Loose tenons

[Victor Robinson]

Loose tenons sure seem to be all the rage these days. Probably has a lot to do with two popular loose tenon tools (Domino and Mortise Pal), of which I will probably get one in the near future...probably the cheaper one!

Aside from when you want true tenons for aesthetic reasons, is there really any reason to go with true tenons over loose tenons? Are they actually any stronger? (I realize we're in the theoretical realm of strength here as I'm guessing both types of tenons will withstand real-world loads equally.)

Aside from any theoretical strength advantage, or possible aesthetic utility (e.g. through-tenon), loose tenons seem superior, at least from my novice perspective.

Pros:
Easy. Heck of a lot stronger than biscuits. Can mill your own tenon stock. If you screw up the tenon, you're not trying to salvage an entire workpiece.

Cons:
Size? I can see at a certain size larger single loose tenons may become impractical.

Thoughts?

[Sean Hughto]

Historically, traditional mortise and tenons have had the advantage because when working by hand, they are actually easier to make and fit. Imagine chopping a mortise into endgrain, for example.

[Kirk Poore]

Properly sized, a regular tenon is almost certainly stronger than a loose tenon. However, a loosen tenon would be strong enough in most cases.

Regular tenons can be sized to the specific piece.

With the use of wedges regular tenons will have a mechanical reliability that does not depend upon glue.

I suppose you could peg loose tenons like you can regular tenons, but it would take twice as many pegs.

You can't drawbore a loose tenon. Well, I guess you could, but then you're back to pegging both ends again.

Kirk

[John TenEyck]

For the joints most of us make, most of the time, loose tenons have plenty of strength. They have all of the advantages you noted in your posting, plus they are faster to make then a traditional M&T, and typically more precise. Before you run out and spend serious money on a Domino or similar machine, however, consider making your own horizontal mortiser. I made one for less than $50, based on various designs I saw, and it cuts very precise mortises of nearly any size very quickly. Here's a link to some pictures, in case you're interested. http://picasaweb.google.com/JohnTenE...eat=directlink There are other ways of using your router to cut mortises that cost darned near nothing, but there are advantages to having the router fixed and moving the work piece, which this type of machine allows you to do. The next link will take you to some more pictures where I used this machine to cut some loose tenons joints in curved doors with beading. You can do a lot with this little machine. http://picasaweb.google.com/JohnTenE...eat=directlink

[Sean Hughto]

loose tenons ... are ... typically more precise.

Speak for yourself!

Seriously, all joints are as precise as the given maker is willing and able to make them.

[Cody Colston]

I think loose tenons are strong enough for any application where integral tenons are used. However, one of the problems I see with loose tenons is that both sides of the joint are entirely dependent upon the glue and that cross-grain glue joint will eventually fail. On an integral M&T joint, only one side depends on the glue and that side can be pegged and even drawbored. I suppose you could peg both sides of a loose tenon but aesthetically it probably wouldn't look right.

[Chris Padilla]

I think loose tenons are strong enough for any application where integral tenons are used. However, one of the problems I see with loose tenons is that both sides of the joint are entirely dependent upon the glue and that cross-grain glue joint will eventually fail. On an integral M&T joint, only one side depends on the glue and that side can be pegged and even drawbored. I suppose you could peg both sides of a loose tenon but aesthetically it probably wouldn't look right.

Well, I suppose the glue could fail...so could the wood. My take on integral vs. floating for strength: since the glue is stronger, having glue in both pieces and fully surrounding the tenon on all sides would make the floater stronger. That said, either one is likely fine and it is a matter of preference or project-dependent.

[Norman Pyles]

The best thing about loose tenons is, I can cut my stock to the finished length. I don't have to do any adding, then subtracting for the tenon length. I really like my Mortise Pal.

[John TenEyck]

So I looked up the most recent joint strength test in FWW. From #203 the rank of joint strengths was:

1. Half Lap = 1603 lbs to failure
2. Bridle = 1560 lbs
3. Splined Miter = 1498 lbs
4. 3/8" M&T = 1444 lbs
5. 3/8" Floating Tenon = 1396 lbs
6. Miter = 1374 lbs
7. 3/8" Wedged M&T = 1210 lbs
8. 3/8" Pinned M&T = 1162 lbs
9. 5/16" M&T = 988 lbs
10. Beadlock = 836 lbs
11. Dowelmax = 759 lbs
12. 1/4" M&T = 717 lbs
13. Pocket Screw = 698 lbs
14. Domino = 597 lbs
15. Biscuit = 545 lbs
16. Butt 473 lbs
17. Cope & Stick = 313 lbs
18. Stub Teneon = 200 lbs

There was minimal (5%) difference between a 3/8" M&T and 3/8" Loose Tenon joint in terms of ultimate strength. Wedged and pinned M&T joints were actually weaker in these tests, probably due to reduced glue area. And you may want to rethink buying that Domino machine.

[Sean Hughto]

Uh, this "test" was roundly critized by many for a slew of reasons. Unless you are making a table for use in a trained elephant act, I don't think strength really is the most important determinant if which of these joints to use in a given typical application. It might start to get important in something like chairs which endure a variety of major stresses and often have significant size limitations for their joints given the size of the sticks making up the chair etc..

Far more important in deciding on the joint to use:

- How long do you need the piece to last (e.g., modern glues are not likely to fail in the first 50 years or so)
- How much time do you have to build the piece
- What tools do you have
- What methods give you the best results/are you comfortable with
etc.

[Ray Newman]

'Gonna hafta' go back and re-read the Fine Woodworking joint test cited above. Surprised at how "weak" the Domino was/is rated.

[Victor Robinson]

Interesting - why did the Domino test so weakly? Must have been a thin domino? I would have thought a domino would perform equally well to a loose tenon of the same size?

[Chris Padilla]

The Domino suffered because it is only available in certain sizes. To be fair, the test should've included an integral tenon of the exact same size of a domino but I do not think it did.

[Geoff Chapman]

I have been using loose tenon joinery in a set of Chippendale side chairs I am building. The great advantage has been my ability to do compound-angle joinery with them, using a home-made router jig. The project would have probably been beyond my reach with traditional M/T joinery.

[Forrest Bonner]

I first used loose tenons when I had to build 2 'open' bookcases 6x3. My design needed 96 M&T joints each! I recalled an old Norm Abrahm show where he built a huge mahogany exterior door using loose tenons to join the rails and stiles. I built a jig to rout every mortise with my handheld router - each was exactly the same width, length, and depth. It was then a simple matter to mill the loose tenons 'en masse' and then cut them to length. They fit as snuggly as I wanted and on the length allowed some play for precise part alignment at assembly. I cannot imagine how long cutting 96 tenons would have taken.

As for decorative through tenons or pegged tenons: make the desired side of the 2 mortises a through mortise, make the loose tenon a 'perfect' fit in the through mortise and there you have a decorative through tenon. I contend that is an easier and just as 'woodcrafty' as fitting a 'normal' tenon to a through mortise.

Since at least the FWW test of M&T vs loose tenon should excellent strength (does anyone have any other test results showing a significant difference?) you would only need to peg one side - not 2. In most cases with current glues, a well fit tenon does not need to be pegged unless it is a decorative item.

And why not drawbore loose tenons? Glue one side, let the glue cure well, and drawbore the other side. Heck, wedge the exposed side of a through loose tenon.

There are no constraints on loose tenons, IMHO, other than do you have the upcut bit size that you need? Thicknessing the loose tenons is a fundamental task.

What I recall seeing in print several times is that wood properly glued (even a M&T joint) tends to fail the wood and not the glue surface.