Edge Geometry + (What?) = great distal taper?

[Brian Avila]

I hear you tedinatl, speaking from a scientist point of view the R and D and revisions happen and are tough some times.

 

[Rick Marchand]

I'm still not sure that defining strength in relation to knives is as simple as quoting a definition out of a book.

It actually IS that simple. Physics and metallurgical science can predict, reproduce and measure these things. Strength is an attribute. What you are talking about is combining attributes to serve a function. THAT is where it gets complicated and we as knifemakers are forced to make compromises. Hopefully, we have developed the consistency and control to harness these attributes.

 

[james terrio]

It actually IS that simple.

Rick is right again. Please refer to his earlier post re: definitions of strength, toughness, and ductility. I stand by my assertion that removing steel cannot possibly make a blade stronger.

When we get down to designing a knife, of course we have to make compromises. We're trying to find a balance of several attributes (do I want a chopper, filet knife, or something in-between?). But if we confuse one characteristic for another, we're just flailing away in the dark and hoping to get lucky.

 

[Brian Avila]

Agreed, my knowledge is all theoretical, but it agrees with Rick and James. Now all we need is someone to test the different distal tapers.

 

[stezann]

Not to create confusion, but if strenght is the ability to oppose to deformation (flex maybe?) then why if i dig a channel on the flats of a blade (removing material) i am increasing this ability? I think it's not only the amount of steel, but also it's geometric disposition to build the features of the blade, in the tradeoff of compromises. Given this i agree that given two test pieces (wich geometry is standardized), strenght remains a charachteristic of the very material in it's condition.

 

[Justin King]

Not to create confusion, but if strenght is the ability to oppose to deformation (flex maybe?) then why if i dig a channel on the flats of a blade (removing material) i am increasing this ability?

You aren't...in spite of claims to the contrary, fullers do not make a blade more ridgid. I have demonstrated this to myself by grinding fullers into a sword blade for approx. 2/3 its length. The results are plain to see upon flexing the blade, the fullered section will pull into a tighter radius while the un-fullered section keeps a larger radius. FWIW the blade in question is hexagonal in section and the fullers were ground into the flats, so the maximum thickness of the blade in the fullered section was not reduced.

 

[AVigil]

Great conversation guys. I love this stuff. Thanks

 

[gte805i]

Strength is basically the maximum load that can be carried for a given amount of material (load / area). Stiffness, however is the resistance to deflection. While there are relationships between the two, having a high value for one does not necessarily imply a high value for the other.

From an engineering point of view, a distal taper is similar to a cantilevered beam of tapered cross-section. Since the maximum bending load occurs at the base of the beam (i.e. the handle), that's where the most material is needed. The taper simply removes material where the bending load is lower (i.e. toward the tip). Additionally, it could be used to influence the deflected shape of the blade, which could be used by the knifemaker to achieve a desired characteristic.

For what it's worth.....while I wish I could speak on the topic as a knivemaker, I cannot (see my post count). I can, however, as an engineer. Stay tuned for my first exploits on the path to 'maker'...

Meanwhile, I'm watching the thread, as it's interesting learn the viewpoints of the craftsmen with years of experience and countless blades under their belts.

Mike

 

[NickWheeler]

Weatherman- As someone that started out adult life as a mechanical engineer, I can appreciate your attempt at making an analytical approach to this. So, with that out of the way... Please let me say, you are over-thinking this. :foot:

A lot of folks get really overwhelmed trying to calculate angles for their primary and secondary bevels. Which, in all honesty, is almost laughable. The reason I say this, is because it's just showing they haven't ever walked up to a grinder with a 50X belt moving at 5,000 surface feet per minute and tried to grind a blade to their calculations. I'm pretty damn particular, have some very nice and relatively expensive equipment, yet my approach doesn't require any calculating.

I use good 'ol redneck engineering. What's the knife for? What steel does the customer want (because I told them which one to choose j/k ) What hardness does it need to be?

Then get the steel hot, hammer it to shape, surface grind the ricasso so that I have a nice set of flat/parallel surfaces to build off of... then rough grind the sucker until it has a nice taper, a very thin edge with a little convexity to it, and is as symmetrical as my two hands/eyes will allow. Harden and temper it, then do the finish grinding with the same approach as the rough grinding.

 

[Brian Avila]

Nick- I understand what you are saying. In all honesty I haven't used a grinder yet, but I want to. I am a scientist at heart and to me calculating will make it easier.

If I could understand the process of grinding a little better instead of hearing "practice" it would be a lot better for my understanding, ( for example I saw a video with Fred Rowe talking about his bubble jig and he used a progressive change in angles to reach the final angle, I haven't heard or seen that info before yesterday), most people just do it and don't think about what they are doing or how to explain it. I figured that by going the analytical approach would lead me to info that I could make my own conclusions about the method and create my own procedures.

I haven't got to the point where customers are even in the picture, I just want to make awesome knives for myself and if people want something that I create then awesome. I have almost finished my first knife, working on the handle, and then I started on a second and files work but time consuming, why not move to a grinder.

 

[stezann]

I discovered, when upgraded from files to grinder, that the less i think the better i do... Is something like the hands feel before the brain the shape of knife inside the extra material, and if i try to figure it out too much a pass i'll screw it. The same with forging. I think calculations could be suitable for a cnc machine more than handcraft...but is only my approach and i'm not very good yet.

 

[Rick Marchand]

I discovered, when upgraded from files to grinder, that the less i think the better i do...

+1

That is probably one of the most usefull revelations you'll ever have as a maker. Like in any art form, learn the techniques from the ground up... then FORGET ABOUT THEM and trust you insticts. Most of the mastakes I make are directly linked to over-thinking.