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Does plywood orientation matter for strength?

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Forum topic by HokieMojo posted 02-19-2011 06:31 AM 12401 views 0 times favorited 9 replies Add to Favorites Watch
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HokieMojo

2103 posts in 3192 days


02-19-2011 06:31 AM

Topic tags/keywords: plywood

I’m just wondering if the direction of the face gra matters when it comes to using plywood. I know OSB is intended to be placed in a direction so the strength spans gaps in joists/rafters.

I assume a 5 ply plywood will be stronger in the direction that 3 of the 5 ply’s run. I’m just wondering if this would matter at all if I were looking at sheet with 11 or more ply’s. Is the only implication of breaking down the sheet cross-grain, worse aesthetics?

I’ve got a project that is going to require a few 4 ft long pieces. Using the factory width as the length would be a nice time saver. Just wondering what you think, particularly from those of you that build cabinets for a living.
Thanks!


9 replies so far

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cabmaker

1507 posts in 2273 days


#1 posted 02-19-2011 06:43 AM

If the ply will be exposed the grain orientation may be a consideration. As far as strength goes, what is the application for. Structural integrity for a roof deck or a subfloor is under a differant scrutiny than cabinetwork but tensil strength may be a consideration for you. Where is the ply going and what is it for?

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HokieMojo

2103 posts in 3192 days


#2 posted 02-19-2011 07:25 AM

I’m simply building a rolling bookshelf. It will be on casters and will be 4 ft wide, 3 ft tall and 20 inches deep. There will be a divider in the middle so the top and shelves won’t span 4ft continuously. The top will hold about 100 lbs of benchtop tools and the shelves will hold miscellaneous hand tools like circular saws, cordless tools, etc. Does this explanation help? Thanks!

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cabmaker

1507 posts in 2273 days


#3 posted 02-19-2011 07:41 AM

Yes it does. Youll be fine with that ctr support. Hope you get lots of use from it. See Ya

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rogerw

262 posts in 2154 days


#4 posted 02-19-2011 09:48 PM

I don’t know about your building codes but mine dictate that plywood sheeting has to run perpendicular to the supporting structure. In your case with 4×4 sheets, the exposed grain is perpendicular to the joists. And joints have to be staggered.

-- >> my shop teacher used to say "do the best at everything you make for your mom because you're going to see it for the rest of your life!" <<

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HokieMojo

2103 posts in 3192 days


#5 posted 02-19-2011 10:55 PM

just to reiterate, I’m building a rolling shelf for the workshop. The OSB was just an example of a time when I know you need to orient the board a certain way. I was just wondering if it mattered with something like hardwood ply.
Thanks!

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rogerw

262 posts in 2154 days


#6 posted 02-19-2011 11:10 PM

in that case i wouldn’t think it would matter. i was thinking structural

-- >> my shop teacher used to say "do the best at everything you make for your mom because you're going to see it for the rest of your life!" <<

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DLCW

530 posts in 2119 days


#7 posted 02-20-2011 01:21 AM

Go for what looks the best in grain orientation.

What I think you are inquiring about is a sagging issue from weight. I would suggest doubling up two pieces of 3/4” plywood for a 4’ span considering the potential for weight addition in a shop. Another option is to laminate a 3/4” and 1/2” piece of plywood to help with sagging. A third option is to attach 3/4” thick by 1.5” wide pieces of solid wood matching the shelf material on the front and back of the shelf effectively adding stingers along the length to help reduce or eliminate sagging from the weight. I would use biscuits to attach the stiffener to the shelf material.

-- Don, Diamond Lake Custom Woodworks - http://www.dlwoodworks.com - "If you make something idiot proof, all they do is make a better idiot"

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canadianchips

2352 posts in 2461 days


#8 posted 02-20-2011 05:16 AM

Roof sheathing is to be laid 90 degrees to the rafter to prevent bowing between rafters, floor sheathing is the same. If you want, do a home test, cut 2” pieces 48”long and lay them on top of 2×4’s. Cut one with the grain and the other across the grain. Place weights on top and see which one will bend quicker.

-- "My mission in life - make everyone smile !"

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childress

841 posts in 3006 days


#9 posted 02-20-2011 07:49 AM

Hokie, cabinet grade ply has the grain running perpendicular with each successive layer (usually), so whatever way you want the face grain to be doesn’t matter. It’s your preference, although industry standards is to have the grain run up and down, but that’s just an aesthetics thing.

The osb direction is a structural shear thing for buildings

-- Childress Woodworks

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