Large Through Mortises?

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Forum topic by jacobgerlach posted 11-10-2013 08:30 PM 1807 views 0 times favorited 18 replies Add to Favorites Watch
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29 posts in 1792 days

11-10-2013 08:30 PM

Topic tags/keywords: joining question

We’re having lots of family and friends over for our sons first birthday, so I’m on the hook to build a bench for some extra seating.

My wife liked this one and asked for something similar:

I try to use every project to learn something since I’m still a novice, so I don’t want to put it together with pocket screws. My wife liked these through tenons (I think at Pottery Barn?):

So my plan is to use similar through tenons (about 1.75” square) to join all the 4×4 pieces (legs and stretcher).

My question is on the best way to cut the mortises. I don’t have a drill press. I would consider buying a decent mortise chisel for this project, but it seems like a lot of material to remove by hand since they are so big.

I have a router, but no edge guide – I’d also consider buying that for this project.

My tentative plan is to saw the 4×4’s in half, cut the mortises with my dado stack, and then glue them back together. The more I think about that, the more I’m nervous about cuts not lining up perfectly, and subsequent trouble with gluing it back up and/or fitting the tenons. If I were to do that, I could saw the 4x stock with my TS (flipping to finish the cut) or my BS.

Any thoughts or recommendations?

18 replies so far

View jacobgerlach's profile


29 posts in 1792 days

#1 posted 11-11-2013 02:14 AM

I did a test piece: resawed a piece of 4×4 in half on the bandsaw. Clamped them back together and laid out the mortise, cut it with the dado stack no problem.

As expected, the fit of the two halves isn’t glue ready coming off of the bandsaw. I tried cleaning it up with a hand plane with OK results, but between the bandsaw kerf and the thickness removed planing, I’ve lost about 1/8”, which shows when you’re joining it to an untouched 4×4.

So if I line up the cuts perfectly on the TS, that might be easier, but I’d still be 1/8” under.

I’d love to hear any suggestions for how to do this on a router without an edge guide.

View GFYS's profile


711 posts in 3497 days

#2 posted 11-11-2013 02:34 AM

I’d have to use a router and build a guide platform and cut the mortise from both sides.

View paratrooper34's profile


915 posts in 2978 days

#3 posted 11-11-2013 02:40 AM

Jacob, the method you are using sounds fine. You lose a little width due to the saw kerfs and planing which leaves the joining pieces a little fat. You could always shave a little off the joining pieces to a width that looks correct. Easy. Run those pieces through the band saw to take off half an inch or so and clean it up with the hand plane. Personally, I wouldn’t attempt to remove the waste with a router on 4×4s. Thats too deep for me.

-- Mike

View Don Broussard's profile

Don Broussard

3575 posts in 2278 days

#4 posted 11-11-2013 02:53 AM

If the mortise was square to the leg, the router would be one way to go. That said, what about using the method you described, and then trim the mating 4×4 width to match? That way, the stock would have matching thickness at that M&T joint. As an alternative, I remove the bulk of the mortise waste with a Forstner bit and then use hand chisels to clean up the sides. I usually cut the mortise with a standard sized bit and then match the tenon to fit.

-- People say I hammer like lightning. It's not that I'm fast -- it's that I never hit the same place twice!

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4258 posts in 3187 days

#5 posted 11-11-2013 03:13 AM

Cut it into thirds, not in half. Then plane the pieces before reassembly so you get a good glue joint. Here’s a sketch.

Sort of a false mortise? I hope it is clear what I was poorly describing.

-- Backer boards, stop blocks, build oversized, and never buy a hand plane--

View endgrainy's profile


251 posts in 1915 days

#6 posted 11-11-2013 05:36 AM

That’s a huge mortise to chop entirely by hand. To do it with a router would require a very long bit and would be difficult to make square given the angle (the Ana White plans seem to place the legs 10 degree angle, the pottery barn picture almost seems to be a compound angle with splayed legs.) I’ve spent the last three weeks making stools with compound-angle splayed legs, and boy does my brain hurt.

I second Don’s idea of removing the bulk of the waste with a hand drill then hand chopping the edges to fit. If you use a dado stack to cut half the mortise you’d have to use the miter guage for the angle – but if you used stop blocks for both sides I bet it would line up well. The downside to gluing up the legs is you may be able to see visible glue lines on the outside face.

Either way looks like a cool project – happy first birthday to your son!

-- Follow me on Instagram @endgrainy

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237 posts in 2704 days

#7 posted 11-11-2013 05:45 AM

+1 for Rance’s method that would be the easiest way to do the mortise with your tool set.

-- A friend will help you move, a good friend will help you move a body

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4258 posts in 3187 days

#8 posted 11-11-2013 02:23 PM

In reality, you don’t cut it into thirds, you just use smaller lumber to begin with and then glue it up.

1) Careful selection of wood could help in eliminating the possibility of seeing the construction method. The pieces should all have the grain going the same way.

