the mass principle in one sentence

[scp]

PatM, I already said twice in this thread that bow making is an art, not science. All I'm trying to do here is to make all the implicit assumptions of the mass principle explicit. I even suggested a way to expand the principle by using the knowledge where energy is stored in a bow limb. But for whatever reason, many people here think I am attacking the principle. Go figure.

[PatM]

It isn't just art.  However the art side of it is the very reason it can't be expressed explicitly because there is always a factor that has the potential to throw it off a bit. Moisture content, local environment etc.

[Justin Snyder]

Pretty vague answer.
Why don't you show us some of your work?

You don't have to trust me. Have you at least read the whole thread?

You expect him to read all your ramblings when you wont read the section of the book that you have rambled on about. The book at least made sense. As for teaching, Badger was walking us through this before you even saw it in the book. A lot of us have a decent grasp of the principle, and understand what it was intended to do. It was not intended to plug into a computer and let lasers cut out the bow. It still requires a bowyer or at least a  bow maker with a little common sense.

[scp]

Justin Snyder, if he wants to comment on the issue, he better be willing to read the whole thread. If he just wanna express his gut feelings, he can do that without doing so, I guess.

[scp]

Is anyone going to address the issue of how to incorporate heat treatment into the mass principle? How about you, Marc?

[Robert]

I think the mass principle is intended for practical use by bowyers.  To get much more precise and exact would require impractical measurements, like cutting off the tips of your bow to see how much mass they have.  The mass principle allows you to make an excellent bow just by monitoring the total mass of the bow and by taking other easy measurements like length of bending limbs, etc.  You might say it's "low resolution", where a high resolution method would involve chopping the bow into inch long pieces to see exactly where the mass is placed, the obvious problem being reassembly.  At least that's what I think you're getting at when you mention "where energy is stored in the bow limb".

As far as underlying assumptions, I think it is that a bow's ability to perform work is fundamentally dependent upon how massive it is.  The "mass principle" is more of an empirical determination of what the ideal mass is for a given amount of stored energy from a bow made of an "average" wood.  The big revelation was that the ideal mass didn't change much from one wood to another, that you could basically use the same mass for a bow made from any wood.  But there small discrepancies for certain woods, and for things like cross-section, reflex, and heat-treating and so it gets fudged up or down.  It sounds like you want a fully fleshed out theorem that deals precisely with all of these factors.  But that starts to get extremely complicated so fast...and even if you were ambitious enough to try, the average bowyer wouldn't be able to measure enough dimensions accurately enough for it be practical to actually implement. 

The whole discussion reminded me of the ideal gas law (PV=nRT, iirc) from chemistry.  It relates pressure volume and temperature for gases.  It is based upon an ideal gas, which doesn't exist, under an abstract set of conditions called standard temperature and pressure, which probably only occur in a laboratory.  But it is applied everyday for non-ideal (i.e. real) gases in all sorts of different conditions nowhere near the standard.  It is close enough, and I think the mass principle is similar for wooden bow.

So if you ever get bored you can go to the chemistry boards and question their "implicit assumptions"

[Hillbilly]

Scp, I'm just a redneck off a dirt farm in the mountains, and I'm as dumb as a sack full of rocks; but after reading Steve's chapter about the mass principal, I can understand it enough to apply it to what little I already know and make better bows as a result. I'll never be able to make bows like Steve, Marc, or some of the other bowyers here, but if I listen to them instead of argue with them, I learn, and can see results of that in my own work. One thing I have learned from hanging around here for years, also, is something that you don't seem to have grasped yet-let's call it the "wooden bow principal." In it's simplest form, it states that each piece of wood is a unique entity. Coming from a living tree, it has its own unique character and characteristics, unlike a sample of fiberglass or carbon fiber, which is pretty much standardized and consistant with any other sample manufactured to the same specifications. Therein lies the interest, challenge, and joy of building wooden bows. If you want a set formula that will allow you to build a completely predictable bow to pre-set measurements every time, get you some fiberglass lams and a calculator. Maybe building wooden bows isn't your thing. If you want to experience the challenge of working with the individual personality of the piece of wood you're working on at the moment; and try to get the best bow from it you can, then you have to accept this fact: wood isn't wood isn't wood. Steve's mass principal, when combined with a certain amount of experience and a desire to learn from and listen to the wood, is a very useful tool for making a better bow. It is not a machine that works by itself, it still requires a bowyer to operate it. Start with the ideal design for your wood, then work with it within the limitations of your particular piece of wood. There may be a knot here, a place there where a woodpecker pecked the wood, the grain may swirl, there may be a spot where the growth rings crown up or dish in. These anomalies can't be answered by mathematics, only by experience, feel,  and attention. This is the very thing that attracts many of us to building wooden bows-the challenge of making them, the process of learning to read and feel wood, and the uniqueness of the finished product. This is the very thing you seem to not want to accept. It's a simple concept. It's not all quantifiable or measureable, there are too many variables. But-it can be predicted to a certain extent, which is what Steve's principlal does as well as any other method could. The rest relies on your skill as a bowyer, there's no way to get around that. Steve's theory seems sound to me, and seems simple to understand if you've built some bows. After the dozens you say you've built, you should already understand this and accept it instead of try to argue about it. I'm not very scientific at alll when I make a bow. Like Eddie, I have never weighed a bow while I was making it-but the better performing ones I have made, when weighed tend to agree in mass with Steve's ideas.