Needed: Advice on best material for special application

Hi,
I'd like to get some advice for material to use for a very specific application. Please bear with me here, because I need to give you a little background first.
I'm a martial artist involved in Japanese sword training.
Most of the time, we don't actually use a real swords. We use a substitute training sword called a "bokken" (BOH-ken) for safety reasons. Traditionally, bokken are made of various kinds of wood. However, there are lots of problems with this approach.
For one, they are prone to splintering and/or breaking. We spend alot of time hitting the bokken with great force. Some wood types can't even stand up to a single session without breaking or splintering to the point of actually being dangerous for attacker or defender.
Another problem is that wood is generally too light in weight. Ideally, it should approximate the weight and balance of a real sword (about 3 lbs).
So, it tends to be a trade-off. Woods that are sturdy enough to be used (like hickory) are too light and woods that are heavy enough (like iron wood) are too brittle. (You could do things like make a light wood bokken very thick to appoximate the weight, but that just gets the student used to holding something _much_ too thick.) Finally, I'm not ruling out _all_ wood as an option. Its just that I've never seen any so far that wasn't prone to one of the shortcommings mentioned.
Why not plastics? Well, plastics tend to conduct the force of impact. Someone using plastics will tend to get a tremendous vibration conducted directly into themselves. (That is, it has been true for all the plastic bokken we've tried so far.)
So the rules are:
1) heavy as steel
2) non-splintering
3) non-conducting of vibrations
4) can be molded to approximate the length shape of a traditional bokken
5) won't break if violently struck with another bokken of any type.
Thanks for your time. :) If you have any ideas, please let me know.
TIA, -Tennis

Tennis Smith wrote:
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Why not put a strip of lead along the back of the hickory blade?
Cheers,
Phil Hobbs

Phil ever thought of using a PEEK & carbon fiber thermal plastic I could probably provide you with TOP per the material composition if requested.
have a good one
ME.Misuraca- GET Design Engineering
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traditional
type.

Steel has about 5 times the density of any plastic that would be tough enough for your application, like toughened Polyamide or Polycarbonate.
Perhaps a plastic-metal hybrid or inlay technique ought to be used, where you overmold a thin elastic metal rod to strip with a suitable tough plastic. The technique is mentioned here: http://plastics.bayer.de/pdf/A5405DE.PDF for example. The metal insert would provide the weight and the overmolded plastic the toughness.
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Steel has about 5 times the density of any plastic that would be tough enough for your application, like toughened Polyamide or Polycarbonate.
Perhaps a plastic-metal hybrid or inlay technique ought to be used, where you overmold a thin elastic metal rod to strip with a suitable tough plastic. The technique is mentioned here: http://plastics.bayer.de/pdf/A5405DE.PDF for example. The metal insert would provide the weight and the overmolded plastic the toughness.
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Tennis Smith wrote:
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Steel.
Michael Dahms

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A unidirectional fiber glass composite may work. Covering with a layer of tough elastomeric plastic may protect surface. Someone that manufactures archery equipment, bows, may help. If you still need weight, you could add a lead core. Fiber glass is heavier but Kevlar aramid would reduce vibrations better. So if you need the lead core, I would use Kevlar. Frank

tennis snipped-for-privacy@yahoo.com (Tennis Smith) wrote in message
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Interesting problem. All the background information helps a lot. Would you be willing to moderate this group to make sure that all the questions have this much information? (Just kidding).
You can increase the density of plastics by adding heavy fillers such as various minerals or metals. Corian is a good example, being ~70% calcium carbonate. They do supply Corian in small widths for use as a tread between tile floors and carpeting. If you can locate a helpful tile installer, you should be able to get a long piece to at least play around with and see if it's close to what you are thinking about. I don't know if it will meet requirement # 5 however. I'm not sure about #3 either. I can certainly try to handwave a b.s. argument about how the fillers should help reduce vibrations, but it would be easier and more effective to just try the experiment yourself.
Vibration damping can be specifically designed into the swords, but it would be more difficult to make and pricier as a result. My son has an aluminum baseball bat that is nearly impossible to vibrate (unless you hit the ball an inch above your hands, and if the pitch is that far inside, the kids are most likely running for cover and not trying to pull it to the opposite field). It's a two piece construction with a dampning section in between, so it's not something that you would be able to craft in your garage.
My suggestion would be to try the Corian and then give us some feedback from that. We can then offer additional suggestions on how to proceed.
John

