- Joined
- Oct 17, 2010
- Messages
- 2,424
That's a pretty heavy leap on the question of an ellipse vs hole. If you're comparing a slot of roughly the same area as a hole, in a rectangular piece of stock, then yes, it makes sense, when breaking the stock across the short axis, that the slot is stronger, because their is more homogeneous (not removed) material in this dimension. It's also worth mentioning, that in any piece of stock where you have a hole and less total material, it's lower strength and thus, more prone to breaking there, as opposed to either side of the hole, which has significantly more material. I would very much like to see some actual data comparing hole breaks vs ellipses where the long axis of an ellipse of equal area to a circle is on the same plane as the break. Even further, I would expect serious changes in results based on the radial aspects of the acute ends of said ellipse. If an ellipse is stronger in the short dimension, it will be equally weaker in the long dimension, and because of the more acute radii at the ends of the long dimension, should in fact have a higher stress riser factor, than a circle, assuming all things being equal otherwise.
I also feel it's important to consider a distinction; stress risers resulting in material yields (micro cracking, etc) during extreme stress precipitations such as during austenizing, and ones that compound forces in use that yield at those stress points, resulting in failure. The article alludes to this, but it's a very difficult distinction to make in casual, unscientific, "shop destruction tests".
I've broken a large number of blades in destruction testing, and been amazed at the number of obvious material flaws that could be seen under magnification, with high quality, seemingly homogeneous material straight from reputable sources or the manufacturers.
I appreciate Larrin's article, but the illustration in regards to holes, makes it look like the reason a rectangular section of stock with a big hole in the center of it breaks, is strictly because of stress risers, and not, as is more likely; because that's simply the point of lowest strength due to removal of material, resulting in the lowest volume of homogeneous material. Stress fractures, compounds, can certainly contribute, but if you take a homogeneous rectangular section of steel, and drill a hole in it, the area with the hole is going to be the weakest point because of the material removal, not because of possible stress concentration. I'm sure it wasn't Larrin's intent to imply that it's simpler than it is, but I can already see you guys jumping to conclusions. He makes a clear point that it's a point of stress concentration, all other things being equal.
In fairness, I haven't had time to read the whole article, I'm not on here much anymore, but someone mentioned this to me (the hole issue), so I read that section, but I'm mostly here try and curb the leaps of logic that I'm worried will setup a whole new wave of misinformation precipitating to potential customers, when some new maker starts spouting a bunch of half-formed ideas about ellipses on their poorly finished knives, as a reason their work is better than the rest, regardless of how obviously un-true it is by looking at them, hypothetically.
Why is it every time Larrin writes an article, someone wants to come up with some TLDR bullet point, distilling (dumbing down) the whole thing into some blanket statement/assumption? I'm not pointing any fingers, just advising caution in jumping to conclusions. If what I'm saying pisses anyone off, you're taking something personal that wasn't intended as such(though I'll be glad to hear counter-arguments). I know with most of us here, it's out of enthusiasm, and a desire to understand this complex art we're so desperately in love with, but remember that in an attempt to share that enthusiasm, we often proliferate misinformation, when less enthusiastic people start repeating an abbreviated, half-understood version, of our attempt to simplify; as the gospel.
Anyway, as always, thanks Larrin, for the article, and the continued effort to enlighten the community. I see your work as a great attempt to shine light on the infinite complexities involved in our thing, but I feel many just want to see them as cementing finite "absolutes", simplifying something which, I feel (and I suspect you agree), isn't remotely simple. If there is a TLDR, in my opinion its this: any removal of material has a cost, and must be done strategically, and with great consideration. The bar of steel you started with is always going to be stronger than each subsequent object after removal of material, but that bar isn't a knife. Even if some makers think slapping an edge on a slab of steel is good design for a "strong knife". Our job, is to determine the intent of the tool, and how to balance the performance characteristics between nominal strength and cutting performance, or other factors (weight, flexibility, etc, etc.). Don't assume something is good just because you've seen other makers do it. Make, test, and find out for yourself. Blanket broad assumptions like "full tang is stronger than hidden tang" oversimplify complex factors and are a disservice to our craft. Yes, all things being equal, two pieces of steel, of the same specs where one is larger in a certain dimension, it should be stronger, but it will be commensurately heavier. However, twice as wide, with a shit ton of holes to bring the weight in line, may very well be significantly *less* strong in the real world, than a thinner monolithic stick tang. However, even still, there are a huge number of other factors, when it comes to what causes an actual failure in real use.
