the mass principle in one sentence

[Justin Snyder]

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?

It does...... Maybe you should go back and read it again. Then use it to build 6 or 7 bows and you will begin to understand. Nobody ever learned to drive by reading a drivers handbook.

[half eye]

Hey Marc,
       Ya that was me...you can do proportions with a stick but the formula was the easiest way to explain it and it sure was not put forward as a "principle".
       I am well aware I'm not part of the old boys, I didn't write a chapter in Bowyers Bible IV, I don't have a website to sell bows and I know you are one of the "Global Moderators"......the other thing I'm well aware of is your sarcasm....and will give it all the respect that it is due.
half eye

[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.

[Badger]

    Half eye, if you look closely at the few remaining remnants of primitive designs that we have to work with you will quickly see they are very well engineered. Better than we do today. If you study them a bit it becomes apparent there was quite a bit of logic involved in them and I suspect this was discussed by bowyers of that day similar to the way men have discussed hunting and war weapons throughout history. The english long bow is almost perfectly designed for what it does, the mollabet and holmgarde are also good examples.
One that had puzzled me for years but I think I finaly figured out is the Solomom island bow. These bows at a glance seem to be contrary to any kind of logic. But when examined closely are absolutely stunning in their design.
       A solomom bow is extremely long in the upper limb and very short in the lower limb, most long bows like this would have a very heavy draw weight and very long draw, these are medium weight bows with average draw lengths. A bow like this would be extremely shocky and inefficent with a normal weight arrow. The bows are also made in an s shape which doesn't seem to make sense.
      These bows are used for fishing as the fishernman wades through shallow water, the short bottom limb is obvious it needs to stay dry. The top limb is not so obvious, it is wide and thin with a very narrow tip, this would vibrate a lot and loose most of it's energy before it ever got to the arrow. I suspect that these fishing arrows were very heavy so they could penetrate water and only had to shoot a few feet. The length of the bow would store a lot of energy and offer a smooth draw, the heavy weight of the arrow would allow the bow to be efficient regardless of it's wide thin limbs. They would also dry out faster if they got wet for some reason. The curve in the bow used to puzzle me, I think now it is the equivalent to a sight window so they could see their fish. They dont anchor these bows at the face like we do shooting a deer. I have to wonder how long it took them to figure all this out. They obviously passed it down from generation to generation and improved on it as it went. The bow eveoloved just as animals do in special circumstances. For us hobby bowyers to fully get the experience we are looking for we pass info back and forth and sometimes look for shortcuts. Understanding the logic behind the bow is the key to proper design. Steve

[George Tsoukalas]

 Again, scp, your initial assumptions are flawed. Almost any human activity involves science but building bows is NOT science. and therefore needs no independent testing.  It's art. I also believe the mass principle  is verifiable but if it isn't applicable all the time so what? It's a viable technique. Beginners are lucky to get a bow made. Forget about worrying about mass considerations. Jawge

[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:

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.

[George Tsoukalas]

So, scp, you all set? Jawge

[Marc St Louis]

Hey Marc,
       Ya that was me...you can do proportions with a stick but the formula was the easiest way to explain it and it sure was not put forward as a "principle".
       I am well aware I'm not part of the old boys, I didn't write a chapter in Bowyers Bible IV, I don't have a website to sell bows and I know you are one of the "Global Moderators"......the other thing I'm well aware of is your sarcasm....and will give it all the respect that it is due.
half eye

Ah so you recognize the fact that it was well deserved.  Good

[Marc St Louis]

So, scp, you all set? Jawge

Exactly

[avcase]

This has been a pretty good read.  Of course, monitoring the mass of a bow won't design the bow for you but it is another reference point that has been useful for many.  I see it as a tool that takes a similar approach as an arrow spine chart.  There is a basic assumption that correlates very well to an easy to measure property, then a number of incremental adjustments to suit the particular circumstance.  Steve has done a great job with this in it's application to wood bow building.

Whether it is intended or not, there is plenty of SCIENCE to support this mass idea.  Wood from trees is amazingly consistent.  There are several places in research publications from the US Forest Products research where it closely correlates most engineering properties of wood to the density (Elastic modulus, Maximum Strength in Bending, etc.).  So, I guess you could say the mass/density idea has been used for a long time for designing wood structures.  With these same properties you can calculate the minimum amount of bow wood required to store the amount of energy for a given draw weight and draw length.

Or, you can just bypass all the intermediate formulas and calculations and take Steve's approach that the minimum amount of wood needed to store the energy for a given draw length and draw weight is proportional to the mass.  That is pretty much it.  I like it.
-Alan

[scp]

Jawg, I make bows for physical exercise. After making several dozen flat bows mainly in pyramid style while reading the Traditional Bower's Bible a couple of times, I'm asking myself whether I wanna make bows for mental exercise as well. Definitely not, unless I have to! Don't make me, please. ;-)

[George Tsoukalas]

Not I, scp. I did 35 years of mental exercise. I just make them and shoot them. Jawge

[Justin Snyder]

Jawg, I make bows for physical exercise. After making several dozen flat bows mainly in pyramid style while reading the Traditional Bower's Bible a couple of times, I'm asking myself whether I wanna make bows for mental exercise as well. Definitely not, unless I have to! Don't make me, please. ;-)

I don't do it for mental exercise, do it for a mental break.

[NTD]

Jawg, I make bows for physical exercise. After making several dozen flat bows mainly in pyramid style while reading the Traditional Bower's Bible a couple of times, I'm asking myself whether I wanna make bows for mental exercise as well. Definitely not, unless I have to! Don't make me, please. ;-)

I don't do it for mental exercise, do it for a mental break.

ME TOO!!! And what a mental break it is... 

[Badger]

   Half I pointed out they were making bows just fine for the last 10,000 years with no need for the bowyers bibles and he was right on when he said that, instead they were using 10,000 years of experience that was lost a while back. The quality of bows has come up immensely in the last 10 years I think because of internet sharing of experience. a new guy can come in today and be making excellent bows in a very short amount of time. If he chooses he can still strive to make them better. If not he can just enjoy the journey. I enjoy both, I have the greatest appreciation and respect for the ancient bowyers, I can't say it enough times, they really knew their stuff. Just for the record, in some cultures bows were not measured by draw weight they were measured by mass weight, so it is nothing new. Steve