Wedged Through Tenons


If you are looking for the piece on linen fold panels, please click HERE.

During a recent remodel of our house, I enlarged the living room and added a small closet next to the front door. A full size door was out of the question, as it would  require 3' of clear space for it to open,  and I wanted a door that would use as little floor space in front of it as possible.  A pair of sliding doors would not open wide enough, and a single bi-hold door still required too much space for the furniture I have in mind that will go in front of the closet.  The answer was a 4 panel bi-fold door - it would only  protrude into the space in front of it by a foot or less.

Unfortunately, the selection of bi-fold doors available commercially either aren't available as a 4 panel door in that size, or simply look horrendous.  Fine for a bedroom, but this was our living room, so I decided it was an opportunity to make my own frame and panel bi-fold doors.  Part of the construction techniques for those panels include wedged through tenons, which I thought I would document here for anyone else who might benefit from my adventures.

For these door panels, I wanted a joint that was strong - this is a door that will see frequent use, and have odd, twisting stresses put on it.  I had already decided upon using a frame and panel construction for aesthetic reasons, and for that style of construction a mortise and tenon is entirely appropriate.  While a shorter mortise would work, I thought making through-tenons would be fun - along with the fact the fact that I don't have a helper and am short on space as anything.  Using a wedged through tenon allows me some slop in the construction of the joint, necessary for how I am to assemble it later.  More on that when I get to that part...

First, a couple of graphics to help show some of what I intend to make.  First, some of what the terminology I use is referring to:

As you can see, a "haunch" simply refers to where the shoulder is only deep enough to reach the bottom of where the panel slot is cut into the stile.  For the record, on a frame and panel door such as this, stiles are the vertical elements, and rails are the horizontal elements.  All mortises are cut into the stiles, and tenons are cut on the rails.

Next, a few diagrams showing how a tenon is assembled:

The left side shows a standard wedged tenon, assembled on top, and disassembled on the bottom.  The right side shows a haunched tenon, with a disassembled graphic underneath to orient the reader on how it all fits together.

Drilling and Paring Out the Mortises

Since it's a through mortise - and a fairly deep and wide one at that - drilling and paring will work better than chopping the mortise out with a mortise chisel.  These are too long and deep for me to do with a chisel with any economy of time, and because they will show, the drill press affords a bit more accuracy in getting them straight through the work piece.  

I've already got the channel routed (done on a table saw with a dado blade) for the panels in the stiles to use as a guide for one side, and have marked out the same width for the mortises on the other with a mortise gauge.  I true the fence on the drill press to parallel with the drill bit, and drill out the mortise from both ways, choosing a slightly-smaller-than-the-mortise-is-wide brad point bit to do the work, making sure to clamp the piece to the fence to keep it from wandering.  Why do it from both sides?  Well, first - even drill bits can wander a bit - it's best to drill from each side to keep it as parallel to the outside of the work piece as possible.  And second - the drill bits weren't long enough to go through the entire piece anyway....

After drilling, it's time to take a bevel edge chisel after the rough, and open up the mortise a bit:

You can use the holes left by the drill bit as your guide to ensure you are paring the walls of the mortise straight.  This work goes pretty quickly with a sharp chisel - the wider the chisel you can use, the better.  One that can take a mallet helps too - the goal of this first task is to remove as much of the waste as quickly as I  can.

When most of the waste that I can safely remove with a mallet and chisel is removed, I continue paring by hand, keeping an eye on the sides of the holes left by the drill bits:

Notice that I've damaged the edge of the channel, there - right below the ferrule on the rasp that's sitting on the bench.  This is OK here, as it's not visible when the piece is assembled - but I should be a bit more careful as I go along.

