Ideas for greenhouse joint - Woodworking Talk - Woodworkers Forum
 
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post #1 of 10 Old 03-24-2012, 04:38 PM Thread Starter
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Question Ideas for greenhouse joint

Hi all,

I'm building a greenhouse from Western Red Cedar, and I'm trying to figure out the best joint to use to construct the uprights.

The idea is that 6 x 24" lengths of 2x4 will be joined end on at a 12 angle; two of these then form an arch:

Ideas for greenhouse joint-structure.jpg

Now let me just say that I realise this isn't a sane way to build a greenhouse. I never liked doing things the easy way.

The joint I'm imagining would look something like this, to ensure the outward pressure on the joint is directed downwards onto the section below:

Ideas for greenhouse joint-joint-2.jpg

The best way I can think of doing this would be to use 8 x 5/16" glued hardwood dowels in a 4x2 pattern:

Ideas for greenhouse joint-joint-1.jpg

Can anyone think of a better (i.e. stronger but still make-able!) way of constructing this joint? Because it's on show it should look tidy if possible.

I've tested the joint using pocket hole screws without glue and it is amazingly strong; I haven't tested the dowel approach yet but I'm assuming it should be stronger still?

Thanks for any ideas!

Toby
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post #2 of 10 Old 03-24-2012, 05:51 PM
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Just wondering why you wouldn't use 2 - 2x12. Then you'd have only one joint.

Barring that, I think your joint will work. It does put a little more pressure to the outside in that the joint is equal.

An option would be a scarf joint. If you really want to get fancy, a joint that would look awesome and never come apart is a "hammer head" joint.
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post #3 of 10 Old 03-24-2012, 05:57 PM
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I would probably use a spline. Or this may be a good place for some of those Kreg screw joints.

George
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post #4 of 10 Old 03-25-2012, 04:27 AM
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If you round off end and make a socket to suit then any angle OK. Then stainless screws internally using a Kreg.
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post #5 of 10 Old 03-25-2012, 07:23 AM
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I would lay out the joining members and figure a long half lap (or longer), to the angle. Something like this:

Ideas for greenhouse joint-greenhouse.jpg


.
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post #6 of 10 Old 03-31-2012, 04:38 PM Thread Starter
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Thanks for your ideas everyone!

I'll do some more experimenting and see if I can make a decent half-lap joint of this size without a table saw and a dado set, which I can't afford.

Toby
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post #7 of 10 Old 04-10-2012, 07:19 PM
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Here is some info on building your own greenhouse that includes an easy technique for making the joints in the dome struts.

Build your own biodome greenhouse.
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post #8 of 10 Old 04-15-2012, 08:31 AM
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Quote:
Originally Posted by tobynicholas View Post
Thanks for your ideas everyone!

I'll do some more experimenting and see if I can make a decent half-lap joint of this size without a table saw and a dado set, which I can't afford.

Toby
I think it's going to come down to being more than the joint technique. If you were going to be using a more solid wood like yellow pine you might be able to do it. Using cedar I can't picture any joint other than a steel bracket that would hold up to the stress of wind against the greenhouse. Personally I would probably make the entire framework out of steel and cover it with the cedar for aesthetics.
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post #9 of 10 Old 04-16-2012, 09:07 AM Thread Starter
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Thanks Steve,

I'm sure you're right. I'm not familiar with working with cedar but I know it's very soft. I'm resigned to needing reinforcing 2x2s to keep the structural rigidity, and I think (hope) this will do the trick.

Ideas for greenhouse joint-reinforcers.jpg

Best,

Toby
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post #10 of 10 Old 04-16-2012, 01:32 PM
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That looks a lot better. Structurally cedar is not much and the extra pieces will add a lot to it.
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