Sharpening freehand on a benchstone - formula

Yeah, I think it mainly comes down to lack of understanding of what needs to be achieved. Usually a few minutes worth of instruction solves all major problems.

-Cliff
 
I'm not sure what one of my friends does with his knives. He can put this crazy mirror finish on an edge with a Lansky, and it won't even scrape hairs. I'm going to try to grab one of his knives and look at the edge under magnification. It looks like he's making it to the edge, but he can't be. He's handy with all sorts of tools and can do a little metal fab, I don't know what he's doing wrong. He'll grind away through multiple grits, so he should at least be resetting the angle easily.
 
He could be leaving a large burr. In the worse cases these have little to no cutting ability.

-Cliff
 
Could you guys here see the attached photo of the triangle?
I was just wondering If you could see it, because it's taken from my yahoo mail server.
 
Cliff Stamp said:
DoW said:
All of which leads me to conclude that when sharpening freehand it's much more practical to not worry about accuracy when cutting relief, just make sure it's substantially more acute than you want the final edge.
Click to expand...
Yes, that is what Lee recommends but you should be a little more focused as it is ground to the same actual constraint as the edge (minimal cross section for durability) but in most cases outside of the extreme (heavy tactical) that is often reduced to the lowest you care to grind. I just grind them all basically flat to the blade, even for large chopping knives which get only a few degrees of "roll" as Fikes demonstrates, as the primary grind is usually about 5 and I want the relief grind for the edge to be about 8-10 at maximum.
Click to expand...
Actually the best reason IMO for controlling bevel angles and edge geometry is to make studying of performance more meaningful. My knives seem to be in a state of always being studied anymore :) .... kind of looks like many of yours are too, Cliff, and you've been doing this a lot longer than me.

OT but related to your comments .... having now worked with more knives with fairly acute edges, I'm interested in what kind of secondary bevel you're adding to knives when running the primary/relief at 8-10 degs. I had settled on 12 degs/side as a good compromise some time ago but have come to think even that may be pushing it a bit for many knives that are going to see hard all-around utility use. I add the lightest of microbevels, just visible to the naked eye under bright light. I'm assuming you're adding a more substantial secondary .... or else your skill level using a knife is much higher than mine (or both.) It isn't often that I need the extra durability, but then there are those situations where you need the knife you have available at the moment to still be useful after cutting stuff like steel banding, prying, scraping, opening a locked cabinet or desk drawer, etc.
 
Good info if you can consistently hold a blade exactly .25 inches or whatever (measured in the middle of the spine) off the whetstone.

I can't, so I cheat.

I attached a little alligator clip (the springy thing that holds papers together) to the taped blade spine. You can get a handful of them at any stationary store for $1.00. I rest both the clip and the blade on the stone and sharpen away with my thumb behind the clip to keep it from sliding off. Since the clip is being ground down as well as the blade you have to occasionally replace it with a new one. I know this is redneck engineering but it it easy. It doesn't cost much. And most importantly, it works! It gives you a constant angle. You can use different sized clips for different angles. I haven't ever scratched up a blade using this technique. Just put some tape on the blade so the clip doesn't accidentally scratch it.

I use this technique effectively on x-course DMT 8" stone for profiling.
http://www.dmtsharp.com/general/basicsharp.htm

It's a po' boys Edge Pro!
 
Dog of War said:
Actually the best reason IMO for controlling bevel angles and edge geometry is to make studying of performance more meaningful.
Click to expand...

Yes, unfortunately there is too much focus on steels to the exclusion of geometry but that is simple due to the heavy manufacturer influence. Obviously you can't really sell heavily on geometry because it would raise the obvious arguement, well can't I just buy a $5 knife and resharpen it (or have it reshapened) and have it cut just as well. Pretty much yes, but that won't sell a lot of expensive knives.

I'm interested in what kind of secondary bevel you're adding to knives when running the primary/relief at 8-10 degs.
Click to expand...

That is a chopper so about 12-14 for most work with the bevel about 0.015" or so thick at maximum. I can shave off a degree or two if I limit the work to thick wood, and for really poor woods (dead branches) I'll add another degree or two. That is on the strongest steels, on the weaker ones you have to give them more steel, but about 0.025" and 16-18 works well even on machete class blades for the secondary bevel on the hardest to cut local woods.

For small knives which are more utility tools than actual cutting instruments I will work in the 15-20 degree range for a micro (sub-visible) at times, but I mainly interested in trying to determine cutting techniques that prevent damage so I generally run standard profiles, so 5 primary and 10 secondary and then work on minimizing lateral loading. Direct compressional strength is insanely high in any steel, it is the twisting which damages the edge in static work.

I also have a fairly high tolerance for damage and don't mind having to sharpen my knives on occasion after harder work to remove some visible edge roll/chipping if it gives me a very high level of cutting ability. I am talking about micro-bevel damage, <0.5 mm deep. I have some knives which are basic utility tools, nail cutters and the like, Fulcrum, for example, but that really isn't a knife as much as it is a knife-like object.

