Re: Needed: Advice on best material for special application

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.

"Tennis Smith" <[EMAIL PROTECTED]> schrieb im Newsbeitrag news:[EMAIL PROTECTED]
> 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