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Main Boards => The Bowyer's Bench => Topic started by: daveycrockett on February 01, 2016, 10:21:00 AM
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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?
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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 :dunno:
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Not true, it's all in the design.
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Originally posted by Roy from Pa:
Not true, it's all in the design.
2x
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oh poo to you guys anyways :biglaugh:
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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 :laughing:
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That's right ya saddle maker.. :)
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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?
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Yer right about one thing farmer...
cos many many years ago when i went to school
Yup many many years ago. LOL
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Originally 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.
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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.
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Originally 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.
Originally 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.
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that is an illuminating little treatise there Nezwin!. Great information! :thumbsup:
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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.
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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
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dead heat
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It will never end, LOL....
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It can't be answered by us rednecks
:smileystooges:
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Mark, I'm having trouble figuring out what FOC is in that chart page.
Close as I could come is "For Old Coots". :)
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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 ....
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Front of center Roy
X2 ben
This post is going nowhere, over and over and over
:knothead:
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The people who built the Holmegarrds figured this out. I have great respect for mathematics and engineering, but they did it from the gut.....unless maybe there were aliens involved :eek:
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Originally posted by bigbob2:
that is an illuminating little treatise there Nezwin!. Great information! :thumbsup:
You know me, Bob, why use one word when you can use ten? :D :D :D
Originally posted by LittleBen:
Fastest core will always be the lightest/stiffest material you can get.
X3 for that, but are the stiffness of the belly/back materials more of a factor than that of the core? Another benefit of a dense core, aside from stiffness (usually), is reduced set.
Reread the original question and it's covering performance AND smoothness, which are related but not always dependent on one another. You can have an inefficient but smooth shooting bow, for example.
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The stiffness of the core has little to do with storing energy. The core doesn't feel tension or compression. Cores feel sheer. This is why the best core materials are diffuse porous (no earlywood to fail along) like maple, black walnut, bamboo (sort of!)and of course a great core needs to have great gluing properties and a low/medium density.
The core is simply a spacer to keep the back/belly surfaces the required distance apart for the desired draw weight.
Anybody ever looked at an H-girder and wondered why it is that shape?
So osage isn't a great core material because it is quite dense :( and heavily ring porous it's also not the best gluing wood out there...but of course modern epoxies mean we don't have to think about that last point much.
I wouldn't dream of using osage for a core lam it's properties are much better put to use as a belly lam on a wood bow.
I've used 0.030 thckness lams of it in glass bows under clear glass and it works in this respect but I definately would use it for the full core.
Heavy tips are often held to blame for handshock but it normally is more to do with a poor tiller or limbs out of timing.
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This is getting funny. And you can apply all the mathematics and principles you desire. But I will still take Osage over any other wood out there. A 1/4 sawn Osage belly with action bamboo core lams, backed with natural bamboo, tillered to equal limb timing, has zero hand shock and just kicks ass...
Another sweet core material is Yew..
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having one of Roysters bows- i concur- it is a super sweet shooter.
you know whats funny- this post was moved over from Pow Wow- dont think the o.p. realizes that it was moved- he has never been back to this thread- he doesnt realize the mayhem he has caused- the virtual WW111- the wedge between friends, the irrecoverable chasm of despair, confusion and hatred conjured by virtue of the most innocuous of questions :biglaugh: :biglaugh: .
never pick a fight with an irishman- you will always lose!!
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That's nothing Wayne.
My wife is Irish / Italian!
And she has the temper of both those nationality's combined into one body. That's why I walk the line, LOL...
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Hmmm, she always seemed so sweet when I was there. Maybe it depends on who she's dealing with.
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quote:
Originally posted by fujimo:
having one of Roysters bows- i concur- it is a super sweet shooter.
you know whats funny- this post was moved over from Pow Wow- dont think the o.p. realizes that it was moved- he has never been back to this thread- he doesnt realize the mayhem he has caused- the virtual WW111- the wedge between friends, the irrecoverable chasm of despair, confusion and hatred conjured by virtue of the most innocuous of questions :campfire:
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320 @ 195
350 @ 188
Doesn't require a chart.
energy is equal to half the mass times velocity squared.
I could do that with pencil and paper, or a calculator - could likely do it in my head, given a few minutes.
Charts are so much more convenient. Someone's already done the work. No point re-inventing the wheel.
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Monteray....
I made myself a Holmegaard last year, out of maple.
Cost me $20
#52 @ 28"
Sweet shooting bow.
Working on another one - adding recurve to the tips and going a bit thinner in the static outer limbs.
At the start of tillering with the long string.
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I made one from an oak board. Came in at 25#. Gave it to one of the grandkids. It has proven adequate for bunnies.
The eye opener for me was the very very little additional thickness that is needed to make the tips effective.
Would like to see the one you are working on!
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Here's the bow I was referring to.
http://tradgang.com/cgi-bin/ultimatebb.cgi?ubb=print_topic;f=125;t=002204
The steam bent oak thing didn't work out. I'm pretty sure it was a dry spot in the glue up that failed (some would disagree).
Love the Holmegaard.
I've built only 5 bows. Two broke.
The two that broke are the only two I've photographed the process of making them.
I'm not particularly superstitious, but ......
I'll post pics of the one I'm working on when I get to shoot it!
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Very nice looking bow.
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It's basically been proven that arrow KE isn't a good measure at all at predicting penetration. It's a useless number.
Osage is as fine a material as many others, but I'll say from experience that it can be design dependent whether or not you'll get handshock. I don't think it can be computed. Basically if a deep core bow is all Osage, I'd give it away. A thin limbed bow, or a mixed stack where there's more than just Osage would likely be fine. I think it's probably connected to the thickness of a very dense wood vs the thickness of the rest like the glass and other lams and such. It's a great strong self bow material though if you want to work with a pain in the butt wood. I'd take hickory or ash any day.
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thats dangerous talk around here mister :biglaugh:
any body dissing the "yella" betta be a tough fella :laughing: :laughing:
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oops!