Recommendation? Flat Grind Confusion

C

Cushing H.

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so far I have been doing pretty long kitchen knives with relatively low curvature edges and full flat grind bevels - so this question has not really arisen for me yet. I am about to start grinding a much shorter length skinner for a friend where the geometry of the thing has me thinking about this - and a review of online videos makes me think I have the answer - BUT the videos are not exactly clear....

Here is the question: Walter Sorrells is pretty clear that when doing a Scandi grind, you set your angle, then rotate the blade so that the belt is always running perpendicular to the edge as you move down the edge and around the curvature of the blade. Ok, clear... and this is pretty much what I have been doing - but I think is wrong for a true full flat grind (but with my low curve edges it has not stood out as a problem.

On the other hand - for a true full flat (and saber) grind, Sorrells and others (Ekim for example) say "set the angle, then pull horizontally across the belt". Visually, they do not appear to rotate the blade as for a Scandi grind .... but the geometry of the edge against the belt gets really weird (especially for a highly curved edge) if you just continue to pull the blade across the belt without changing the orientation of the blade relative to the belt.

What makes sense to me, and what I **think** I see Sorrels and Ekim doing (but they do not SAY it) is that as they pull the blade across the belt, as they come to the curved part of the blade, they keep the current "bevel" angle constant, BUT they pull the handle "towards" themselves so that contact between the edge of the blade and the belt is kept constant.

Is this correct? this makes sense to me when you are freehanding .... but how on earth would you make this work when using a jig????
 
I think it mainly has to do with where your point is.

If the point is near the spine, then rotate blade as you do the bevel.
07.jpg


Otherwise, just keep it simple and dont rotate.
IMG_6518_1024x1024.jpg
 
For your example on the top (poi t near spine) how do you rotate the blade? Like a clock wheel versus the belt, or by pulling the handle towards you as you come up to that point ?
 
I think the answer to your question is a little bit of both pulling the tang away and following the curve, at least until you are down to your final passes with your structured abrasive belts. When I swap to those I have a consistent flat surface established, and the Norax belts just finish it off for moving to the scotchbrite.
C820A7AB-9A0C-449A-A552-9B8E9C5977CD.jpeg
 
What do people who use a jig that sits on the work rest do? Natlek - i am thinking of you! :-)

im wondering why this is not discussed more explicitly in posted videos...?
 
Was wondering the same when trying free hand grinding last week, but since I am going for a full flat grind it seemed to lose importance if I follow the curve too exactly. I stopped doing it when I realized I am taking too much material at the tip and switched to what you described as pulling the handle to yourself. At the start of the grind it made sense to knock of the edges and have a initial bevel to easy in the grind. Still a newbie though but it worked for me.

Here is my first try pre HT, I think the pics show what I mean.
Awulvrn.jpg

S5w6JZt.jpg
 
Yes, as you described when guys are grinding bevels without rotating the blade (along the profile of the blade, as if the handle's butt and the blade's tip were two opposing hands rotating on a clock), the handle is pulled toward you to follow the curve of the edge. You'll find if you don't pull the handle slightly towards you, then the belly and tip portion on the edge/blade won't make contact with the platen.

It honestly seems to be personal preference when it comes to things like flat saber grinds.

Btw, I do remember Walter mentioning that he does pull the handle toward him in one of his videos, I'll see if I can't find which one.

~Paul
My Youtube Channel
... (Some older vids of some of the older knives I made)
 
coldsteelburns said:
Btw, I do remember Walter mentioning that he does pull the handle toward him in one of his videos, I'll see if I can't find which one.

~Paul
My Youtube Channel
... (Some older vids of some of the older knives I made)
Click to expand...
Please do! Ive watched a lot of his videos (i like his sense of humor!), but dont remember him actually saying that - though it seems visually that is what he is doing. I dont know, maybe it is just me, but that seems such a fundamental technique thing, i am surprised more people dont talk explicitly about it.... ??? Maybe it is such an unconscious thing they dont really realize they are doing it?
 
You just have to be careful not to pull the handle too far out and thus grind off the tip. As Walter noted, the main difference is in the scratch pattern left by the belt. I think on certain grinds, the scratch pattern can look much more attractive when the blade is rotated, such as on smaller blades like folders, but I've yet to get used to grinding that way. I think it's best to learn both techniques so that you can pretty much grind anything that comes at ya.

It is a bit difference on hollow grinds, where the geometry of the blade actually changes whether you rotate the blade of pull the handle towards yourself, because the curve of the wheel changes depending on it's relation to the blade. Guys who grind an "ura" (a large, yet shallow hollow) on the backside of chisel ground kitchen knives for example, are able to increase the radius of the hollow grind using the same contact wheel merely by pulling the blades across it at an angle, like if the tip is further to the ground and the tang is higher in the air, like a 45 degree angle to the floor. Hope that makes sense.

