Trestle Table Part 2: Joinery For The Base

In any work surface not supported by a leg at each corner, it is even more important than usual to combine the engineering of time-tested joinery with the skills to produce joints that are tight and without (much) error. This table is almost solely reliant on the venerable mortise and tenon joint, even the bridle joint that connects the top brace to the leg is a form of mortise and tenon.

While my joints may not look this good, I hope to make them precise enough so that they will outlast at least my great-great-grandchildren’s lives.

For the last blog post, I had milled the stock for the feet, braces, legs and stretcher slightly oversize and stacked them to ensure good airflow. They’ve been sitting for about 4 days in the garage and since they began this new life with 50 years of drying in a barn, I’m confident that they won’t move much more. They are ready to mill to final dimensions so I can start cutting the joinery but first, I want to cut the pieces for the top so they can be acclimating while I work on the base.

Out to the stack for more timbers:

These pieces had a few nails still embedded in the wood that took a little time to remove. No problem, they were only 12 inches (30cm) long 🙂 .

After a couple hours on the jointer and bandsaw I’ve got enough to make a top that is 100 x 180 cm (39 x 70 in.), including breadboard ends.

As mentioned in the previous chapter, I don’t mind the extra work as it is more economical and, in addition, I get to recycle some perfectly useable wood. Another advantage is that since this is not pristine wood, I don’t have my usual angst regarding making pieces as “perfect” as possible. I can even relax a bit (phew…).

As described in the article written about this table, all the joints except one are mortise and tenons. There is a great video produced by Paul Sellers here where he demonstrates a really great method of making a mortise and tenon joint. In his video he uses stock that is the same thickness and this works well for the foot/leg joint. It can also be adapted for use with unequal pieces as you’ll see a bit later.

The first step is to decide how thick the tenon will be and set that dimension onto your router plane (I didn’t acquire one of these for many years and if I could do it all over it would be one of the first 10 hand tools on my list). You then use the router plane to mark where the cut lines for the tenon cheeks, and then to mark the cut lines for the mortise walls on the opposing piece. You could do the same with a marking gauge but this way the router plane can then be used to fine tune the tenon to exact thickness very easily.

Instead of chopping out the mortise completely by hand as Paul does in the video, I use my drill press to hog out the bulk of the material.

The sample tenon block is then clamped to one side of the foot and can be used as a chisel guide to chop out the remaining waste right up to the cut line. The sample is clamped to the other side to finish the procedure. This is my first time attempting this method and I must say it worked brilliantly, my tenon fit just right the first time out. You’ll notice below that on the bottom side of the foot, I enlarged the ends of the mortise just a bit to allow for wedging later.

I’m taking a departure from the original plan in that the tenon width is the same as the width of the stock, in other words, there are only two shoulders on the faces of the cheeks and none on the ends. Since I plan on making them tight, there shouldn’t be an unsightly gap at the ends and there will be more glue surface to help increase the strength of the joint.

The joint that attaches the top brace to the leg is a blind bridle joint and I can adapt the Seller’s method to help with this joint also.

Bridle joint:

The stock is 60mm thick and I want the “tenon” to be a little more than a third of that (~24mm) so I subtract that from 60, divide by 2 and set the router to 18mm. Now I mark from both faces of the leg to define the mortise cut lines and from both faces of the brace to define the tenon cut lines.

For the mortise on top of the leg, I use my tablesaw jig to define the cheeks and then a coping saw to cut out the waste. Finally a chisel to pare it nicely.

I set the height of my tablesaw blade to just under 18mm and make two passes to define the shoulders and then two more in the middle so it is easier to chisel out the waste.

After that, the router plane is still set to the exact depth to pare the tenon faces to the correct depth.

The test fit more than acceptable, and this was just as quick as if I used a dado stack on the tablesaw (which is illegal in most of Europe by the way). It was way faster than setting up and using an electric router.

Now it’s time to cut the tenons on each end of the stretcher and the mating mortise in the legs. Before I do that I have to cut the stretcher to final length and even though I’ve kept the same overhang as in the article (12″ or 30cm from the brace to the end of the tabletop), I want to get a visual and ensure the proportions still look pleasing. I dry-fit the leg assemblies and lay a couple pieces for the top and step back.

I have the option of decreasing the overhang by up to 10cm on either end or increasing it by the same however, it looks good to me. To borrow an expression from boatbuilding: “If it looks fair, it is fair”.

Someday I’d like to build a boat, and if I do, it will probably be something like this:

This is a Welsford Navigator and if I actually get to build this, it probably means I’m having more money coming in during retirement than I expected. 🙂

</End Tangent>

So I mark where the top of the tenon will be on the leg and again, I make a sample tenon to help with chopping the mortise.

