Loose tenon joinery

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I've done a lot of "regular" mortise & tenon joints, but am moved to try loose tenons for my next project (a dining room table). Are there any situations where loose tenon joinery is NOT recommended? Any hints or advice?
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John B wrote:

The only time I used them was when making a bunch of passage door. Worked fine.
The mortices were 1/2" x 2" deep in both rails and stiles, cut with a spiral bit. Duck soup to make the tenons...prepare a long piece to width and thickness, round over all edges as needed to fit the mortices, cut off a bunch to correct length. I did make them a tad shorter than the combined depth of the mortices and cut a shallow groove along one side with a thin kerf table saw (before rounding over) to provide a place for excess glue to go.
Only caveat I can think of is to be sure to cut the mortices so that they are either centered (two passes, one from each side) or offset from the *correct* side.
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John B wrote:

Built a lot of tables and chairs using loose tenon joinery here.
You will find that throughout every test published thus far the difference between loose and integral tenon joinery is basically negligible with modern glues.
The big plus with loose tenon, in my experience, is the ability to batch cut your aprons and rails, thereby gaining a great deal toward the squareness of your project, as well as the cost effective use of expensive wood.
IOW, I would not hesitate to continue planning to use loose tenon joinery on your project.
My tuppence, FWIW ...
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Swingman wrote:

That's true. In every test I've seen (including one posted here, recently), the wood fails before the glue.
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-MIKE-

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I agree that loose tenon joints are not really much weaker and obviously these tests you mention (I haven't seen them) seem to prove that out but I have seen some 200+ year old windsor chairs that had proper mechanical fits and they are still going strong. I don'tthink I could say the same about 200 year old Titebond x but check back in 200 years and maybe my opinion will change.

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SonomaProducts.com wrote:

Likewise, I have handled some 200 year old pieces containing much "pocket hole" joinery that is standing the test of time, yet the debate still rages on that joinery technique ...
Until I see some evidence that loose tenon joinery must be pinned on both sides in order to stand the test of time, it will remain conjecture/supposition, without support, in my book.
... no disrespect intended, you're too damn good of a furniture maker, and, unlike many of those proffering advice hereabouts, we get to actually see pictorial evidence that that is so on your website ...
:)
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No problem, just spouting opinion.
I have a dirty little secret that I love pocket screws. I've built many a coffee table and end tables that use them exclusively and I have every assurance they will stand the test of time. I do also count on the sort of box truss concept of the geometry to contribute to the strength of the structure. I did a sort of Federal pencil leg table, that I still use myself and those pocket screw connections from leg to apron surely will not last. I am very careful with that little piece but it looks nice.

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SonomaProducts.com wrote:

Shhhh, not so loud! ....
:)
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John B wrote:

Loose tenons don't work well in cases where the tenon shoulders would normally be very thin. Consider a table apron going into a thicker leg. With a regular tenon you could use a 1/8" shoulder (just enough to cover any imperfections) to keep the tenon as thick as possible for strength.
With loose tenons you would be forced to use a thicker shoulder to keep your mortise walls thick enough. This translates into a thinner tenon, and possibly a weaker joint.
Chris
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Chris Friesen wrote:

To the OP ... Chris is correct in that regard, however there is alway a point where common sense and practicality span the gap of the theoretical proving of a negative ... use of the traditional "1/3 the thickness of the rail/apron stock" for tenon thickness and the above generally becomes a non issue on most projects, loose or integral tenon notwithstanding.
That said, If you feel you need really thicker tenons for joint strength, then your project would likely benefit from thicker stock for your aprons/rails to begin with.
Besides, departing from the ubiquitous "3/4 inch stock" mindset of most woodworkers today will generally do wonders for your project, in both looks and durability.
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Swingman wrote:

My understanding is that the basis of the "1/3 thickness rule" is to ensure that the mortise sides aren't too thin, so it's actually the thickness of the piece being mortised that matters, not the piece being tenoned. If the two pieces are the same, this makes no difference. If the mortised piece is thicker, this can make a big difference in tenon thickness.
Of course, this is only important if strength is an issue.
Chris
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"Chris Friesen" wrote:

SFWIW:
During my time on the design board, it was common practice when designing a knuckle fitting for a pivot on the end of a cylinder for example, to make the knuckle twice the width of the pin diameter, thus insuring that the knuckle had the same cross section in shear as the pin.
The 1/3 rule for M/T joints in wood is would appear to be based on similar design concepts.
Lew
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Depending on what device (machine\tool) you have to cut the mortises they can be a real rpoductivity and accuracy help.
However, important consideration is what stress will the joint need to accomodate. A classic pinned mortise can resist an enormous amount of twist, pull and down forces and even if the glue fails, after 100 years that mechanical joint of one continuous piece of wood (tenon) held inside another (mortise) will still have most of it's integrity.
A loose tenon on the other hand, unless it is pinned on both sides will not have the same longevity and ability to withstand the racking forces.
Table leg to apron connections take lots of stresses. Chair rail and spreader connections also. Maybe a picture frame where no stress is really present or a box where the basic geometry adds to the strength reauire no second though but structural type connections need to be closely considered.

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SonomaProducts.com wrote:

Cites please ...
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Swingman wrote:

Tough to cite anything related to long-term joint durability. It would require some realistic form of accelerated aging. Looking at surviving pieces, we know that pinned joints have lasted a long time. We don't know how loose tenons hold up over hundreds of years.
All glue fails eventually. This could be accelerated on a wide apron if the loose tenon is of a species with different expansion rates and humidity swings are wide.
However, this is stuff that only matters if you're building for the really long term. And in that case, yellow glue probably isn't the best choice since it isn't repairable. Hide glue, resorcinol, polyurethane, epoxy, or plastic resin are all better choices in this respect.
Chris
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I know hide glue is repairable. Are those others?
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Chris wrote:

"-MIKE-" wrote:

Long after the wood has returned to compost, epoxy and resorcinol will still be there, thus what's to repair?
Lew .
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Lew Hodgett wrote:

Ask him, he wrote it.
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Lew Hodgett wrote:

Epoxy degrades with heat and UV. In either case, under humidity cycling I could see the layer of wood immediately next to the glue failing.
Chris
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"Chris Friesen" wrote:

As I said, " Long after the wood has returned to compost, epoxy and resorcinol will still be there, thus what's to repair?, and that includes the conditions described above
As for heat degradation, by the time the epoxy is softened, the wood will be scorched.
If you are going to use epoxy as a coating, then UV protection is required.
If you are going to use epoxy as an adhesive, no UV protection req'd since only the outside edges of the joints are exposed.
Lew
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