tangential and radial wood strength

[floatingkiwi]

So, we have a piece of timber with a square end. Whilst securing each end, and force is applied in either A or B directions, which annual ring orientation is strongest?
http://im1.shutterfly.com/proctaserv/47a0db02b3127ccefa7b7c590ba000000037100AZtGbhu3cs2 QPbz4a

[David G]

I'm sorry, but your question in un-answerable as stated.

You're asking an engineering question without the precision of engineering terminology.

By 'strength' do your mean -- maximum force of a blow that can be sustained without failure? Or maximum sustained weight that can be carried by a beam without permanent deflection setting in? Or one of several other traits?
Are we talking wet lumber? Air-dried? Kiln-dried? What moisture content? What species?

You might read Chap. 4 of the FPL Wood Handbook. On page 4-3, strength properties are discussed, and in table 4-3a, many variations are delineated for a variety of species. You can use this information to decide what you're trying to measure, and answer the question for yourself.

http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/ch04.pdf

If you have questions, though, after reading this stuff - ask away.

[floatingkiwi]

Dry timber. To take weight in the centre before breaking.To carry a load.
I understand about modulus of elasticity and rupturing hernias and all that so I'll be specific as far as the job I need it for.
I have an old mast with the rings running clean through it.One piece of timber. It looks like Doug Fir clear and straight as. Nice piece of wood. Seems a shame to cut it but it is what I have for the job. I am going to use the timber for rails for the companionway and wondered if it mattered which way is best to place the things.

[David G]

OK, here's the short version --

In your illustration, A will be stiffer. Deflect less. B will take more of a bang before breaking. It'll bend, instead of breaking... up to a point.

Practically speaking, there's probably not enough difference to make it important in your applications, though I have only a rough grasp of what they are.

One factor that will come into play is Splitting. Old, dry douglas fir (Oregon pine) is prone to splitting. So you might want to plan your work so that fasteners enter the workpiece like the arrow shown on B.

You're right - it is a shame. I'd look hard for a plan B. Hit a local cabinet shop and see if they won't give you a bargain price on some white oak (or somesuch) scraps that are large enough to do the job.

[floatingkiwi]

Thanks David. Most helpful. Splitting was actually another factor I was considering, as the hatch must slide back and forth on these things a few thousand times without getting all splitty on me.
I think having A as the up and down as pictured would be best as far as rigidity goes.

[Tom Lathrop]

In a practical sense, it apparently makes no difference. If it did then FPL Table 4.3 would show a difference for these two loading orientations. It does not even mention them but just gives one answer for all stress orientations. Of course. the ring orientation must be straight through the length of the timber and there must not be any internal stress that will cause warping in one direction or another for a test to be legitimate.

Width of growth rings is stated as important but ring orientation is not.

This may not seem intuitive but I've never seen a span table that considered ring orientation as a factor in bending or rupture modulus. I'm no expert but tried to measure this before having the wood properties books and could find no difference.

Fir is wonderful wood but would not be my choice for a sliding surface. Something harder would be better.

[floatingkiwi]

Yes, perhaps I should take both of your advice and save the fir and wait until I get something harder. I already made these rails out of mahogany and they have been removed because of their splittiness, among other things.
Wouldn't want to do it again.Remove made ones, I mean.
Or maybe not.