sword and iaito mods

[charlesl2]

I have a couple of friends that have these stamped out WWII blades that they use for iai, and another friend that is very tall and whose iaito is pretty long. All three of these blades are top heavy(?). I've used a real blade for iai and the balance on it is as perfect as I can imagine, but when I use one of these other blades, it's like training with an executioner's sword, the balance is completely different, and there's definitely less control over the weapon.

What I'm wondering is could you add weight at the butt of the weapon to balance it out, and what adverse affects this would have. All three of the blades are overly heavy already, but if you were to add maybe somewhere between 8 and 12 ounces to the back end, would the extra weight be compensated for by a better balance? Anybody done this before, have ideas, suggestions?

-Charles Lockhart

[Graham Wild]

I don't know to much about the swords your talking about but I do know physics (sometimes :)). First find out where the centre of mass (CoM) is then find out where you want it to be. Now you want to calculate a moment of rotational equilibrium about the point of where you want the CoM to be.
Simply put multiply the distance between the CoM you want and the current CoM by the weight of the sword then equate this to the distance from the CoM you want to the bottom of the tsuka multiplied by the weight needed to be added.

|<-----distance 'A'----->|<-distance 'B'->|

==========|===========================> (This is a sword :))

^bottom of tsuka______^CoM wanted___^CoM now

Let the weight of the sword be 'X' and the weight needed to be added 'Y'

X.B=Y.A
X.B/A=Y

So the weight you need to add to balance the sword will be a ratio of the distances multiplied by the weight of the sword so you need 'A' to be big compared to 'B' so the additional mass is minimised. So if the sword is really out of balance then I can't suggest much.

If you have any more questions just ask.

[Howard Quick]

Hi Charles,
I'm definately no expert, but I believe the easiest/best way to alter the weight and balance would be to go for a heavier tsuba. Either larger diameter, different material, or if the original is somewhat ornate, perhaps a solid iron/copper/brass item would suit.
Good luck
Howard Quick