Making Laminate Beams

[Tom B]

I am considering building a few small Quonset-hut shaped greenhouses/hoophouses, and after some review believe common designs for them would be improved greatly by constructing and using laminated arched wooden beams at each end of the structure, and perhaps spaced along the structure, depending on its length. The beams will have cross sections on the order of 4"x4". The arches would be 16 ft in total length, the length of common steel cattle panels that will be used on most of the hoophouse surface. These will result in an arched structure about 6 ft tall, and 9 ft wide. I propose to construct a full sized jig and glue/clamp the beams.

I would appreciate any advice or comments on what materials to use for this. One could simply rip thin exterior plywood, marine plywood, or with some more work, resaw and plane hardwood or softwood lumber for this. If lumber is used, what type would you recommend? Can a fairly large radius bend like this be reasonably done with these materials? What adhesives would you recommend? I don't have immediate access to a planer, but if its use would result in a significantly better result, I could find one.

Thanks for any advice you have to offer.

Tom Birdwell

[Sandy]

On Sat, 15 May 2004 03:58:02 GMT, "Tom B" posted:

If you must use wood, get a few large drums of epoxy resin and a large stack of clear pine of some variety, as well as a thicknesser.

Have you thought of PVC pipe? It's the usual way of doing this.

[Tom B]

PVC makes a decent temporary structure, but will not handle winter snow loads, and is not suitable for putting better pane over. The arched cattle panels are self supporting, and much stronger than PVC. The wood beams will support the ends of the panels, but more importantly will provide solid support for the end walls, windows, and door, which is just about impossible to do well with PVC. Thanks.

Tom B

[bridger]

rather than laminating up solid beams, consider building an arched version of a truss joist. you'll get a lot more support from the same amount of wood.

[Rick Samuel]

[Tom B]

Thanks Rick. I am not familiar with the acronym you used however, and didn't find it in my web search. Can you give me a bit more information about APA, what it is, and where/how to find the workbook or its source? Thanks again,

Tom B

[Charlie Self]

Tom B asks:

American Plywood Association.

You can learn more about softwood plywood than you ever though existed and still have more to read.

Charlie Self "Bore, n.: A person who talks when you wish him to listen." Ambrose Bierce, The Devil's Dictionary

[bryanwi]

The current (or perhaps by now just previous) issues of Woodenboat

has an article about the technology used to build a similar sort of structure for boat ribs. Includes cleverness about using a firehose and a compressor to make a laminate press, etc.

bmw

[Sandy]

On Sat, 15 May 2004 17:24:47 GMT, "Tom B" posted:

Fair enough. I understood that you could use whatever size (strength) pvc was needed, but I've never considered snow loads (I've never seen the stuff :)

What is "better pane"?

Then there is galv steel or aluminium. I'm worried about rot in the wood in the humidity and warmth of a greenhouse. Perhaps treated pine?

[Tom B]

I appreciate the suggestions given, but have two more questions.

I will be bending wood, essentially in a semicircle with a radius of roughly

5 feet. If I used dry solid lumber, pine for example, what is the greatest thickness that could be used, yet still avoid splitting/breaking the wood in doing so?

Gorilla glue claims to work well with treated lumber, so long as the moisture content is between 10% and 20%. How does one determine the moisture content for this?

Bridger, thanks for the truss suggestion. I am considering it. Given the fixed size of the cattle panels, I start with a limited height inside. A truss would reduce that further, but I do have to consider strength as well.

Tom B

[bridger]

there are too many variables to give you a firm answer like 1/2". you'll just have to start bending some up and see how far the wood you have will go before it breaks. my guess is it'll be somewhere between

1/8" and 1/2". you'll be bending over a form, so build the form first and start clamping your resawn plies over it. if they break, cut them thinner. though this may sound like a smartass answer, it's not.

either by weight or with a moisture meter.

you're welcome.

[Tom B]

Thanks, and it didn't sound smartass at all.

Tom

[Grant P. Beagles]

Have you considered steaming the lumber?

Tom B wrote:

[Rodney Myrvaagnes]

To measure moisture content, cut off a piece, weigh it, oven dry it, and weigh it again.

Rodney Myrvaagnes J36 Gjo/a

Ask not with whom the buck stops . . .

[Lew Hodgett]

You should be able to laminate 1/4" thick pieces without much trouble, but do yourself a favor, forget the Gorilla glue, use epoxy.

Gorilla glue has a short shelf life, is tremendously overpriced and compared to epoxy, very weak.

HTH