How many edge touchups before you back bevel again?

[Donut]

It depends on how many nails I cut through. :)

[Cliff Stamp]

When I do 50 passes and I'm not sharp enough, I get exasperated, swap out for a sharper knife in the drawer, and reset the back bevel when I have time.

All that you are seeing is the micro-bevel thicken requiring more metal removal to be easily achieved on a fine stone. All you need to do is simply use the diamond/cbn rods first to do the bulk of the work. It should be possible to keep sharpening on the micro-bevel for much longer than a few times without having to reset the main edge bevel. It also sounds like your stones are possibly fairly loaded.

[razorsharp]

I generally reset the back bevel every dozen or so touch ups. I don't mind the microbevel getting a little big (like 0.4mm wide) when I reset the bevel I destress like evilD describes. I also do that occasionally to the microbevel.

[bearfacedkiller]

These questions puzzle me. My definition of sharp is different than yours and my definition of dull is different than yours. I touch up often and do not let my knives get very dull. Therefore I do not have to remove very much metal to get them sharp again. If I let them get duller then I would have to remove more metal to get them sharp again so I would be getting less touch ups between rebevels. It also depends on the knife, the steel and the use of the knife as well as what the back bevel and microbevel are set at.

If you must have number than I will say two dozen on a light use edc folder and maybe as few as five on a knife I use rough while camping, hunting, backpacking, fishing, gardening or landscaping. Just depends how dull it gets in between touch ups and what is acceptable for you as far as the micro bevel consuming the back bevel. I have just done touch ups until the 40 degree bevel completely consumed the 30 degree back bevel and I have no idea how many that took but it was probably a few dozen. Not my preferred method though.

[Steel_Drake]

All that you are seeing is the micro-bevel thicken requiring more metal removal to be easily achieved on a fine stone. All you need to do is simply use the diamond/cbn rods first to do the bulk of the work. It should be possible to keep sharpening on the micro-bevel for much longer than a few times without having to reset the main edge bevel. It also sounds like your stones are possibly fairly loaded.

Hi Cliff,

For clarification, are you saying that it should be possible to re-sharpen the micro-bevel using a three step (cut-off the existing edge, shape, sharpen) process a few times rather than re-setting the primary bevel and forming a new micro-bevel every time?

It had been my understanding that it was better to shape the edge back to your chosen back bevel angle each time and form a new micro-bevel. What are trade-offs in terms of sharpness for following the three step process on the micro-bevel alone?

[Cliff Stamp]

It had been my understanding that it was better to shape the edge back to your chosen back bevel angle each time and form a new micro-bevel. What are trade-offs in terms of sharpness for following the three step process on the micro-bevel alone?

On the extreme end each time you sharpen, the primary bevel and edge bevel are reset and finished with a micro-bevel. This method ensures that the cutting ability always stays the same. Murray Carter sharpens this way among others, it is very common in Japanese style sharpening. However it makes each sharpening time very long and it makes people who see it view sharpening as a very complicated process, and they often decide to avoid it.

The other method is to minimize the time spend each sharpening by using a micro-bevel. When the micro-bevel thickens to the point that sharpening times are becoming too long then the edge bevel is reset and the pattern repeats. Most people don't use knives enough to ever move beyond this step. However with enough use the edge bevel itself will start to thicken and at that point the primary grind has to be recut which is beyond most people and most systems and thus a common method is to use a transition or relief grind which is simply the lowest setting of whatever jig you are using.

Now as to how many times you have to sharpen the micro-bevel to have it thicken to the point the edge needs to be reset to keep sharpening efficient simply depends on how much the knife is used. A sharpened apex is about 0.5 microns wide, unless the knife is blunted to such an extent that you can see it, this means that the apex is about ~20 microns wide. After about 5 sharpenings the micro-bevel is going to be ~100 microns wide, about 0.1 mm, still very small.

The reason why most people have problems maintaining micro-bevels is because of very inefficient approaches to sharpening because they do things like break sharpening up into honing, maintaining, full sharpening, reprofiling, etc. and they often don't think about what they are doing and just follow some preset path. For example if you try to "hone" using just the fine rods on the Sharpmaker you will notice that after just a few sessions the micro-bevel isn't responding and ~50 passes doesn't make knife very sharp.

