Sliding dovetail vs. M&T

[Osvaldo Cristo]

A few months ago I made a small side table for my mother in law.

It was my chance to try something new for me: I used only sliding dovetail joints. The legs were connect by sliding dovetails plus glue. It looks me very strong, actually comparable to traditional M&T but way easier and faster to make. The table top was attached dry (no glue) thru tappered sliding dovetails.

I was wandering why I did not see similar work previously... all I found for similar project was M&T.

What do you think about sliding dovetail to replace some M&T? Do you have use tappered sliding dovetail for table top attachment? Do you have any experience with them to share?

F411767.jpg

Thanks in advance for your feedback.

[Ralph Okonieski]

No comment on m&t vs sliding dovetail; but really like the side table and wanted to say so. Very nice! Well done.

[David Eisenhauer]

Nice table Osvaldo. I don't know about strength of the sliding dovetail vs M&T, but I believe that my M&T work goes quicker and easier than my sliding dovetail work. I'd guess that a properly cut sliding dovetail with a decent male/female part fitup should be strong enough, but I have to tweak mine lots more than my M&T. Also, the layout for my M&T goes quicker. I never have tried to pull a sliding dovetail joint apart by brute force, but assume it is strong enough never mind a little glue in the right place.

[Brian Holcombe]

Dovetails are considerably weaker than mortise and tenon joints, be cautious as to where you employ them.

I attached a table with sliding dovetails recently, they were 36” long joints. I’m a glutton for punishment sometimes.

[David Eisenhauer]

While I was responding above, I was trying to think of what the optimal angle (of the dovetail sides) for a correct cut sliding dovetail would be. I'm thinking that the angle would enter into a strength discussion. I do know (firsthand) that a too shallow angled dovetail combined with a too loose sliding male part will definitely pull apart. I wonder if it is known what angle results in the strongest joint? Steeper equals more strength it would seem. I would definitely say that a glued or pegged M&T joint would be stronger, but I cannot quantify that with any empirical data. As to Osvaldo's dovetail connected legs, how strong is strong enough? Pull various joints apart with a fish scale in line on the pull-apart line to see what's what?

[Jim Becker]

Brian is correct...the nature of sliding dovetails has some strength disadvantages vs M&T. That said, for a small table like that, it's less likely to be a factor. I've even used pocket screws and glue for similar small table constructions with no issues because there is little stress on them. Most of the time, of course. But M&T is going to shine far brighter when you do need strength, whether they are traditional M&T, loose mortise, Dominos, larger dowels, etc.

[Ben Grefe]

Why are sliding dovetails weaker? Is it due to the shorter ‘tenon’ length compared to a M&T? Volume wise a sliding dovetail, even if 1/2 as deep probably has more wood contact area for glue and volume of material in the joint.

[Brian Holcombe]

It’s due to many factors, the dovetail literally splits the joint open as it’s levered. It can also sheer the sides off of the dovetail, which are short grain.

Compare to a draw-bored mortise and tenon which relies upon a host of forces retaining it in place. It is harder to leverage because of end grain abutments top and bottom. It is retained by a peg that is under shear, so for the joint to move it must first shear the peg or split tenon (or mortise walls) all while the joint is provided with little wiggle room.

Dovetails are not used in Japanese carpentry because they risk ripping out of their sockets during an earthquake.

Sliding dovetails in a table top running cross grain are fine, there is no short grain issues and if the joint features a shoulder the tail can be lightly compressed as it enters the joint.

Chris Hall recommended 18 degrees to me, I’ve gone as far as 14 degrees (per side) so far to very positive effect.

[Rod Sheridan]

Nice table Osvaldo, it looks very nice.

I've used sliding dovetails on carcass construction where I've had cross grain situations.

For attaching table tops I use wood buttons which are screwed to the top and have a tongue that goes into a mortise in the aprons. It allows for wood movement and is strong and easy to make...............Regards, Rod.

[glenn bradley]

For those of us who have good results with sliding dovetails, they come to be a solution we turn to for our designs. Your table is a winner with nice clean, traditional lines. My use of sliding dovetails for this type of joint is kept to smaller pieces and thinner stock where they are a great solution when other joinery can be a challenge. On thin stock it is easy to leave weak areas as shown here.

e-NWC Top profile 3.jpg

Using epoxy for the adhesive I think I got to a joint of reasonable strength for the purpose despite my cutting the socket deeper than I should have.

Deb Bath Cab (7).jpg

On a different piece the same "side to top" joinery is used with thicker stock.

GnG Wall Cab (24).jpg

This cabinet is hung from vertical keyhole slots in the sides so the top-to-side joint is not load bearing.

GnG Wall Cab (178).jpg

[David Eisenhauer]

Thanks for the info Brian. In the past I have used 10 deg for sliding dovetails, but I will lay them out a little more next time to see how that works.

[Derek Cohen]

The choice of mortice-and-tenon vs sliding dovetail is horses for courses. The strength advantage lies with a M&T, especially if it is pinned or drawbored. However, a sliding dovetail takes up less area, and the wedging action is capable of much strength in a small area.

M&T would be the first choice in a table, joining legs and rails ...



Similarly, joining a frame, such as in a frame and panel construction. There are areas in a table where a sliding dovetail is very useful, such as where depth is restricted ....






(Inside the mortice-and-tenon legs/rails is a hidden drawer ..)






The drawer blades in this chest are fitted with sliding dovetails ..





However, the runners are all mortice and tenon ...





Regards from Perth

Derek

[ChrisA Edwards]

Wow, that's inspirational....

[Osvaldo Cristo]

No comment on m&t vs sliding dovetail; but really like the side table and wanted to say so. Very nice! Well done.

How kind of you to let me know!

[Osvaldo Cristo]

[...]
As to Osvaldo's dovetail connected legs, how strong is strong enough? Pull various joints apart with a fish scale in line on the pull-apart line to see what's what?

That is the key point.

No dispute between what is stronger but it looks me sliding dovetail can replace traditional M&T in some cases. For that particular table it looks me sliding dovetail gave me the same end results...

On the other hand sliding dovetail is way easier and faster to do than M&T for my skills.