sharpening direction

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laurens

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Apr 28, 2006
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I have noticed that sharpening in a circular motion doesn't leave the bevel as polished as sharpening in straight lines even if the same grit is used, has anyone else noticed this. Would this leave the knife edge more susceptible to damage. Are there any other downsides to sharpening in a circular motion?
 
Hi Laurens

I'm sure Cliff or some of the other knowledgeable people here will confirm or refute this one. But it was explained to me many many years ago that it's a bad idea because it damages the edge you just produced. Look at it this way, when you do the stroke "edge-first" the metal from the bevel is left behind on the stone after the edge. However, when you reverse the stroke so it is "spine-first", you drag the metal filings that come off the bevel across the edge you are trying to restore. This chips bits off the edge and deforms the edge. So within each complete cycle, you consecutively improve the edge and then damage the edge.

While this made sense to me at the time, I can't quite understand while polishing the edge on a strop spine-first doesn't cause the same damage, but that question is for better minds than mine!

Cheers
 
Though I defer to Cliff's expertise, I find sharpening in a circular fashion actually produces a very sharp, toothy edge that is typical of using the small pocket field stones that are readily available. I wouldn't use this technique on a larger bench stone that I could use the full surface of the full stone to sharpen for a finished edge but on a full size coarse or diamond stone you could remove a lot of steel quickly prior to preparing the finished edge. It's also a quick, easy way for a novice sharpener to rebevel an edge without a guide. My $.02. :D
 
On small stones you can't use long single pass cutting. I prefer short back and forth motions. When you use circular ones you end up with abrasive scratches running parallel to the edge which cause fault lines plus the teeth are all in random alignment. Imagine a saw blade with the teeth pointing in many directions and compare such in use to one with the teeth all set uniformly with the blade. Of course if you take this up to a *really* fine polish it doesn't tend to matter because the surface is then dominated by the grain of the steel and not the abrasive anyway.

-Cliff
 
I think the question is how sharp do you want the blade to be? And what is the blades intended purpose, besides cutting.
First of all use oil when you use a sharpening stone. when using circular motions use this teqnique on a blade that is furnished in a way the permits it to be sharpened this way. Not a chefs knife etc. When the blade travels across the stone its always going to remove metal deplicting the degree of sharpening and at the angle you sharpen the blade.

hope this touches the subject.
 
Thanks for the replies i don't sharpen knives in a circular motion but used to sharpen axes that way,somtimes i still do.Is it okay to sharpen the axe this way I normally sharpen back and forth from the toe to the heel of the axe bit,but i find circular movments slightly faster when the stone is held in you hand.I would be sharpening the axes up to 4000 grit maybe 8000.
 
On axes it is common to go in circles as the stones are small and circular. This is only for the shaping, the finishing honing and usually polishing on loaded leather is linear.

-Cliff
 
Cliff--

Does what you say about the disadvantages of a circular sharpening motion apply to BOTH the relief grind and microbevel, or only the microbevel? I can see how it would apply to the microbevel but I've been using circular motions for the relief grind (per Juranitch). This works well, but I don't want to continue if this is damaging or weakening my knives, especially since some of them are for heavy use such as chopping.

Thanks!
 
Generally not, the only concern would be on large chopping knives where the edge can be stressed above the micro-bevel. On knives which are just used for cutting, even a very tiny microbevel, <0.1 mm wide, is still far wider than the actual extent of the damage so only the shape of the primary matters. However on chopping knives the entire bevel is under stress and if you shape with a really coarse grit you can leave deep scratches which run parallel to the edge and serve as fault lines. However the effect is going to be far less significant than the effect on the micro-bevel due to the massive difference in scratch depth vs actual steel thickness.

-Cliff
 
I hadn't thought it through in near as much detail as Cliff explained but you can see he's right. I've used a circular motion many times, but only on an edge that's really dull or needs a little ding taken out of it. You can grind it down quicker that way. But definitely go back to straight strokes as soon as you have the bevel set and get it all straightened out.


Cliff: what's your opinion on sharpening "backwards"? Spine-first as omniphile described. Many years ago I read a Bill Bagwell article that recommended this, and I've found it works well and fast on most of my knives. However, some steels get too much of a burr this way, and you can spend all day chasing the burr back and forth across the blade...
 
Generally edge trailing tends to be sub-optimal as it is prone to burr formation as you noted. The only reason to use it is generally because if you try edge-into the knife cuts through the media, like leather.

-Cliff
 
I often start with circular motion just because I can grind down faster that way. When the edge has just about reached the point I want, I switch to linear strokes at the same grit until the scratches look more vertical instead of circular/random. From then on out, as I refine the edge with finer grits, I use linear motion. This way, when I'm done all scratches are vertical, but I used circular motion to speed up just the initial edge reprofiling step.

Joe
 
Thanks for the great info!

Since circular sharpening motions are faster I'll use them when I have to remove a lot of metal from the relief grind (which is often since so many fixed-blade knife manufacturers like thick edges), then stay with linear strokes on future relief grinds to avoid causing problems, such as weakening the edge.
 
Joe Talmadge said:
I often start with circular motion just because I can grind down faster that way. When the edge has just about reached the point I want, I switch to linear strokes at the same grit until the scratches look more vertical instead of circular/random. From then on out, as I refine the edge with finer grits, I use linear motion. This way, when I'm done all scratches are vertical, but I used circular motion to speed up just the initial edge reprofiling step.

Joe
Click to expand...


I think joe sums it up perfectly, I think the main point is that a circular motion implies that you are spending a bit of time on one bevel before switching to the other side, which is fine for removing noches or re angling the bevel.

It is my absolute belief and experience that the most important thing is for keep the sharpening angle exact. And you sould use what ever motion you can do that the best

next come alternating the sides and move though to finer grades of stone.
 
I've never noticed any damage on any of my knives and I almost always use the circular motion--I've experimented with the "back and forth" motion but I could never keep the angle exactly the same and I was never taught how to use angle guides--so I just use my small, fine Arkansas stone and do the circles until I've got a good edge. I've gotten it down to an art over the past seven or eight years.
PMZ
PS--I'd have to agree with Cliff and the others--whatever works best for you as far as the edges you're producing, stick with it. I've found that the slicing motion, for me, never produces enough similarity on both sides of the blade, so I just stick with the circles. Although I suppose it wouldn't really matter now that my new CRKT has that chisel-grind......would this factor in?
 
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