This isn't because the micro-bevel has thickened, it is simply because all that weakened metal was left on the edge and after doing that a bunch of time there is a bulk of fatigued metal left on the edge. If this is a high carbide steel it is even worse as there will likely be significant fractures through and around the carbides. This often makes people retreat back to working on the edge itself which is where they use the coarse abrasive and this then "works". Of course the reason why it worked was that the coarse abrasive ground off all the weakened metal and now when the "honing" is done then it is on quality steel again.

If you use an abrasive on the micro-bevel which is actually capable of grinding off the weakened metal then you will find it takes a long time before you would want to grind the micro-bevel off. Now of course in any time where you use the knife and the damage is extensive and extends deeply into, or beyond the micro-bevel then you likely want to cut the edge back off and then micro-bevel just make sure to use sensible abrasive choices to make the process efficient.

[Steel_Drake]

The reason why most people have problems maintaining micro-bevels is because of very inefficient approaches to sharpening because they do things like break sharpening up into honing, maintaining, full sharpening, reprofiling, etc. and they often don't think about what they are doing and just follow some preset path. For example if you try to "hone" using just the fine rods on the Sharpmaker you will notice that after just a few sessions the micro-bevel isn't responding and ~50 passes doesn't make knife very sharp.

This isn't because the micro-bevel has thickened, it is simply because all that weakened metal was left on the edge and after doing that a bunch of time there is a bulk of fatigued metal left on the edge. If this is a high carbide steel it is even worse as there will likely be significant fractures through and around the carbides. This often makes people retreat back to working on the edge itself which is where they use the coarse abrasive and this then "works". Of course the reason why it worked was that the coarse abrasive ground off all the weakened metal and now when the "honing" is done then it is on quality steel again.

If you use an abrasive on the micro-bevel which is actually capable of grinding off the weakened metal then you will find it takes a long time before you would want to grind the micro-bevel off. Now of course in any time where you use the knife and the damage is extensive and extends deeply into, or beyond the micro-bevel then you likely want to cut the edge back off and then micro-bevel just make sure to use sensible abrasive choices to make the process efficient.

Very informative. My first question would be whether you would still recommend cutting off the existing edge with 1-2 90 degree passes into a stone (e.g. a Spyderco medium Sharpmaker rod) as a first step? Secondly, would the Spyderco medium rods be sufficiently aggressive for this, or should the diamonds be used? And finally, approximately how many passes should be made on the coarsest abrasive, given that you recommend 5-10 pps at each stone progression for micro-beveling?

[Laethageal]

I think you just made me understand what I'm doing wrong, in the sense why I almost always find it best to simply retouch the bevel back to the edge before micro'ing every 1 or 2 sharpening. I'll have to try to reset bevel more often to avoid deep damage so I can avoid that long sharpening step.

Thank you Cliff!

By the way, I would really need you to give me sharpening lessons. I could get my knife to shave better then your elmax blade prototype you sent me but I'm doing something wrong with the micro as when I finally get it perfectly sharp it's 20 times or more bigger then yours and not so a micro anymore! Plus I must have spent 30x the time you spent working on the edge.

[bearfacedkiller]

Cliff, your posts are always filled with good information but often it may fly over some peoples heads. Not your fault, we all have a different base of understanding and some can decipher your explanations better than others and some of your explanations are basic and some get really in depth. This last description is excellent and explains the process and theory in a very short clear concise manner. This is exactly what I try to describe but it is not ever nearly as cleanly and clearly executed as this. Thanks so much, I am going to bookmark it for future reference.

[me2]

I use just a slightly smaller back bevel on my knives, with a little increase for the primary bevel. My favorite knife is an old Cold Steel Scalper in Carbon V. It has a 12 degree per side (dps) back bevel with a microbevel from the Sharpmaker's 15 dps slots. I use a 220 grit Norton Coarse water stone to backbevel, then add the microbevel. I tried it with the Sharpmaker and only redoing the back bevel every few times, but the backbevel took so long after a few times that it's easier for me to redo the whole thing every time. Even when using this knife for yard work, it's only taken 5 minutes or so to reset the back bevel.

