Tenon Length

I'm looking at the current issue of popular woodworking and I'm puzzled about the length of mortises they're recommending for a face frame construction. The piece can be found here: http://www.popularwoodworking.com/feb08
A better pic can be found here: http://tinyurl.com/ys4pkt
On 2 3/4" stiles they are recommending 1 1/4" mortises for tenons from the rails. The stiles are 3/4" thick. All maple. It's hard to tell from the picture, but there are 5 rails, 5.5" at the top, 3" at the bottom and 3 that are 1 1/4" for the drawer dividers.
The entire piece is 78" tall and 21" wide. 10" deep.
I don't have a mortiser. I have straight chisels and a router. I don't know if I can mortise that deep with the router, but if it's necessary I guess I could.
My question is: Do the mortises have to be that deep for this kind of construction, or could I go with something shallower? If shallower is acceptable, would it be ok to go 3/4"?
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Tanus

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I've run across 1 1/4" long tenons before. If I decided to make them 1 1/4", I might rout the mortises to 7/8" depth and finish them with a mortise chisel.
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Tanus wrote:

In this case the face frame is there to help resist racking forces. In general, longer tenons are stronger. The standard rule of thumb is 5x the thickness of the tenon. I'm guessing that they're using 1/4" thick tenons?

With the right bit you can go a lot deeper than that. I recently made some 2" deep mortises with a router and chisels, and some more with a drill press and chisels.

Going shallower will weaken the joint. The shallower you go, the weaker it will be.
Chris
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Deeper is better because you provide more surface for the glue. The shallowest mortises I do are 7/8"s for crest rails - which I generally pin. If you have a plunge router and a 1-1/2" bit, you should have no problem making 1-1/4" mortises.
Cheers, Jeff
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I think you could get close, and finish with chisels and a forstner bit referenced from the routed section.

How big is the door?
For a smaller door, you'd be fine. For a larger door, like the lower cabinet kinds kids like to ride on, I'd go the distance.
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Bonehenge (B A R R Y) wrote:

Ok, that was pretty unanimous. 1 1/4" it is. The door is 44" x 15 1/2". I'm guessing that fits into your larger door category, so it'll have 1 1/2" mortises too.
The tenon is 1/4", so the 5x rule is being followed. That wasn't a rule I knew, but it seems easy enough to remember.
Thanks very much., guys. I don't know when I'll get to this project, but I"m glad I asked this. I've done a few mortise/tenon joints, and read up on them, but never really knew how long they should be. I've always just eyeballed before. This makes more sense.
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"Tanus" wrote

I would not believe a damn thing I see in print, particularly from many of the "experts" writing "how to" articles in some of these woodworking rags in just the last five years or so. :)
Instead, stick with traditional "proportions" for joinery parts whenever possible. When it comes to mortise and tenon joinery there is ample evidence of traditional methods standing the "test of time"
Looking at just the picture of the project, I see nothing that would make me deviate from the above, and below.
For future reference, the time honored/traditional "proportions" for a standard "stopped mortise and tenon" joint:
~ Tenon thickness of a standard "stopped mortise and tenon" joint is approximately 1/3rd the thickness of the rail, and usually runs the entire width of the rail (except when it would weaken the stile/leg, then "double tenons and mortises" are preferred).
~ The depth of the mortise of a standard "stopped mortise and tenon" joint is approximately 3/4th the width of the stile/leg.
It is _always_ a good idea to get as close as possible to these "proportions" if you want your work to be around to be appreciated for many years.
Strictly my tuppence, and the way I would spend it ...
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Swingman wrote:

Your tuppence is good enough for me. From your post and others, I have a bunch of easy-to-follow rules that now make sense. Well, maybe they don't make perfect sense, but I'm not about to argue with hundreds of years of trial and error.
Thanks Swing.
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FWIW, You've just posted what Chris Schwartz writes several times a year, with one clarification.
Machine made mortises in 3/4" stock are often 3/8" thick, due to the fragility of 1/4" mortise machine tooling. The advantage of a 1/4" tenon when hand cutting is there is less of a likelyhood of levering out the sides, compared to a 3/8" chisel in 3/16" sides.
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