Build Along ( building by mass)

[PK]

Do I have to Know this Mass fomula, to be a good Bowyer? Talk about strain the Brain.

[Justin Snyder]

No but some of us like #'s and brain teasers.  Brain cells are like muscles, use it or lose it. Justin

[Badger]

Pk, I don't believe anyone ever sugested you have to know the mass thing to be a good bowyer. Plenty of good bowyers have never heard of it. just another method that can be applied by anyone choosing to use it. I am pretty sure know one would mind if you didnt use it. Not mch of a brain strain either, seems like it at first but I use it because it's less brain strain. The turks used it 3,000 years ago, so nothing really new either. Steve

[nailbender]

  I never liked math when I was in school(not that I didn't understand it, I just thought it was boring). Now that I have grown up(alledgedly ) and have found practical uses for the stuff they were pushing on me when I was younger, It's not so boring anymore. This is definitely one of those practical applications that makes it interesting. And once you get the formula worked out, it's really just simple 'rithmatic. I know I will find this formula very useful. I have yet to make a bow that I have been really satisfied with(I would describe my best efforts as mediocre) and hopefully this will be just the thing to help me achieve satisfaction.
  Dale.

[Badger]

   I never took any advanced math in school, not even basic algebra. The formula is derived not from computers but by building bows and making comparisons of weight and set based on performnace. I always take the stats on bows and just kept looking for some patterns to develop, after a few thousand bows patterns do start to show up that even a dummy like me can see. I have never just made one type of bow either, I make all kinds and a wide variety of draw weights up to about 150#, even some I never heard of, I make about equal numbers of stave bows, board bows and glue-ups. As much time as I spend doing it I am looking for ways to make it easier on myself instead of harder beleive me. It.s like the perfect love affair to me, the more I do it the more I want it LOL. Steve

[jwillis]

I've always been impressed with your rational thinking and approach.  I look at it kind of like reading music.  Some of the best players play by ear but others can learn to read and play sooner than they could by practicing for a lifetime.  What I like is the concept of observing and measuring and being intentional about the process.  Jim

[George Tsoukalas]

I'll play.  Badger, I'll sacrifice myself for the interest of science, math and the fine art of selfbowyery. LOL.

Bow #1-  23 oz; made 1/07 from a log stave; 52# at 26 in.; 66 in ntn; 8 inch stiff handled section. Killed a deer 10/07.

Bow #2- 24 oz; 1/2 inch of reflex to start; made 1/08; the rest of the info is the same as bow #1 except for the killed deer part. Lord willing I will make meat with this one too.

Bow #1 and 2 are selfbows. Each is stained and each has multiple coats of spar urethane.



Jawge

[DanaM]

George glad ya joined the party, I ran them thru his spread sheet, now I'm going to wait and
see if what I figured is what Badger figures. To bad wasn't this much fun in high school or college
for that matter.

[Badger]

Jawge, I made one assumption, correct me if I shouldn't have. I also like about 52# at 26" for myself but I build the bows usually to 55#@28" for a little safety factor. The calculator gives 22 oz, for a stave bow there is usually a little character which 23oz and 24 oz would be plenty close enough. Thats the whole idea, not being exact just being in the ballpark. Most importantly you didn't underbuild them. If the bow were maxed out at 26" and 52# 20 oz would be ideal. Thanks for playing!!!  Steve

[Bishop]

Okay, after reading through all the posts, thanks for all the work Badger,i understand the idea. i think i just need some practical application on a bow of my own. this is good stuff. i continue to be amazed at what i learn on this forum, this stuff is priceless....
Bishop

[Justin Snyder]

George, how about some pictures.  The weight and draw length and such are all set #'s.  I want to know more about how to determine the length of the stiff handle. I know you get yours bending good in the fades, but Steve also uses stiff tips to adjust that # and I would like to see if he changes the 8" at all so I can better use the formula. 
Steve, Ill post some pictures of mine when the finish dries.    Justin

[Badger]

       Justin, good questions you asked Jawge, I think you have a grasp on it, I figured his bows more pyramid but I was just thinking that jawge builds his more paralell. This would use about a 12" figure for stiff handle and fade, changing Jawges mass to about 23.5 if I use the 55# 28" draw. I think most of us like to build a couple inches over our draw length in real life. Steve

[DanaM]

When I entered Jawge's numbers it came out at about 21oz, but I'm starting to see
how flexible this calculation is and need to apply a little common sense with it.

[Badger]

Dana, the handle and fade part of it and learning how to apply that to different styles and tillers is really the whole key. The basic formula for 8" handle and fade would in reality only be used with a pyramid design. One thig we commonly see and I do myself sometimes is to use a paralell limb say to a little over 1/2 the limb but still give it a tiller shape like a pyramid. Obviously won't hurt anything but can contribute to handshock and reduced performance. Gradually increasing the bend throughout the paralell section of thelimb is what the formula is based on. The reason the handle and fade part of it is so important because it correlates into working limb and the mass figure gets generated off of the draw length to working limb ratio. Steve

[DanaM]

So paralel limb say 2/3 rds of limb length then tapering to the nocks = elliptical tiller with a gradual bend
bend from the fade to where the taper starts leaving the last third stiff. And you would assign this design with 10" for
the non bending handle? Assuming a 4" grap and 2" fades.

On another note on my thread "A new Project" I have that elm D bow going. It is essentially floor tillered(a bit stiff) its mass is 27oz
So using your formula I assigned the following values: NTN =60", DL=27" , 4" handle, 2" of reflex and 60#
I looking for 55#@26" with a slightly stiff handle. The formula kicks out 17.5oz.  If I play with the draw weight until the mass = what its is presently
it comes out to about 105#, what I'm getting at is you can use this as an aid in not only building a bow but as an aid in designing a bow before you take any wood off.