[Cliff Stamp]

My first question would be whether you would still recommend cutting off the existing edge with 1-2 90 degree passes into a stone (e.g. a Spyderco medium Sharpmaker rod) as a first step?

In general this is usually a good idea, especially for higher carbide steels because you don't want fatigue to set in on those steel. There are other benefits as well so you might want to do this even if the abrasive is so coarse it will likely grind away all damaged material (CBN rods). For example when you use a knife the wear on the edge doesn't tend to be even as you will likely use one part if it more than others, plus different parts of the apex could have more/less carbides and take more/less wear and fracture. A light cut into a stone ensures that you even out the dulling over the blade and keeps the general blade shape and curvature in tact. How much of it you do depends on how much work was done with the knife and if you are taking an approach which is geared towards always getting maximal performance or if you are trying to minimize metal loss.

Remember though, if you grind into the edge just enough to see it, then all that means is that you likely removed about ~10 microns of material from the edge. It takes 100X to do this to remove a mm of material from the width of the knife. In comparison even a mild contact with a staple or a single cut on a plate will do far more to the edge. In general, very general, it is usually a benefit to do even if for no other reason than to allow ease of non-burr based sharpening.

[Cliff Stamp]

... when I finally get it perfectly sharp it's 20 times or more bigger then yours

The knife has a 600 DMT bevel, sharpness is decent on a slice but on a push it was maybe 25% of optimal, or close to that as push cutting sharpness is directly correlated to grit finish, slicing not so much. The simplest way to to get that kind of sharpness is to take the same approach and use a single micro-bevel which is a finishing step. Something similar to :

-Suehiro Chemical to almost apex
-Naniwa Superstone 400 to apex
-Naniwa Aotoshi 2000 to prepare for the micro-bevel

and then micro-bevel on a Spyderco fine ceramic or similar. If you try to actually micro-bevel in stages it will be very difficult unless you are jigging to get them to line up well and you will thus end up with a very faceted bevel. If you use sandpaper it is a little easier because it will conform slightly even if it is on a hard backing as the paper itself will compress. A standard sheet of paper is about 50 microns thick and if you put a bunch of them together and squeeze them you will see how easy they are to compress. Sandpaper backings are usually much thicker again.

[Steel_Drake]

Remember though, if you grind into the edge just enough to see it, then all that means is that you likely removed about ~10 microns of material from the edge. It takes 100X to do this to remove a mm of material from the width of the knife. In comparison even a mild contact with a staple or a single cut on a plate will do far more to the edge. In general, very general, it is usually a benefit to do even if for no other reason than to allow ease of non-burr based sharpening.

Thanks again, Cliff.

I still would like your thoughts on whether the Sharpmaker medium rods would be coarse enough to resharpen the micro-bevel or whether the diamonds would be necessary, as well whether the number of passes per side at each grit would be the same 5-10 you have previously recommended in forming an initial micro-bevel.

[Bolster]

These questions puzzle me. My definition of sharp is different than yours and my definition of dull is different than yours.

Be not puzzled; I am trying to understand averages and ranges, not a particular number. You are saying "There is no answer because there is variability" and I am saying "I understand there is variability, but I'm curious what the central tendency and range is." And this thread delivered on that, so I'm happy. Thanks all.

[bearfacedkiller]

Counting passes is not very effective either because again there are a few variables.

I may be wrong but the 5-10 passes is saying that after you apex at 30 you then go to 40 and just do 5-10 passes per side with each stone to create the initial micro bevel. It will take more passes each time you resharpen the microbevel after that because the micro bevel will be getting wider thus requiring the removal of more metal. It will continue to vary even more each time as the degree to which your knife dulls will be different with each sharpening plus the pressure applied and the cleanliness of your stones will all cause variability in the number of passes neccesary. Also, as the bevel gets bigger, as cliff stated, it becomes harder to maintain the stone perfectly against the flat of the microbevel due to extremely subtle variations in the angle of the blade to the stone and this is basically skill and muscle memory. If you tend to have less consistency in your ability to hold the knife perfectly vertical then some of your passes will just be riding on the shoulder between the micro bevel and back bevel. The recommendation of 5 to 10 passes per side when initially switching from 30 degrees to 40 degrees works because that range covers most steels of various grindability and when making that initial jump it is almost impossible to not put the stones directly on the edge of the apex. Predicting the number of passes after that gets increasingly difficult with each touchup because of all of the variables mentioned as well as the steel being sharpened. When either the number of passes necessary is too many for you or edge retention is suffering then it is time to reset the back bevel and this is subjective. I do not use the diamonds on the microbevel and usually just use the mediums and then the fines depending on the knife and it's steel and/or it's application.

