View Full Version : Birdsmouth grain orientation

David Bixby
11-06-2005, 02:02 PM
What is the best way to cut the staves for birdsmouth spars, with the grain running across the short width of the stave from the center of the spar out to the outer surface, or with the grain paralel to the wide outer face of the stave.

One article I read says the grain should run across the short width of the stave, meaning the grain patern would run from the center of the spar out to the surface once the staves are glued up.

This doesn't make sence to me. If I think of the spar as a beam, when it deflects, the greatest shear force is focussed on the sides of the spar relative to the direction of the bend. Running the grain across the short width of the staves would make it easier for the staves to split down their length on either side of the bend.

Also, running the graing across the short width of the stave would make the little triangular sections that make up the birdsmouth, more likely to fail.

I may be missing something. Any opions would be welcome.

Bob Smalser
11-06-2005, 03:01 PM
I've done them both ways and my opinion is that is doesn't much matter.

Do the staves vertical grain and you have more fragile birdsmouths. Do them flatsawn and you have a tad more wood movement and a tad less stiffness. Both are much more than sufficiently stong in the scantlings commonly specified.

But as those differences are microscopic, it matters not at all in a small spar....but the larger the spar the more I'd lean toward VG, if only because the less seasonal wood movement, the longer your finish lasts.

[ 11-06-2005, 03:03 PM: Message edited by: Bob Smalser ]

11-06-2005, 03:21 PM
...and rip the strips off the edge of a piece of flatsawn stock and you will save a penny or two into the bargain. Using the tablesaw to cut the mouths, I've never had a problem with splitting or breakage on the vertical grain strips.


Don Kurylko
11-07-2005, 01:35 AM
I just built a 37’ long, 7” diameter bird’s mouth mast for my gaff cutter and I can tell you unequivocally that edge grain is the way to go. Not only does the spar look better, it was much easier to plane to a nice smooth finish. The few places where the grain was a bit rangy and came out on the flat side, I had problems with tear out when I was planning it down. An edge grain spar will be stiffer too, as well as more stable, in my opinion.

Frank Wentzel
11-07-2005, 08:05 AM
If you look at the way you were told to hold the bat when you learned how to play baseball, you will see that you put the vertical grain into the ball. The asumption was that the bat was less likely to break with this grain orientation. Carrying that notion to spar-making it would seem that you would want the edge-grain facing outward. What with the other advantages mentioned, that's what I have gone with.

/// Frank ///

Tom Lathrop
11-07-2005, 08:59 AM
Both Bob and Don are correct. Makes no difference in strength but cutting from flatsawn boards with resulting edge grain around the mast makes working easier.

The baseball example may be a myth but it is probably different from bat to bat.

Bruce Hooke
11-07-2005, 09:30 AM
The baseball bat orientation is based on a particular property of ash, the usual wood used to make bats. Ash has very hard winter wood and much softer summer wood. If you pound on flatsawn ash (or on the outside of an ash log) you can get the softer summer wood to basically fall apart, and then you can peel off strips of the harder winter wood. This is how you make split ash for baskets and the like.

However, this trick will not work with most woods, which is a tip off that most woods do not have as strong a tendancy as ash to split easier in one orientation than the other orientation. Try grabbing a bit of clear spruce and splitting it both across the grain and in-line with the grain and I don't think you will be able to find much of a difference in the amount of force required to split the wood.

11-07-2005, 09:32 AM
The baseball example may be a myth but it is probably different from bat to bat.You guys must be youths from the age of the aluminum bat. A wood baseball bat will break on the first hit when held improperly, and the tepid swing of an uncoordinated 7th grader will do the trick.

Frank Wentzel
11-07-2005, 10:00 AM
I had no idea that discussing baseball bats would show, yet again, what an old bat I am!

/// Frank ///

11-07-2005, 04:24 PM
I'm not convinced. I think David's point about shear could be important. Also the 'more fragile birdsmouth' is all that you're gluing to. What we call "short grain" here, and I expect you do too. I guess we ought to build a couple and load them to destruction to answer this question.

Tom Lathrop
11-07-2005, 05:37 PM
Originally posted by PVanderwaart:
</font><blockquote>quote:</font><hr />The baseball example may be a myth but it is probably different from bat to bat.You guys must be youths from the age of the aluminum bat. A wood baseball bat will break on the first hit when held improperly, and the tepid swing of an uncoordinated 7th grader will do the trick.</font>[/QUOTE]If that is correct, how do we explain how to use "proper" growth ring orientation with a painted bat?

