Bo-hi or no bo-hi

[Rasmus]

Today I tried tameshigiri with two different Cheness Cutlery (www.chenessinc.com) Mokko 1060 (http://www.chenessinc.com/mokko.htm) blades. One with bo-hi and one without.

I liked the one with bo-hi best. It was a little lighter, felt more like my iaito, and forced me to really concentrate on making a correct cut. The heavier sword on the other hand felt a little swifter and its extra weight made for eaiser cutting. Compared to a Citadel sword they both felt a bite crude but lined up against a Cold Steel katana I cannot complain.

The bo-hi sword is better suited for kata practice than the one without but since I am nowere near ready to practice kata with a live blade that doesn't really matter. I will use it only for tameshigiri at our dojo.

Having said so I've got a couple of questions and please don't go "Ask your sensei..." on me now. There are no experienced cutters in my dojo nor in the rest of Sweden to match those lurkin' here at e-budo. And belive me when I say that we've begin incorperating tameshigiri in our practice under guidance of the most knowledgeable ones available to us.

Questions:

1. The bo-hi sword felt better but is at an disadvantage when it comes to lateral strength. How significant is the difference? The heaviest target I will ever cut with it is rolled single or half tatami omote mats.

2. Disregarding my preference; which type of sword is the prefered choice when it comes to serious cutting and expert cutters?

3. I've googled Cheness Cutlers and found both positive and negative opinions. The positive ones seems dominate. Anyone here that want to dispute or challange my impression? I know about the incident with the sword that snapped and how it resolved so no need to bring that particular story up again.

4. How well does a Chennes Moko 1060 retain its sharpness? As far as I've been told the Cold Steel katana we've got will lose its edge rather quickly because of it's spring steel tempering. Is a monosteel blade like the Mokko better or worse?

[Douglas Wylie]

Having said so I've got a couple of questions and please don't go "Ask your sensei..." on me now.

Well, that's the only person who matters. You dont know anyone here from jack, why are you going to take the advice of someone who may not know what they are talking about?


There are no experienced cutters in my dojo nor in the rest of Sweden to match those lurkin' here at e-budo. And belive me when I say that we've begin incorperating tameshigiri in our practice under guidance of the most knowledgeable ones available to us.

Umm, thats kind of cryptic. Sounds like you dont have a teacher and are trying to get by the best you can.

If that is the case, you need to put the swords down and devote all your time and energy to finding a good teacher, someone you can come to with questions like this. I understand that it may be difficult and you may need to travel to find one, but that is part of it. I know there are ZNIR MJER Iaido teachers in Belgium, France, Germany, Finland etc... I found a ZNIR MSR Dojo in Sweden just by using Google- http://www.kvac.uu.se/~agback/iaido/iaido_frame.html

Here is a page with 7 more iaido dojo in Sweden- http://www.iaido-jodo.ch/english/dojo_in_sweden.htm


2. Disregarding my preference; which type of sword is the prefered choice when it comes to serious cutting and expert cutters?

Expensive ones, you are talking 4 digits. Definately not the $200 cheapies.


3. I've googled Cheness Cutlers and found both positive and negative opinions. The positive ones seems dominate.

This is where you need to trust the opinion of your sensei. You finding a lot of positive reviews of the $200 el cheapo? Who is giving the review? A know nothing fanboy who thinks swordz r kewl? Someone selling them? Anyone above 6 dan in iaido? A thousand positive reviews from newbies isn't worth one review from someone with a decade or two of training under their belt.

Sorry to hit you with the standard line but it is the only answer-

Ask your sensei, if you dont have one- get one.

[Ken-Hawaii]

Doug is definitely correct on all counts, Rasmus. Find a sensei somewhere in your country, or if you really can't do that, find one you can hire to come in & set up a tameshigiri curriculum. If you can't manage even that, then find one on-line. Not only will you learn more & faster, but you'll also be a damn sight safer than cutting on your own!

A blade with a bo-hi is definitely stronger than one without, as well as being lighter. Simple engineering. Correct hasuji will always count more than weight.

I use a highly-tempered & customized shinken from Orochi Shinken for tameshigiri, while my wife uses a Cold Steel shinken. If there's any difference in cutting ability, we haven't found it in several years of frequent practice. Neither has lost any of its edge, either, & we cut multiple tatami omote, bamboo, & sometimes both together. If you start with a sharp blade, you'll have no problem with cutting ability unless you manage to screw up royally - another reason to have a sensei.

