I tested some Lemonwood today.
Posted: Fri Nov 21, 2014 8:38 pm
Daryl (Greybeard) has recently come into some Lemonwood, and he was kind enough to send me some samples to subject to bend tests.
I first read of Lemonwood when I was about 14, and just starting to make bows. I'd read about it in Adrian Elliot-Hodgkin's 'The Archer's Craft', and I spent some considerable time looking for it, only to be met with uniform quizzical looks from even the most experienced woodworkers.
I thought the days of Lemonwood were long gone, and that I would never get to work with it.
And now I've broken some. But it was all in the name of science, I promise.
I'd read that bowyers made their bows with reckless abandon, caring nary a bit about the grain, which was almost impossible to make out in any case. I didn't know how this could be possible but seeing it now, they were all right. The grain is extraordinarily difficult to determine.
The test was a setup much like Tim Baker's in TBB vol.I, except the spreadsheet I use can accommodate different widths and thicknesses.
The wood eventually failed with an almighty bang right at the fulcrum, and the nature of the fracture looked to me to be a classic 'too-dry' fracture, as the sample took very little set (6.25% of deflection) before breaking, and there was little to no splintering of fibers. I think this would qualify for a 'brittle' description. However, do not think this makes it unsuitable for bows. It just means the wood doesn't take much set before failing (with vigor).
MoE: 15,921 MPa
This places it just above the range of results of other testing (10,000 - 14,688 MPa). Compared to other woods, its stiffness is similar to Birch, Osage, Maple and Ash.
Working stress*: 120 MPa
This bending stress means the working strain should be 0.75% to deliver a bow that has a safe bending stress, and has a set of about 6.7% of the deflection.
*Now, the sample withstood 130 MPa bravely, at 80 mm deflection. However the fact that it came asunder at 90 mm means I'd want to ratchet the bending stress in a bow back just a little bit to that observed at 70 mm deflection, which was 120 MPa.
Thus, the Bow Wood Merit Figure is 75.15921
(this is to be interpreted as: the working strain should be 0.75%, and the stiffness is 15,921 MPa.)
To put these numbers in real-world terms, the below dimensions should make a 66" long, perfectly rectangular cross-sectioned longbow about 50 lb at 28". I removed many of the measurements to save space. It's for illustrative purposes only, and dimensions are given in mm:
distance from tip/thickness/width
0 /8 /8
250 /11 /24
480 /14 /28
840 /16 /32
Daryl, if you want to test the hypothesis, I can send a more detailed layout to see how far off I am.
My plan is to leave the other samples for a week or two to see if adjusting to the local climate makes a difference to the results.
That is all for the evening.
I first read of Lemonwood when I was about 14, and just starting to make bows. I'd read about it in Adrian Elliot-Hodgkin's 'The Archer's Craft', and I spent some considerable time looking for it, only to be met with uniform quizzical looks from even the most experienced woodworkers.
I thought the days of Lemonwood were long gone, and that I would never get to work with it.
And now I've broken some. But it was all in the name of science, I promise.
I'd read that bowyers made their bows with reckless abandon, caring nary a bit about the grain, which was almost impossible to make out in any case. I didn't know how this could be possible but seeing it now, they were all right. The grain is extraordinarily difficult to determine.
The test was a setup much like Tim Baker's in TBB vol.I, except the spreadsheet I use can accommodate different widths and thicknesses.
The wood eventually failed with an almighty bang right at the fulcrum, and the nature of the fracture looked to me to be a classic 'too-dry' fracture, as the sample took very little set (6.25% of deflection) before breaking, and there was little to no splintering of fibers. I think this would qualify for a 'brittle' description. However, do not think this makes it unsuitable for bows. It just means the wood doesn't take much set before failing (with vigor).
MoE: 15,921 MPa
This places it just above the range of results of other testing (10,000 - 14,688 MPa). Compared to other woods, its stiffness is similar to Birch, Osage, Maple and Ash.
Working stress*: 120 MPa
This bending stress means the working strain should be 0.75% to deliver a bow that has a safe bending stress, and has a set of about 6.7% of the deflection.
*Now, the sample withstood 130 MPa bravely, at 80 mm deflection. However the fact that it came asunder at 90 mm means I'd want to ratchet the bending stress in a bow back just a little bit to that observed at 70 mm deflection, which was 120 MPa.
Thus, the Bow Wood Merit Figure is 75.15921
(this is to be interpreted as: the working strain should be 0.75%, and the stiffness is 15,921 MPa.)
To put these numbers in real-world terms, the below dimensions should make a 66" long, perfectly rectangular cross-sectioned longbow about 50 lb at 28". I removed many of the measurements to save space. It's for illustrative purposes only, and dimensions are given in mm:
distance from tip/thickness/width
0 /8 /8
250 /11 /24
480 /14 /28
840 /16 /32
Daryl, if you want to test the hypothesis, I can send a more detailed layout to see how far off I am.
My plan is to leave the other samples for a week or two to see if adjusting to the local climate makes a difference to the results.
That is all for the evening.