percentage of glass

[Miguel Gasso]

Hello all together,
Im Miguel Gasso, Im following this board since 2 years and learn a lot about bow building, thanks to all of you.

My cuestion is the following:

As known the glass proportion for a longbow(my are based on Kennys longbow designe) have to be between 20%- 25% percentage.
So I wnat to know which things happend if I be over 25% of glass, which behavior of the bow or negative isues on limbs I can expect.
In my case the bamboo core that I use are not stiff enough and I will change from 0.4 to 0.5 glass resulting 28% of the total stack.

Excuse my poor english, I hope you can understand my cuestion.

Miguel

[Crooked Stic]

What draw weight you wanting? When you say stiff do mean more draw weight? Maybe add more bamboo.

[Miguel Gasso]

What draw weight you wanting? When you say stiff do mean more draw weight? Maybe add more bamboo.

I mean my Bamboo is so poor in drawweight that I take moore glass thickness as an option, it is roasted Bamboo floor glued on end, but not dense enough.
Of course I can ad some Bamboo and I have done it in the last one, but beside I wish to know which things happens when I go over 25% of glass on the limbs.
I can imagin the limbs are going slow because of the weight or maybe the bow will be not so durable, what ever which is the reason we normaly did not go over 25%.
Im curios.
thanks in advance

[kennym]

The 25 percent came from a survey of bowyers who on longbows , liked 20-25 percent glass in stack .

If you think the bamboo is weak I would try a different type or source . Putting a .050 on the bow belly may help too.

[Miguel Gasso]

The 25 percent came from a survey of bowyers who on longbows , liked 20-25 percent glass in stack .

If you think the bamboo is weak I would try a different type or source . Putting a .050 on the bow belly may help too.

Thanks Kenny, I already order  a thick board of suger maple, because it is imposible to get an other quality of Boo.
I was simply curios about this top of 25%, now  I know nothing critical can happens, beside more weight or drawing behavior are points to consider.
Thanks both for your quick answere.

See you soon, Miguel

[kennym]

The maple will make a couple more lbs but won't be much faster bow in my findings. The added thickness of glass will also make a couple lbs more as it is stiffer than wood at same thickness.
It's all a SWAG , so everyone should keep good records , Renee bought me a book to write it all down in so I could find it later. Sadly, I still have very little in there and stacks of notes.

[Mad Max]

SWAG meaning----A good guess

[Crooked Stic]

Scientific wild a-- guess

[Kirkll]

With traditional long bows that bend more uniformly along the limb the core material is not subjected to serious compression issues that are common with hybrid long bows or R/D long bows with shorter working portions of the limb.

You will find that bamboo is higher in tension strength than many hardwoods, but it’s terrible in compression rating. This is true for high quality moso bamboo too.

As far as performance goes, thinner glass and deeper core will always out perform the thicker glass ratio. But longevity and durability is higher with thicker glass. It’s a trade off….     Kirk

[Miguel Gasso]

SWAG meaning----A good guess

Thanks for the translation, I have had to google it.

[Miguel Gasso]

Hello, I have build an other bow.
The woodcore is hard maple (vertical grain), taken Kennys geometri and adding 0.5 glass(bearpaw) to back and belly instead of 0.4 glass(bearpaw) I finally land at 67#.
Of course far to much for me. So I sand the glass carefully,patiencely and uniform down to 46#.
It is a great shuting bow and whith too little silencers very quite. No idea how fast the arrows are, but comparing it to my 45# recurve it penetrades the target similar.
Tomorrow I will start building the same bow with 0.4 on back and belly, I will report my result.
I wish you a blessedly new year.

[Miguel Gasso]

Ups, 0.04 back and 0.05 on the belly.  Shooting!!!!

[Kirkll]

SWAG meaning----A good guess

"Scientific Wild Ass Guess"

Core to glass ratio is typically ignored by most bowyers. The industry standard is .040 on most bows ranging from 30-65 pounds in draw weight. But some bowyers prefer using .050 to have more flexibility on sanding the glass for weight reduction. I go up to .050 glass for 70-100# draw weights for durability.  but realistically you could use .030 glass for anything below 40, but most guys don't do it for durability and stability reasons.

if you build two Identical 50 # bows using .040 and .050 glass. The .040 bow will be higher in performance just due to the mass weight decrease in the limbs.

 The over all limb thickness is typically what determines the draw weight. 

You will be surprised how close your actual limb thickness will be between .040 and .050 glass for the same draw weight bow. Probably be within .010 -.015 more for the .040..... but that core is much lighter in mass weight....

A lot of guys say cores don't matter, and in many cases its true to a certain extent. But.... the compression and tension values of the core wood can and will make a big difference in longevity and have an effect on performance as well.

[Mad Max]

I make these with .030 glass, 50" NTN