I tried a friend's Cheness, & didn't like it a bit. Personal preference & my own opinion, of course. Our Sensei also uses an Orochi Shinken, by the way. Loren can customize yours to whatever specifications (& budget) you have.

[Rasmus]

I guess the "disclaimer" I wrote was a pretty stupid idea and it truly backfired. However; I've sen't personal messages to Douglas and Ken-Hawaii putting the record straight. I won't do it publically because I don't want to write anything about my seniors in the Swedish iaido community and naming people for all to read.

I can't be the only swede here and I would really appreciate if someone else could write a couple of lines about what's going on in our little corner of the globe.

[Solinde]

Having said so I've got a couple of questions and please don't go "Ask your sensei..." on me now. There are no experienced cutters in my dojo nor in the rest of Sweden to match those lurkin' here at e-budo. And belive me when I say that we've begin incorperating tameshigiri in our practice under guidance of the most knowledgeable ones available to us.

This is pretty much correct. There are no experienced cutters in our dojo, tameshigiri-wise, as it is an iai dojo first and foremost. Those interested in tameshigiri have brought teachers from outside the dojo to come teach, but noone in this dojo has had the possibility to practise much.

While there are a few more or less experienced cutters in Sweden, not many are interested in teaching tameshigiri, and most only practise it to improve their iai. There's nothing wrong with that of course, but the result is that there are not alot of teachers available.

Oh, and I can assure you that Rasmus is in a dojo, so no need to worry about that. :)

[socho]

... which type of sword is the preferred choice when it comes to serious cutting and expert cutters? ??? Serious cutting? As opposed to frivolous cutting? Expert cutters? As opposed to amateurs?


...not many are interested in teaching tameshigiri, and most only practise it to improve their iai. Ahhh. :) Kind of the point, no? Be wary of those that teach cutting as just cutting. The context of cutting is within the framework of whatever sword art(s) you train in. Training. Application of technique, kata, waza. Not just standing still and whacking mats.
Whatever sword you use, should be the sword you use. For everything. Use what feels right, use what works, and whatever sword you use regularly will be the one that feels right and works. And don't just focus on the blade, the fittings need to be reliable as well.

Dave

[Erik Tracy]

A blade with a bo-hi is definitely stronger than one without, as well as being lighter. Simple engineering. Correct hasuji will always count more than weight.

Ken,
I'm not sure that the above statement is entirely correct. Everything I've read from more experienced cutters, smiths, and 'engineers' is that a blade with bo-hi is not signicantly 'weaker' from edge to back than a blade with out bo-hi, but that a blade with bo-hi IS weaker for lateral (side to side) stresses because you've removed material.

My personal experience with several blades I've personally owned seems to bear this out. Those with bo-hi are easier to bend due to bad hasuji than those without.

There's a web paper out there - I'll have to dig the link up where an engineering budoka did the mathmetical analysis to show this.

Just tossing out my opinion on this, ymmv.

Respectfully,
Erik Tracy

[Ken-Hawaii]

Erik, as a solid length of steel is supposedly stronger than an I-beam, why do you suppose I-beams are used in buildings...? I've been a professional engineer for 40 years, & a lot of what I used to do for a living was to calculate just how much material can be cut away/omitted in the manufacturing process while still maintaining the required strength of materials.

Yes, you can break a sword - or just about anything else - with enough lateral pressure, but where will that pressure be coming from? Lord knows I've messed up enough strikes with incorrect hasuji to have broken my shinken many times over, but that just hasn't happened. I guess you could manage to break a blade by striking something hard enough, but I don't think a bo-hi would make much difference. I can run some stress/strain calculations using my AutoCAD model of a Nihonto when I get the time - that should resolve the question.

[Erik Tracy]

It has been my understanding that the I-beam is used to reduce the amount of steel used in construction to reduce material cost while not compromising load bearing structural integrity - not that it *increases* structural strength.

Also, the load bearing vectors are from top to bottom not from side to side.

Hence, in the case of swords, when you take material *away* from the sides of the blade, you weaken it in regards to lateral stresses - making it more prone to bending when compared to an identical blade geometry that has no bo-hi.

In regards to historical katana, some togishi speculate that bo-hi were sometimes carved in to remove weld flaws in the forging process as well as to lighten the blade - but not specifically to *strengthen* it.

I will quite readily concede the point of debate if it can be shown from an engineering analysis that bo-hi *strengthen* a blade from lateral stress (side to side, not edge to back).

Respectfully,
Erik

[Charles Mahan]

Erik and Ken,

I think you are both right. It's a matter of how you define the problem.

