the mass principle
scp
principle in one sentence?
scp
> I think I understand. I think I understand. But what is the mass
> principle in one sentence?
Badger, you are talkng as if the mass principle is "being guided by mass"
and the totality of our knowledge in bow making. Nobody would say mass
does not matter in designing a bow. But we need to be more specific about
how to be guided by mass. Guided by your table in the Traditional Bower's
Bible? How do we know that the table is correct or optimum?
Don't get me wrong. I'm not trying to challenge the principle or your
understanding of it. I just wanna have a more handy exposition of the
principle. Is it more like wisdom than knowledge?
scp
I read the chapter three times. Saying that the mass principle works is
rather like saying justice works. But how? If you already know how to
make a good bow, it works. Even if you have no idea how to make a bow,
still you would think mass matters. But where exactly? It's well
explained in the above mentioned chapter. But that means we need to know
all about the bow profiles and tillering. We know how to apply it; but
what is it that is being applied? Can it be expressed in a sentence? Mass
matters but where exactly? Can anyone make a terrible bow that has the
recommended weight in the table?
Does common sense work? If so, what is it? In a sentence, please. ;-)
How about in a paragraph? Let's see. If you already know how to make a
good bow in theory, say you have read the Traditional bower's Bible three
times, you can use the weight of the bow you are making to figure out
when you are done, when you need to scrape the side, or when to apply the
sound bow design principle in tillering. What really matters is where we
put the mass. Do we even know how to measure the weight of a particular
section of the bow? Not exactly. So we use the width and the thickness as
guides. Does that mean the width and the thickness natter? Of course. But
how?
One of the specific sentence about the mass principle is that it assumes
that "for bow making purposes all wood is equal." Is that why we look for
certain kinds of wood or a particular stave with certain characteristics?
Of course, we can make the principle work. And I do believe the
underlying intuition is correct. But to make it work for everyone, we
need to know what it is. Is it just common sense about the total mass and
its proper distribution in a well designed bow? If so, can it be
expressed in a succinct paragraph?
scp
Let me be a little more constructive.
IMHO the mass principle say that, if we assume that for bow making
purposes all wood is pretty much equal, the optimal total mass of a bow
is predictable and attainable through the use of the table obtained
through the experience of many good bowyers. Of course, it also matters a
lot how we distribute the mass. There we should use the sound bow design
principles, especially concerning the proper tillering for a specific
profile. We also need to know how to adjust the figure in the table
according to the length of the nonworking grip, the unbending tips, and
etc. How to do this is in the directions after the table.
[Here we need to put the table and the directions.]
This principle is a work in progress. The proper issue is not whether it
works or not, but how we can make it work and refine it to make its
application easier. I still don't know how to use the total weight in
figuring out the proper distribution of the mass. Is there any way we can
refine the principle to tell us how to do it, other than invoking the
sound bow design principles? I guess the mass principle is a part of the
design principles. If so, what does it say about the proper distribution
of the mass by itself?
scp
Thanks. That must be a major part of the mass principle. If so, it might
also mean that the tips need to be as light as possible. Does the mass
principle say anything about the proper length of the unbending tips? All
other things equal, is it correct that the unbending tips should be as
long as the optimal table allows? How do we know when to scrape the side
of the working part of the rims instead of lightening the tips? Can the
mass principle be rephrased to help us in answering the question?
scp
Badger:
The distribution of the mass is determined by width only,
the depth is what you use to control your bending.
Mass logic simply means that the full drawn side profile
of a bow should agree with the front view of a bow.
I don't think the first sentence above is correct. The relative
distribution of the mass can be measured by using the width and the depth
of sections.
As for the second sentence, it appear that the total mass would be
optimal if "the full drawn side profile of a bow should agree with the
front view of a bow." Does that mean the mass principle is a way to tell
whether the profile agree with front view?
scp
Quote from: Badger on January 15, 2010, 03:36:05 PM
Better yet, let me e email you a calculator, you feed in the handle size,
the length, draw length, and draw weight, it will give you back the mass
needed, you control the mass by controlling the width. Now to use the
calculator you have to know how to manipulate the stiff handle area
number to accomadate your tiller shape, and the draw length to accomadate
stiff tips. Steve
I'm afraid we can control the mass by controlling either the width or the
depth or both. I agree that given the profile/style and "the handle size,
the length, draw length, and draw weight," we can probably figure out the
optimal mass of the bow. That means, as you have written in the book, the
mass principle can tell us when to stop tillering and even when to start
scraping the side instead of the belly, as doing so would change the mass
much more without affecting the draw weight too much. But it probably
cannot tell us whether we need to lighten the unbending tips instead of
scraping the side of the working part of the limbs. Can it? Better yet,
can we refine the principle to do so?
scp
Badger, I am not saying that you didn't say it well or fully in the book.