I don't get it to "finished" depth - not yet, anyway.  I'll use the actual tenon that's destined for this hole, so I can fit each one individually.   But I do want to get it close, and evenly done, so I continue paring until I'm satisfied it's as good as I can do with a chisel.  Then, I square up the ends of the mortise with the proper width chisel:

And finish the squaring up the ends with a large file:

The chisels can leave a pretty rough surface behind, so I level it off with a pattern makers' rasp.  These are great rasps because they are at once thin enough to fit into the mortise, and fine enough to leave a fair surface.  However I do need to be careful that I'm  using a straight stroke when using this method - its easy to round off the corners of the hole.

Work to the marks left by the mortise gauge and the channel for the panel on the other side, and don't go past... Going past will leave gaps that will have to be filled later, and the less gaps, the better.  At this stage, it's best to get it so its just a bit shy of where it needs to be.  I usually keep a scrap of wood handy that's just a hair thinner than the tenons I'm going to be fitting, and use that to "gauge" how I'm doing - whether I'm keeping it straight, where more needs to come off, that sort of thing.    Just a hair thinner, because I like to do the final fitting with the tenon that will actually be used.

Before I had these particular rasps, I used coarse wood files (not rasps) to accomplish the same task - actually the same one as shown in the photo above where I'm squaring up the corner with a file.  These rasps work faster, but both will function adequately for the task if you haven't had the money to acquire the more expensive rasps.

Also, it's worth noting that you only need a "perfect" fit where the tenon will be seen - its not that important that it fit perfectly all the way through, so concentrate your best skills where they will be seen.

Preparing and Fitting

Preparing the Tenons

There are a  few processes to go through that need to be accomplished to get the tenons ready for fitting.  First, due to the size of these particular tenons, I cut them on the table saw - no fancy jigs, just a trued blade and a fence.  I prefer doing smaller tenons with a handsaw, but the table saw allows for a bit more accuracy when working such a large surface.

After cutting the tenons, I mark out the haunches and where the wedges are to be fit.  The wedges will be around 5/8" to 3/4" in from the end of the exposed tenon end - that gives the tenon enough material on each side that it won't split as easily as a narrow one, and still not be too wide as to be difficult for the wood to spread apart as the wedge is driven into place.  At the bottom of the where the slot for the wedges, I drill a small stop hole to help keep the wood from splitting when I drive the wedges in - it breaks the grain and give the wood a place that stresses can pivot on, rather than continuing to crack as it would if the hole were not there:

The particular pieces of wood I'm using for these rails (red oak) seem especially prone to splitting, so I thought the stop holes especially prudent here.  Woods less likely to split may not require them, but I usually err on the side of caution - as there is no bigger pain than to have one split during glue-up.  The only cure then is to disassemble it and repair or replace the piece - and that can mean a lot of clean up or preparation to get it ready to assemble again.

After drilling the stop holes, I use a tenon saw to cut the haunches and the slot for the wedges:

 I like a good, thick bladed tenon saw to do these cuts with.  A thin bladed saw will not provide a wide enough slot for the wedges, and that adds difficulty to getting them installed later. This particular saw is from a batch of saws I made where I used larger saws for the steel, specifically to have a saw for purposes like this.  This way, I don't worry about cutting the taper into the slots, as just the wider saw cut will do.

After sawing, I clean up the edges of the tenon with a sharp chisel:

Here's a shot of the finished tenon, complete with haunch, stop hole, and slot for the wedge - sorry for the focus quality.  Notice the number "2" penciled in on the face of the rail - the same number is penciled in on the face of the board that has the mortise this tenon fits into.  I always number my joints, with the number always written on the face of the pieces;  this helps me to keep my assembly all in order, and that I don't mix them up and have 2 that might not fit together when I assemble the whole affair later.

Since I did these tenons using a table saw, I don't have any reason to trim their thickness or use a shoulder plane to clean up the cheeks.  I used no special tenon jigs (I don't own any, anyhow), just a trued, sharp blade and fence...  But that's the beauty of the machine over doing tenons this wide by hand.  That sort of accuracy isn't necessary for smaller tenons, though.