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> Why not plastics? Well, plastics tend to conduct the force of impact.
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Corian does not contain calcium carbonate. Filler, when I was associated with group 10 years ago, was alumina. I also doubt it's tensile and flex strength would hold up under this usage. Frank

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Thanks for the correction. I know better but my mind was in a whirlwind yesterday. (Today it's only in a dust devil).
John

Why not use steel? It has all the characteristics you are looking for, and will behave like a real sword.
Just make sure the edges aren't sharp and the pointy end is not too pointy.
:)
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I wouldn't use steel. It's too sharp, and it doesn't behave like a real sword.
Steel is dense, so a "sword weight" of steel is going to be narrow. Too narrow for an impact to be safe, even if not sharpened (and this does happen from time to time).
Secondly, steel doesn't have the balance of a real sword, unless you go to a lot of trouble in profiling it. Handle a real sword sometime - you'll be amazed at how well balanced it is. OK, so this is different for a Japanese sword (relatively blade heavy, and useless for fencing) compared to a 19th century European sword, but it's still an issue.
I'd favour wood - hickory or ash. Both are strong enough to survive dojo use. If they don't, then look at the quality of the timber you're using. Both these timbers are potentially strong, but highly variable. Look for _coarse_ growth rings, especially in ash, as fast-grown timber is stronger than slow grown (for a ring porous species like this)
Being light, you can also make a wooden sword much fatter than a dense sword, improving the impact safety aspect.
(I practice iaido, and I'm also a woodworker)
-- Die Gotterspammerung - Junkmail of the Gods

Sorry, I must be missing the "point" here. The original set of rules was:
1) heavy as steel
2) non-splintering
3) non-conducting of vibrations
4) can be molded to approximate the length shape of a traditional bokken
5) won't break if violently struck with another bokken of any type.
Unless I am very much mistaken, steel is as heavy as steel, and seems to fit 4 out of 5 rules above (provided the second bokken is also made of steel). Obviously, in a real fight with real steel swords there would be vibrations transmitted, so using blunt steel swords would also transmit vibrations. Make the things round to take the "edge" off it.
No matter what you make the training sticks from, some idiot will still hurt themselves. You may as well make it as realistic an injury as possible :)
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Steel isn't "heavy", it's dense. As swords are fairly light, we can match weight with almost any material. My argument is that low density is good, because it gives us a blunter edge for a given weight.
Secondly, this is a Japanese sword, not European-style fencing. There's no shield to clang your claymore against, and contact between blades is relatively rare. It does happen, but it's not a core part of technique, as with fencing.
-- Smert' spamionam

On Fri, 17 Oct 2003 13:23:08 +0100, Andy Dingley
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Lots of free Green Ash available just now in eastern USA. Here in Ann Arbor they used it as the "standard" tree for curb extensions, so the streets are lined with it. Now with Emerald Ash Borer infestations, these trees are being condemned faster than they can be cut down. But you gotta move quick before they burn it!
Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis www.daqarta.com

Check out the specs for "synsteel" or "polysteel" It's a filled UHME-PE It's manufactured for the pulp industry, but just might be what you're looking for
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Great idea. I'm told it is UHMW-PE, correct?
It really sounds promising, but I can't find it in "dowel" form. Any ideas who might have it?
-Tennis
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Hi Guys,
Thanks for all the wonderful ideas. Great start. As a followup to this though, I'd like to put one more condition/restriction on it:
I'd like to have the individual bokken (practice sword) be producable for $50 - $100. They will be produced in small quantities of between 5 and 20 at a time.
Given these caveats, how many ideas get ruled out?
TIA, -Tennis
tennis snipped-for-privacy@yahoo.com (Tennis Smith) wrote in message
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