the mass principle in one sentence

[scp]

I think I understand. I think I understand. But what is the mass principle in one sentence?

[Josh]

I think I understand. I think I understand. But what is the mass principle in one sentence?

"Bows that weigh the proper ammount relative to the wood's density perform better."   

Just kidding.  I don't know

[Justin Snyder]

Bows of the right mass aren't to overbuilt or underbuilt.

[Badger]

         I am going to think about this and try to describe it in one sentence. " Using mass as a guide when designing a bow" .

    Funny thing about this is I seem to be getting more interest on this from our Euro friends. I also see mass mentioned more often when stats are posted leading me to believe mass is being kept in mind.

    Some of the obvious benefits to the mass principle for the everyday bowyer, it will quickly tell you if the wood has too much moisture, if it does you can't make target mass without excessive set.
    It can also help you to design a bow, for instance a couple of years ago we talked about making an English longbow form boo backed ipe at 50# for flight shooting. An elb is a good one to use as an example because it has to meet specs for both width and depth. It is impossible to make an arc of the circle tillered elb from ipe over 66" long without becomming extremely whip tillered. The formula suggested the bow be about 60" long and weigh about 11 0z. 3 months later Dan Perry broke a 50# world record using thos exact demensions.
   A good way to evaluate the mass principle is to reverse design a bow. Go ahead and choose the demensions like you normaly would. Instaed of selecting a target draw weight simply build the bow as heavy as you can without taking more than 1" of set from the original profile. When doing this the front view has to agree with the tiller shape, this is critical. If the limbs are pyramid it should have an arc of the circle tiller, if the limbs are paralell the bend should increase down the length of the paralell limbs. When you get finished see how close it comes to target mass.
    I see lots of examples of bows below mass but in most cases they have dropped a lot of draw weight from being underbuilt. You see this a lot in heavily reflexed bows, they may not break but they get a bit rubbery.
Any questions I will always be glad to chime in. Steve

[scp]

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?

[Badger]

  Scp, no problem with challenging something. It should be challenged. If you read the chapter in detail you would see how radicaly the mass changes as the bow design changes. The table is only for two basic designs. There were several hundred bows built of all different types to test this out. It never will be exact but does claim to be pretty close. as working limb decreases mass increases. Two bows tillered differently put radicaly different amounts of strain on the limbs, yet you will usually see the same width recomendations for different tillered bows. The criteria for judging proper mass was based on how much set a bow would take and how well it performed speed wise. In other words if a self bow was shooting 170 fps and took less than 1" set I would say it likely had the right amount of mass well distrubuted. if a bow limb is too wide it not only creates extra mass slowing the bow down but it also is thinner and vibrates more causing even more energy to be lost. If a bow limb is too narrow it will often take too much set or in some cases not take set but become a bit softer and less stiff. I did several surveys beyond my own bow building on different bowyers regarding performance, set and mass. The formula is simple once understould but useless if only glanced at. I use it with every bow I make. Steve

[Badger]

Scp, when you said be more specific had you read the entire chapter. It is actually very specific about when and how to add or subtract mass depending on design. There is no substitute for being familiar with the wood you are working with, but the truth is even wood within the same spiecies varies greatly in density. Suggested widths for bows are usually safe numbers. It also deals with mass logic, in other words simply putting the mass where you need it. And it can help to dial in a design, especialy in the case of very dense woods. If you were to tiller out a 69" 50# ipe bow for instance at only 1 1/8 wide and compare it to the mass principle it might say you are 4 oz too heavy. If you were to make that same bow with a slightly more elyptical tiller and stiffer tips it would say you had the mass right on. If you like put up a couple of bows and I will show you how I would estimate the mass. Steve

[George Tsoukalas]

The mass principle works. Steve, the mass of the bow I just built is 18 oz. Just about spot on with your chart in Vol 4.  Jawge

[Badger]

Jawge, I was hoping a school teacher would chime in in my defense, I enjoyed that buildalong very much, bow came out nice, I was happy to see you not get carried away for that absolute perfect tiller which is almost impossible on a character stave.

[George Tsoukalas]

Thanks, Steve.  The bow shoots really well. Good stuff, Steve, the mass principle. Tillering character staves is much different from tillering straight staves. I didn't always build osage bows. They have to be trimmer than whitewood and BL bows. The mass principle helps a bowyer get there. Jawge

[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?

[Badger]

SCP, you seem to have a pre-occupation with shortcuts. When we speak of mass in bows we are speaking of width most of the time. One of the most common questions you will see on any bow making forum is how wide to make a bow or how long to make a bow etc. There is not all that much difference in how different woods perform but there is some difference, yew for instance can be made a bit lower in mass, some woods you might want to lean toward the high side but for the most part the mass numbers given will give good results. I don't totaly follow your question, but if I could have expressed it n a sentence I would not have written a chapter on it. The prnciple take a bit of practice and study to learn but once learned is very simple.
   After reading your post again I can see you might need to go back and reread the chapter. Sometimes things will make sense when you have more experience. There is a portion of the chapter dedicated to Mass logic that answers several of your questions.
      The best I can say is the next time you start a bow send me an IM and we will do a buildalong together using the mass principle. We could do it right here in the forum if you like. I think you would have fun with it.
  Steve
   

[scp]

I'm trained in philosophy and law. It's almost natural for me to ask people to make themselves clear and succinct, if they don't mind. After several dozen stave selfbows, I think I know how to makes simple selfbows. I'm not trying to discredit the mass principle. I just want to see it expressed in a short paragraph. If you are comfortable with the exposition you have made in the book, I guess it's up to me to come up with a better one. Maybe after making a few hundred bows?

[zenmonkeyman]

Steve, I am trying to remember if you discuss heat-treating, and how it jives with the mass principle.  If a finished bow is heat treated, it will often pick up several pounds.  Does that mean the mass principle needs a fudge factor? How do you deal with this?

I'm very impressed with your willingness to keep answering everybody's questions; you're obviously a man of character.

Can I take a stab at the one sentence thing?   "All (usable bow) woods are equal when expressed as elasticity per unit of mass."

[PatM]

I think  "getting the most(performance) out of the least (mass)" pretty much covers it.