by Professor Gene Wengert
Q.
I am in need of some technical support related to the bending of air dried ASH strips. The strips are used in the manufacture of the hoop portion of small, handheld trout fishing nets. The strips are approximately 3/8" x 1" x 54" and are to be bent to a radius of 5-6 inches.
I have had good and bad success in the steambending process and am of course interested in eliminating as much of the bad as possible.
Specific questions would then be:
1. Would the best results be achieved by using quarter sawn as opposed to flat sawn wood?
2. What does one ask for to avoid pin knots and even larger knots, which of course create local crossgrain which in turn encourages breakage during the steam bending process? I seem to receive one good batch of wood and then another which has a very high percentage of breakage. Each time the wood grade is noted as FAS...?
3. What is the best moisture content to have? And after the moisture content decreases from sitting in the shop for a period of time will the bending success decrease?
A.
1. Results would be better with quartersawn.
2. FAS grade does not permit very many knots--the piece of lumber must be perfectly clear on the worst face in one or two areas that total 83% of the piece minimum! It sounds like you are not getting FAS if you find pin knots, etc.
3. Moisture content is the most important variable that governs success. For a gentle bend, we would suggest 16% MC or higher (up to 25%). For severe bends, 22 to 28% MC. The next most important factor is steaming time and temperature--always steam with saturated steam too.
Professor Gene Wengert is Extension Specialist in Wood Processing at the Department of Forestry, University of Wisconsin-Madison.
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