Complex Harmonics in swords

[Vincent Le Chevalier]

One thing to note is that nodes on the blade are only half of the story, and possibly not even the most interesting half Unfortunately employing the same mehod to spot nodes on the handle will prove even more difficult...

It will be interesting to see up to which mode of vibration you'll be able to go. Spotting the nodes of the first primary mode is easy enough by eye and hand, but higher modes are often invisible, or only noticeable through compounded effects, because of the higher frequency and diminished amplitude.

According to my simulations (see here) the difference between edge-to-edge and flat-to-flat nodes is minimal in the blade, more noticeable in the grip.

Personnaly I think there are more important blade properties being currently under-studied, that have nothing to do whatsoever with vibrations. Thus I never got to the experimental part What are you going to use all this node knowledge for after that?

[RionMotley]

Screw off, I'm just having fun!

:-p

But honestly, this is what I can contribute.

I don't have a rockwell tester, or a temperature controlled oven, but I do have some electronics experience, and I can add that to this big pot of stone soup we call knowledge.

If this info isn't helpful to me, even, it adds to the collective, and anyone looking for more info later is likely to find it. If it helps even one person, the it's worth the blood, sweat, and beers that I spend on it this weekend.

There's also some CFD info to be had if anyone would look for it - thinner, wider chord members cut more effectively than thicker wider ones (duh?) which is one reason the blade I'm working on now will have the cross section that I depicted in my other thread http://www.swordforum.com/forums/sho...29#post1037429

What other areas of blade design are you speaking of when you say they're underinvestigated?

I personally feel that if any blade property is overlooked it makes for an inferior blade - a perfectly balanced, poorly hardened blade is as bad as a perfectly hardened blade with horrid geometry, particularly when those two features are not in conflict.

I particularly feel that when one aspect of a blade is overlooked it tends to detract from the other features. A beautifully executed pattern welded blade with perfect geometry and a computer controlled heat treat mounted with a dime store pommel is an injustice to the smith and the art.

So out with it man! What other features are being overlooked? (Keep in mind that this particular thread is all about harmonics...)

[Vincent Le Chevalier]

I'm tempted to say... Screw off, I'm just having fun!

:-p

Oh sure, I don't mean to spoil your fun... Just putting the fun in context

Actually it could answer a question Michael Tinker Pearce raised in another topic about complex harmonics:
http://forums.swordforum.com/showthr...789#post964789

So if you can get to see the second mode of vibration I think some people will be interested.

What other areas of blade design are you speaking of when you say they're underinvestigated?

They have to do with moment of inertia, rarely measured though it is tremendously important in the feel we have of a sword and in cutting, moreso that vibration nodes in my opinion. The most common manifestation of this is called 'pivot points' in the community (though it is not the correct term in the physics context).

You can read about that here, with some comparison of the effects:
http://tinkerswords.com/forum/viewtopic.php?t=232
And here for a use I have of these properties:
http://forums.swordforum.com/showthread.php?t=91498

But as you say this thread is not about that at all, so it's not the place to discuss it...

Best of luck for your experiment!

[RionMotley]

Gun.

I really wish I hadn't taken a 4 month break from the anvil.

*rubs shoulder*

Anyhow, this might not be the thread to discuss it, but it's certainly worth discussing. Moment of inertia is actually a pretty easy thing to figure out experimentally. I've decided to hang the blade from fine thread, horizontally, so I can show off a few things with that as well.

I actually think they're rather related - if you can get a fundamental node and the inertial center to line up, then voila - you got yourself the hardest hitting blade on the planet.

Wooo!

More later - I have to actually build a new forge since mine isn't quite shallow/long enough to handle the blade length I'm trying to create. Great for knives and general smithy work, but not so great for blades longer than about twice the width of the fire pot.

It does get up to welding temp VERY fast tho... ;-)

[RionMotley]

that one could in fact measure the CoP of a sword blade by striking the edge of the sword, while suspended from nigh on massless and frictionless pivots (i.e. very fine thread) horizontally, with the flats parallel in all dimensions to the floor.

I propose a highly scientific media with which to strike the blade, namely a carrot. This would provide a consistent momentum transfer media, since no more momentum could be transferred than the mechanical strength of the target media (The carrot) could support. Thus, manually striking the edge of the sword and observing the rotational versus transverse movements should locate the CoP. Specifically, this will give us reference points that are IMPACT derived versus harmonic-derived, potentially being more accurate to the cutting performance of a blade than anything else. Later correlation to vibratory modes and center of gravity (indicated by the hatched round symbol in the middle of the blade) could provide valuable insight to distinguish between perceived performance and actual parameters.

[Vincent Le Chevalier]

that one could in fact measure the CoP of a sword blade by striking the edge of the sword, while suspended from nigh on massless and frictionless pivots (i.e. very fine thread) horizontally, with the flats parallel in all dimensions to the floor.

Yeah that would probably work... One might be able to spot the CoP associated to one of the threads by finding the point that does not make this thread move when struck. I'll try this out, maybe it will turn out to be easier than both the waggle and pendulum test...

Slight variations of the transfered momentum should not change the result much though, so maybe we can spare some carrots

Later correlation to vibratory modes and center of gravity (indicated by the hatched round symbol in the middle of the blade) could provide valuable insight to distinguish between perceived performance and actual parameters.

If you're interested in the relationship between harmonic nodes and pivot points/CoP, you might like to read this other post I wrote:
http://www.myarmoury.com/talk/viewtopic.php?t=10788

Regards,

[RionMotley]

I had a Eureka moment last nigh. Coated a disk of steel with my last handful of refractory and dropped it in the bottom of my forge fire pot. Woo!

Raised the fire up about an inch and a half, so now I don't have to put 30,000 pounds of charcoal in it to get the fire up to where the bar stock can go straight through!

I might have this test set up sooner than I thought.

Btw, thanks to Sam Salvati for the forge geometry lesson ;-)

It's all well and good to have a forge designed like a jet engine and doesn't need refractory in it, but it sure helps to be able to fit your work into it!

And as far as saving carrots goes...

I forgot to add the stew pot into the diagram... if you put it right below the blade, the carrot pieces fall in, and you're killing two birds with one stone... soup!

If you can video tape your tests, then I can just grind a piece of mild steel out tonight and try to set up the vibration tests for thursday/friday and have a vid up over the weekend of the nodes!

Two more birds killed! Hypothetically, of course...

*puts on GreenPeace baseball cap*