Build Along ( building by mass)

[Badger]

      Thought I would do a building by mass buildalong as the tb4 will be comming out soon with a chapter dedicated to this. This particualr bow will be a 50# 65" long boo backed osage, It will have a 10" stiff handle and fade area and initial glued in reflex will be 2". Tiller will be slightly elyptical with stiff outer limbs. Hopefully when the bow is finished it will maintain about 1" reflex. Projected mass for this bow will be about 22.5 oz. Including the glued on handle, Mass was projected as follows.

65"=5.5oz
2" reflex=1oz
12" stiff handle and fade=6oz
draw length 30"=1.75"
50#=10oz

        You will notice that the numbers I used to calculate don't match the numbers I was going to use to build the bow. A slightly elyptical tiller will equate to a longer handle and fade section and a stiff outer limb equates to a longer than actual draw length because the inner limbs have to bend more to make up for the stiff outer limbs. The draw length figure works off a ratio of working limb to draw length and I will explain this is I go.
        Tomorrow I will rough out the bow and glue it together. I will be looking for the rough glue up to weigh around 28 oz, about 6 oz for the boo and about 22 oz for the belly stave. Hopefully if weather permits I can tiller it out on monday. Steve

[Justin Snyder]

Thanks Steve, this is a great idea.  I will be watching close.  Maybe when you get to tiller you could show pictures of a couple of bows and explain the tiller and how it adjusts the length of the riser in the formula a little more. Justin

[DanaM]

What Justin said Pictures of the tiller will also help.

[Jesse]

I have been interested in your formula but it seems a little difficult for me to fully understand how to use it. Maybe seeing it done will help.

[mullet]

 This is great Steve, a step by step would help me too.

[jwillis]

I'm watching and following closely.  Please give us as much info as possible.  I think you are on the cutting edge on the formulas, so please explain as much as you can.  Jim

[Red Dwarf]

Really looking forward to this one Steve. I read your earlier post explaining the formula with great interest. I love it when science and art get together.


Red Dwarf

[Badger]

      I am really glad there is some interest. I hope to be able to show some of the more practical uses for the formula. I wouldn't expect that everyone would be running back and forth to a scale as they build their bows. I hope the weather holds up so I can get started tomorrow but in the meantime I want to go over some of the practical ways it can be used even if it isn't something someone might want to incorporate into their everyday bow building. Optimum mass can be established using sound tillering tecniques and monitoring the bows set and signs of wood fatigue. But these same tecniques will not always tip you off if you have a piece of wood that is still a bit high in moisture even if it appears dry. The mass formula will tip you off before you get very far. It will also tip you off if you have a design that is bad, either underbuilt or overbuilt before you get too far. I think most importantly it simply gets a person thinking about his design and his demensions and how they relate to each other. From a logical standpoint if a man likes his bows in a nice perfect arc of the circle tiller and bending right out of the fades the only design that will really come into target mass would be a pyramid or very close to a pyramid. This is simply because if wood is bending the same it should be the same thickness. I look at the width of the bow the same way i look at the governor on a diesel truck, the thickess determines how far a piece of wood can bend and the width determines how far it will bend.
          Just for instance, lets say i was going to make a 55# bow, 8" handle and fades and a simple attractive even tiller throughout. The mass would project out as follows'
length-66"= 6 oz  ( .5 oz for every 1" past 54")
tip set back-0=0oz ( 1oz for every 2" set back)
handle and fades-8" = 4 oz ( 1oz for every 2")
draw length-28"= -5 oz ( add.5 oz for every 1" of working limb less than draw length)
                     figured as follows, 66" bow - 8" handle=58" working limb divide that by2=29" working limb for a 28" draw so take away 1/2oz.
Draw weight-55#=11oz  ( 1 oz for every 5# draw weight)   
total would be about 20.5 oz 

girl friend is calling be back in a while LOL.

i

[Rich Saffold]

"Girl friend is calling' It's good to see you still have your priorities straight Steve ..  By weighing some of your existing bows and comparing the weight to Steve's formula will give you a good perspective since there will be a corelation between how it performs and the actual mass.

Steve's formula really put numbers to the "traditional " definition of a bow being overbuilt and underbuilt.  When Steve came out with this formula I weighed all the bows I had, and my personal bows were all underbuiilt which is what I had expected. I had been weighing my bows for years, but never had anything to really compare the numbers to other than how fast the bow shot..Now I know exactly where I am with a bow well  before shooting it.

Rich-

[Marc St Louis]

There's always interest in your threads Steve.

This is an excellent method for new bowyers to learn how to impove the performance of their bows quickly.

[Badger]

 Both Mark and Richard are known for successfully making some of the lowest mass bows you can imagine. Marks heat treating and how it affects mass can be a topic of it's own, and Richards work with bamboo and heavy tropical woods is a great example of how properly matching the belly to the backs can produce extremely low mass bows. It's funny that both of these guys just replied because I used samples of both their bows when fine tuning the formula. Richards bows will often have a slight flex in the handle area that he strategicaly takes advantage of by making his limbs scary narrow but still stable. On the bows I have looked at made by Mark he has trimmed all the fat and gotten the limb working close to the fades for maximum energy storage allowing him to keep the outer limbs narrow and light. They still fall below projected mass figures but I attribute that to just pusing the limits a bit. I have another 1 1/2 hours before daylight so I figure I will just get some stuff layed out waiting for the sun to come up so I can work,   Steve

[George Tsoukalas]

Good stuff, Badger. This is a board bow? Jawge

[Badger]

Jawge, it will be an osage board backed with bamboo. maybe i will do a stave of mulberry while the bow is drying. Steve

[Red Dwarf]

Steve

Noticed that the formula that you are using for this build along is a little different from that in the "How To" section. Is this because this will be a backed bow or just evolution/refinement of the formula itself?

Red Dwarf

[Badger]

Red, I will have to go back and look at the formula in the how to section, there are two floating around and one is incomplete. Steve