Main Discussion Area > Flight Bows
drying conifer woods for arrow shafts
avcase:
Willie,
Just to clarify, did you measure the impact of heat treating on the wood strength, or was it change of stiffness?
I measured a pretty dramatic change in stiffness for heat treated spruce arrow shafts. I heated them around 375-385f for a shorter period of time. Maybe 20 minutes. It left the arrow shafts a shade darker. They were also significantly stiffer, smaller in diameter, and lighter than they were before going in the oven. Unfortunately, much of the benefit faded away as the arrow shafts re-hydrated over the next week.
The amount of change due to heat treating will probably depend on the humidity level where we live.
Alan
willie:
--- Quote --- lignins to harden up if that actually happens when we heat.
--- End quote ---
I seem to recall some papers that indicated that might be happening, but if I remember correctly, the effect was not very consistent, and not all the experiments started with wood at the same moisture content, so it might be hard to isolate the "lignin hardening" effect from stiffness gains from simple drying. I deliberately chose a lower temperature than one normally uses to heat treat a bow limb, so that I could observe any discoloration that might be hidden by the browning that we expect at the higher temps. the spotting on the heated samples seem to suggest something melting or vaporizing (besides water, as the the wood was fairly dry to begin with), but if it is lignin, I have no way of knowing. Just guessing, but if lignin is formed by the tree to reinforce the cell wall, and it is subsequently displaced, than it's possible the cells could become relatively weaker.
I have since retested the samples, and after a few days, the arrow blanks that lost strength a few hours after heating, seemed to have regained their strength back to pre heatreat levels. The idea of a curing or hardening that happens over time rather than changing with temperature or moisture seems reminiscent of the "seasoning vs drying" debate of bow staves. At any rate, the samples will go back in the warm box and be tested again later.
Alan, I have been measuring deflections as one would with a typical spine tester. The strength differences reported are % change in deflection. Are there strengths in different directions that might be useful to look at?, or a more useful criteria to quantify stiffness?
avcase:
--- Quote from: willie on November 08, 2017, 12:33:04 pm ---Alan, I have been measuring deflections as one would with a typical spine tester. The strength differences reported are % change in deflection. Are there strengths in different directions that might be useful to look at?, or a more useful criteria to quantify stiffness?
--- End quote ---
Thanks for clarifying. I was just thrown off track when you mentioned the heat treatment effect on strength, but meant stiffness. I think strength often goes down as a result of heat treating, but stiffness almost always goes up.
Perhaps the spots you saw on the surface of the wood was due to the outgassing of moisture, and this carried various resins with it to the surface. Just a guess.
I would like to try heat treated spruce arrow shafts again and see if I can maintain the stiffness benefit by keeping the arrows stored in a sealed box with a desiccant in order to keep the arrows from rehydrating.
Alan
willie:
Alan, Did you see significant reductions in MOR when you heated your sitka spruce?
I guess I think of stiffness (bending strength) as governing design, but I best not ignore ultimate strength if my bow hand is going to be in the line of fire.
Btw, In the flight community, is there a commonly used spine test standard for short arrows? Otherwise I can make my spreadsheet accept any length/thickness etc.. And calculate MOE to predict spine.
Badger:
As for spine I seldom measure beyond the finger pressure test but when I was measuring I just measured at actual length of whatever arrow I was testing. Figuring out optimum spine requirements is another ballgame. I think around 25# spine for 26" arrow of about 200 grains works pretty well, even a little less has shown good takeoffs.
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version