All I'm asking for now is a simple paragraph we can use to understand the
principle and to learn how to apply it, even if we cannot express it in a
sentence. Of course, what I have said in my version is all in the book.
Otherwise I would be calling it my mass principle.
I think you would agree with me that the mass principle is not a fixed
and explicit rule but a working hypothesis that seems to be working so
far or a work in progress that can be made to work. Either way, according
to the mass principle, given a particular specification of a bow, its
optimal total mass is reasonably predictable and attainable.
We can stop there or we can make it also deal with the proper
distribution of the mass. You appear to opt for the latter as you say "It
is more about having enough mass and having it in the right places." Now
we need to say what it means to "have enough mass in the right places."
You say "The thickness controls how far a piece of wood can bend before
it takes any set and the width controls how far it actually will bend
when drawn." If this is the case according to the mass principle, of
course when all other things are equal, what is the relationship between
the mass and the width and the thickness that makes it so?
You also said, "The distribution of the mass is determined by width only,
the depth is what you use to control your bending." Does that mean we
cannot control the distribution of the mass by changing the thickness?
scp
Quote from: Badger on January 15, 2010, 06:39:23 PM
Yes, you ignore thickness when distributing mass, thickness is never
negotiable if you have a particular tiller in mind.
That sounds like an oversimplification. Do you ignore thickness when you
try to properly distribute mass in an ELB style bow? You must be talking
about the case when you have reached at a certain stage of bow making,
say when you have reached the target draw weight at the target draw
length but still the total mass is a little high. Does that mean we are
not allowed to scrape the belly and heat treat it?
scp
Jawge, a principle must be much more than a technique. I BELIVE in the
underlying intuition. But unless you formulate the principle to make it
falsifiable, you are not there yet.
Badger, I don't hunt. Not even fished lately. But I shoot at targets. I
chase "principles" and understanding. I have no doubt you know what you
are doing. But you might be calling the totality of your experience the
mass principle. Of course, bow making is an art, not science. Still if
you are going to call something a principle, you might have to provide a
succinct exposition that can be used by everyone.
Your said "you ignore thickness when distributing mass." What do you mean
by "when distributing mass"? It cannot mean "when we are tillering," can
it? How can we ignore thickness when we are tillering? Does it mean "when
we are applying the mass principle after most of the tillering is done"?
You also said, "The distribution of the mass is determined by width
only." Then I have to ask when? When we are designing a bow? You might be
thinking about when the bow is almost finished and you are trying to
apply the mass principle to that bow. Why can't we determine the proper
distribution of mass by thickness when we are designing a new bow?
Don't get me wrong. I'm not saying you are wrong. I'm saying good bowyers
need to make their assumptions more explicit. Knowledge mining is never
easy and can be quite irritating sometimes.
The mass principle in a paragraph, anyone?
scp
The mass principle says that it always takes the same amount of wood mass
to do the same amount of work in a bow. But, of course, how can it be
otherwise? Still, is this principle falsifiable?
scp
Justin Snyder, you are talking about the PRIMARY mass principle.
"According to the mass principle, given a particular specification of a
bow, its optimal total mass is reasonably predictable and attainable."
Nobody seems to have any problem with that.
But Badger goes much further than that. He thinks the principle is useful
in predictng or prescribing the proper mass distribution in a well made
bow. When I ask him how, he just invokes the sound bow design principles.
I'm sure mass is relevant in there somewhere somehow. But where, when,
and how?
scp
Quote from: George Tsoukalas on January 16, 2010, 11:46:35 AM
scp, no, it is not and that's why it can be called a principle. The
underlying principle is the concept of density (d=m/v).
"A hypothesis, proposition, or theory is 'scientific' only if it is
falsifiable."
http://en.wikipedia.org/wiki/Falsifiability
Are you trying to say that the mass principle is a semantic one?
scp
Quote from: Badger on January 16, 2010, 12:25:59 PM
I believ it is falsifiable, build a bow 20% under the recomended mass and
see how it performs, or build it 20% over the recomended mass and see how
it performs.
Me too. The PRIMARY mass principle is falsifiable. Or at least, it
appears that we can make it so.
The mass principle says that it always takes the same amount of wood mass
to do the same amount of work in a bow.
If we wanna go further and talk about the mass principle concerning the
proper distribution of mass in a well made bow, we probably have to talk
about the relationship between the mass, the width, and the thickness of
each sctions of the bow. You have been making several interesting
statements about it. I don't think you are wrong. But I do believe that
many of the underlying assumptions or qualifications have to be made
explicit. I repeat:
scp
Badger, I agree. That's why I have said earlier, "as you have written in
the book, the mass principle can tell us when to stop tillering and even
when to start scraping the side instead of the belly, as doing so would
change the mass much more without affecting the draw weight too much."
