second sentence is, again, cutting a "relief bevel". You can do it convex and leave more meat at the shoulder, you can do it flat and leave less, or you can do it concave and really thin out behind that edge, but YES it increases mechanical advantage = cutting depth and efficiency. Just keep in mind that there is such a thing as "too thin", and the best way to avoid that is by going convex :thumbup:

Have lived in Upstate NY nearly my entire life, in houses heated to some extent or almost entirely with firewood , including the 3 story farmhouse I grew up in. I don't believe you have any advantage re geographic location or in application of the concepts we're discussing.

I stick by my assessment of the felling axes, the pics are what they are, and application is what it is. Felling axes do not penetrate to the depth of the cheek under normal use except on the chip-throwing side....Hmmm the chip-throwing side always has a concave face exerting pressure on it past the first two inches or so.

Flat sided single wedges are used all the time solo, who wants hold onto one while a partner takes a swing?!! Just use a smaller sledge to start it or just choke up on the longer sledge and start it in with a few taps. Is nice to have two of these. While its nice to have company, most splitting and stacking is done solo in my experience.

I've used regular wedges, wooden wedges cut off of smaller rounds, flat sided mauls, mauls that had spring loaded lugs on the side that work just like the Fiskars concave wedge, starts shallow and increases with penetration.

Again, we look at same pic and see different things. The Fiskars mauls transition directly to a concave shape right behind the V bevel. Yes it starts out shallow but is a concave arc anyway. The idea is to begin the split while the head has inertia. The flare increases as it goes - the mfg presumes by the time it buries halfway up most resistance has collapsed and the round will fly apart. At the very least even with a shallow strike it should have split/crushed/ it enough to pull the maul out without a wrestling match. Those mauls are not intended to be a two man job like a flat maul and hammer duo - here's a pretty good review, also showing my point about it not getting stuck, shallow penetration prior to splitting etc. I actually own a similar no-name maul like this one, it seldom needs to be struck with a hammer to get the job done, but then I split my wood when its still green as much as possible. Fine grained hardwoods are no fun to split once they're seasoned.

https://www.youtube.com/watch?v=gpsQFNZB8ZU

 

[HeavyHanded]

Yes . . . I totally agree with that statement.
It also demonstrates why the final edge should NOT be stropped. Leave it the heck alone and just use it off the stone.

I can see where you are going with the round the edge off the apex thing but


Would you be so kind as to correct the drawing ?

And for a specific I can see where the convex is better for carving. Running on the convex carvers can vary their cut depth and have fine control. I understand that wood carvers strop the heck out of their edges and on the rough side of the strop no less.

But
I am thinking more along the lines of push cutting across the grain as if say . . . cutting a pencil cross wise in half.

As far as free handing and Japanese blade culture an interesting bit of information that knife people may not know but every Japanese hand tool Shokunin does without thinking :

• The blades are bimetal. The hard steel is one thin layer on top of a thicker iron backing.
• The Japanese craftsmen use no secondary bevels
• They use no rounding
• They sharpen one wide bevel much like the theory of a Scandi knife.
• The bevel is flat
• They never strop
• The edges are considered to be the best in the world

How do they do it you may ask ?
By feel you can easily tell when you are lifting the iron off the stone. When the iron is down on the stone there is a certain drag. As it comes off the stone there is a slick sensation which instantly makes you want to get that bevel back down flat on the stone.

An interesting side note, and some argue this to be untrue is that the iron from 100 years ago or so has contaminates in it which helps to actually abrade and clean the sharpening stone which the modern more pure iron does not.

Anyway that there is how we get a freehand flat bevel.
As I have said before "It's not the easy way (or fast way) but it's the cowboy way".
Here is Toshio Odate putting his back into a full width bevel just like he was shown by his master. It is a huge bevel but the majority of it is the soft iron acting as a jig, as it were, for guiding the thin hard steel.



This is a page from his book by the way. I use secondary bevels once in a while but don't tell him.



And finally since you mentioned stropping here is one of my non agreeable, or is it disagreeable illustrations. Note it is the best case scenario for stopping, no convex and no small bevel and we still have geometry destroying destruction to that wonderful edge.
Yuck, I can't watch . . .



For a hard strop on the finished side of the leather that is an exaggeration but the majority of woodworkers they use the store bought carver's strop, rough side up, on a plane blade or joinery chisel.
Not good.

As far as knives . . . when I make a ten degree per side angle or a fifteen, you know, for cutting cars in half and stuff. I don't want mister strop coming along and messing with that angle and turning it into, oh I don't know, twenty or thirty degrees per side after a a few misguided sessions on the strop to "touch up the edge" which never really works all that great anyway compared with just sharpening the dang edge with a couple of stones at my desired angle.

PS: those Japanese blades are on the order of 64 hardness . . .how many here can say that about our little girly man pocket knives ?

My issue with your earlier convex drawing is the convex example is notably rounded at he edge and the pics aren't clear enough to show side to material interaction with the V or convex.

No argument when it comes to woodworking with one exception. If the strop surface is hard enough there will be little or no appreciable rounding of the edge - in the order of what one would experience sharpening freehand on a hard stone on the bevel side, and on the flat side no more than what one would get with a muddy 1k-1200 grit JIS. If you bury it on a leather strop, or use it over too long a time, you'll have trouble, but again I don't ever use leather for a strop unless its bare leather for a final few passes. Even then I prefer a linen paper over a hard surface.

For flattening the backs of my irons and chisels I have rectangle of hard rubber cut from an old wheel chock. I can sandwich the iron between the rubber and the stone and get a lot of my hands on the upside instead of just my fingertips or one palm. This lets me really get on it. I haven't tried doing in a low crouch like that but it makes good sense! I am borderline fanatical re the backs of my chisels and irons.

In any event there is a big difference between shaving off thin strips of wood with or across the grain, and chopping into hard or semi hard materials, even if you include squaring off an augered hole. Without the flat contact area, there won't be sufficient steerage on the surface, or leverage to stay flat when slicing across the grain at a shallow angle. You want all the applied force to line up on the edge dead behind the flat. That wouldn't be possible with any other configuration.

Fine woodworking = flat bevels all day long. However, it likely doesn't matter much if the up side has some curvature as long as the contact bevel is super flat. Chip breakers are normally arced where they meet the iron - sometimes very pronounced.


Here is an image of a traditional Japanese felling axe - they DO know a thing or two...