As before, I hog out the waste on the drill press and use the sample tenon to guide me while paring the mortise walls.

Once the mortise is done, I go about trying to ensure a successful tenon fit. It may be additional work, but by cutting the tenon on some scrap first, I can set the router plane to the exact depth needed and take the trial and error out of the equation. This highlights a good practice that for some reason took me many years to adopt: make sure there are a few decent sized scraps of the finished dimension.

I first set the router plane as close as I can to the proper depth and then the tablesaw blade to that same height. On the tablesaw I define the shoulders and cut a few kerfs to help with chiseling out the waste. A good tip from the Seller’s video is for longer tenons, leave a little bit at the end to support the router plane.

Here I use the router plane to clean up the cheek of the tenon. At the finish, I chop off the end bit and use another scrap cut from the stringer to support the router plane.

It takes me two further adjustments but when the scrap tenon fits snug I know the router plane is set just right.

Since the tenon doesn’t actually span the entire width of the stretcher, I could have saved myself a little work by notching it beforehand however, I didn’t mind the additional practice. Also, because there are identical tenons on each end of the stretcher, once I set up the stop in order to define the shoulder on one end, I just flip over the stretcher to do the other end. Then I leave the stop untouched so that when I need to cut the notch, it’s already set exactly where it needs to be.

After the notch is cut out, I taper the outside edges of the mortise in preparation for wedges, but I won’t glue it up until later.

This table is long enough that a middle brace is necessary so I turn my attention to what will become a half-lap joint in the center of the stretcher. Again, I set the router plane to the depth needed and use it to mark the cut line. After the waste is removed, a few passes with this plane and the bottom of both sides of the joint is cleaned up easily.

I only have to make a minor adjustment with the plane for a nice flush fit. I should have bought a router plane 20 years ago.

The last joint to prepare is for the top brace/leg. I drill two holes offset for drawboring, fit the joint, and using a brad point bit, mark the hole center on the tenon. Until drawboring becomes second nature to me I always stop and think before drilling the corresponding tenon holes. A good hint that keeps me honest is to just remember that you mark the hole slightly offset towards the shoulder you want to pull the tenon towards.

I use an 8mm dowel, pointed at one end and waxed, to test the drawbore. This is softwood however, very thick, so I only offset by about 2mm. The dowel is beech, a strong hardwood.

I do the same thing to prepare the stretcher/leg joint except that I’m using 10mm dowels for this (and the leg bottom/foot joint). It’s now that I realize that it was a good thing I didn’t glue up the stretcher first. You’ll notice in the picture below that if I had done that, I couldn’t have properly installed the dowels on the top brace. Well, a miss is as good as a mile!

Just a few more things to do before breaking out the glue. I previously made some templates out of MDF for the foot and the brace. If I think there is even a remote chance I’ll build something similar again, I’ll make templates. I use them not only to trace outlines but like storyboards. With the foot template I know I’ll need 75mm wide by 860mm long stock, I can trace the top slope of the foot, mark where to position mounting holes if used, know exactly where the center point is,

And even use it to set the miter gauge on the tablesaw in order to cut the ends.

I made myself a taper cutting jig for the tablesaw years ago but unless I’m cutting stock less than 2″ (51mm) I really don’t care for it. For the feet and braces on this table I use the bandsaw to rough cut the slopes and then a jointer plane to clean it up. Way safer, and I can still hear the music (Pink Floyd for planing….).

Since it is way easier to do this before glue-up, I use a block plane to make chamfers on all the edges and corners. Not huge, but enough the break the sharp edges. I also plane the major surfaces free of any saw marks and other blemishes, being careful not to get too close to the joints. One errant swipe of a smoothing plane in the wrong place and a formerly tight fitting joint becomes loose.

Lastly, I cut kerfs in the tenon for the wedges, slop on some glue, tap in the pins and wedges, and set the two assemblies to the side for a while.

While the glue on the feet is drying, I chamfer and smooth the three braces. In addition, I mark the locations of the tabletop mounting bolts. Given the number of times Bruce has moved in the last few years, I want him to be able to remove the top easily for transport. I plan on using threaded inserts on the bottom face of the tabletop that accept 6mm bolts from underneath the braces.

Sometimes it takes me a while to learn practical steps. After occasions too numerous to mention, I finally got it through my head that if I use the forstner bit to make the counterbores first, the center point of the bit makes a nice divit in the center of the bore to start the 7mm bit I’ll use to make the bolt holes.