2) Also, build this oversize by 1/8” and then plane down the outside. This is my Woodism #3 ‘Build Oversize & Cut To Fit’. This helps imensly in making the glue line perfectly flush.

Hope this helps.

-- Backer boards, stop blocks, build oversized, and never buy a hand plane--

View jacobgerlach's profile


29 posts in 1792 days

#9 posted 11-11-2013 04:22 PM

Thanks everyone for all the replies. As usual, LJ’s come through with tons of help!

Cost is key for this project, so construction grade 4×4’s are the name of the game, otherwise I would definitely think about laminating smaller stock together.

Rance – wish I had your “build oversize” advice before the last project. Laminated S2S 4/4 stock to make 2×2 bookshelf legs, and everything was too small by the time I trimmed it perfectly flush. Learned that lesson the hard way. Considering that I’m sticking with my 4×4 stock, is there any advantage to cutting thirds rather than my original plan? Seems like I’ll increase my work and thickness lost without saving anything.

I hadn’t really thought about how the router wouldn’t work because of the angle – guess that idea is out.

Trimming the stretcher to match the thickness seems like a tricky endeavor – 65” of 4×4 across my 10” bandsaw. Plus, I’d want to roundover the cut edge afterwards so that it matched the rest of the stock.

I’m starting to lean towards the idea of just drilling everything out with the hand drill and then cleaning it up. Probably a comparable amount of work to planing all the sawn pieces so they glue back up nicely, except no risk of glue lines. I’ll check craigslist – maybe it’s time to add a drill press to the shop.

Thanks again everyone.

View crank49's profile


4032 posts in 2997 days

#10 posted 11-11-2013 06:28 PM

Why not use 2×4s instead of 4×4s.
Rip the rounded edges off before you cut the mortise and your legs will be about 3-1/4×3.

I did something similar with my workbench except my legs were 5 layers of 1×4s.
The mortises I made were two layers, 1-1/2” thick. No dados needed, just gaps. Worked great.

View rance's profile


4258 posts in 3187 days

#11 posted 11-12-2013 04:56 AM

Jacob, if you demand the full width of your 4×4, then you severely limit your choices. You’re only left with chiseling, with or without pre-drilling.

The advantage of cutting into thirds and planing is you are working with milled surfaces on your table saw when you make your cuts. With bandsawing in half and using your dado, you have a rough sawn surface from your bandsaw against the top of your table saw, trying to cut an accurate dado.

Regardless, when you do your glue-up after your bandsaw/dado method, or the 1/3rds method, insert a dummy tennon in the mortise during the first part of the glue-up for alignment. Then once you have all your clamps tight, then remove that dummy tennon and clean up the mortise.

And as Michael suggested, consider 2×4s. Plane the outside ones to 1 1/8”(from one side only), and the inner one to 1 1/4”(from both sides). This would accomodate a 1 1/4” tennon.

-- Backer boards, stop blocks, build oversized, and never buy a hand plane--

View Woodknack's profile


11800 posts in 2406 days

#12 posted 11-12-2013 05:31 AM

I would go with Rance’ method of gluing up thinner boards but if you want more thickness then use 2×4s, cut each half of your dado and glue them up to make a mortise. To get good alignment, make a test tenon, wrap in clear packaging tape and insert into the mortise during clamping to hold everything together. The glue won’t stick to the tape and you’ll be able to pull it back out.

-- Rick M,

View GFYS's profile


711 posts in 3497 days

#13 posted 11-12-2013 05:54 AM

mortise in a 4×4 would be a breeze with a router even at an angle since it has 4 flat square sides. Its much more complicated through a rounded unsymmetrical piece.

View jacobgerlach's profile


29 posts in 1792 days

#14 posted 11-15-2013 01:53 PM

After thinking about this a lot, I came down on the side of making the mortises in 4×4’s instead of laminating.

Basically, I have more confidence in my ability to do that then to use my very limited hand plane selection and skill to make glue quality surfaces.

I also feel like it’s less total work to drill then to plane 2 surfaces on every board in the project.

Thanks again for all the advice!


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29 posts in 1792 days

#15 posted 11-18-2013 11:46 AM

Wow, I’m learning a lot from this project. For example, 4” of quill travel won’t get you there if your drill bit is only 2 1/2” long.

For the first couple mortises (straight ones for the long stringer), I used a 1” forstner bit. This gave me a slight overlap at the centers (mortises are 1 3/4”). I had a fair amount of cleanup, especially since I squared the corners. (I also learned that I need to sharpen or replace my cheapo home center chisels).

The depth limitation wasn’t a big deal for the straight mortises. I just flipped the work at each fence/stopblock combination to get all the way through. This also helped with preventing tearout.

For the angled workpieces, it won’t be so straightforward. The only thing I can think of doing is completely laying out the mortise on both sides of each leg. Any misalignment from cumulative marking/drilling error will just be extra cleanup.

Should I be using a different type of setup for such deep holes? I experimented with a standard twist bit on some scrap, but I was not happy with the results.

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