# Communities > Modern-era Swords and Collecting Community > Modern Production Katanas >  To Bo-Hi or not to Bo-hi??

## mark p. smith

I am looking at the Chinesse 9260 Spring Steel Katana - "Shura" being sold at SBG for $239.00.
Very impressive review. Looks like a very forgiving sword for a bigginer.
They give you an option weather or not to have the Bo-Hi on it. 
Not being familiar with either design I'm looking for some opinions. 
Is it better with or without? Which gives it more flexibility and which gives it more strength?

----------


## tom_urso

You will find several different theories for the bo-hi's purpose. In terms of a live blade, is generally agreed that its use is to lighten the weight of the sword. Concerning its use in tameshigiri (test cutting), all my instructors have requested that the blade not have a fuller. The idea is that it may weaken the blade or that the hi will create too much drag. 

You will find others that will negate this and say that the hi actually strengthens the blade...think of an I-beam. Obviously, I tend to believe my instructors.

Your profile doesn't mention any training, so as a word of caution, if you intend to use the sword to cut, please be very careful. It would be wise to seek legitmate instruction.

Thank you

----------


## Bogdan M.

> You will find others that will negate this and say that the hi actually strengthens the blade...think of an I-beam. Obviously, I tend to believe my instructors.


Obviously, your intructors are right. The bo hi or I beam proveides more stiffness for the same amount of material. But the strength is only dependent on the amount of material, so if you take off material you weaken the blade. A blade with bo hi might be stiffer (some may take this for stronger, but it's not the same thing) but weaker than the same blade without bo hi.

----------


## mark p. smith

Everybody keeps comparing the Bo-Hi to a steel I-beam. Having been in structural steel for a good portion of my construction career in my opinion this comparison is wrong. The strength in the I-beam design is in the top to bottom strenth or otherwords downward pressure. The top of blade would be the same as the top flange of the I-beam while the blade or grooved out part of the Bo-Hi would be the same as the web of the beam. IMHO the Bo-Hi doesn't add strength to the side to side deflection in the blade. When you turn a large I-beam over on its side it loses its rigidness almost completely. The beams very own weight will cause it sag in the middle.

----------


## Bogdan M.

Top to bottom pressure on an I beam results in a lateral bending, the I beam still flexes, but it flexes less.

In a built structure an I beam doesn't flex a lot because of the more complex geometry and relationship with the other beams. But the top to bottom compression is still translated into lateral forces at some point. And the geometry doesn't change the strength, only the stiffness.

Anyway if you are careful enough, I think even the bo hi version of the Shura is forgiving enough...

----------


## mark p. smith

I also read in some of the sword reviews online that showed the 3 different blade configurations that the B0-Hi was more to maintain the blade's rigidness while removing some of the weight for a lighter, faster blade.

----------


## mark p. smith

It's on the bottom of the attached link/page from SBG.
http://sbg-sword-store.sword-buyers-...ei-Katana.html

----------


## Bogdan M.

> I also read in some of the sword reviews online that showed the 3 different blade configurations that the B0-Hi was more to maintain the blade's rigidness while removing some of the weight for a lighter, faster blade.


That's about the same thing as I said. stiffnes = rigidness. If it's maintained or enhanced depends on the exact geometry of the blade...

Some blades are also design,ed with the idea to have a bo hi from the start, especiallyy for long blades. Not enough stiffness might mean bad energy transmission on cuts...

----------


## Erik Tracy

The accepted fact is that if you take two identical blades and then cut out bo-hi, the one with bo-hi will be weaker to lateral stresses and so bend easier than the one without bo-hi.

Anytime you take material away from a blade by cutting bo-hi you make it weaker to lateral stress.

Smiths agree to this and practitioners agree to this.

However, that is not to say that ANY blade with bo-hi is *always* weaker to one without bo-hi.

If you are comparing two different blades, then you have opened the discussion to endless variables to material used, geometry, heat treat, etc.

So, it depends....

----------

