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

Brian Avila

Brian Avila

Joined
Jan 2, 2011
Messages
1,286
So I have been doing research on grinds and using a grinder to preform the grinds and I came across the thread about edge geometry, it was a very good read:

http://www.bladeforums.com/forums/showthread.php/838481-Edge-geometry

Lets talk about the specifics of the flat grind:
1) If you have a 4" blade
2) Blade width of ~1.5"
3) Drop point that is just around .5" drop from spine,
4) 5/32" thickness
5) You have a "perfect" flat grind that is somewhere in the number of 3.25 degrees,
6) You have decided not to break the spine and leave 1/8" left on the flat of the knife to the spine

If you grind your knives and just drag your blade across the belt without putting any pressure on the tip, the thickness of the tip located at the 1" mark from the edge of the blade would be ~.1138". (I sat down and did the math and this would depend on perfect angle and the width and thickness of the material)

That would lead me to believe that pressure must be applied around the tip area to create a distal taper. The "correct" thickness of the tip around the distal taper would probably depend of the intended use of the knife, type of steel, shape, etc.

What do you guys think about when you make your knives and are doing the distal taper?
 
Your post hurts my old brain. My only comment is: Grind a few hundred blades and the distal taper comes pretty much naturally.

Robert (Who has a pretty small brain anyway)
 
I couldn't swear to it, but your numbers seem correct at first glance. Any knife that has any sort of belly or point to it will end up with some degree of taper at the end. Doesn't matter if it's flat, convex or hollow-ground. A blade that ends abruptly, perpendicular to the edge and spine (like a straight razor, perhaps) will not "automatically" have any taper unless you want it to.

However, when I think of distal taper as being done on purpose, I think of a full distal taper that flows smoothly all the way from the plunge or ricasso to the tip. Looking from directly above, the spine will look like one long isosceles triangle, rather than a rectangle with an isoceles triangle on the very end.

Except for heavy-duty choppers, combat knives and "sharpened pry-bars" (which aren't necessarily a bad thing, sometimes that's exactly what you need), I like full distal tapers on most any knife. It lends grace, balance and fine cutting ability to the blade.

I try not to overthink it when grinding a full taper, I simply scribe a centerline down the spine and try to keep it even and symmetrical on both sides.
 
So is a distal taper something that is just placed into the system because it helps and not thought of very much, more of an artistic thought?
 
I mostly think about not burning my fingers .. The distal taper allows the knife to feel balanced and to create a smooth transition to a pointy tip. I'm pretty bad at math..
 
I grind the distal taper of a blade after the profile is complete and before the bevels are ground. If the distal taper is ground at the same time as the bevels it makes the work much harder to accomplish. It takes but a few minutes to grind the distal taper first, with the blade attached to a strong grinding magnet.

Distal taper is used to lesson the weight on an other wise over balanced blade. As mentioned above they can add beauty to a blade. Distal taper or the lack of it is what controls the geometry of a blade; especially the tip and the radius.

I'm decent at math but my poetry is lacking.
 
haha, I didn't mean to imply that you guys couldn't do the math.

I do like the idea of doing the distal taper first and then doing the bevels though. I haven't started grinding yet and I just use files but the process that I would have followed lead me to the first post so I figured I would ask about how you guys approach it.
 
All good stuff as written above. I want to add disal taper when used through to the tip does create a thinner area of blade for better cutting as well. Certainly, a false edge or swedge will also do this. Frank
 
For me, distal taper comes automatically when doing a smooth horizontal grind straight from tip to plunge (no angling of the blade). It's just something that happens as you work your grind up the blade. The only exception I've noticed is the sword I did recently, and that's only because there was a fuller above the grind line.

Dave
 
With full distal tapers done first, the angle of the bevel often (depending on the profile) has to be modulated to accommodate or compensate for the distal taper... more obtuse where it is thickest, and more acute towards the point. I find it very difficult to do completely with a grinder.

I usually forge it first, then do some grinding, then filing,... it may be a bit slower, but works fine. One nice thing about filing is that you can see the side you are working on while you are working on it.
 
For a single edge blade, a full height grind is pretty much a prerequisite for a clean and proper distal taper, IMO. Given that, the way the edge and spine taper towards each other along the length of the blade will determine the rate of distal taper. It is a product of both the profile and the edge geometry of the blade. I don't bother to grind the taper into the blank before starting the bevels, except on a long, narrow blade, or one that is double-edged.
 
I tend to forge the tapers and start off the the bevels by forging, before going to the grinder.
 
Never gave it much thought, but when i want a distal i introduce a slight movement with my wrist and thumbs. I grind in the style RW Wilson teaches which includes a motion that naturally brings a distal taper, and my first blades all had distals, but as i ground more i learned i could remove a part of the motion to supress it, or bring it on more aggresively. But theres lots of ways to get it done!
 
Distal taper also transfers stress more evenly when the point area is sideloaded. In my opinion, other than being more artistically satisfying, that is the main purpose of having it.
 
What about the thickness in the area of the point of your knives? Mapping out the thicknesses from plunge line to tip?
 
LRB said:
Distal taper also transfers stress more evenly when the point area is sideloaded.
Click to expand...

After hearing that for years and subsequently having several long and detailed conversations with a mechanical engineer, and breaking several blades on purpose... that's a myth. The lateral strength of the blade depends entirely on it's thickness at the point of the most stress. As far as whether or not a tip is going to snap off, tapering it simply removes steel and only makes it weaker. A non-tapered tip is flat-out stronger than a tapered one, when everything else is equal (I'm talking two blades made from the same bar, ground to the same profile, HT'ed by the same professional at the same time.)

Transferring energy and stress-risers do come into play when there is a sudden and dramatic change in any dimension, which is why we round tang shoulders and why gentle curved and/or angled plunges are stronger than abrupt, square ones.
TheWeatherman said:
What about the thickness in the area of the point of your knives? Mapping out the thicknesses from plunge line to tip?
Click to expand...

The correct thickness will depend on whether or not you want to pry or dig with it. For example, Rick Marchand makes some of his knives so their edges are thicker at the tip than at the flat of the blade, specifically because he wants strength there. I'll ask him to explain further.
 
Me too! I sent Rick a message and asked him to join this conversation.

To me, it all boils down to, what/how do you want your knife to cut? That's always the first consideration. My CDP (chop, dig, pry) prototype is 1/4" thick and full-convex-ground, non-tapered with a square "point" with a short chisel grind for... chopping, digging and prying. It performs very well at those things, but it would not be my first choice for filleting fish. ;)
 
I understand what you are saying James. I was jus trying to go down the road of looking at the design in a more scientific view.

I think the flat grind is probably the easiest so I started there, and would just like to have a better understanding behind the thought and form. When I get to making knives with a grinder and doing it more than just 1 or 2 I would like to be able to reproduce the results without fail. To do that I believe there is an "equation" that can be followed. Some will disagree with me and say that there is art involved and to an extent there is, but I could make something look a certain way and have it all modeled out so the dimensions and thicknesses are what I expect when I am done and not have any hiccups.
 
TheWeatherman said:
...I would like to be able to reproduce the results without fail. To do that I believe there is an "equation" that can be followed.
Click to expand...
You seem like a person who likes to measure things out and be consistent. :thumbup: I sincerely think you should check out Mr. Rowe's Bubble Jig. It's a tool that helps you maintain a consistent angle all throughout your grind. Again, I will let him explain further :)
 
You must log in or register to reply here.
Back
Top