Did a bend test of some White Cypress Pine.
Posted: Wed Sep 02, 2015 6:29 am
Tonight I finally got around to testing a sample of White Cypress Pine (Callitris glaucophylla) off the back of Nezwin's success using the wood.
I got four fence palings from the local hardware shop. I managed to find some that had at least a short section of straight, unadulterated grain.
I cut one up into 13 x 13 mm sections just over 500 mm long. So far, I've only tested one sample.
The results were interesting...to me anyway!
Modulus of Elasticity: 6.6 GPa
Allowable Strain: 0.85%
Let's see how that compares with some other Australian and other timbers:
Rose Gum:
MoE: 17 GPa
Allowable strain: 0.71%
Spotted Gum:
MoE: 21.6 GPa
Allowable strain: 0.75%
Red Oak:
MoE: 12 GPa
Allowable strain: 0.83%
A quick reminder: the MoE is the stiffness. How hard it is to bend. The allowable strain is that strain the produces a set that is 8% of the total deflection.
So, this sample was about half as stiff as a given sample of Red Oak, and Spotted Gum sampled at about three times as stiff! Regardless, the allowable strain is quite impressive. I did some calculations for a 66", eliptically tillered, bend through the handle longbow. The thickest and widest section is of course at handle center. For a 40 lb bow, this is what we'd need:
White Cypress: 43 x 17 mm
Rose Gum: 29 x 15 mm
Spotted Gum: 19 x 15 mm
Red Oak: 25 x 17 mm
These samples should not be seen as representative of the whole species. My sample tested less stiff than published figures...by a fair bit. I'm confident the moisture content was sufficiently low (though I couldn't measure it), so it is probably just an anomaly of the sample.
The way to make a stunning bow form it would be to back it with some other wood, and add Perry Reflex in the process. This would allow for a narrower bow (by viture of the fact a Perry Relfexed stave is stiffer) while taking advantage of its impressive allowable strain. The fact that Nezwin has recently made a nice bow, and Perry's (not of the reflex phenomenon fame, but our own forum member) reports of the unbreakable bow mean there must be better samples out there. One of my other boards might be one.
For the information of anyone that might care.
[edited to fix the numbers]
I got four fence palings from the local hardware shop. I managed to find some that had at least a short section of straight, unadulterated grain.
I cut one up into 13 x 13 mm sections just over 500 mm long. So far, I've only tested one sample.
The results were interesting...to me anyway!
Modulus of Elasticity: 6.6 GPa
Allowable Strain: 0.85%
Let's see how that compares with some other Australian and other timbers:
Rose Gum:
MoE: 17 GPa
Allowable strain: 0.71%
Spotted Gum:
MoE: 21.6 GPa
Allowable strain: 0.75%
Red Oak:
MoE: 12 GPa
Allowable strain: 0.83%
A quick reminder: the MoE is the stiffness. How hard it is to bend. The allowable strain is that strain the produces a set that is 8% of the total deflection.
So, this sample was about half as stiff as a given sample of Red Oak, and Spotted Gum sampled at about three times as stiff! Regardless, the allowable strain is quite impressive. I did some calculations for a 66", eliptically tillered, bend through the handle longbow. The thickest and widest section is of course at handle center. For a 40 lb bow, this is what we'd need:
White Cypress: 43 x 17 mm
Rose Gum: 29 x 15 mm
Spotted Gum: 19 x 15 mm
Red Oak: 25 x 17 mm
These samples should not be seen as representative of the whole species. My sample tested less stiff than published figures...by a fair bit. I'm confident the moisture content was sufficiently low (though I couldn't measure it), so it is probably just an anomaly of the sample.
The way to make a stunning bow form it would be to back it with some other wood, and add Perry Reflex in the process. This would allow for a narrower bow (by viture of the fact a Perry Relfexed stave is stiffer) while taking advantage of its impressive allowable strain. The fact that Nezwin has recently made a nice bow, and Perry's (not of the reflex phenomenon fame, but our own forum member) reports of the unbreakable bow mean there must be better samples out there. One of my other boards might be one.
For the information of anyone that might care.
[edited to fix the numbers]