Badger-Assisted Sapling Bow: Mass-Ness to our Method

[zenmonkeyman]

 Okay, Steve has kindly offered to do a Mass Principle buildalong, and I jumped all over the opportunity.  Hopefully my fledgeling tillering abilities can bring us all to the point where we can reach Mass Enlightenment. 

I have a chokecherry stave all roughed out that only today quit losing weight.  I hope I haven't gone so far with the rough-in as to interfere with options for Steve to work with.

I've got 68" tip to tip.  I planned for a hybrid bending handle 4" + 2" fades.  I'm about 1 1/2" at the fades tapering more-or-less evenly to the tips which I've left at 3/4" in case early tillering moves the string off-center.  There's some rollercoaster on the bottom limb, and an ugly trifecta of knots radiating from the pith on the upper limb.  The stave started with 3 or so inches of deflex, but I clamped her up green to put reflex in to compensate.  Both tips have some prop twist, but nothing too serious.

She moves a bit when I lean on her, so I'm ready for some long-stringing.

Starting weight:  21.6 oz.





Trifecta knot #1


Trifecta knot #2


Trifecta knot #3


At rest starting profile


I should probably heat up the bottom limb and try to correct the whoop-te-do... What do youse guys think?  I don't think it's too bad, but it doesn't quite match the location of the upper limb reflex.  I figure on heat treating the belly at some point anyways to hopefully prevent the rampant frets I got on my last stick.

Over to you Steve!

[Badger]

   What is your target draw weight? and draw length? Also you said bending handle and fades, normally you wouldn't really have fades on a bending handle, is the handle going to slightly flex? Is that what yoiu mean? Steve

[zenmonkeyman]

More technical information:  Dunked some of the part that didn't look like a bow to get an idea of SG.



Dunked from both ends to get an average.


Used the metric side to ease my math-troubled mind.


Looks like about .78 SG to me.  But I didn't seal up the sample first, don't know how much that would skew the results.  Also, the water was straight out of the tap, it may have been aerated to some extent.  And then there's surface tension:  would it suck the plug down, or try to spit it out?  Maybe we should just go with .78.

Oh, almost forgot.  Draw length 30", target weight 50-55#.

[Badger]

What about the Handle is is bending or stiff, confused here about the fades and it being a bending handle. Steve

[zenmonkeyman]

Oh, sorry.  I just mean to allow the handle to flex slightly, I've narrowed it slightly to 1 1/4, and by "fades" I guess I mean the transition area from wider and thinner to narrower and thicker.  I had problems with my last attempt chrysalling all over, so I want as much working limb as possible.  Of course the last one was 60" ntn and had a stiff handle, so maybe I'm overcompensating.

Garett

[Badger]

   Ok , we are starting out a bit light from the start, the bow is tapered from the fades to the tips so will call for a cirular tiller, if the fades and handle did not bend at all it would call for 23 oz.  I would say in your case get it bending in a full arc of the circle tiller and start the bend right into the fades, I doubt if you will be able to keep the mass up over 19 oz with the tips being as wide as they are now but at 19 oz you should be ok if you can get it bending in close enough to the handle, Careful not to get too much bend there. If the bow strts showing signs of taking set as you work it down consider dropping the target weight to 45#. Steve

[Badger]

   Badger's Mass Method Calculator            
               
   component   statistic   Mass Figure      
   NTN length (inches)   68   7      
   nock pos'n (+=reflex, - =deflex inches)   0   0      
   handle (non bending center) length   8   4      
   Draw length (inches)   30   0      
   Draw weight (lb)   55   11      
   Is the bow bamboo or wood backed? (Y/N)   n   1      

               
   Total Mass (oz)   23         
   Total Mass (gram)   652.03896         


   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.            
The figure on the right is the mass in ounces, it just adds them all up. Steve

[Badger]

               
   Badger's Mass Method Calculator            
               
   component   statistic   Mass Figure      
   NTN length (inches)   68   7      
   nock pos'n (+=reflex, - =deflex inches)   0   0      
   handle (non bending center) length   4   2      
   Draw length (inches)   30   -1      
   Draw weight (lb)   50   10      
   Is the bow bamboo or wood backed? (Y/N)   n   1      

               
   Total Mass (oz)   19         
   Total Mass (gram)   538.64088         

This one I shortened the handle area non bending to 4" and lowered the draw weight to 50#

[zenmonkeyman]

Thanks for doing this Steve, much appreciated.  Looks like I DID pare down a bit too much to play with variables, then.  Can you show how to calculate the numbers based on the table in TBB4 and how to do the fudging? 

The tip to tip length is 68" so the ntn length is likely to be closer to 66".  How much does that change things?

Garett

[Badger]

Garret, I think I put nock to nock in the book but now I use bow length, heres how it changes it
            
   component   statistic   Mass Figure   
   NTN length (inches)   66   6   
   nock pos'n (+=reflex, - =deflex inches)   0   0   
   handle (non bending center) length   4   2   
   Draw length (inches)   30   -0.5   
   Draw weight (lb)   50   10   
   Is the bow bamboo or wood backed? (Y/N)   n   1   

            
   Total Mass (oz)   18.5      
   Total Mass (gram)   524.46612   

Note how it changes a bit at your draw length figure and also your bow length figure. Each line show how much was calculated for each figure you gave me. Making the handle bend will lower weight more than anything else. Steve   

[Badger]

   As you get closer to the finsih, if you see some set you may want to lwer the thickness on the handle a bit so it slightly flexes, it might not even be visible but it will extend the draw another 2" or so.

[zenmonkeyman]

So at this point, I just tiller normally I assume?

At what point would I reevaluate to see if I should take some wood off the sides?

[zenmonkeyman]

Shoot, I also forgot to ask how the high crown affects things?

[Badger]

Aside from narrowing the tips I don't think you will be narowing any sides on this one, your biggest issue will be fighting for more bending limb which lowers the projected mass. Steve

[Badger]

The crown will work a little in you favor, most woods are stronger in tension so could stand a bit of trapping which I seldom do but does work. The crown acts a bit like trapping a limb and if you go a bit under it should be slightly more forgiving. Steve