Rounding tenons or squaring mortises?

[Brian Grella]

Tempting. Very tempting. I'm actually considering building a horizontal mortiser with Z axis control.

[SonomaProducts.com]

Interesting, I would have thought they would make rounded tenons. I know that is how the Leigh FMT works.

If you will square the slotted mortises you can make a cool tool that I learned about from Darrell Peart. Use the chisel from a square chisel mortiser as a hand tool to square up the ends. I th> I've cut all my mortises for the kitchen cart I'm crafting using my new

[darkon]

The Woodrat looks like a mill machine with the sliding table upside down, and some other modifications for woodworking. Pretty cool.

[Chris Friesen]

This paper from the "Dept. of Forest Industrial Engineering" in Turkey shows square-ended mortise/tenon joints to be about 15% stronger on average than round ended ones.

not going to be the deciding factor in the design, but if you're borderline on strength you might want to go for the square ends.

Chris

[Swingman]

last test by "Fine Woodworking" shows 3/8", square cornered, traditional M&T joints to be only roughly 3.5% stronger than round cornered, 3/8" loose tenons.

is obviously full of it ... ;)

Either test notwithstanding, IME, it is nothing to be concerned with. AAMOF, the 3/8", rounded corner, loose tenon joint is almost twice as strong as the ubiquitous 1/4", square cornered, traditional M&T joint.

Not to nitpick, but in that case I personally would first consider a thicker mortise and tenon if possible.

[Larry Jaques]

On Sun, 13 Dec 2009 11:55:25 -0800 (PST), the infamous routerman scrawled the following:

Yeah, doesn't anyone use chisels any more? It's also an RCH stronger with it squared up. 'Course, I bought a Shop Fox Mortiser for that purpose, the Normite version of a v-groove chisel.

True, but...

[Larry Jaques]

On Sun, 13 Dec 2009 17:25:26 -0600, the infamous Swingman scrawled the following:

Fess up! Where'd you see the x-rays of those, Swingy? We wanna see, too!

-- Every day above ground is a Good Day(tm). -----------

[Larry Jaques]

On Sun, 13 Dec 2009 15:23:33 -0600, the infamous -MIKE- scrawled the following:

So, it's OK for GM to use untempered Chiwanese steel for head bolts on your new pickemup truck's engine? They'll be covered in oil and hidden under the rocker covers for...days?

Now go wash those impure thoughts out of your mind, young man.

-- Every day above ground is a Good Day(tm). -----------

[Larry Jaques]

On Sun, 13 Dec 2009 14:55:26 -0800, the infamous "Lew Hodgett" scrawled the following:

P'raps not, Lew, but wouldn't you really rather have the squared tenons if you were seated on the wagon behind said flying horse?

-- Every day above ground is a Good Day(tm). -----------

[Lew Hodgett]

Putty those joints with epoxy and don't sweat the small stuff or pet the sweaty stuff.

Lew

[Steve Turner]

Likewise on the nitpick, but before you increase the thickness of the tenon first consider the wall thickness of the mortised piece. The tenon isn't the only part of the joint that can fail.

[Swingman]

"if possible" ...

[Steve Turner]

[Steve Turner]

I thought about writing my response so as not to get that reply, but I was too lazy. :-)

What's that rule? The walls of the mortise shouldn't be any thinner than the thickness of the tenon? For example, a M&T joint in 3/4" stock shouldn't have a tenon any thicker than 1/4"; Zat sound right?

[Lew Hodgett]

A guide from my days doing machine design.

Allow the tenon to be 50% of the stock thickness which means the cheeks of the mortise will each be 25% of the stock thickness.

Based on the above, for a piece of 3/4" stock, the tenon would be 3/8" thick and each cheek will be 3/16" thick.

The cheeks and the tenon equally share the load, thus have equal total thickness.

Works for me.

YMMV

Lew

[Chris Friesen]

For machine cut mortises, the walls of the mortise combined shouldn't be thinner than the thickness of the tenon. This equalizes the amount of wood in each component. For 3/4" stock, the tenon should be 3/8".

For hand-cut mortises, you'll often see the 1/3" rule, which results in

1/4" tenons. There are two reasons given for this: 1) hand cutting is harder on the piece being mortised, so this gives a bit more wall strength, and 2) it's quicker to cut a 1/4" mortise since you're removing only half the material.

And note that it's the thickness of the piece being mortised that is the main criteria here...there's no real downside of having a fat tenon on the piece being tenoned as long as there is still some shoulder left. So if you have a table apron joining with a thicker leg, you can use a tenon thicker than half the thickness of the apron.

Chris

[Larry Jaques]

On Mon, 14 Dec 2009 08:01:51 -0600, the infamous "Leon" scrawled the following:

S/B "Swingman and me", too. When you say the people individually, it becomes clear. "Come join Swingman down that slippery slope." and "Come join me down that slippery slope."

Hmm, inviting guys to play with the sloap with you? No comment.

-- Every day above ground is a Good Day(tm). -----------

[Leon]

Interesting to see. Swingman showed me a few weeks ago. Almost shocking as to the lack of uniformity inside those joints.

[Larry Jaques]

On Mon, 14 Dec 2009 06:47:20 -0800 (PST), the infamous Brian Grella scrawled the following:

Remember David Marks playing with that $3500 multirouter thang? Cool toy, could be built for 10 cents on the dollar. David sells it for $2695 now

Speaking of David, I never saw this particular video:

jigs for curvilinear wooddorking.

-- Every day above ground is a Good Day(tm). -----------

[Swingman]

Here's mine ... scroll down to "Mortises in curved work, "Method 1"":

of the most productive tools in a productive shop ... it's paid for itself a few times over in the time it would have taken me to build one for "10 cents on the dollar", and undoubtably will a few times more.