What is proper mortise depth ?

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Forum topic by opalko posted 03-11-2011 01:48 AM 5873 views 0 times favorited 5 replies Add to Favorites Watch
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148 posts in 3034 days

03-11-2011 01:48 AM

Topic tags/keywords: cherry mortise tenon

I’ve been trying to make a project from some plans I bought online for a nightstand. The plans call for 1 1/2” square legs with 2 mortises on each leg (Cherry, btw) for rails. The mortises are shown to be centered on each leg, 3/4” deep, 3/8” wide, 3/8” from top of leg. Being the ignorant plunderer that I am I didn’t realize this would mean the tenons would intersect. (Of course, on another page of the plans they show the side mortises as being 3/4” deep and the back mortises being 1/2” deep, so I should have already been suspect of the plans.) By the way, I see in Tage Frid’s book that he uses tenons that intersect and then miters the ends of them so they will fit together…hmm.

2 of the legs split at the top of the leg above and between the two mortises in different stages of either assembly or disassembly. I did not force any of the tenons before you get on your high horse.

It simply appears to me that there is just not enough “meat” above the mortises that would ever keep them from cracking – am I wrong here?

What is the general rule of thumb for making a mortise in terms of mortise depth vs. stock width and considering mortises that will be adjacent (perpendicular to one another).

Back to square one…sigh.


5 replies so far

View Loren's profile (online now)


10394 posts in 3646 days

#1 posted 03-11-2011 02:17 AM

Generally you make them so they intersect inside as Tage Frid’s
method, but they can be made with a sort of lap joint too.

For your problem, make each mortise and tenon with a “haunch”
which preserves the tenon’s ability to hold at the shoulders, but allows
more of the mortised material to remain for strength in that member.

Here’s a picture that shows how a haunched tenon is made


View Gofor's profile


470 posts in 3785 days

#2 posted 03-11-2011 03:36 AM

To prevent top blow out, where possible, I make the top depth at least equal to the thickness of the tenoned piece and move the tenon down so the bottom shoulder is minimal. (Like the haunch Loren illustrated without the top step).

You can miter the tenon ends, cut a slot in one to match a “pin” in the other, or step the ends so one rides over the other. (There are several other ways to to do this also, including actually cutting a dovetail joint where the tenons meet, but are complicated and require some very exacting cuts). Regardless, ensure they are short enough to fully seat with both side pieces in place.



-- Go

View smithburt's profile


2 posts in 2632 days

#3 posted 03-11-2011 05:47 AM

Yeah sounds good. But I have read that Cut the mortise about 2 or 3 milimeters deeper in the bottom region. So It make the mortise much stringer than soon. While My colleague told me that 1/3 thickness of mortise is preferable.

View DLCW's profile


530 posts in 2653 days

#4 posted 03-11-2011 11:50 PM

Mortise 1/16” deeper then the tenon is long. This gives the glue that is pushed down a place to go without creating the dreaded hydraulics problem of “you can’t compress glue” not allowing your joint to come together completely.

-- Don, Diamond Lake Custom Woodworks - - "If you make something idiot proof, all they do is make a better idiot"

View Nomad62's profile


726 posts in 2957 days

#5 posted 03-12-2011 12:18 AM

I’ve learned that 1/3 is good for your application, and if you don’t have the two tenons coming together you should go 1/2 depth of said leg. Just the ole 2 cents worth…

-- Power tools put us ahead of the monkeys

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