If you take two lumps of steel of exactly the same mass and turn them both into shinken, then the one with bo-hi will be slightly stronger than the one without in the plane that runs from hi to mune, but weaker in every other plane.

If however you take two lumps of steel of the same mass and turn them both into shinken without bo-hi, and then carve a bo-hi into one of them, then the one without bo-hi will be stronger in all planes. The one with bo-hi will still be nearly as strong in the plane which passes through the mune and hi, but somewhat weaker in the other planes.

As for I-beams, they are used because they are a good compromise between weight and strength.

[Enfield]

It depends what you're comparing. Comparing beams of the same mass, the I-beam will be stiffer. Material farther away from the centroid is more effective at resisting bending. So, rearranging the material to get it farther away from the center, makes the whole thing stiffer.

But that's not what hi are doing. No one is using them to make a sword wider with the same mass. For swords with and without hi, we're comparing beams of the same outer dimensions. In that case, the I-beam is less stiff, more so side-to-side if it's laid like an I. The reduction in stiffness isn't as much regarding bending up or down, which is why they're usually I-beams and not H-beams.

So, if you wanted to use hi to rearrange the same amount of material, making the sword wider, it would be more resistant to sideways bending. It'd also be less effective as a sword. Using them the reduce weight does make the sword less stiff, but not as much as making the sword thinner over all. And since swords aren't of uniform cross section, and the hi need not extend the entire length of the sword, they can be used to change the location of its center of mass and polar moment, changing how it feels and whether it "wants" to swing in big circles or small, tight cuts.

ETA: Charles posted while I was editing.

[kdlarman]

Just to add a "Yes" to the discussion...

I-beams are have a better strength to weight ratio than a solid beam of identical outside dimensions. Obviously a solid beam of similar external dimensions would be incredibly heavy.

But take a blade with a robust cross section without bo-hi. Test it's strength to lateral bends and twists. Take the same blade and cut in a bo-hi. The resultant blade will be very similar in strength edge to back, but it will lose some of it's ability to withstand lateral and twisting forces. Hence it will bend more easily.

The problem with making any statement about bo-hi is that it depends completely on the blade. A gigantic, thick blade with bo-hi can be stronger than a thin wide blade without.

But it is an "all thing being equal" deal here. You cannot remove steel from a blade and make it "stronger". You can remove steel judiciously and improve the strength to weight *ratio* however.

In construction you are dealing with weight issues as well. Solid beams would be silly compared to properly used i-beams as solid beams would be way too heavy. The vastly lighter I-beams makes for a structure that is "stronger" but that is also because it is also vastly lighter.

How much cutting in a bo-hi affects a blade's strength depends on how the bo-hi is cut (most production swords cut them with a ball and cut way too deep), the shape of the blade to begin with, then how the swordsman happens to abuse the thing. With perfect form the loss of strength by cutting in even a super deep bo-hi probably won't matter. But screw up your form... Bad day.

edit: note to self -- do not read thread, walk away, do an errand, then come back and post without refreshing the display. Because then you say basically the exact same thing everyone else already said... ;) Ironically enough I'm right now polishing a bo-hi... Lord do I hate bo-hi...

[Swordy]

Hey guys, does the shape of the fuller matter to it's stress resistance? Like for example )( (concave inward curve) instead of an I (I beam shape).

I've never seen a fuller before. But i wonder if it is this )( shape. Does it work the same way with the concept of the arch?

Wikipedia arch (http://en.wikipedia.org/wiki/Arch)

[pgsmith]

Hi Andreas,
You've had several replies regarding your other questions, so I thought I would throw my two cents in on one that nobody has hit on yet. You asked ...

3. I've googled Cheness Cutlers and found both positive and negative opinions. The positive ones seems dominate. Anyone here that want to dispute or challange my impression? I know about the incident with the sword that snapped and how it resolved so no need to bring that particular story up again.
I've used several different Cheness swords, taken them apart and inspected them thoroughly, and cut several targets with them. The conclusion that I came to was that they were poorly finished, the fittings and wrap were very poor, the balance and shaping were horrible, and the tsuka were a serious accident waiting to happen (two of them were already cracked). I do not allow that brand in the dojo anymore. I realize that they are very inexpensive swords, but they are very inexpensive for a reason. You'd be way better off saving up money to purchase a bit better grade of sword. For that matter, I would say almost exactly the same things about the Cold Steel swords that I've used in the past. None of the Cold Steel tsuka that I inspected happened to be cracked yet, but it appeared to be only a matter of time to me. I don't allow them in the dojo either.

There you go, my two cent's worth, since you asked.