On the occasions I do tenons by hand, there is always some cleanup involved no matter how careful I try to be. Then,  I use either the widest chisel I have to do most of the work or a patternmaker's rasp if there is a lot of material to remove.  A skewed iron block plane might work best in such a case, but I've never owned one...  A straight bladed one tends to get caught up going against the grain, and is more difficult to use.  One is on my list of things to get, though, I've been jonesing over a Lie-Nielsen copy of a Stanley 140 since they came out.

After that, a wide cabinetmaker's file will clean up the face of the cheeks nicely, and serve to make them flat.  It's easiest if you are working to a set of scribed lines on all the edges of the tenon.  A pencil line isn't enough to get that clean edge you need to work to here.  It's easier to "split the line" if the line is incised into the surface of the wood, and besides, the scribed line helps reduce tear out.

For the shoulders, it's much the same story - but I use a Stanley 92 shoulder plane where cleanup is called for.  The table saw had done a pretty good job, but I did need the shoulder plane where on one rail where the stop hole didn't work.  The entire rail split (fortunately before glue up) and had to be glued it back together.  During glue up, I got it slightly off (it slid something less than 1/32" when I clamped the 2 pieces back together.  Not much, but enough to where you would see the gap in the final product. The shoulder plane worked perfectly to correct that slight misstep.

Fitting the Tenon into the Mortise

I'm finally ready to start fitting the tenons into their respective mortises.  The fit is tight enough that I can start it by hand, but can't get the tenon very far into the mortise without resorting to a mallet, which I don't want to do yet.  Forcing the tenon into place by using a mallet could split the wood, and I'm too far into this to want to make a piece over again.

So, I slide the tenon into the mortise as far as I can just using hand pressure, and turn it over to see what's happening inside.  A quick check shows where the tenon is tight against the wall of the mortise, so I use a pencil to mark where the "high spots" of the mortise wall are located.

And yes, the floor of my shop is covered with sawdust, shavings, cutoffs, and wasted sandpaper.  Lots of it.  I know, I know!  (You should see the bench!)

Note - use a light pressure on the pencil, as I'll want to erase the marks later, as I'll be repeating this process.    Here, I see the corner isn't quite as square as it should be.  It's a perfect time to use one of the planemaker's floats I made  - as they are made specifically for getting into corners:

A file is another tool that can be used in place of the float.  For the face of the mortise, a patternmaker's rasp can also work, though by this stage the fit should be close enough that all you need is a file.  Once the corner is straightened out, I put the tenon back in, and try again - and continue repeating this process until the tenon slides almost fully into place by simple hand pressure.  I don't usually mind if I have to drive it the last 1/4" or so with a mallet, as by the time it's there it's usually sized pretty close to where it should be - enough so that it shouldn't split it.

If using a mallet at all during this process, do not use a great deal of force as you don't want to damage the end of the tenon you're bashing on.  And use a wood mallet, not a metal one - you do have a wood  mallet, don't you?  Metal hammers and mallets are simply too unforgiving in this situation.  A rawhide mallet might be a good substitute, however.  I have quit hitting things with my bare hands - a few years of that and I've found the hands just don't work as well as they used to... in more ways than one.

I go through each and every tenon in this manner, carefully hand-fitting each until they slide on with ease.  They don't always come apart with the same ease, so keep a small scrap that fits into the mortise that you can use to drive the rail back out, when needed.

Assembling the Pieces

Assembling a panel with so many joints is a difficult task when you have a helper, and nearly impossible if you don't.  Because I needed to be able to do the task myself, I broke the assembly down into manageable portions.

Forgive me, but I didn't get photos of every step - so bear with me if you would.  To start, I was able to glue each rail into one of the stiles, then set that aside to dry, planning to return to glue the other stile on later.  I did use a clamp to get them to fit tightly and while I drove the wedges into place - but after that, the slip fit along with the wedges was tight enough that once the rails in place I could remove the clamps.  I did leave the clamp in place on the bottom ones just as a precaution in case I bumped it while setting it down.  Make sure to use a clamp that won't damage the end of the tenon - I used some Jorgensen Cabinet Master clamps.

