Chopping Physics 2

Keep thinking on this topic intermittently. Had a chance one night to work on a graph, but decided to spend that time out in the shop grinding steel instead. :)

I was gonna make up some graph paper to draw on in Excel or something, but was wondering if there's any common Windows program that will work. I know Excel can draw a graph from numbers, but in this case I want to draw the graph myself & have the computer tell me the numbers at each point on the line.
 
hardheart said:
... some real numbers and be easier to visualize...
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Assuming both are swing at the same speed you would expect just a scaling with mass which would then be just proportional to thickness. However in general the mass distribution changes significantly so the balance points are not the same and the mass doesn't scale as well with the thickness. But as a first approximation mass will get you to within a decent perspective especially if the knives are similar (using the term loosely).

For example I have a long leuko at 140 grams, now compare this to the SHBM at 660 grams. A first estimate would be about a 20% chopping ability for the leuko (mass based) as the balance points are similar. This has to be adjusted by the fact that the leuko will penetrate further under a given force. Given the edge is significantly more acute and the stock thickness is thinner I'd estimate you would want to correct this by about 25% for the edge angle (as a rough estimate half the angle ratio) and a further 25% for the stock thickness (this is a small amount even for large changes because wedging decreases rapidly u from the edge). When the knives were actually compared the result was 34 (3) % in agreement with the prediction.

...everyone at least has a notion that thin kitchen cutlery and thick 'outdoorsy' profiles chop differently.
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Yes, one is suited for high speed and the other high inertial impact.

Can this be combined with forces at the edge, influenced by bevel angle and thickness behind the edge?
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Yes, one discussion is on the ability of a knife to generate power (mass, inertial moments) and the other is on the ability of the knife to efficiently transfer this power into cutting ability (cross section). Since they are acutally constrained by the same factors they can not be independently varied.

-Cliff
 
the possum said:
but in this case I want to draw the graph myself & have the computer tell me the numbers at each point on the line.
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Other than a CAT program, I can't think of any. What kind of graph are you thinking about?
 
It would be a simple line graph with the length (inches) on the horizontal axis, and mass (ounces) on the vertical axis. The line would show how much mass there is at every inch along the blade. I planned to make a couple different ones showing different possible ways I'd make the blade. One with a relatively lighter blade & pommel (Falchion), and one with a heavier blade & no pommel (Grossmesser). If this were done on a computer, it would be easier to do calculations, find the actual CoM, and change things to investigate other possible ways to distribute the mass.
 
Cliff Stamp said:
Yes, one discussion is on the ability of a knife to generate power (mass, inertial moments) and the other is on the ability of the knife to efficiently transfer this power into cutting ability (cross section).
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Just thought it might be worth clarifying that mass distribution is not just about generating the power- it also helps determine how much is transferred to the target along with the other stuff like edge geometry.
 
I'm just sayin' in general that the mass distribution & pivot points do affect power at impact, so the mass affects things both during the swing and on impact, whereas the edge geometry only effects things on impact. I'm sure you've been saying the same thing; your last comment seemed to divide the ideas a bit too much.
 
Yeah, I see what you are saying, I oversimplified there as a starting point and I think information was lost. You can defend the position I stated because you can in general reduce impacts accordingly, note a pommel just effects tip impact for example because it gives the blade a greater inertial momentum, but I think this would not clearify the issue and in fact would make it more confusing to most. In general the perspective you outlined would be more beneficial because it makes some things like dynamic balance points much more obvious.

-Cliff
 
I think asside from a cat program your best bet is still Excel. You have to toggle back and forth between the spreadsheet and the graph, but you can read of the values on the graph by placing the cursor over it. To actually modify the graph, you would have to go back and change the datapoint accordingly though. Excel would also make the calculations very easy.
 
The weekend has come & gone, so I'm bumping this up for Mr. Devanna. I'm curious to hear whether he was able to use any of these ideas for the cutting comp school he attended.
 
There have been some things happening in my life lately that are far more important than knives, or I probably would have gotten back to this thread by now. As it is, it will probably be a while before I get to work on this stuff again. Just wanted to let ya'll know I haven't forgotten about it.
 
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