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Master firewood maker
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Discussion Starter #1
Or are they all pretty much the same strength?

Note that 2 of them are built by laminating 3 pieces together, while the other 2 are solid. Some people say that glue is as strong as wood, but I'm not sure ...

Your thoughts?
 

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I'm suspecting that they would be very close in strength, with more actually dependent on joinery quality and fit. also when the "strength test" is performed, how is it directed toward the joint. i.e. in joints 3 and 4 the beam will be weaker, an would break easier on any side load test.
 

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where's my table saw?
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agreed

I'm suspecting that they would be very close in strength, with more actually dependent on joinery quality and fit. also when the "strength test" is performed, how is it directed toward the joint. i.e. in joints 3 and 4 the beam will be weaker, an would break easier on any side load test.
Exactly!
What direction are the forces? racking? twisting? pulling? pushing?
direct? lateral? combination?
What's the application is what I'm getting at. :blink:
I would guess they would all be very strong within a close range.The laminated ones would have some advantages I would think....
 

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Master firewood maker
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Discussion Starter #5
Thanks. They would be for supports for a 40" high table I am thinking about making for my office. Something along these lines:
 

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where's my table saw?
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I like either no. 1 or no.3 for those verticals and the legs and top supports. It would be easy to do with 3 separate pieces, leaving a gap for the intersection, then gluing all at once. Maybe have a helper with lots of clamps handy... just sayin' Then probably a single tenon for the horizontal brace.
 

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Cant remember where I saw it but there was test of joinery that showed mortise and tenon was the strongest at joining piece perpendicular to each other.
 

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IMO the mortis and tenon joint is stronger than the bridle joint particularly against racking forces. Assuming the glue up is sound and the glued up tenon and mortis fit as well as the cut tenon and mortis the strength would be nearly identical.
 

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Old Methane Gas Cloud
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I have to agree with Mike, the M&T would be the strongest. There is a slight mechanical advantage to the M&T joint.

HOWEVER

If the directions provided by the glue manufacturer are followed, the joints are well made and adequate clamping pressure is applied any glued area is stronger than the wood.

My personal experience tearing apart glued joints, TB-III appears to be stronger than Gorilla Polyurethane. In both case it was the wood that failed and not the glue.
 

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Master firewood maker
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Discussion Starter #12
thanks guys. good info here!
 

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Like others mentioned any of them would be plenty strong for the application if well executed. In terms of absolute strength, the solid wood M&T is the way to go. The solid wood piece will look significantly better than a laminated one and will allow you to make the bottom horizontal member slightly thicker than the upright which IMO would be a more appealing look for this specific design.
 

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Master firewood maker
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Discussion Starter #16
How about finger joints, or multiple tenon joints? Since they provide more glue surfaces, I am thinking they are probably stronger?
 

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Multiple tenons are called for from time to time, I use them in some designs. If you don't have a very fine tuned method for cutting them however they just add another element to get right or wrong.

Finger joints would serve no functional purpose in this application.

With the design you presented you have zero concerns with strength. A single M&T or two of them, you could stand on the top and be fine. I guarantee my pieces for life and I would feel fine delivering that piece with a single well cut M&T. Two won't hurt, but won't increase the functional strength by ANY measurable amount. If you are concerned, you can peg the tenons from the inside of each leg with a peg that goes 2/3 of the way through.
 

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bzguy
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What no one seems to have addressed here is that assuming the premise that glue is at least as strong as wood is correct, #3 is by far the least work to get a perfect fit.
 

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where's my table saw?
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that's what I was thinkin' here

I like either no. 1 or no.3 for those verticals and the legs and top supports. It would be easy to do with 3 separate pieces, leaving a gap for the intersection, then gluing all at once. Maybe have a helper with lots of clamps handy... just sayin' Then probably a single tenon for the horizontal brace.
What no one seems to have addressed here is that assuming the premise that glue is at least as strong as wood is correct, #3 is by far the least work to get a perfect fit.
I also think a laminated piece is "stronger" than a solid piece in most applications, hence laminated beams where strength matters. It may not have the desired look or style so that would rule it out.

It seems to me that the most important issue here is "racking" along the length of the table rather than across it's width. It will want to shear off any tenons that don't have enough shoulder to stop it from moving. The bridal joint in no. 3 will have more resistance to that, in my opinion. I would like to see a load test on these joints, but that's a whole 'nother issue.:yes:

Thanks for the interesting discussion Chris.
 

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Old School
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Or are they all pretty much the same strength?

Note that 2 of them are built by laminating 3 pieces together, while the other 2 are solid. Some people say that glue is as strong as wood, but I'm not sure ...

Your thoughts?
The way your question reads is which selection would be the strongest. You didn't specify under a variety of conditions, such as certain directional forces. So, I stand by my choice of the solid M&T.






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