movement for the belly

awestib

awestib

Joined
Dec 29, 2008
Messages
1,647
Hi guys,
I have noticed some problems with what I think is the more complicated part of a knife, the belly. If you guys use a stone to sharpen, how do you follow the belly towards the tip? Do you turn the handle to have the edge always perpendicular to the stone or are you lifting up the handle to archive virtually the same? The latter would be what we are supposed to do on the sharpmaker, is it not? On the sharpmaker you either turn the tip downwards as you come close to the belly or you move the knife handle sideways, right? That would also be similiar to a belt sander. You would have to decide whether you stay perpendicular or whether you pull the handle towards you when you are at the belly. What do you guys do? If I mark the edge with a marker, I can clearly tell that something changes towards the tip. either I am over, or, more commonly, behind the edge.
Suggestions?
 
Around 16min I explain my method.
[video=youtube;bYyUDeqjgx8]http://www.youtube.com/watch?v=bYyUDeqjgx8&nomobile=1[/video]
 
the movement that allow to get to the tip without chaging the angle is lifting the handle, or pulling it toward you if you sharpen on a vertical surface. that and nothing else

the movement that keeps the cutting edge portion perpendicular to the stroke only serves as scratch pattern alignment. no harm, not much good ... it depend on your finishing grit, keeping things aligned can helps sometimes.

what you should never while lifting is rotating the knife on the tip/butt axis. this changes the angle.
 
pwet said:
what you should never while lifting is rotating the knife on the tip/butt axis. this changes the angle.
Click to expand...

For me personally it's easier to do exactly that, lifting the handle and rotataing the blade so the edge movement is perpendicular against the stone. Easker to visualize the angle being the same, only flows to different part along the edge.

I guess YMMV :)
 
cbwx34 said:
I haven't been on the forum in a while, so this may be old news... but your videos are great. Very informative. :thumbup:

cbw
Click to expand...

Cbw, good to see you back around and thank you.
 
Chris "Anagarika";10932899 said:
For me personally it's easier to do exactly that, lifting the handle and rotataing the blade so the edge movement is perpendicular against the stone. Easker to visualize the angle being the same, only flows to different part along the edge.

I guess YMMV :)
Click to expand...

not talking about that. keeping the edge perpendicular to the stone is good. i was talking about accidentaly changing the angle in the process wich is quite easy to do if not carefull or not trained. rotation along the tip-butt axis isn't keeping the edge perpendicular, it just changes the angle you're sharpening at.
 
Knifenut1013, you don't seem to "check" your angle at all while you are sharpening. So do you go by feel totally? Would you do the same motion with a much bigger knife, let's say a 7-8 inch blade of a camp knife or so?
Thanks, Andy
 
Yes, mostly by feel. I visually inspect every time I wipe down the blade too.

The basics always stay the same though the style can change. I have a video sharpening a BK9 too you could watch for tips and techniques on a larger blade.
 
pwet said:
the movement that allow to get to the tip without chaging the angle is lifting the handle, or pulling it toward you if you sharpen on a vertical surface. that and nothing else

the movement that keeps the cutting edge portion perpendicular to the stroke only serves as scratch pattern alignment. no harm, not much good ... it depend on your finishing grit, keeping things aligned can helps sometimes.

what you should never while lifting is rotating the knife on the tip/butt axis. this changes the angle.
Click to expand...


Trying to verbalize this aspect gives me a bit of a headache.
Not sure exactly what Pwet means by
what you should never while lifting is rotating the knife on the tip/butt axis. this changes the angle.
Click to expand...
Generally I run all my grind path at about 45 degrees to the cutting edge, so they sweep down into the drawing path (see some of my pics for an example). Toward the tip this angle might be closer to 60 degrees, especially on blades with a lot of belly I wind up changing the orientation of the tool overall to the stone while elevating and lowering the handle.
Recently I did a Panga pattern machete
yhst-29358752693524_2214_5924736