11-07-2005, 06:00 PM
Since we have some people here talking wood. I have a question about sawing/milling white oak for frames. When is the best time of year to do this so the wood does not turn black. Bruce seems to be very knowledgable about woods and thier properties. What is your opinion.

Frank Wentzel
11-07-2005, 08:48 PM

I always was told to keep the lable on top. The label was always burned into the face-grain so the bat would hit the ball on the edge-grain side.

/// Frank ///

11-07-2005, 10:34 PM
Yup. Keep the label facing you and your good to hit. (Or in my case good to get hit.) The label is on the "eye" of the face grain.

[ 11-07-2005, 10:36 PM: Message edited by: emichaels ]

David Bixby
11-07-2005, 11:04 PM
Your baseball bat comparison only supports my original point.

By puting the face grain on the sides of the bat compared to where it strikes the ball, you use the face grain to stand up to the shearing force that happens along the sides of the bat.

I am assuming most folks here understand how a beam behaves under a bending load. The surface on the inside of the curve is under compression and the surface on the outside is under tension. The material along the center plane of the beam experiences the shearing force made up of the difference between the compression and the tension forces. I am not a baseball player, but I would assume that one would hold the bat so that the ball's impact would be taken by the cross grain (harder to dent), and the shearing forces in the bat would be born by the face grain like the webing in an I beam.

Since a mast is not going to have to deal with the impact of a baseball, and because it will be bent in all directions on different points of sail, why not put face grain all they way around so that it can bear the shear forces no mater which way the mast bends?

As for the finishing concerns, ya'll have a point there.

11-07-2005, 11:06 PM
Lable up.

Bruce Hooke
11-08-2005, 12:24 AM
Regarding David Bixby's comments:

I'm quite certain that the baseball bat orientation has nothing whatsoever to do with shearing forces and beam strength and everything to do with not crushing the layers of summer wood and causing them to fail. See my earlier post for more details.

In the published strength tables for wood I have never seen any distinction made between quartersawn and flatsawn wood, which leads me to conclude that if there is any difference in strength between the two, it is not enough to be signifcant.

11-08-2005, 07:22 AM
bruce makes a good point above. having worked with wood under severe loads for almost thirty years( concrete forming big structures) i have never heard a word concerning grain orientaion either, obvious dimention orientaion, but never grain orientaion. aththough, by placing the dimension in position for best load bearing, with plain sawn lumber, grain orientaion will usually be at right angles to load.
that said, i might think that with a small spar and thin staves, grain orientaion might be something to consider. with large spars, the mass alone may allow enough strength in the bird's mouth joint when quarter sawn staves are used. in a small spar, i might lean towards radial orientaion to get the most strength in the bird's mouth grain, where the grain's run is shortest and continual stressing and flexing may cause seperation in the small ears of the bird's mouth sometime down the road.
editted for typo.

[ 11-08-2005, 07:25 AM: Message edited by: merlinron ]

Tom Lathrop
11-08-2005, 10:55 AM
Now we all know that I am not and never have been a baseball player. I do have a copy on "The Thinking Fan's Guide To Baseball" which I refer to for all intimate knowlege of the game. It did not have anything about orientation of the bat but I will accept the judgement of those who have played baseball.

I have run deflection testing on wood for booms, masts and foils and find zero difference if the wood is close grained (lots of growth rings relative to thickness).

Bruce Hooke
11-08-2005, 11:28 AM
In the interest of full-disclosure I should also note that I have not played much baseball either but I have watched someone make ash splits for basketmaking, and I have certainly come across the related explanation for bat orientation in a variety of locations, including in Understanding Wood, which is one of my "bibles" when it comes to wood.

HOWEVER, in checking the above I also noticed that this book says that in woods (like ash) that have natural planes of weakness, failure in bending is more likely if the planes of weakness are perpendicular to the force (i.e., a birdsmouth mast made of quartersawn wood). So, in certain woods grain orientation does matter. HOWEVER, as I said before, Ash is the classic (extreme) example of this, and in most woods I don't think this is nearly as important a factor as it is with ash, if it is a factor at all.

In the end, to me, the arguments FOR using quartersawn wood strike me as stronger than the arguments against, with a possible exception for woods like ash.

Tom Lathrop
11-08-2005, 09:09 PM
Yes Bruce, I should have checked with Hoadley (my wood bible also) since it sits on the shelf just over my head.

When I was in the 3rd grade, I split green oak for basket weaving for a neighbor. A great experience that taught me a lot about wood at an early age.