Believe it or not, I think we can milk the mass principle a little more
than we have done so far. I suspect it is implicitly used in the sound
bow design principles. But saying that "the distribution of the mass is
determined by width only" seems to be too blunt. In the pyramid style
bow, the distribution of mass is usually determined by width. If so, we
can use the way where energy is stored in a bow limb (pp. 116-117 of TBB4)
to set the proper width of each sections, according to the mass
principle. But in an ELB style bow, we might use the thickness instead.
In both cases, we will be using the mass principle to put the proper
amount of mass in a particular section as required by the amount of work
it has to do.
scp
Jawge, I already said and believe that bow making is an art, not science.
I would even say that it should remain that way! That does not mean we
cannot use rigorous reasoning to understand what goes into making a well
designed bow.
I don't know and haven't tried to figure out how they did that, but we
even have the chart showing where energy is stored for a D-longbow. That
means, using the mass principle, we can design a decent bow rather easily.
This is the chart from p. 117 of TBB4:
Quote
Inches from center --- energy
0 - 7" 30%
7 - 14" 27%
14 - 21" 22%
21 - 28" 15%
28 - 35" 6%
I bet most well made bows will have the similar mass profile.
scp
Quote from: Badger on January 17, 2010, 04:11:07 PM
SCP, heat treating hardens up the belly and will allow you to go with
less mass than a non heat treated bow. It doesn't really change the mass
of the wood than much but it does change how much wood you need. Steve
Fascinating. Does that mean heat treatment defeats the mass principle?
scp
Quote from: Badger on January 17, 2010, 04:49:03 PM
No, SCP, it means a bowyer has to know what he is doing and allow for
various things. Lots of things change projected bow mass, trapping,
backing a bow, heat treating a bow, excessive dryness in a bow. It is not
designed for idiots, more for advanced bowyers. Steve
I'm afraid you are not thinking clearly here. If you can reduce the mass
required by the WOOD mass principle through heat treatment, that means
the principle is no longer applicable.
Let's look at the nature of heat treatment. If it somehow changes light
wood into heavy wood, the WOOD mass principle should hold even after the
heat treatment. That is, still same mass is required.
If it somehow changes wood into something other than wood, say
fiberglass, we don't expect the WOOD mass principle to be valid anymore.
You appear to be thinking this is the case. That means we cannot use the
same mass principle for the heat treated wood bows, just as we cannot do
so with fiberglass bows. Of course, each different materials will have
their own mass principles, so long as they are cohesive enough.
Now, what is the nature of heat treatment? Does it change light wood into
heavy wood? Or, does it change wood into something else?
scp
Quote from: Badger on January 17, 2010, 05:22:49 PM
None of the above, it changes the typical ratios of compression to
tension strength, allowing for a lower mass bow.
I don't think you understood what I said. If heat treatment "changes the
typical ratios of compression to tension strength, allowing for a lower
mass bow" does that mean heat treatment renders the mass principle
useless?
scp
Quote from: Gordon on January 17, 2010, 05:51:43 PM
scp, I'm not sure why, but heat treating (when proprely done) makes the
belly wood more resistant to compression. I even use it to tweak a tiller
when I don't want to remove wood. For instance, I will sometimes lightly
temper the outer limbs when I want them to bend slightly less. You have
to be careful, however, because too much can throw the whole tiller out
of wack.
You can think of it as scraping out a certain amount of wood and
replacing it with the same mass of OTHER MATERIAL, say bamboo, horn or
even fiberglass. For the belly, that other material better be something
that has more resistance to compression. You are basically turning your
bow wood into something better than it was. It is possible that, as
Badger says, heat treatment "changes the typical ratios of compression to
tension strength."
Whether it can do so enough to become an exception to the WOOD mass
principle is another story.
scp
Quote from: PatM on January 17, 2010, 06:31:26 PM
It should be pretty clear that even with heat treating you're just
turning wood into slightly better wood. Better wood needs less mass to
reach a goal.
Badger said NO to the first sentence. See, above.
As for the second sentence, Badger said, the mass principle assumes for
scp
Quote from: Gordon on January 17, 2010, 07:14:39 PM
scp, the base assumption of Steve's theory is that all wood is equal.
However, Steve acknowledges that heat treating changes that calculation
and that an allowance has to be made. No model can perfectly predict an
outcome for something that has as many variables as constructing a bow
made of all natural materials. But is seems to be a pretty good
approximation and a useful tool for any bowyer who is serious about the
performance of their bows.
I believe it works. If not, we can always make it work! But we can't do
that if we are not willing to think, ask questions, experiment, and
communicate. I mostly ask questions.
scp
It would be extremely difficult to incorporate the heat treatment into
the mass principle, mainly because it does not work the same way for all
kinds of wood.
scp
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.