Birdsmouth v solid sticks
I'm a big fan of birdsmouth, not because it's stronger (all else
being equal a hollow stick will NOT be as stong as a solid one), but
because it's easier and uses significantly less wood. (The savings on
the inside is minimal, its the outside that counts. There is MUCH
LESS waste using birdsmouth--think of all those corners you have to
cut off a solid mast that starts out square, and think of all the
excess you have to factor in so that the mast will end up reasonably
straight, because the blank you start out with probably won't be.) As
a result of using a lot less wood you can buy better wood, or,
equally true, you can buy cheap, knot-ridden wood and CUT OUT THE
KNOTS. Scarfing a small cross-section stave is a piece of cake on a
table saw.
If you want the same strength as the solid mast, increase its
diameter by 10% and use a wall thickness of 15% or 20% of the overall
diameter and you will see no significant decrease in strength, and
you may see an increase in strength, and even a significant increase,
because it's so ridiculously easy to get rid of knots and so much
easier to use good wood efficiently.
Do try to orient the grain radially, that is, perpendicular to the
face of the mast, so planing it after glue-up will be a lot easier.
If the grain is parallel to the surface tear-out can be a problem, in
which case jut fire up the sander. A little Stanley block plane will
work wonders. (You'll have even less waste to plane off if you use 12
staves insted of 8).
John O'Neill
being equal a hollow stick will NOT be as stong as a solid one), but
because it's easier and uses significantly less wood. (The savings on
the inside is minimal, its the outside that counts. There is MUCH
LESS waste using birdsmouth--think of all those corners you have to
cut off a solid mast that starts out square, and think of all the
excess you have to factor in so that the mast will end up reasonably
straight, because the blank you start out with probably won't be.) As
a result of using a lot less wood you can buy better wood, or,
equally true, you can buy cheap, knot-ridden wood and CUT OUT THE
KNOTS. Scarfing a small cross-section stave is a piece of cake on a
table saw.
If you want the same strength as the solid mast, increase its
diameter by 10% and use a wall thickness of 15% or 20% of the overall
diameter and you will see no significant decrease in strength, and
you may see an increase in strength, and even a significant increase,
because it's so ridiculously easy to get rid of knots and so much
easier to use good wood efficiently.
Do try to orient the grain radially, that is, perpendicular to the
face of the mast, so planing it after glue-up will be a lot easier.
If the grain is parallel to the surface tear-out can be a problem, in
which case jut fire up the sander. A little Stanley block plane will
work wonders. (You'll have even less waste to plane off if you use 12
staves insted of 8).
John O'Neill