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Drawbored Mortise & Tenon Joint

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Blog entry by thewoodwhisperer posted 03-29-2012 01:50 PM 6408 reads 3 times favorited 18 comments Add to Favorites Watch

The mortise and tenon is one of the strongest fundamental joints available to woodworkers, but there are a couple of ways we can make the joint even stronger and longer-lasting. One option is to simply reinforce with pegs. While this doesn’t really make the joint all that much stronger, it does help hold the parts together in the event of glue failure. I have repaired numerous chairs where the only thing preventing the piece from catastrophic joint failure was a small 1/4” dowel driven through a key tenon. So if you don’t mind the way it looks, pegging your mortise & tenon joints is not a bad idea. But we can do even better.

The Drawbored Mortise & Tenon
A drawbored mortise & tenon joint is similar to the pegged version, only the hole in the tenon is slightly offset so that when the peg is driven home, it pulls the tenon further into the mortise. Most of the time, a joint with this much mechanical strength really doesn’t even require glue! But being the “belt and suspenders” kind of guy that I am, I like to use glue anyway.

This technique can be used on anything from door frames to workbenches. I’m using the drawboring technique on all of my mortise & tenon joints on my Roubo workbench. I want this sucker to be bullet-proof!

How to Drawbore
Drilling through the moritseTo drawbore, you need to have a finished mortise and tenon that is already cut and ready to go. Drill two holes through the mortise piece, making sure you go deep enough to penetrate the material on the other side of the mortise.

Offset Marks in the TenonDry assemble the joint and use a brad point bit to locate and transfer the hole centers in the tenon. Disassemble the joint and for better visibility, use a pencil to darken the marks in the cheek of the tenon.

Drawbore Offset HolesMeasure and mark the offset (the offset should be located closer to the shoulder of the tenon). How much offset depends on the wood and the application. A softer wood and a more demanding application might require a 1/8” offset. A small door frame made from a dense exotic hardwood might require only 1/32”. But I would say on average, 1/16” offset is probably a safe bet. Drill holes in the tenon at the new offset marks.

Homemade Dowel Pins
You can use commercial dowel stock for the pins but I find it much more fun to use a dowel plate to create my own. The advantage here is that you can use any species you have in your shop! Once the pins are cut to length, use a chisel or utility knife to sharpen one end to a blunt point. If you don’t do this, the pin will never be able to maneuver around the offset and you could very well break the pin or the tenon.

Lie-Nielsen Dowel Plate Drawbore Pegs Made With a Dowel Plate

Hammer it Home!
Drawbore Flush CutHammering the pins in place does take a little more effort than you are probably used to but keep at it. When the pin contacts the offset hole you will actually notice it starts tilting slightly. Once you reach the stock on the other side of the tenon, the pin straightens out again and bottoms out. Simply let the glue dry (if you used glue), and then use a flush trim saw to trim the excess pin stock.

I recommend practicing this technique a few times before trying it on an important project. Once you get the hang of it, you’ll be drawboring mortise & tenon joints till the cows come home. I don’t own any cows so I’m guessing that’s going to be a really long time for me.

-- For free video tutorials and other cool woodworking stuff, check out http://www.TheWoodWhisperer.com



18 comments so far

View NBeener's profile

NBeener

4806 posts in 1894 days


#1 posted 03-29-2012 02:11 PM

Ma-TAY-o

Ma-TAAAAAY-o.

Daylight come, and me want go home.

Sorry, Marc, but … you’re nothing but your kid’s dad, now :-)

Love the M+T’s, by the way !

-- -- Neil

View superstretch's profile

superstretch

1509 posts in 1413 days


#2 posted 03-29-2012 02:33 PM

Good to see you guys back in action. Mark, you’re like the ww-ing version of Zachary Levi.

-- Dan, Rochester, NY

View thewoodwhisperer's profile

thewoodwhisperer

601 posts in 2904 days


#3 posted 03-29-2012 03:06 PM

lol this week I have been compared to Joe Rogan, Zachary Levi, and some soccer player. What did these people do to deserve looking anything like me?!! :)

Ma TAAAAAY-O indeed!

-- For free video tutorials and other cool woodworking stuff, check out http://www.TheWoodWhisperer.com

View superstretch's profile

superstretch

1509 posts in 1413 days


#4 posted 03-29-2012 03:21 PM

I also noticed you went through at least 3 hair/beard combos during the video.. LOL

-- Dan, Rochester, NY

View John's Woodshop's profile

John's Woodshop

347 posts in 2736 days


#5 posted 03-29-2012 04:50 PM

Marc,

Thanks for sharing that tip. I am going to use that in my next bench build!

