Applying Mass Principle and BBI in Archery: Theory, and Scientific Discussion Forum Forum

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Applying Mass Principle and BBI

Author	Comment
animalhands	Applying Mass Principle and BBI	Lead	[-]
Posts: 135 Mar 14 12 4:47 PM Reply Quote More My Recent Posts	Tags : None If this is the wrong forum, please move to where appropriate. Hi all I picked up my first laminated bow blank from Ken at the last Pasadena meet. A sweet looking BBI. I am a noob, Id like to say Ive made 30 bows but a more accurate statement would be that Ive handled 30 staves and 10 or 12 of those became decent bows. Ive never worked with bamboo or Ipe. I just started to grasp the Mass Principle theoretically and am curious as to how I can apply it to this bow. Specs: Length: 69.5" Width at fades: 1 5/16" Width at tips: 5/8" Non bending handle area: 10.5" Working limb length: 29" It looks like it has 2" of reflex. If Ken sees this maybe he can chime in if the measurements are off. Im planning on 55# at 28" draw and I initially came up with 22oz. I know Ipe is a bit denser and Im not sure if I should calculate in the epoxy mass as well. Is 22oz in the ballpark? If not, what is the more accurate mass and why am I off? Currently the blank comes in at 30.1oz Thanks all!
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badger5149		#1	[-]
Posts: 5345 Mar 14 12 8:54 PM Reply Quote More My Recent Posts	Animal, I am assuming this bow is a D/R design. If so the limbs are likley parallel and the tips will remain stiff. You will narrow the tips and outer limbs as you get closer to finsihing. I would suggest about 24 oz plus or minus a little . The paralell limbs take an elyptial tiller so increased your number for handle and fade to about 13 and your tips are stiff so I figured a slightly longer draw length. I would say 23 to 25 oz should be fine.
animalhands		#2	[-]
Posts: 135 Mar 14 12 9:14 PM Reply Quote More My Recent Posts	thanks badger i really dig the mass principle
toxophileken		#3	[-]
Posts: 12957 Mar 15 12 9:08 AM Administrator Reply Quote More My Recent Posts	No deflex in the handle, just reflex in the outer midlimb to early outer limb (with maybe a little in the inner limb, but not much). Casey, I don't remember the measurements, so whatever your tape tells you is right, I'm sure. You'll be narrowing those outer limbs quite a bit... You could end up at 3/8", easily. The limbs are fairly parallel, with some taper from maybe 2/3 out. You could increase the taper, but don't get nutty in the reflexed area. Hope the bow works out for you. I told you Steve would be able to finagle the numbers! I haven't gotten that good with his system yet. I can mainly check on elbs, using his chart... Ha ha. I do use his principles, though. Just not a big math whiz. Ken VillarsCustomBows.com
badger5149		#4	[-]
Posts: 5345 Mar 16 12 7:21 AM Reply Quote More My Recent Posts	Ken, just bu chance I am working on pretty much an identical bow. I have not glued it up yet although I did pre-tiller it. My mass weight before glueup is 22.5 oz. I am questioning myslef here that I may need a slightly thicker backing to give myself some room to work. I don't worry too much about comming in a tad under though the formula is admittedly conservative where many wood combos are concerned.
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toxophileken		#5	[-]
Posts: 12957 Mar 16 12 9:56 AM Administrator Reply Quote More My Recent Posts	Steve, I did some experiments before but I forget the actual results... But your post brings it up. There is an increase in weight from the glue, if you measure mass before and after glue up. If you haven't already glued it up, you might check it out and see how much. Ken VillarsCustomBows.com
badger5149		#6	[-]
Posts: 5345 Mar 16 12 10:34 AM Reply Quote More My Recent Posts	I would imagine if you are weighing in grains you may see some difference. I proably use about 1 oz of glue and I know a lot of that squeezes out. I will check it on my grain scale and see.
animalhands		#7	[-]
Posts: 135 Mar 25 12 11:33 AM Reply Quote More My Recent Posts	The bow is just about finished. Some fine tuning and handle shaping is all that is left. The outer limbs are still a bit wide to the nocks, 9/16 at the nocks. Ive been avoiding reducing there due to my lack of skill with the scraper. When I see you, Ken, at the Chamberlain shoot it might be reduced more but not sure. Right now its coming in at 25.5oz. Im guessing that with more taper, handle shaped out and fine tuning it will be right around 24oz. A bit overbuilt for 55lbs but Im pleased so far. Also, Im realizing that my draw should be closer to 30inches. So Im taking that into consideration and going to try to get a few more inches out of this thing.
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Traditional Bowyer's Bible Books By Jim Hamm

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