Scratch pattern angles

[Gary W. Graley]

Well, at least that's what I've had rattling around in my brain lately.

Ever notice the edges on those brand new knives you get, I mean the ones that are quite keen right out of the box? you can usually see the grind marks down onto the edge bevel itself. That got me to thinking most everyone I've known or seen will make a sweeping motion across the sharpening stones, which will make a sweeping scratch pattern onto your edge bevel, makes sense right? So those fine tooth sharp edges are no longer perpendicular to the edge of the knife, but are now at odds/angles which at first probably will cut ok and you can sharpen a knife fine the way it's always been taught/done, but I wondered what if I kept the blade's edge bevel more straight on when I go to sharpen on the stone, that should make those fine scratches more perpendicular to the edge bevel and make it a more aggressive cutting edge in the process.

So, I did that, well on a test knife for now, a thin one too, my Opinel Slim #10 and it certainly feels toothier, and when I stropped the blade, I also maintained that straight on type motion, I didn't sweep it in an arc across the strop, but kept it in a straight forward motion, forward and backwards.

Just thought I'd toss that out, most likely this has been rehashed previously, but I didn't find anything exactly as what I had been thinking.

Now in order to do this, it is very important that your stones are flat, no high/low spots, otherwise of course you'll be missing parts of your blade. Since I am using Shapton stones mounted on an edgepro metal backing, they are only 1" wide so that's pretty easy to maintain and also to see if the blade is not making contact fully. I hold the stone in my left hand, pinched between my thumb and ring finger while I sharpen the knife by holding the knife in my right hand, this way I have a sense of where the stone and the blade are meeting and for me at least, I get better control, but, that really is just me, but I do find this the an easy way to sharpen, small to very large blades. This also helps if you are out in the field without any 'good' stones and have to use a smooth stone you pick up in the stream, you would be use to holding the stone in one hand while you sharpened.

Keep them keen guys and gals,
G2

Edited to change the title and also for those checking this thread, see the link in Bucketstove's thread, GOOD info within that thread from last year about scratch patterns...

 

[bucketstove]

Hi, see 1259287-Scratch-pattern-when-sharpening
and consider this image,
when you're slicing toward yourself,
which scratch pattern will have more slicing aggression,
which one will bite first?

Saws have similar idea, some are pull stroke saws (teeth angled toward handle), some are push stroke saws (teeth angled away from handle), some work equally well on both push and pull stroke (teeth straight down, not angled).

 

[Gary W. Graley]

Thanks and yep those are similar to what I was thinking/trying to say, for the very small teeth on the blade, the perpendicular would care not so much as to which direction you tried to cut, it should be quite aggressive, where the other two might cut better depending on the motion you use.

With the knife I just sharpened, it sliced through some canvas more readily than another knife that was also razor sharp, while they both cut the material, the one did make the cut quicker than the other, that toothiness but still razor sharp as well.

As with most any sharpening conversations, there are a LOT of ideas and strong feelings as to what works best. So is what my post said was right or wrong, I'm not saying that either way, but wanted to give it a go and will try this some more before I decide it's the way I will continue or not.

G2


Edited to add, Thanks! for the link to that thread too, will give that a read through but at first glance it looks pretty interesting!

 

[eKretz]

Now for another wrench in the works! What if you sharpened one side of the bevel with the scratches pointing toward the tip and the other side with the scratches toward the heel! Best of both worlds?

 

[bucketstove]

As with most any sharpening conversations, there are a LOT of ideas and strong feelings as to what works best. So is what my post said was right or wrong, I'm not saying that either way, but wanted to give it a go and will try this some more before I decide it's the way I will continue or not.

yup, thats life, try stuff, see if you can make it work for you,

yup, thats life science, try stuff, see if you can make it work for you,
try to figure out why you can/cannot by ruling stuff out, seek advice, repeat

 

[bucketstove]

Now for another wrench in the works! What if you sharpened one side of the bevel with the scratches pointing toward the tip and the other side with the scratches toward the heel! Best of both worlds?

Hi,
Is it a monkey wrench?

I have an idea,
based on the idea of crossing the scratches when deburring using double angle edge leading alternating passes,
if you do perfectly even alternating passes,
it makes for shorter teeth,
which might translate to more edge retention on a push cut
and less aggression on a slice , equal for push/pull, like straight non-angled teeth

But if you're not even, if one side gets longer passes or more pressure or ...
then you get teeth angled that way, but only half as many,
so slicing aggression is half of what it could be

making smaller saw teeth in green

 

[HeavyHanded]

Thanks and yep those are similar to what I was thinking/trying to say, for the very small teeth on the blade, the perpendicular would care not so much as to which direction you tried to cut, it should be quite aggressive, where the other two might cut better depending on the motion you use.

With the knife I just sharpened, it sliced through some canvas more readily than another knife that was also razor sharp, while they both cut the material, the one did make the cut quicker than the other, that toothiness but still razor sharp as well.