-- John -- Racine, WI -- Woodworking..."It's not just a Hobby, it's an Adventure"

View BTimmons's profile

BTimmons

2164 posts in 1205 days


#6 posted 03-29-2012 05:00 PM

Cool video, as usual.

-- Brian Timmons - http://www.BigTWoodworks.com

View Philip's profile

Philip

1148 posts in 1258 days


#7 posted 03-29-2012 05:44 PM

Very nice, I’m making a dowl-pop as we speak…too genious!

-- I never finish anyth

View CalgaryGeoff's profile

CalgaryGeoff

937 posts in 1201 days


#8 posted 03-29-2012 06:45 PM

Hey Marc it could have been worse you could look like me and get compared to horses.

Nice video as well.

Cheers

-- If you believe you can or can not do a thing, you are correct.

View zindel's profile

zindel

257 posts in 1370 days


#9 posted 03-29-2012 08:03 PM

Marc, great tip! I am pretty sure I have watched every video you have out there and I look forward to the rest keep them coming! Thanks again!

-- If you can't fix it with a hammer, You've got an electrical problem.

View RobWoodCutter's profile

RobWoodCutter

111 posts in 1950 days


#10 posted 03-29-2012 08:53 PM

That is the same joint that L-N uses on thier workbenches. When I had to shorten the legs on my C-L LN workbench and I had to recut the joint and redo the M-T and dowel.

I had thought originally that they had just driven in a dowel with some glue, but nope, it just tapped right out of the hole. Rob

-- Rob-Yorktown "Shop's still not done, Tools are bought, Wood is bought, need to find time to start a project.."

View Craftsman on the lake's profile

Craftsman on the lake

2408 posts in 2157 days


#11 posted 03-29-2012 10:02 PM

This technique also works on an open edged tenon joint. We use it to place guitar neck tenons in the neck block. I’d make a straight (parallel) tenon that fits the neck into the neck block. Then place a shim behind the tenon where it meets the mortice in the block. Drill two holes that straddle the joint line from the top on either side of the tenon, So half the hole is in the mortise, half in the tenon. Pound two dowels into the holes and it pulls the neck tight against the body of the guitar.

-- The smell of wood, coffee in the cup, the wife let's me do my thing, the lake is peaceful.

View kckevin's profile

kckevin

41 posts in 1958 days


#12 posted 03-29-2012 11:05 PM

One tip I learned while taking a workbench building class from the Schwarz, is to use paraffin to wax up your peg before driving it home. It goes in a lot easier. It’s an old timber-framers trick.

-- KCkevin

View Eric_S's profile

Eric_S

1521 posts in 1915 days


#13 posted 03-29-2012 11:57 PM

Another great video Mark.

I have a question if you don’t mind. Would a drawbored M&T be equivalent to just clamping a M&T very tight and putting a peg through it?

-- - Eric Indianapolis, IN

View Mainiac Matt 's profile

Mainiac Matt

4316 posts in 1048 days


#14 posted 03-30-2012 01:00 AM

I used draw boring on a Timber frame that I cut out of rough cut timbers and square rule layout….

It may be the way the old timers did it… But I’ll never do that again… At least not on a large scale project.

You need a very precise layout…. If your off, you can wind up cracking your pegs and having misaligned joints…. And a slightly miss placed hole is often an error you can’t recover from.

If I ever get to cut and raise another TF, I’ll pre-drill the mortices and NOT the tenons. Then assemble the frame with straps and come-alongs holding it together,

Tighten every thing up REALLY tight, rack the frame square and THEN chase the mortice holes to drill the tenons in exactly the right spot. Drive the pegs and when you relieve the tension on the straps they’ll take up some pre-load.

I realize Marc’s using the technique for furniture joinery, but perhaps some of the principals from the TF world carry over.

Happy Trails

-- Pine is fine, but Oak's no joke!

View Gerry's profile

Gerry

253 posts in 1960 days


#15 posted 03-31-2012 03:40 PM

Marc,
Thanks for the sharing this technique! So good to see you back in action. Keep up the great work!

-- -Gerry, Hereford, AZ ” A really good woodworker knows how the hide his / her mistakes.”

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