~Paul
My YoutubeChannel
... (Some older vids of some of the older knives I made)
 
A full flat grind on a kitchen knife makes it almost unusable on some foods with striction.
All food sticks to the blade,some like wet potatoes stick like s#£t to a blanket
With a convexed blade food falls away from the blade,nothing sticks
 
Cushing H. said:
What do people who use a jig that sits on the work rest do? Natlek - i am thinking of you! :)

im wondering why this is not discussed more explicitly in posted videos...?
Click to expand...
First we must clear what is FULL FLAT GRIND ....I see here many FFG knives which it think they are not FFG .Grinding bevels flat right to spine don t make FFG knife .
FFG is true FLAT BEVEL from plunge to tip ......at least that s how I understand that and how I grind them ..........
When you put something flat on one side of blade should make contact on all length ....
BROBNC4.png
 
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Good luck with your internet natlek! (Try rebooting your computer to clear cache?)

so ... would you maintain that a true full flat grind has the spine the same thickness along its entire length? Otherwise the geometry of what i think you are claiming just does not work, unless you have an edge that is straight from tip to plunge ... which is not the case...
 
coldsteelburns said:
Here's at least one where he discusses what's going on. Skip to about 2:47 to see.
I made)
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Ok ... saw it - thank you. I think he is a little inconsistent though - at one point he says pull the handle, and at another (doing essentially the same thing, he says rotate the blade). I guess in the end it just depends on what you are comfortable with (or what scratch pattern you want)?
 
Natlek said:
First we must clear what is FULL FLAT GRIND ....I see here many FFG knives which it think they are not FFG .Grinding bevels flat right to spine don t make FFG knife .
FFG is true FLAT BEVEL from plunge to tip ......at least that s how I understand that and how I grind them ..........
When you put something flat on one side of blade should make contact on all length ....
BROBNC4.png
Click to expand...

This is not a full flat grind by any common standard. Full flat grinds offer the lowest wedge angle from edge to spine.
 
John mc c said:
A full flat grind on a kitchen knife makes it almost unusable on some foods with striction.
All food sticks to the blade,some like wet potatoes stick like s#£t to a blanket
With a convexed blade food falls away from the blade,nothing sticks
Click to expand...
Yeah ... but on other softer foods a good sharp FFG makes a world of difference. A non-mirror finish helps. But on the other hand, this is why we have multiple knives. :-).
 
Cushing H. said:
BUT they pull the handle "towards" themselves so that contact between the edge of the blade and the belt is kept constant.

Is this correct? this makes sense to me when you are freehanding .... but how on earth would you make this work when using a jig????
Click to expand...

IF you pull handle "towards" when you start to grind curved part of blade grinding angle is CHANGING..If angle was set 3 degree for flat part of blade when you pull the handle towards you that angle would be much more then 3 degree ....and you will end up with thick belly and tip of blade .IF you rotate blade so edge LINE is always in same spot/height/ on belt you will end up with more thin belly and tip ....
Grinding with jig DON T make any difference ,why you think that ?
oWxrVnp.png
 
Natlek said:
Grinding with jig DON T make any difference ,why you think that ?
Click to expand...
It is very hard to convey the geometry. If you have a highly curved edge, and if you set a grind angle, then just pull the blade across the belt (without rotating it, without "pulling" it, or without changing the grind angle), then as you transition to the curved part, the "lower" (assuming you are grinding edge up) highly curved part of the blade starts to lose contact with the grinding belt. If you keep pulling, you just end up making contact with the edge of the belt with that lower highly curved part of the blade.....

Natlek said:
IF you pull handle "towards" when you start to grind curved part of blade grinding angle is CHANGING
Click to expand...
Again - the geometry is hard to visualize - I am not sure if what you said just above is true. If you keep the angle the blade is tilted at unchanged, and you consider the point-of-contact between the blade and the belt to be a "pivot" point, then the angle between a vertical line on the blade below that point and the corresponding vertical line on the belt - that angle does not change. It is weird - but take a highly curved blade and just move it across the face of your platen - and you can see that is the result (at least I think so.....)
 
Cushing H. said:
It is very hard to convey the geometry. If you have a highly curved edge, and if you set a grind angle, then just pull the blade across the belt (without rotating it, without "pulling" it, or without changing the grind angle), then as you transition to the curved part, the "lower" (assuming you are grinding edge up) highly curved part of the blade starts to lose contact with the grinding belt. If you keep pulling, you just end up making contact with the edge of the belt with that lower highly curved part of the blade.....


Again - the geometry is hard to visualize - I am not sure if what you said just above is true. If you keep the angle the blade is tilted at unchanged, and you consider the point-of-contact between the blade and the belt to be a "pivot" point, then the angle between a vertical line on the blade below that point and the corresponding vertical line on the belt - that angle does not change. It is weird - but take a highly curved blade and just move it across the face of your platen - and you can see that is the result (at least I think so.....)
Click to expand...
It s not true .What I really mind is that if you DON T pull towards you handle to make contact on curved part of blade with belt , grinding angle must be increased .... if this make sense , it is hard to explain on Macedonian not on English language .I give up :) I can grind whatever kind of grind I want easy ,but not easy to explain how i do that
 
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