[Cliff Stamp]

[...]

I still would like your thoughts on whether the Sharpmaker medium rods would be coarse enough to resharpen the micro-bevel or whether the diamonds would be necessary ...

It is going to depend on what you cut, in some detail have a look at :

-http://www.cliffstamp.com/knives/forum/ ... p?10,26465
-and a series of videos I did such as : https://youtu.be/72eEBMeWUjw" target="_blank

In the web link I do a number of edge retention trials with various Sharpmaker abrasives and see how the edge retention changes with subsequent runs without cutting the edge off (destressing).

In short, what I found is that the more abrasive and harsh material the more the edge damage build up was a concern and even though the fine abrasives would get the edge sharp, the edge retention would be lower because the edge was forming on that damaged material.

As just a few examples :

-cutting carpet is so harsh that it is almost visually obvious the damage should be removed to ensure a quality apex will form
-cardboard can be so harsh that even the medium rods won't inherently remove the damaged material before they form an apex
-in contrast, cutting hemp and similar clean ropes is so easy that there is almost no edge damage buildup even if you only use fine abrasives

Therefore if you are cutting carpet and cardboard then likely you want to remove damage from the edge before sharpening (assuming you have done much cutting) or always start (and apex) with coarse abrasives. However on natural ropes and foods the edge can often be sharpened with just fine abrasives with no loss in performance and no need to cut off damage as it never significantly builds up.

However as noted before, there are still lot of other reasons to cut the edge back before sharpening. Even if you don't do it every time as you might be only cutting soft materials (hemp) I would still recommend it periodically just to check the edge to ensure even wear. Some people also do it every time because they don't burr sharpen and thus cutting the edge off gives a strong visual reference.

Now some people view it as a negative as it makes sharpening more work. If you start off by doing 1-2 light cuts into the medium rods then it takes more work to sharpen and even forces you to move back to a more coarse abrasive to be efficient. However if you don't do it then it is very like that if you have cut harsh materials then the edge retention will be compromised.

But of course perspective is critical here. Maybe the user is ok with lower edge retention if it keeps the sharpening very simple, just a few passes on the medium vs a few passes on the fine. Not everyone really wants/needs an ultra-sharp knife and for a lot of people just "ok" sharpness/performance is enough.

[Steel_Drake]

For anyone who is curious,

I decided to try distressing and sharpening only the micro-bevel on my Caly 3 SB to see how quickly an edge could be produced that would true push-cut newsprint in both directions.

I followed the following procedure:

1) 2 passes at 90 degrees into a Spyderco medium Sharpmaker rod to distress the edge. Checked using a direct light-source that the edge reflected light along its entire length.

2) 5 passes per side on the Spyderco diamond sharpmaker rods, cleaned blade, checked light reflecting off the edge under a direct light-source, saw a couple of spots.

3) 5 more passes per side as above, no light reflecting off the edge.

4) 5 pps at very light pressure on the medium rods at 15 dps (the angle I use for micro-bevels), 1 pps on the 20 dps setting to deburr (cribbed this idea from one of Cliff's videos)

5) As above with fine, ultra fine, and ultra fine oiled with mineral oil (omitted the deburring step on the oiled ultra fine)

6) 5 pps on a balsa wood strop loaded with chromium oxide paste, very light pressure.

At this point the edge was capable of push cutting newsprint in both directions and whittling hair trivially. Total time taken was less than 10 minutes. I am quite happy with the results, as I prefer to polish my edge bevels and get the smoothest 10 dps edge possible before micro-beveling thus making shaping the edge bevel to a new apex a fairly time consuming process for me.