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Strength of laminate versus solid wood

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Forum topic by wildcatwoodworks posted 04-21-2009 01:18 AM 4240 views 0 times favorited 8 replies Add to Favorites Watch
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wildcatwoodworks

12 posts in 2913 days


04-21-2009 01:18 AM

Does anyone know if laminating 2 pieces of 23/32 birch plywood would be as strong as a dimensional 2X6 for a load bearing application?

The reason I ask is, I am building a loft bed that will be around 70 inches off the floor. I downloaded plans and they use 2×6’s for the vertical legs.

The problem I am seeing right now, is dimensional lumber in this area is bad. If I could find a straight clear SYP 2 X 6 I would use it. No luck at any of the lumber suppliers as they are not much better than the big boxes. I spent an hour and a half looking through the stacks and could not find one board. Got frustrated and left.

I could do poplar for the legs, but If the plywood is just as strong I would use it as I have some on hand.

Thanks for any ideas

-- Bret - Ky "Insanity: doing the same thing over and over again and expecting different results."- Albert Einstein


8 replies so far

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cabinetmaster

10874 posts in 3024 days


#1 posted 04-21-2009 01:22 AM

Are you using them for vertical or horizontal application? How long are they going to be?

-- Jerry--A man can never have enough tools or clamps

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wildcatwoodworks

12 posts in 2913 days


#2 posted 04-21-2009 01:28 AM

Jerry,
They will be used for the vertical uprights for a queen size loft bed. length will be 75 overall with 2×4s glued horizontally and screwed into notches every 11 inches. The plans were from college loft beds. Not looking for anything fancy, just sturdy.

Thanks for the reply

-- Bret - Ky "Insanity: doing the same thing over and over again and expecting different results."- Albert Einstein

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cabinetmaster

10874 posts in 3024 days


#3 posted 04-21-2009 01:38 AM

OK, from that I would think that you would have no problem at all. Should be very sturdy. I would use some Titebond 2 or 3 glue and clamp them up good till dry.

-- Jerry--A man can never have enough tools or clamps

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JuniorJoiner

463 posts in 2906 days


#4 posted 04-21-2009 01:50 AM

two pieces of 3/4 inch plywood laminated to make legs for a bed standing 6 feet off the floor?
not sure i understand the plan 100%, but plywood can deflect quite a bit away from it’s axis while under a load, even laminated together.
when it comes to something i would have to climb on, then sleep through the night on(tossing and turning). well…I would want something stronger.
plywood is quite strong, and infinitely useful, as long as it is supported for shear in application. so with the right plan this is more than possible. just think it through.

-- Junior -Quality is never an accident-it is the reward for the effort involved.

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wildcatwoodworks

12 posts in 2913 days


#5 posted 04-21-2009 01:59 AM

Great Point Junior. I was also thinking of using a solid piece of poplar between the plywood. I usually overbuild, but after driving to 4 different lumber yards and 1 big box, I was ready to quit. Shear over the length is a concern.

Thanks

-- Bret - Ky "Insanity: doing the same thing over and over again and expecting different results."- Albert Einstein

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cabinetmaster

10874 posts in 3024 days


#6 posted 04-21-2009 02:02 AM

That’s a good idea about the poplar. Or why not just glue up 3 pieces of plywood?

-- Jerry--A man can never have enough tools or clamps

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wildcatwoodworks

12 posts in 2913 days


#7 posted 04-21-2009 02:14 AM

I wish I could post the plans so you guys could see the construction. I know the horizontals will stiffen it up quite a bit and help with shear. I am concerned about the shear over 75”. I would hate for my son to come falling down on us in the family room. I know he would’nt like it at all :). I am thinking about several ways to do this. Laminated I beams are used for construction all of the time, but they are a different stress grade and the plys are orientated a special way.

Thanks for all the help

-- Bret - Ky "Insanity: doing the same thing over and over again and expecting different results."- Albert Einstein

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Mike

391 posts in 3083 days


#8 posted 04-21-2009 11:29 AM

I used 2×6’s for the uprights. Lag bolted to the frame supports. 2×4’s for the supports between the uprights.

Ply for the base of the matress with deck hangers and 2×4’s.

2×6 and ply for the end steps. It looks fine and and my 9 yr old gets to paint it. The only painted wood in my house.

It had 3 kids, 9 , 9 , and 11 and 2 dogs one 95 lbs and one 75 lbs all at one time on it. It does not rock and is stable.

Took about 5 hours to build.

-- Measure once cut twice....oh wait....ooops.

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