Which of these joints would be the strongest? - Woodworking Talk - Woodworkers Forum
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post #1 of 26 Old 01-30-2014, 12:17 PM Thread Starter
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Which of these joints would be the strongest?

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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post #2 of 26 Old 01-30-2014, 12:30 PM
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I would say #3.

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post #3 of 26 Old 01-30-2014, 02:12 PM
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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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post #4 of 26 Old 01-30-2014, 03:22 PM
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agreed

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Originally Posted by TimPa View Post
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.
I would guess they would all be very strong within a close range.The laminated ones would have some advantages I would think....

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #5 of 26 Old 01-30-2014, 03:39 PM Thread Starter
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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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post #6 of 26 Old 01-30-2014, 04:48 PM
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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.

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #7 of 26 Old 01-30-2014, 06:46 PM
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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.

That bowl was perfect right up until that last cut...
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post #8 of 26 Old 01-30-2014, 07:21 PM
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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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post #9 of 26 Old 01-30-2014, 07:23 PM
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I vote for the second one to the right...the solid wood M&T.






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post #10 of 26 Old 01-30-2014, 09:22 PM
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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.

Use the right tool for the job.

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post #11 of 26 Old 01-30-2014, 10:02 PM
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I like the second one from the left the best. It is commonly used in through mortise doors.
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post #12 of 26 Old 01-31-2014, 12:31 AM Thread Starter
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thanks guys. good info here!
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post #13 of 26 Old 01-31-2014, 06:46 AM
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For your application and if the joints are equally well made I think there is no difference.

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post #14 of 26 Old 01-31-2014, 05:02 PM
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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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post #15 of 26 Old 02-02-2014, 10:52 AM
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There is likely little difference in strength in any of the joints shown with proper workmanship. In all of them the racking strength is greater in the direction with the shoulders.

Putting a shoulder on all four sides of the tenon would add racking strength in all directions.

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post #16 of 26 Old 02-02-2014, 12:40 PM Thread Starter
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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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post #17 of 26 Old 02-02-2014, 01:38 PM
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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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post #18 of 26 Old 02-02-2014, 04:34 PM
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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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post #19 of 26 Old 02-02-2014, 05:46 PM
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that's what I was thinkin' here

Quote:
Originally Posted by woodnthings View Post
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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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.

Thanks for the interesting discussion Chris.

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)

Last edited by woodnthings; 02-02-2014 at 05:48 PM.
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post #20 of 26 Old 02-02-2014, 05:58 PM
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Quote:
Originally Posted by Chris Curl View Post
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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