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Whether to use Pegged Tenons

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Forum topic by MJCD posted 704 days ago 908 views 0 times favorited 11 replies Add to Favorites Watch
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MJCD

452 posts in 1005 days


704 days ago

Topic tags/keywords: pegged tenons epoxy jatoba

Forum Members:

I need some advice …

I’m working on a large, Jatoba-based outdoor bench, which has 40 M&T joints – most of which are load-bearing (there are backrest slats which are not). The bench will be 100 lbs, all-in; and will be permanently outdoors – North East, US.

This is my first M&T project, and I’m unsure of how tight the Tenons need to be in the Mortises – the M&Ts are already created, and within my tolerances, I have a distribution of spot-on to somewhat loose (not that I have experience in these definitions); I believe it’s correct to say that none of them are either catastrophically loose or too-tight for the epoxy glue.

I’m using the West Systems G/Flex 650 epoxy as the adhesive, and I’ve researched the product as having excellent holding strength (greater than the wood, itself) & flexibility – that is, it’s not brittle to where normal racking and wood movement will result in failure.

The Tenons & Mortises are all 1.25” deep by 0.75” thick, and vary in width from 1.75” to 2.5” – these are Integral Tenons, not floating. My concern is that someone will try to lift it bench by an armrest or a back rail (both of which I would peg), causing the joint to fail – that is, the glue, alone, on one or two tenons may not be able to support the sheering effect of lifting 100 lbs.

My thought is to peg the corner tenons at 0.25” above the tenon base, with a 0.25 peg, and to do this while the project is glued & clamped-up.

As always, I appreciate the experience and counsel from the Forum.
Thanks, MJCD

-- Lead By Example; Make a Difference


11 replies so far

View Bill White's profile

Bill White

3421 posts in 2594 days


#1 posted 704 days ago

Not only will it aid in strength, it’ll look so darned GOOD. Get after it.
Bill

-- bill@magraphics.us

View MJCD's profile

MJCD

452 posts in 1005 days


#2 posted 704 days ago

I should add, as an explanation, that the armrest is capped onto the front corner post, and the back rail is capped onto the back corner posts, so that trying to lift the bench by either of them places all of the force on the glue, not the tenon itself.

Bill – thanks for the quick response: I think is will, as well; however, I’m about a mile over my skill level already, and have concerns that if I keep ‘playing with it’ I’ll mess it up – with a smile. Thanks.
MJCD

-- Lead By Example; Make a Difference

View teejk's profile

teejk

1208 posts in 1318 days


#3 posted 704 days ago

pegged does add a great “old world” appearance but you do add another “rot” factor. I think I would go with counter sunk metal fasteners and fill with plugs do give the appearance of through dowels. NE USA is not really kind to anything left outdoors.

View MJCD's profile

MJCD

452 posts in 1005 days


#4 posted 704 days ago

Teejk:

I hadn’t thought of that; and, I’ll have to.

Thanks.

-- Lead By Example; Make a Difference

View nwbusa's profile

nwbusa

1016 posts in 920 days


#5 posted 704 days ago

If you decide to go with dowels to peg the joints, you might also consider using the “drawbore” technique. Marc over at the Wood Whisperer did a good video on the subject. Here’s the link: http://www.thewoodwhisperer.com/videos/drawbored-mortise-tenon/

-- John, BC, Canada

View HorizontalMike's profile

HorizontalMike

6926 posts in 1548 days


#6 posted 704 days ago

I would only add that you can actually wait for the glue to dry before adding either the dowels OR the screw/dowel cap. It won’t be going anywhere once the glue dries, and besides, the dowels are basically a backup/addition to the original M&T joint. Plus, it will make it much easier to drill the dowel holes without wet glue all over the place.

-- HorizontalMike -- "Woodpeckers understand..."

View MJCD's profile

MJCD

452 posts in 1005 days


#7 posted 704 days ago

Great Advice – you’ve evidently been there a few times …

Marc’s video (thanks, nwbusa) is very helpful – how does he and halfinchshy have time to do these great videos? I’ll make 0.25” dowels/pegs from the Jatoba – this should address Teejk’s insight.

Thanks, again.
MJCD

-- Lead By Example; Make a Difference

View HorizontalMike's profile

HorizontalMike

6926 posts in 1548 days


#8 posted 704 days ago

John,
I took the time to watch the video link you attached. Very interesting concept though I was confused by just one claim. How is a “same sized dowel” actually “stronger” when it is drawbored rather than drilled and pinned? Like I said I like the concept, however I think the guy stretched the truth a bit with THAT claim. Tighter OK, stronger I don’t think so… but maybe there is something I am missing here. How about choice of dowel wood making the dowelbored joint stronger? Maybe…

-- HorizontalMike -- "Woodpeckers understand..."

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MJCD

452 posts in 1005 days


#9 posted 703 days ago

For my part, I’ll defer to his experience, though I glossed-over that one. While the concept is interesting, I’m not going to ‘drawbore’ the tenons – with the epoxy and peg, if the joint fails, so be it – the joint isn’t part of a fallout shelter.

Thanks, again, for the great comments.
MJCD

-- Lead By Example; Make a Difference

View casual1carpenter's profile

casual1carpenter

353 posts in 1109 days


#10 posted 703 days ago

Mike, I think his thinking in stating that drawbore makes a stronger joint is the fact that in mechanically forcing the joint tighter and eliminating small movement or slippage it would decrease the fatigue failure rate. The drawbore technique was demonstrated on ‘the woodwright shop’ I believe, by a guy who does colonial era reproduction and museum work. If it makes a rock solid joint with no glue at all, then the finished joint with glue bonding and bridging any small gaps can only be better. At least that’s my take on it. My biggest concern would be just how much to adjust the hole alignment. I do not imagine if a little is good a lot is better. Wood species, moisture contents, etc could likely play a part if you look real close at small issues.

View HorizontalMike's profile

HorizontalMike

6926 posts in 1548 days


#11 posted 703 days ago

@casual1carpenter,
Hey thanks for confirming what I was thinking concerning these joints. I made knock down wedged dovetails on my WW-bench, but haven’t tried the permanent draw bored dowels. For me, it will probably remain a curiosity. At 60yr of age, I am expecting all of my “glued” joinery will outlast me and it will then be someone else’s problem IF my joinery fails.

And like you, I would be guessing “how much” offset to use, much less what woods to use this type joinery on…

-- HorizontalMike -- "Woodpeckers understand..."

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