Once dry, I put them back up on the bench, inserted the panels where they were to go, and placed the other rail on top so it was ready to be glued into place (note the wedges on the bench in the lower left corner of the photo - to be mentioned later)

This step was the biggest reason I went with a wedged tenon.  Had they all been tight fitting tenons, there's no good way I could slip the rail in without damaging the tenon somehow.  The slots where the wedges fit give me a little slop so I can drive the rail home more easily, then add the wedges to tighten the joint.  I don't have the luxury of being able to do one joint at a time, like I did when gluing the stiles into the first rail - here, there's no choice but to do it all at one.

And, being I had to go fairly quickly, there are no direct photos of the sequence... but I think you can get the idea.  First, I set each door panel up just as above, with most of the tenon showing below the rail:

Having gone through and test fit each individual tenon, I knew each would fit, and that the slots for the wedges would give me a bit of room - it's still a good idea to check the fit anyway.  Its almost impossible to get it apart, so I don't actually push the rail on to the stiles, rather I just check the fit as it sits above.  If it looks like it will go, it should - remember, there should be about 1/8" clearance for these tenons that the wedges will close up.

I then fit the stile onto each tenon, making sure they were all started into their corresponding mortise.  Working quickly, I apply glue to all the faces I have access to, and also apply a thick bead of glue on the wall of the mortise at the top, spreading it out with a small stick as best as I can.  When all the surfaces have glue on them, I drive the stile onto the rails with my wooden joiners mallet, and use a pipe clamp at each stile to clamp the whole assembly together.  Watch that there is still access to the slot for the wedges, as they must be installed while the glue is still wet.

The wedges - shown in the above mentioned photo - are made by thicknessing some stock to the same thickness as the tenon, then cut freehand of them on the band saw.  The taper I use is similar to that used on dovetails, something like 1 in 7.  I used walnut here because it contrasts with the oak nicely, but nearly any wood will do.  They don't have to be anything fancy, but the end needs a point that will fit into the slot they are intended for.

Now that I have the stiles clamped in place, I dab a little glue on a wedge and drive it home into its prospective slot:

Note the tenon doesn't reach all the way to the outside of the mortise - I always oversize my outer stiles by an 1/8" or so, that way I can trim off what's gotten damaged while making them.  I also don't bother to wipe up the glue right away, as that would just spread it around - it's better to wait until the glue gets leather hard, then scrape it off.

Now's a good time for the first inspection of the visible parts for gaps.  Fill any larger ones first with glue and a sliver of wood, and trim off the excess with a chisel.  It's best to fill any larger gaps that you can while the work is still in a rough stage - it gives you the opportunity to remove any glue that might squeeze out onto the face of the wood.  The less glue you have to deal with on exposed surfaces, the better.

Once the gaps are filled, I trim the panel to it's finished size, and round off the edge with a 1/8" round over bit in a laminate trimmer, and inspect the exposed parts for gaps again - here's what I ended up with:

Not  too bad - but not perfect, either - I did have 3 or 4 small areas where tiny gaps appeared after trimming the doors to their final width.  I doubt you would have even been able to see them after staining the wood (I couldn't even photograph them well enough to be seen), but I took the time and filled them anyway - more for my own satisfaction than anything.  A bit of wood glue and fine sawdust (from sanding) to fill them does the trick nicely.  

The assembly is now ready for the next step, whether it be it planing, scraping, or sanding.  I must say that I really love the subtle look of these joints - they've always been on of my favorite things to find on a piece of furniture.  Well executed joints such as these always tell me that the maker has gone the extra mile to make something of good quality.   I only hope that can be said of what I've made here someday.

Here's a shot of the door in it's finished state, with a closeup of the end of one of the tenons inset on the right:

Thanks for reading!