As with most any sharpening conversations, there are a LOT of ideas and strong feelings as to what works best. So is what my post said was right or wrong, I'm not saying that either way, but wanted to give it a go and will try this some more before I decide it's the way I will continue or not.

G2


Edited to add, Thanks! for the link to that thread too, will give that a read through but at first glance it looks pretty interesting!

You're on it pretty good in my experience. If you run the grind angle dead perpendicular you get a balanced cut on a draw in either direction. If you sweep it one way or the other it will be more aggressive in one direction and not so much in the other. I sweep mine back at a 45° into my draw so I get max aggression on a pull, and when doing pressure cuts I push forward and down into the object. Ultimately I don't believe it makes a huge difference as you get into more refined edges, is most notable at fairly coarse levels. In practice I find I don't normally run the edge with a shearing action in a forward direction, so no real advantage to balancing the scratch pattern just for effect.

In reality, I sweep mine as much for freehand control as for any cut advantage, I get less wooble in my mechanics when I run the edge at a 45.

I've also found grind patterns such as crossing 45s from one side to the other result in a fairly neutral cut, and a circular pattern winds up being random neutral - depending it will exhibit all manner of micro efficiency characteristics as you execute a cut - no advantage either way and no real disadvantage.

I talk about why a 45 at about 4 1/2 minutes in:

[video=youtube;SuGwd9YZ8_g]https://www.youtube.com/watch?v=SuGwd9YZ8_g[/video]

 

[Chris "Anagarika"]

I found that the normal 45° heel to tip sweep, ending at EEF & UF, a draw/pull slice bites but tears toilet paper. A push (sawing forward) slices the paper nicely. Sometimes having less aggressiveness works better .

 

[Obsessed with Edges]

I tinker with the rake angles constantly, in attempting to form a clear opinion about it's effects on cutting. Only time I've consistently noticed a big difference, is when I've tried a completely parallel (to the length of the edge) stroke; there's an obvious loss of 'bite' in doing so with the grind lines running parallel to the edge (one of many reasons why I don't like pull-through sharpeners, which do exactly this). Otherwise, the bigger differences I've seen have always come about by further thinning and/or refining the edge geometry, and less about the rake angle itself. Any differences created by the rake angles seem to be less of a factor, once I've gotten the edge geometry where I want it. This is the same effect I've seen in comparing edge finishes, i.e., very coarse vs. very polished; if the edge geometry is optimized past a certain point, the edge finish becomes less of a factor. I'm sure there are smaller, subtler differences due to the rake angle of the grind; but I haven't viewed it as a major factor thus far.

BTW, most of my sharpening is done in a manner similar to what Chris has described, being something approximating a heel-to-tip diagonal sweep of the blade down & across the stone. In looking at my edges under magnification, the grind lines are usually around a ~30°-45° angle (should be biased for a pull/draw cut), relative to the edge. BTW, I've also noticed the same forward & down cutting efficiency he described, in starting a cut in the edge of a piece of paper, which is interesting to me. I suspect, in my case, part of that may be due to the down & forward initiation of the cut being started nearer to the belly portion of the blade, as opposed to starting a draw/slice cut nearer to the heel. For me, the belly portion of the edge has always gotten sharper, and sooner, and perhaps at more acute geometry, than the rest of the edge; so, it always seems to have the most wicked 'bite' in slicing. I know it's the portion of the edge that's most consistently made me bleed, when trying a 'three finger sticky' test of the edge.


David

 

[Gary W. Graley]

good ideas guys, appreciate your input! always looking for different things to try out.
G2

 

[Chris "Anagarika"]

David,

Can't remember but probably you're right that I might have started on the belly. Still, interesting observation.

Edit to add:
Tried again. Started with belly with push slice, and reverse to pull slice in the midst of it. I note that it has more drag with pull slice.

However,

It might have to do with the angle of blade against the paper. With tissue paper, the way I did it, the blade is not 100% perpendicular to the slice. If I try perpendicular to the paper, pull slice is smoother.

Note to self: eliminate differentiating factor before putting forward observation.

 

[HeavyHanded]

Chris,

When I tweaked my freehand to lay in the scratch pattern with a leading or trailing sweep I did a bunch of testing on this, just to see if it was a manipulation bias or a true grind path bias.

Sure enough when I reversed the scratch pattern I "lost" some efficiency on the draw, and a forward press became notably more catchy. A slight pull with a press cut with less grab.

 

[Chris "Anagarika"]

Martin,

No disputing on your findings knowing the way you experiment.
I'll test more and report back, my theory is that if it's more catchy but not immediately slice through, it'll tend to tear tissue paper/toilet paper.
On the other hand, if it immediately slice through, then it will result in smoother cut.

Edit to add:
Test further, I did some touch up and strop 1u on my GB. Free hanging tissue paper slice, the pull is cleaner. My rake should result in this, more agressive bite for pull. WIth 1u edge, it seems to 'immediately' slice through.