Author Topic: You'd think this one would blow, no?  (Read 5364 times)

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Offline David Long

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You'd think this one would blow, no?
« on: November 15, 2008, 05:03:46 pm »
A few weeks back I posted a sinew backed Rocky Mountain maple (Acer glabrum) bow, 67 inches NTN, 55 lbs at 26 inches. I've been interested in this maple species, which is native to my area, for awhile now. I've been pretty happy with the wood (it's like butter, beautiful clear stuff, pay no attention to the knot behind the curtain on the left limb). I've decided to push it to see how it stacks up against the "good" woods-yew, osage, hickory, etc. This bow is my next step, and I'd like your opinion as to how other woods you've worked would hold up under these design conditions. This bow is 55 inches NTN, 1.5 inches wide, pulls 50 lbs at 26 inches, and weighs a mere 13.75 ounces. A feather in the hand. It's a decrowned sapling. According to TBB etc., a maple bow of these specs should probably blow, but I see no sign of pending disaster. Not much set (the bow was dead straight before tillering with the exception of a crook in the left limb I removed with dry heat) and no crysalling on the belly at all. I measured the specific gravity of the wood at 0.63, right in line with what you'd expect from hard maple. I'm going to sinew back this bow for safety and to get 55 or 60 lbs at my 26 inch draw. How much reverse bend would you put in at sinewing? Do this bow's specs make "sense" to you? Feel free to comment on the tiller too. I'm trying to use all the limb I can! Thanks much, Dave

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NW Montana

Offline sonny

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Re: You'd think this one would blow, no?
« Reply #1 on: November 15, 2008, 05:44:14 pm »
unless you enjoy the process of sinew backing a bow I don't think I'd back it......
shoot it as is and see what happens.

Oh,, and don't worry that TBB seems to indicate that that bow is underbuilt. You can't believe everything you read !  ;)   
Never argue with an idiot. They'll drag you down to their level and beat you with experience.

Offline El Destructo

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Re: You'd think this one would blow, no?
« Reply #2 on: November 15, 2008, 06:07:12 pm »
You say that this is Decrowned.....so you violated the Back Rings?? If this is so....I would definitely back it with at least Silk or Rawhide....preferably Sinew.......David the Bows Tiller looks spot on....you did agreat job on that for sure..I really like Maple so dont always beleive what others state.....I have Vine....Hardrock.... Japaneese and Sugar Maple Bows.....I love them all
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Offline Badger

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Re: You'd think this one would blow, no?
« Reply #3 on: November 15, 2008, 07:22:59 pm »
  Love that bow David, I am likewise a big fan of any maple I can get my hands on. Great tiller, your 13.9 oz is not that far off what tb4 mass principle recomends considering 10% mass is just thrown in as a safety margin. You did a great job getting that bending right into the fades without hinging it, thats a more sofisticated tactic than it might appear on the surface. good Job! Steve

Offline George Tsoukalas

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Re: You'd think this one would blow, no?
« Reply #4 on: November 16, 2008, 12:22:53 am »
David, beautiful tiller. Great job. Jawge
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Offline Gordon

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Re: You'd think this one would blow, no?
« Reply #5 on: November 16, 2008, 01:51:00 am »
You really did a nice job getting everything you could out of those limbs. That will be a killer bow after you add some sinew. :o
Gordon

Offline Badger

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Re: You'd think this one would blow, no?
« Reply #6 on: November 16, 2008, 02:14:58 am »
            
   Badger's Mass Method Calculator         
            
   component   statistic   Mass Figure   
   NTN length (inches)   55   0.5   
   nock pos'n (+=reflex, - =deflex inches)   0   0   
   handle (non bending center) length   4   2   
   Draw length (inches)   26   0.25   
   Draw weight (lb)   50   10   
   Is the bow bamboo or wood backed? (Y/N)   n   1   

            
   Total Mass (oz)   13.75      
   Total Mass (gram)   389.8059      


   Instructions:         
   In all cases, the green cells are the required fields, the purple are the answers.         
   The converter is interactive.  Known figure goes in green, answer comes out in purple.         

Offline OldBow

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Re: You'd think this one would blow, no?
« Reply #7 on: November 16, 2008, 12:35:53 pm »
Excellent bow. I've had mountain maple break so I'd back it. Keep us posted on the finished product.
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Offline David Long

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Re: You'd think this one would blow, no?
« Reply #8 on: November 16, 2008, 06:39:46 pm »
Thanks very much you guys. By "decrowning" I meant I took my grand dad's hatchet, stood the sapling on one end and went at it until I thought I was done. Then rasp, followed by the cabinet scraper finishing with a flat back with some ring steps in a few locations, but not all that bad. So I am pretty sure I agree with Oldbow it needs a backing. Steve, very interesting to  me your mass calculator is spot on. I was extrapolating from the chart in the book, but apparently you have a spread sheet? Where does a fella get such a handy program? Apparently you guys are unfazed by maple that can go 1.5 inches wide, 55 inches long, 50 lbs at 26 inches. I had no idea that would work! Dave
NW Montana

Offline Badger

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Re: You'd think this one would blow, no?
« Reply #9 on: November 16, 2008, 06:56:54 pm »
David, pm me with your e email and I will send you a calculator you can download for quicker figuring, for it to be useful you need to know how to use the calculator as far as what numbers to use for the handle and fade, your bow was working well into the fades so I only figured your 4" handle. If your stiff handle and fade were 8" the projected mass would have gone up to almost 17 oz, at least 1/2" wider in your limb. Steve

Offline DanaM

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Re: You'd think this one would blow, no?
« Reply #10 on: November 16, 2008, 07:40:15 pm »
Lets see if this works, if it did Badgers Mass Formula Excel spreadsheet should be attached :)

Yup it worked :o

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Offline David Long

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Re: You'd think this one would blow, no?
« Reply #11 on: November 16, 2008, 07:50:43 pm »
You're the man Dana! I assume it's perfectly OK for you to be giving away Steve's intellectual property  8). Thank you both so much. Dave
NW Montana