Build Along ( building by mass)

[Badger]

Jawge, thats mainly when I see it's usefulness, new style, new wood, new length or draw weight. I especialy like it with the bendy handle and elb bows, Steve

[DanaM]

Steve i have a bow going right now Hard Maple 66" NTN aiming for an actual draw length of 27"@55#
Parallel limbs to mid then tapers to nocks no reflex right now but plan on heating in 1" to 2", 4" handle 1.5" fades
Right now I have it braced at 4" and its pulling 55@14" and its mass is 24.5oz

So I plugged these numbers in:
NTN 66"
Reflex 2"
Handle 10"
Draw 29"
lbs 55#

Comes out to 23.5 oz

Question is it seems like I should have more mass at this point, does this seem to be on course?
this is my first bow using your formula so not sure if using it properly or not. I know a picture would help.

[Badger]

Sounds like you got your profile just about right, you should be pretty close by just scraping the belly now, probably only going to loose about 1 1/2 oz,  I was working on one almost identical and I started out too narrow, Mine is down to 18 oz now so i got it working closer to the fades. I cut mine down to 63" nock to nock and am a bit lighter than I want to be but will still go for 50# @27". So far the bow has taken no set and I am at 50# @23". About 1/2 oz wood at the very most will get me to target draw lenght. I wish I had about another 2 oz but am going to chance it. I heat treated the belly. Steve

[DanaM]

Thanks steve, I'm a bit narrow also on this bow if I have to take it 50# I will.

[Justin Snyder]

Dana,   The reason you have a low weight now is because you aren't to wide.  If you have lots of mass to loose you can tiller the sides of the limb to reduce physical and draw weight.  By tillering the belly you loose a lot of draw weight without loosing much physical weight. Remember twice as wide is twice as strong, twice as thick is eight times as strong. Justin

[Woodbear]

Steve,

      Here is a red oak board bow. 
41.7@ 25 (50 @ 28 design, but only drawn to 26)
58ntn, 2.5 max width, 1.2 x 0.75 at handle at center
The back is flat, and the belly is beveled and rounded by 25% in thickness, and 25% in from each side.  (cross section factor = 0.065)

What values would you put in to the formula, especially regarding the amount of handle?



Dave

[DanaM]

I'm at my brace height 6" from inside of grip, she pulling 50# at 20" and mass only dropped to 24oz
so this is actually looking pretty good. I have to get the outer limb bending some more that should take me
out to 24 or 25" then I will put it on the form and add some reflex, Its taken maybe a 0.5" of set that pops right
back so I'm feeling pretty secure at this point

[Badger]

Dave, this should be interesting as I know you have calculated out the strain and mass ahead of time. because of the elyptical tiller I would allow for a 12" handle even though your actual handle is much smaller. For your bow I would project about 20.5 oz, By the way I liked the add on you did to the calculator for the perry reflex deduction on backed bows.

Dana, I think you are right on target, don't worry about being exact just when you see yourself getting real close slow down and monitor closely the set the bow is taking. Steve

[heavybow]

Havent been here much, nice bows. marlon

[Justin Snyder]

I just have to take the time to say thanks to Steve.  On my Ipe selfbow I was shooting for a little heavier bow. It started to take a little set so I ran it through Steve's mass calculator and found I just didn't have the wood to do what I was.  I decreased the target weight to 65# that was about where the calculator said it would come out and it didn't take any set from that point on.  That was the final 15" of tiller where a bow usually takes set if it is going to.  You guys really should try it. Even if it isn't your thing, try it once for fun.  Justin

[Badger]

  Thanks Justin, over the last couple of years I  have made it a point to weigh every bow I could get my hands on. I was expecting to see a lot of overbuilt bows. I think I saw just as many underbuilt bows as overbuilt. Over the next few years I fully expect to make some refinements here and there. The biggest refinement I would like to make is becomming more wood specific. For example, on yew bows I routinely come in about 10% lower than the formula, same as with most wood backed bows. Osage is another one that can often be safely pushed into lower mass bows. The tension and compression characteristics on some woods is just naturaly better matched on some woods but usually not by a large enough amount to have a significant affect on the formula.
     Also, more specific info on how the formula can be applied in everyday bow building. The formula will drive a design on a bow, with some practice we can learn how to use the formula to let us drive the design and use the formula only to help us in our original goal. I am almost convinced that the bowyers of old used this in the elb designs. The old Turkish flight bows were put in classes based on mass weight and not draw weight. I think we are still busy rediscovering old tecniques. Steve

[DanaM]

Ok I have at 55# @25" mass is at 23oz, I lost an ounce but some of it came from
doing some more shaping on the handle, looks like I'm going to be under weight a bit
we shall see, I'm going to add some reflex now so it will be a few days before I can
do any more.

[Justin Snyder]

Dana, I figured 22 if you really get the fades bending.  Every day I'm seeing more logic in Georges advice to get more bend in the fades. Justin

[DanaM]

Thanks Justin, I think its going to take a few bows using his calcs to really get the hang of it.
Next one is going to be a bendy handle so we will see.

[Badger]

The closer you move the bend to the fades the lower the mass you can get away with. Just a little bend near the fades might translate into 3" or 4" of draw length. I always try to leave myself a little room to work near the fades in case I need it when close to final draw weight, very often I do need it. Steve