Above average SG

[k-hat]

What's y'alls opinions on how SG affects wood WITHIN a species.  I'm well aware of Tim Baker's comparison of woods at their various SGs, but what about when a stave has a much higher than average SG?  Would you simply not have to make it as wide?  I'm tempted to think that, but it seems silly to treat a wood as though it is a higher SG wood just because it's denser than normal.  That doesn't change the elasticity as it pertains to tension and compression.

My initial impression is it would allow the limbs to be THINNER (as opposed to making them narrower), but otherwise wouldn't increase the bow's durability, or ability to handle strain.

Whatchall think?  What does above average SG do for a wood?

(I ask because i have some hackberry on another thread that is SG .67, whereas hackberry normally runs around .53, that's a big difference!)

[k-hat]

ttt

[PatM]

I go by the recommended width for the wood choice until it is bending, see how it is reacting as far as elasticity goes and then reduce width  more than thickness to fine-tune.
 It does seem like denser than average wood is more elastic although less dense samples are often surprising as well.

[Josh B]

That's an interesting point to ponder.  Speaking purely from speculation, I would guess that the increased density would affect the compression properties more than the tension.  With an already tension strong hackberry, I would think you could narrow it up a bit to keep mass down.  I would still heat temper the belly though.  If it were a wood such as walnut where tension strength is somewhat marginal, I would probably leave it wide.  This is purely gut hunch with no practical application or experimentation.   So take it with a grain of salt.  Josh

[k-hat]

Thanks for the input Pat, Doc.  Both good thoughts.  Before today i never thought of it being more than "denser is better."  I didn't figure that density might increase compression strength, but it's a possibility.  I'll have to keep these in mind as i continue my bow building, maybe even start keeping a log (i know most of y'all already do.. i'm a slacker in that dept.)

[turtle]

Thanks for the input Pat, Doc.  Both good thoughts.  Before today i never thought of it being more than "denser is better."  I didn't figure that density might increase compression strength, but it's a possibility.  I'll have to keep these in mind as i continue my bow building, maybe even start keeping a log (i know most of y'all already do.. i'm a slacker in that dept.)

I keep logs..............usualy just call them staves. 

[k-hat]

Thanks for the input Pat, Doc.  Both good thoughts.  Before today i never thought of it being more than "denser is better."  I didn't figure that density might increase compression strength, but it's a possibility.  I'll have to keep these in mind as i continue my bow building, maybe even start keeping a log (i know most of y'all already do.. i'm a slacker in that dept.)

I keep logs..............usualy just call them staves. 

Oh man, this could go downhill fast...

[mnviking]

hi guys
I too have been studing wood properties and located a document via google called wood mechanical properties.  It is pretty technical and I have not as yet figured out what it all means but--there is sure a lot of data on different woods relative to tension, compression, elasticity, etc.  higher s.g. makes the wood more dense but what I am looking for is elasticity and speed of limb recovery from bending moment as I think that would affect arrow velocity??  not sure but that is what I am trying to study

[Pat B]

In most cases it is probably true but locust is the strongest wood in compression in the US but because it is brittle it has a tendancy to fret if tiller is not just right.
  I think design will have as much effect on bows as wood density has.

[mnviking]

ok Pat B.
what do you think is the best design for maximizing arrow velocity for any given wood type?  this is my dilemma right now.
I have red oak, curly ash, golden locust, curly maple, and hickory boards, 
thanks pat

[rossfactor]

I think that wood proprieties can very dramatically within a species depending on the conditions that the tree grew in (e.g. tension, soil characteristics, climate, shade/sun). This is supported by a lot of research. 

Conditions of growth  can vary the density of the wood for sure,.. but also may vary the eary-late wood ratio and I think the physical make up of the wood (e.g. lignin to cellulose ratio) can also vary by growth conditions.  The last point would have a strong effect on the tension-compression strength and elasticity of a stave.

Gabe

[Pat B]

The folks that really delve into high velosity arrow speed are the flight shooting guys. They get every bit of available energy into the arrow so they get max shot length. These guys tiller their bows out so they are lucky to get one good shot and they tweek their arrows for max efficiency and minimum physical weight...and they shoot in a high altitude, desert environment for max effects.
 In wood bows you have trade offs. You can go with max speed and efficency or max durability. Most folks split the difference. 

[JackCrafty]

K-Hat, think of it this way:

Let's say you have a bow already made and it has an SG of .53  OK, how would you increase the SG in the wood of that bow to .67, for instance?  You could compress the bow fibers somehow: so that it would be more dense, right? This would make the bow's dimensions smaller in thickness or width or both.  Still the same wood, just smaller in some dimensions now that it is compressed and has a higher SG.  Do you see where I'm going with this?

How do you think the "compressed" bow would perform?  That is the answer to your question.

Normally, as good bowyers, we decrease width in favor of decreasing thinkness when dealing with heavy wood.  This removes more mass, without as much effect on the bow's draw strength, than does the removal of thickness.

[johnston]

Possibly trapping the bow a bit might help.

[k-hat]

I see what you're saying jack, and i guess i really shouldn't have ruled out reducing the width.  It seems that it would be more a combination of less width AND thickness. Cuz if i had an elm stave with osage density, i wouldn't think that i should build it to the same dimensions as osage because the woods have different properties.  It makes sense what was said earlier that the density would impact the compression properties more than the tension properties, but it can only do so much.  I'm sure there are plenty of woods as dense as osage that do not have the compression resistance of osage.

I suppose if i followed badger's mass formula in my build it would all work out how it's posed to be?