How much weaker does a bo-hi make a sword?

QUESTION: Right now I'm planning on buying a tenchi and I'm trying do decide whether or not to have it with bo-hi. I understand that the bo-hi makes the sword slightly less stronger, but by how much?


ANSWER: It is barely much of a difference actually...

For a start, the 'I-beam' design of the bo-hi is much like that used in the construction industry. So while there is less material, it is somewhat reinforced.

Secondly, this is monosteel (through hardened) 9260 Spring Steel we are talking about. So it is already super durable...

The main difference is that a blade without bo-hi is a little heavier and has a more forward balance point - giving it more power, but making it a little less graceful.

Hope this helps.

- Paul

Comments for How much weaker does a bo-hi make a sword?

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balance point
by: Kit

What is the significance of the balance point as far as cutting ability is concerned?

Thanks, Kit

Not much...
by: Paul Southren

It does shift the balance back a bit, which means that it may not have as much 'ooph' behind it as the solid bodied verison, but the difference in cutting power is really only noticable on very heavy targets.

How much weaker does a bo-hi make a sword?
by: Frank Belmares

If you consider steel in any grade having some of the "meat" taken out of the stock by metallurgical, design, structural, strength of material knowledge it is factual that the steel will be made weaker. In consideration of the "I Beam" theory there is one difference. The web and flange of structural steel beams are all solid rectangular formed "I" shapes. TO remove some of the thickness would make it weaker. Katana blades have a hi in the meatiest
part of the blade which does reduce the stress regarding possible breakage but all in all the solid blades ARE stronger.

Bo-hi. Yes or no?
by: Chris Sims

I've heard the same thing many times (so I guess that makes it true). If a katana, daito, iaito, or medieval sword has a bo-hi (fuller, blood groove) it actually makes the blade less likely to flex. So, basically, yes, it makes it stronger. But, on a bokken it will weaken it. I hope this helps.

How much weaker does a bo-hi make a sword?
by: Anonymous

In all the research I've done on this subject.. This explanation is what I believe and makes the most sense.

If we substitute a swordblade for the I-beam, we can conclude that a fuller will lighten a sword, and a sword with a fuller will be stiffer than a solid sword of the same weight, but cutting a fuller in a sword will *not* make that sword stiffer. It will make it lighter while maintaining most of its stiffness.

However, due to the reduced weight, the fullered blade may "feel" stiffer if you wiggle it, because the force of inertia acting on the blade will be smaller. Another factor to consider is the difference between a forged fuller and a cut fuller. According to certain bladesmiths, a skillfully forged fuller will strengthen the blade by locally changing the crystal size or something like that. I assume the key word here is "skillful".

Another interesting observation is that a fullered blade will be stiffer edgeways as well as sideways. The wider the fuller (or the greater the distance between the "spines") the stiffer the blade will be, edgeways.

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