-Cliff
 
Thanks once again, Cliff, interesting how this confirms/clarifies some things I've observed. Interesting too how edge optimization for a wide range of uses actually involves only a fairly narrow range of angle.

Hope to see this kind of thing on the website .... and BTW nice choice of domain names.
 
Dog of War said:
Interesting too how edge optimization for a wide range of uses actually involves only a fairly narrow range of angle.
Click to expand...

Yes, when I started looking at this in detail it became obvious that edges went from fairly fragile to near invunerable very quickly. The reason for this is that lateral stiffness is cubic in edge thickness. This means that if an edge angle is increased from say 10 degrees to 12, a 20% increase, there is actually a 60% increase in ability of the edge to resist bending. What is unfortunate is that you only gain in cutting ability at basically a linear dependance and thus you have to give up massive amounts of durability to gain little cutting ability, 60% vs 20% in this case.

Hope to see this kind of thing on the website .... and BTW nice choice of domain names.
Click to expand...

Yeah, I just have to make the work live up to the name. Right now I just dumped the reviews there but they will be pseudo-archived shortly as I personally want to move towards doing more focused work and writing meta-reviews and articles. There is a rough draft of an article on edge stability there in the articles folder which illustrates the kind of articles I have planned.

I want to create a place where people can have articles peer reviewed, which is very critical. I will also be sponsering reviews, providing knives and equipment if necessary. Something similar to the Bladeforums pass around where you log on, check what is available and then request it for a period of time for feedback, up to say about a year (so a full hunting season) and then return the blade and a report.

That review gets added to the existing reviews and then it gets compiled into a meta-review which is written through a forum discussion by the individuals who wrote the review who discuss details such as influence of skill, physical ability and of course personal preferences in a knife. That is the idea anyway. I'll see how it goes. Anyone interested in participating on any level can drop me an email.

-Cliff
 
Sounds like some excellent ideas for the site, Cliff. I recall maybe a couple months ago you mentioned something along these lines in another thread on BFC, setting up a forum specifically for more in-depth work and testing, and I'm convinced it would serve a valuable purpose - in fact it's the Kershaw/13C26 thread active right now on the general discussion board that really convinced me. The only way I can see to resolve those kinds of disagreements and all the ambiguity is systematic testing and measurement, ideally with a number of contributors.

I assume like you've done with reviews posted to your site any potentially interesting topics could be posted and linked to here .... I can see how this could promote discussions that are geared to the interest levels of all. I think some people misinterpret an interest in comparative, quantified results, for me it isn't in any way being uninterested or unappreciative of experienced opinions, I enjoy hearing what people think when they describe their experience in any kind of depth .... it's just that the only way I, or the next guy, can confirm or build on someone elses work and findings is if the work performed is adequately described and the results quantified.

Anyway I think it's a terrific idea.
 
Dog of War said:
The only way I can see to resolve those kinds of disagreements and all the ambiguity is systematic testing and measurement, ideally with a number of contributors.
Click to expand...

That disagreement isn't about facts, they were provided and ignored. The issue of edge stability does need further experimentation though, specifically to address concerns such as at what point of sharpness does a steel like 154CM outperform 13C26. Landes has showed that the high carbide steels will lose a highly polished edge quickly in acute profiles but they will stabilize once the wear has thickened the edge.

The question thus becomes for the various levels of carbide in steels, 440C (very coarse), 154CM (medium), AUS-8A (relatively fine), at what sharpness do those steels over take an ideal edge stability steel like 13C26 (ideal). This is also influenced by angle as the performance gap will close at high sharpness when the angles are obtuse. There is thus a lot of work which can be done.

Such work would allow the answer of questions such as "Which steel is optimal for an edge of 15 degrees per side which will be mainly used with a 600 DMT finish at 25% of optimal sharpness." Immediately you would rule out the steels like 13C26 but what level of carbide will stability with that edge profile at that sharpness. The actual performance gains from picking the right steel are in fact many to one, so we are not talking about small issues of performance.

I assume like you've done with reviews posted to your site any potentially interesting topics could be posted and linked to here .... I can see how this could promote discussions that are geared to the interest levels of all.
Click to expand...

Of course, once ideas are refined you would expected more public discussion. I am speaking mainly of focused peer group.

I think some people misinterpret an interest in comparative, quantified results, for me it isn't in any way being uninterested or unappreciative of experienced opinions, I enjoy hearing what people think when they describe their experience in any kind of depth .... it's just that the only way I, or the next guy, can confirm or build on someone elses work and findings is if the work performed is adequately described and the results quantified.
Click to expand...

Scientific work in many fields consists of user feedback groups which provide subjective data. However once the data is collected, the tendancies noted are by defination no longer subjective as they are now describing the perspective of a group and are thus population representative. This would also be part of the site, though this is a massive undertaking as you have to collect the raw data and keep the references.

-Cliff
 
You must log in or register to reply here.
Back
Top