I've heard that making a laminated bow from osage will hurt performance, that it will make a smooth design shockey, that there are better combos of wood that will boost performance and smoothness. True or False?

it does have a higher sg. so in theory the tips will be heavier and slower- and may contribute towards being shockey- but i would attribute the hand shock more to design, and poor limb timing in the tiller.
But, yes IN THEORY the heavier tip mass is a contributor- but i would hypothesize and say that the difference would be so negligible- that it would be difficult to attribute all the blame to the core material!

i know lots of folk who make very shootable and smooth bows using osage lams. and have shot some handkillers made with boo lams  

Not true, it's all in the design.

QuoteOriginally posted by Roy from Pa:
Not true, it's all in the design.

2x

oh poo to you guys anyways  

spose your question was posed to bowyers- so i should have refained from responding   :D  
just a plunker pontificating erroneously about subjects in advance of my level of precocity  

That's right ya saddle maker..  

so now- in the spirit of learning- thats me learning- not me teaching   :D   .
lets  say that a sample bow has excessively and unrealistically heavy tips. so the bow would be slower in accelerating those tips forward- but conversely would there not , theoretically be a greater shock when that forward momentum is halted by the string at the end of the stroke- assuming all other things are equal- good design and balanced limb timing.

i understand that the poor limb timing and poor design would lead to a greater vibration at the end of the stroke, but surely there has to be some kind of impact transferred to the limbs when that forward motion is halted- which would be greater where the kinetic energy is increased.
cos many many years ago when i went to school- the greater the mass of an object in motion- the greater the kinetic energy. and so when kinetic energy is abruptly halted it changes to potential energy- which in a bow- i would assume would be vibration in the limbs and down into the riser( Viz-hand shock).- so the higher the mass, the higher the kinetic energy- the greater the potential energy.

but this is all in theory- because i would think two limb tips exactly the same dimensions- one out of boo and one from osage- the difference in weight would be so negligible- so as not to make a noticeable difference???!??

where are all those smarty pants engineers when we need them?

Yer right about one thing farmer...

cos many many years ago when i went to school

Yup many many years ago. LOL

QuoteOriginally posted by fujimo:
where are all those smarty pants engineers when we need them?

Some of us got tired of overthinking this dung and found it easier to just keep quiet and build bows and see what happened. Nowadays if we get different results than our understandings of physics predicted, we drink more beer and take a whack at a new theory.

But IMO, you're basically on the right path.

Never built a glass bow, but something tells me the properties of wood are what they are. I don't make osage self bows 2" wide because they don't need it, I would make a maple bow 2" wide because it does need it. Perhaps osage lams aren't as thick as maple lams. Perhaps the limb width has to be lesser than a maple core limb.

QuoteOriginally posted by fujimo:
lets  say that a sample bow has excessively and unrealistically heavy tips. so the bow would be slower in accelerating those tips forward- but conversely would there not , theoretically be a greater shock when that forward momentum is halted by the string at the end of the stroke- assuming all other things are equal

i understand that the poor limb timing and poor design would lead to a greater vibration at the end of the stroke, but surely there has to be some kind of impact transferred to the limbs when that forward motion is halted- which would be greater where the kinetic energy is increased.
cos many many years ago when i went to school- the greater the mass of an object in motion- the greater the kinetic energy. and so when kinetic energy is abruptly halted it changes to potential energy- which in a bow- i would assume would be vibration in the limbs and down into the riser( Viz-hand shock).- so the higher the mass, the higher the kinetic energy- the greater the potential energy.

Pretty close!

The mass at the end of the limb doesn't really contribute to Potential Energy - the Potential Energy is that which is stored within the strained limb. Mass contributes to Potential Energy in the context of gravity and moving things through gradients.

But the more mass there is at the end of a limb, the more momentum that limb will have, so the more the limb resonates as the string closes the power stroke. Think of it like a pendulum - the longer it is and the more mass there is at the end of it, the more momentum it has. A bow transfers most of the energy into Kinetic Energy through the arrow, but the momentum of the limbs is dissipated throughout the bow as vibration. The more momentum the limbs have, the more vibration there is. The lighter the limbs are, the more energy is transferred into the arrow rather than dissipated throughout the limb. You can also think of it in the context of a tuning fork, which might be a better analogy.

The higher the weight of a bow, the faster the limbs travel, so the momentum is in turn increased. Therefore, more handshock for a given design.

 

QuoteOriginally posted by fujimo:
i would think two limb tips exactly the same dimensions- one out of boo and one from osage- the difference in weight would be so negligible- so as not to make a noticeable difference???!??

Yeeeeeep. I think it was Tim Baker who said something along the lines of "Design trumps materials every time". I think the example he used was of a Red Oak Board Bow whooping the a*s off of a you-beaut Osage Stave Bow.

If you think about it, the denser a timber gets the stiffer it becomes (generally). So that means that, generally, the limb becomes thinner as density increases (and wider, dependent on tension/compression strength and assuming you are maintaining equal draw weight), offsetting the increase in mass at the limb tip.

I recently built a bow with heavy, static tips and thought it would be 'interesting'... Just about threw my shoulder out of joint! Anyway, went off track there a little but maybe it helped a little     :rolleyes:  I guess my point is, unless you're using wildly inappropriate materials, the effect they'll have on handshock is negligible compared to the design.

that is an illuminating little treatise there Nezwin!. Great information!  

If the tip is heavy it will move slower
at the bottom of the page is a calculator

http://www.ultimatebowhuntingtv.com/index.php/archery-tech-tips/archery-calculators/

If you use this calculator on all your bows with 10gpi you will be surprised at which one has more kinetic energy.

You have to know how fast the tip is moving and how much it weights.

Without looking at the chart.
which one has more kinetic energy
A-----   320 graines @ 195  feet per second
B-----   350 graines @ 188  feet per second

dead heat

It will never end, LOL....

It can't be answered by us rednecks

 

Mark, I'm having trouble figuring out what FOC is in that chart page.

Close as I could come is "For Old Coots".  

I don't care how much crap I get for this: mathematics underpins all of these questions and their answers.

If you make a core heavier and less stiff, the limb will be weaker and heavier. That's it. It's therefore also slower. Maybe it's too little to measure or to matter, but it will be slower.

Fastest core will always be the lightest/stiffest material you can get.

We should probably all be using Sitka spruce ....