Laminating Plywood Beams

[purduephotog]

Good Morning-

I googled "Laminating plywood beams" but didn't come up with any responses over the standard 1" or 2 sheets of 3/4 for benchtops.

I would like to create a laminate post 4" or 5" square using plywood. I'd most likely leave the edges rough, but for a better 'look' I could extend the last two pieces at a 45 degree angle bevel cut and slip a another piece on the outside edge.

I'm doing this to increase the structural strength of a (theoretical now, thanks craigslist) winepress. I intend to test the beam under compression to see if it will fail and at what force.

Would it be better to glue up multiple pieces first, then glue them all together (trimming / handplaning along the way) or glue them all up in once massive stack? I'd like to try to minimize warping during the process.

Any insight would be greatly appreciated-

Jason

(and for those that said to buy a wine press- ask and Craigslist shall deliver: I found an 18" wine press and crusher for 200$. I figure it'll take about 150$ to clean up and fix and replace the rusted iron with SS, but it's worth it.)

[RayV]

I assume you're not looking for anything longer than 3'. Why not check a construction site or stop by a lumber yard and look for a cutoff of a laminated beam.

I would think that around 4x4"x3' a homemade plywood beam would be weaker than solid wood. Why not just try a pressure treated 4x4 and see if it will take the pressure. If you could find one straight enough you could wrap it with plywood or hardwood to pretty it up and add some srtength.

Since you are going to be putting stress on whatever you use I would skip trying to miter the edges. They are bound to open up the first time put the squeeze on. Stick with simple butt joints if you wrap it.

Georgia Pacific has a ton of detailed specifications on their site engineered lumber if you want to do some theoretical calculations first. This calculator may help you if you want to try solid lumber.

[Pat Barber]

Uh...it's been done and all worked out by them there engineering types.

can buy them or go by a construction site and they might give you what you are looking for. You may have to look a little but depending on your area, there is always a site using many glulams.

[e-mail] wrote:

[J T]

Thu, Sep 21, 2006, 8:18am (EDT-3) [e-mail] (RayV) doth sayeth: Why not just try a pressure treated 4x4 and see if it will take the pressure.

I hope you're not recommending using pressure treated wood as part of a wind press.

JOAT I am not paranoid. I do not "think" people are after me. I "know" damn well they're after me.

[purduephotog]

I'm trying to avoid PT anywhere in the press, except for perhaps the support legs- everywhere else I'd fear something would flake in.

I was looking for 4' beams because I could then attach them to 4' wide by 6" or 8" solid core wood. I was under the impression, from my materials courses, that laminates were far stronger than the base material.

Like I said I'm concerned now about figuring out how to test the strength of the construction- I've got a press on the way and (assuming) I can file/brush all the bad spots down I'll be using it straight away...

Others have c> Thu, Sep 21, 2006, 8:18am (EDT-3) [e-mail] (RayV) doth

[purduephotog]

I'm trying to avoid PT anywhere in the press, except for perhaps the support legs- everywhere else I'd fear something would flake in.

I was looking for 4' beams because I could then attach them to 4' wide by 6" or 8" solid core wood. I was under the impression, from my materials courses, that laminates were far stronger than the base material.

Like I said I'm concerned now about figuring out how to test the strength of the construction- I've got a press on the way and (assuming) I can file/brush all the bad spots down I'll be using it straight away...

Others have c> Thu, Sep 21, 2006, 8:18am (EDT-3) [e-mail] (RayV) doth

[Lew Hodgett]

RE: Subject

What are you trying to laminate.

Using nothing but 1/2", 4 ply, CDX, and epoxy, can laminate a structure you simply won't be able to destroy with out a tank and some

105 shells.

Lew

[J T]

Thu, Sep 21, 2006, 4:56pm (EDT-3) [e-mail] doth sayeth: I'm trying to avoid PT anywhere in the press, except for perhaps the support legs- everywhere else I'd fear something would flake in.

Trying? Except for the legs? Your project, your money, put any type of wood you want in it.

Just wonder what would happen if a dog or cat, or little kid, licked some spilled juice of a PT leg.

Note to self: Do not, repeat not, accept any type of wine from this guy. Ever.

JOAT I am not paranoid. I do not "think" people are after me. I "know" damn well they're after me.

[lwasserm]

Or maybe a few ounces of kerosene and a match.

[RayV]

I mentioned 'trying' a PT 4x4 because they are easy to come by and reasonably cheap for a test. I have about 5 of them laying behind my shed if you need one.

[fredfighter]

Oops, that one got away from me befor I finished typing.

Making your own glue-lams allows you to cut out the defects so that all the lamiantions are all perfect wood. If you buy a commercial laminated product it is likely (all but certain) that the internal layers will contain defects and voids. That is allowed by the standards orgs for most grades of plywood.

Even then marine grade or aircraft birch plywood, which are supposed be free of internal voids, are cross laminated and for most beams or columns that is weaker than wood with a uniform grain direction. The advantages to cross-lamination are dimensional stablity and resistance to splitting, not basic strength.

You can get a better strength to weight ratio by using composite beams, built-up sections like I-beams or box beams. Probably that was the source of your confusion. Those aren't stronger than solid wood of the same overall dimensions, they're lighter.

I'm not clear on the geometry of how you are using this particular member but you would almost certainly get a stonger piece by gluing 1x or 2x lumber instead of plywood. Three 2x4s glued together in the shape of an I-beam would be much stronger than the same three glued side by side. Unlike the example above, that would keep the wieght the same but increase the strength by changing the overall dimensions.

Like Joat, I don't see any reason to use any treated lumber anywhere in the press.