Rounded mortise and tenons

[Dewald Swanepoel]

Here is something that I'm just curious about. I see people making some very neat joinery on this forum and I'm always impressed at how people would cut a tenon to fit snugly into a mortise. It seems a common way of cutting a mortise would be to use a Forstner bit on a drill press to drill out a rounded hole and then square it off with a chisel. Alternatively you could use a router to cut the rounded hole and again use chisels to square it off.

So it got me thinking; Why do people square off the mortise rather than round off the tenon? I can't remember ever having seen something like this:

 

Is there a specific reason why this is a bad idea?

[Gary]

I actually do this when I use a router to make my mortises. I cut in diagonally across the corner of the tenon against the shoulder with a chisel, then I round the corners of the tenon using progressively smaller facets with the chisel.It is faster for me to do this than to spend time squaring up the mortise. I think Marc demonstrated this in one of his videos... but I can't remember which one.

[wdwerker]

It's usually loose tenon and 2 mortices. Make the tenon stock accurately then cut the length to fit both mortices. Cut the mortices with a router or use a Domino machine !

[Dewald Swanepoel]

It's usually loose tenon and 2 mortices. Make the tenon stock accurately then cut the length to fit both mortices. Cut the mortices with a router or use a Domino machine !

Makes sense. But that reminds me of another thing that I'm curious about. Why bother with making a mortise and a tenon or a loose tenon as in your example at all? Why not just use two or more dowels to serve as round loose tenons and drill holes in the workpiece to serve as round mortises?

[Dan S]

Makes sense. But that reminds me of another thing that I'm curious about. Why bother with making a mortise and a tenon or a loose tenon as in your example at all? Why not just use two or more dowels to serve as round loose tenons and drill holes in the workpiece to serve as round mortises?

More holes means more things need to line up for the joint to go together. Also dowels aren't as strong as one large tenon.

[dwacker]

Crap you said the "D" word. Welcome to the world of joinery evolution and diminished returns. Use what ever trips your trigger a properly engineered and implemented dowel joint is just as good as a old school hand cut mortise and tenon. Use what ever fits your skill level, tooling or budget.

[estesbubba]

Check this jig out:

 

http://www.leighjigs.com/fmt.php

[wtnhighlander]

Personally I find dowels more difficult to align. However, Youtube has several strength test videos that show dowels as being pretty much as good as M&T. I think tradition may play a big part in why many of us prefer the M&T.

[Tpt life]

PB was careful. Notice "properly engineered and implemented." Most of us have seen badly executed and failing dowels. This makes one nervous.

[pghmyn]

Crap you said the "D" word. Welcome to the world of joinery evolution and diminished returns. Use what ever trips your trigger a properly engineered and implemented dowel joint is just as good as a old school hand cut mortise and tenon. Use what ever fits your skill level, tooling or budget.

Hit the nail on the head.

If you can line up the dowels accurately, and execute the drilling the have the holes perfectly match up, have at it. Nothing wrong with dowels

[TerryMcK]

In general dowels have less surface area than a mortise/tenon so not as much glue. Having said that I have chairs held together with dowels after many, many years and are still strong. I agree nothing wrong with dowels - just another method of creating a joint.

Where possible I personally would use mortise/tenon, loose tenons or some other joint in preference to dowels for the alignment problems creating dowel joints as mentioned by others.

[Mick S]

As Terry mentioned, another reason to use m&t over dowels is the amount of long grain surface to glue.  With a dowel, there is very little surface making contact with long grain since it runs across the grain of the female part.  It's mostly glued to end grain.  A tenon is glued to two faces of nothing but long grain - much more surface area.

[Gilgaron]

With perpendicular long grain, does the glue in a mortise and tennon really add much to the strength?  I'd figure it'd be nearly as strong without it in terms of load bearing.  Obviously you could pull it apart more easily, but with proper design the forces aren't going to go in that direction, and if you fearing otherwise you could always pin it with a dowel.

 

In any case, yes, I've used rounded tennons when it is not a through mortise and I used the drill press for the mortise.  Saves a lot of time versus chiseling everything square.

[dwacker]

If you really want to put dowels to the test the Jessum Paralign is as good as it gets. As many dowels as you can fit perfectly every time. If you really want a strong dowel joint a blind wedge dowel will never come apart. You do have to be careful, once its together its done and can never be disassembled. Personally I prefer any loose tenon method to fixed. It may seem like an extra step or two but makes up for it in the construction of the actual part. We run a Unique 3450 and have found that the time and accuracy of loose tenons more than makes up for the time spent on the extra step.