Question regarding orientating grain for strength

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Forum topic by IAmSupernova posted 02-13-2017 08:19 AM 415 views 0 times favorited 2 replies Add to Favorites Watch
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14 posts in 1077 days

02-13-2017 08:19 AM

I guess this is the best place to put this.

Take a post for chair back for instance. Now I know you’d want the grain running up and down (rather than forward to back) but what about the bands made by the rings? Assuming the post is square and you’re working with a piece where the bands run from one side to the opposite side mostly straight, do you want the bands running parallel to the direction of the force/load (front to back) or would you want them to be perpendicular to it (side to side)? Or does that not really matter at all?

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1307 posts in 2963 days

#1 posted 02-14-2017 01:25 PM

I’ll take a stab at this as I have been involved in building two homebuilt aircraft and know the requirements for wood structure according to FAA specifications and have read some of the research that went into this (mostly done in the 1920s and 1930s). When building a wood wing spar and knowing your life depends upon it being done right, you pay attention to these things.

The strongest grain direction is of course lengthwise with bands of growth at 90 degrees to the greatest stress. You can get this information through the Experimental Aircraft Association or the FAA.

-- Always remember: It is a mathematical certainty that half the people in this country are below average in intelligence!

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14 posts in 1077 days

#2 posted 02-14-2017 08:46 PM

That’s actually the opposite of what I would have assumed. Glad I asked. I’m going to be building a lathe soon and while I’m sure my design is fine without considering the bands themselves, it never hurts to take extra precaution. Thanks.

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