I also feel it's important to consider a distinction; stress risers resulting in material yields (micro cracking, etc) during extreme stress precipitations such as during austenizing, and ones that compound forces in use that yield at those stress points, resulting in failure. The article alludes to this, but it's a very difficult distinction to make in casual, unscientific, "shop destruction tests".
I've broken a large number of blades in destruction testing, and been amazed at the number of obvious material flaws that could be seen under magnification, with high quality, seemingly homogeneous material straight from reputable sources or the manufacturers.
I appreciate Larrin's article, but the illustration in regards to holes, makes it look like the reason a rectangular section of stock with a big hole in the center of it breaks, is strictly because of stress risers, and not, as is more likely; because that's simply the point of lowest strength due to removal of material, resulting in the lowest volume of homogeneous material. Stress fractures, compounds, can certainly contribute, but if you take a homogeneous rectangular section of steel, and drill a hole in it, the area with the hole is going to be the weakest point because of the material removal, not because of possible stress concentration. I'm sure it wasn't Larrin's intent to imply that it's simpler than it is, but I can already see you guys jumping to conclusions. He makes a clear point that it's a point of stress concentration, all other things being equal.
In fairness, I haven't had time to read the whole article, I'm not on here much anymore, but someone mentioned this to me (the hole issue), so I read that section, but I'm mostly here try and curb the leaps of logic that I'm worried will setup a whole new wave of misinformation precipitating to potential customers, when some new maker starts spouting a bunch of half-formed ideas about ellipses on their poorly finished knives, as a reason their work is better than the rest, regardless of how obviously un-true it is by looking at them, hypothetically.
Why is it every time Larrin writes an article, someone wants to come up with some TLDR bullet point, distilling (dumbing down) the whole thing into some blanket statement/assumption? I'm not pointing any fingers, just advising caution in jumping to conclusions. If what I'm saying pisses anyone off, you're taking something personal that wasn't intended as such(though I'll be glad to hear counter-arguments). I know with most of us here, it's out of enthusiasm, and a desire to understand this complex art we're so desperately in love with, but remember that in an attempt to share that enthusiasm, we often proliferate misinformation, when less enthusiastic people start repeating an abbreviated, half-understood version, of our attempt to simplify; as the gospel.
Anyway, as always, thanks Larrin, for the article, and the continued effort to enlighten the community. I see your work as a great attempt to shine light on the infinite complexities involved in our thing, but I feel many just want to see them as cementing finite "absolutes", simplifying something which, I feel (and I suspect you agree), isn't remotely simple. If there is a TLDR, in my opinion its this: any removal of material has a cost, and must be done strategically, and with great consideration. The bar of steel you started with is always going to be stronger than each subsequent object after removal of material, but that bar isn't a knife. Even if some makers think slapping an edge on a slab of steel is good design for a "strong knife".
Our job, is to determine the intent of the tool, and how to balance the performance characteristics between nominal strength and cutting performance, or other factors (weight, flexibility, etc, etc.). Don't assume something is good just because you've seen other makers do it. Make, test, and find out for yourself. Blanket broad assumptions like "full tang is stronger than hidden tang" oversimplify complex factors and are a disservice to our craft. Yes, all things being equal, two pieces of steel, of the same specs where one is larger in a certain dimension, it should be stronger, but it will be commensurately heavier. However, twice as wide, with a shit ton of holes to bring the weight in line, may very well be significantly *less* strong in the real world, than a thinner monolithic stick tang. However, even still, there are a huge number of other factors, when it comes to what causes an actual failure in real use.
