Tips for Through Tenons

[Ashwini Kaul]

Hey Folks,

I am in the middle of making a couple of A&S pieces which call for through tenons.
I have no problems with the Tenons but the mortices is what I am worried about.
3/4" Plain sawn white oak - is what I am using.
I am ok with using hand/power tools.
I am most concerned about chip out.

I have been thinking of making a morticing jig for a while... maybe the time has some vs just drilling and chopping with hand from both sides... The layout will be a pain!

Any suggestions... tips etc will be appreciated.

[Bill McDermott]

You are right... layout (on both sides) is the key. That allows you to enter the mortice from both sides and avoid blowout.

A tip I picked up somewhere is to start the tenon inot the mortice, then apply glue to the tenon cheeks. This means the end of the tenon will come through the backside of the mortice without gobs of glue.

If this is something like a picture frame instead of a bed, make might consider making the mortice a bit loose - just keep the far side tight. The tenon can slide most of the way without a problem and you can adjust the exit hole as needed to keep appearances tight. The drawbore will help hold and otherwise sloppy joint. Dry fits will not give you the fits either. No one but you will ever know.

[Jim Neeley]

Not glueing the end is a tradeoff... it makes for a cleaner exit however the glue also serves as a lubricant during assembly, so you can start out with tighter tolerances and end up with more strength from the glue.

All of this distorts if you're talking wedged tendons...

[Chris Friesen]

For tooling, you have multiple options. If it's not too deep a router does a very clean job. For deeper stuff a drill press works fine--forstners will let you drill overlapping holes, and once you get most of the waste gone you can get pretty smooth walls by just incrementally drilling away the higher bits. You can pare what's left with a chisel if you want. With either of these, for through tenons you'll probably want to square up the ends with a chisel.

For something nonstructural like a picture frame Bill has it right, make the inside bits a smidge loose then peg it.

For anything structural, I'd suggest either wedging or drawboring your tenons. That said, my bed frame just has regular (though large) tenons and it hasn't had any problems.

[Kent A Bathurst]

I do a lot of through-tenons. But - my PM719 handles most.

Where the part is too big or unwieldy for that machine, here is what I do:

Layout lines on exit side only.

Drill press to drill most of the waste out - enter on the tenon's exit side; use a backer board to manage tearout.

Use a chisel to chop/pare to lines.

The key for me is to keep in mind that the only part of the joint that will be visible is the very edge on the tenon exit side, where the layout lines are. The tenon shoulders will hide a multitude of sins on the other side of the joint - the tenon merely has to fit in the mortise there, and fit cleanly on the exit side.

I typically do not glue those joints, so I don't even get too jacked up about the "perfect fit" of the tenon in the mortise. Through-pegs - traditional A+C. Some just straight pegs glued in place. Some I drawbore - mebbe glue those pegs, mebbe not - just however I happen to feel at that moment, I guess.

Again - there is only the very edges of the mortise on the exit side to worry about. Always start there, and don't worry about the rest of the mortise - that's my version of reality.

[Stephen Cherry]

The first question would be what tools the original poster has at his disposal?

I've done this sort of thing on the hollow chisel mortiser by starting the hole on the show side, and going almost all of the way through. Then finish the hole with a smaller drill bit, and refining with chisels, rasps, etc. As Kent has posted, the tenon shoulders can hide a less than perfect hole.

It may be possible to joint the show side of the board, cut the mortise, and then rip to width, never tried it though.