That required a great deal of manipulation to keep the scratch pattern in any semblance of orientation to the cutting edge. If I just kept the blade at a 45 or so all along, the grind path would have become an edge trailing stroke at the tip when moving forward and vice versa. Wound up raising and lowering while rotating around the radius of the cutting edge. Bevels turned out sweet too, it can shave along the entire cutting edge right to the tip. That would have made for an interesting video, I was boogying all around that stone, could have finished by pushcutting newspaper across the grain with the very tip for the fade to credits... :)
 
HeavyHanded said:
Trying to verbalize this aspect gives me a bit of a headache.
Click to expand...


don't tell me imagine trying to explain this in french ... :p

i just can't explain the simple movement you do to change the angle when sharpening.that's what i desperately try to explain in the second quote ... i just try to state the obvious saying that it's easy to change the angle when you're in the same time lifting the handle to get to the belly, changing the orientation of the blade to keep the grind pattern at the right angle, and moving the knife on the stone ...


not sure if it's clear now ... always hard to explain all this, we should work on a precise terminology for all this.
 
here's an easy way to visualize it: incline your stone to 10 degrees (upward away from you.) "attack" the stone with your knife blade perfectly flat (one's hand and eye can easily do that.) now, as you move the blade forward, simply move the blade to one side so as to "slash" the stone with the entire edge, while keeping the blade flat.
 
pwet said:
don't tell me imagine trying to explain this in french ... :p

i just can't explain the simple movement you do to change the angle when sharpening.that's what i desperately try to explain in the second quote ... i just try to state the obvious saying that it's easy to change the angle when you're in the same time lifting the handle to get to the belly, changing the orientation of the blade to keep the grind pattern at the right angle, and moving the knife on the stone ...


not sure if it's clear now ... always hard to explain all this, we should work on a precise terminology for all this.
Click to expand...

I took out that Panga and went through a dry-run on my bench. I wasn't raising and lowering the incline so much as twisting it back and forth while moving along the radius. If that explains anything...
 
Pwet,

Thanks. Got what you mean, rotating the blade along tip-butt axis (wrist rotation, like throttling motorbike gas) will change the anglenofbthe edge. What I did was rotating the axis itself against imaginary center of belly curvature to keep edge perpendicular to the stone movement.

This is tough without diagram or video ;)
 
Chris "Anagarika";10936564 said:
Pwet,

Thanks. Got what you mean, rotating the blade along tip-butt axis (wrist rotation, like throttling motorbike gas) will change the anglenofbthe edge. What I did was rotating the axis itself against imaginary center of belly curvature to keep edge perpendicular to the stone movement.

This is tough without diagram or video ;)
Click to expand...

I was actually doing both of these movements to finish the Panga. The key is to "throttle" at the same time you rotate it around the axis of the belly. Take a dinner plate or saucer and press the outer curve against a counter so it tilts up a bit, simulating an edge bevel. Imagine a handle extending from the plate. Moving it along the counter as on a stone, try whatever variation of pitch and rotation you wish needed to keep the rim of the plate in good contact with the counter. With a knife that has less belly (use a bigger plate and only try to keep good contact along a 1 or 2 inch stretch of rim), a lot less pitch/rotation is needed, in reality just a slight change of pitch will do it. As the belly becomes more pronounced more pitch is needed, and in the case of the Panga going thru 90 degrees of curvature, a bit of rotation becomes almost mandatory. Even with a fair amount of manipulation the scratch pattern at the very tip is still quite steep to the edge - probably 60-70 degrees as I couldn't rotate the edge enough without stopping to move the stone, something I was unwilling to do so frequently.
 
HeavyHanded nails it with the knife he shows. If you only lifted up the handle to keep the belly in contact with the stone towards the tip, the last portion of the knife he shows would have a longitudinal scratch and in fact the very tip area an edge trailing patter. I just imagine the edge of a CD that you have to sharpen all around. This CD you would hold in an angle to the stone and only a very narrow portion of the edge would touch the abrasive. Now in order to sharpen that CD, don't you have to turn it "like a stearing wheel" while keeping the same angle relative to the stone. Is that not the same with the belly of a knife, just exaggerated?

Sorry guys, should have read the whole thing. HeavyHanded already used a similar explanation, so forget about my post!
 
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