Natural Bench

Natural Bench

How to make strong joints in slabwood.

By Greg Wood

When I need wood for a project, my first stop is a small
mill near my shop that specializes in local hardwoods. On
one particular visit I noticed a pile of offcuts sitting out in
the rain. As I pawed through the pile, a slab of white oak
caught my eye. The sawn surface was wet and the grain just
popped. The bark was almost completely gone on the flip
side, leaving a smooth, natural surface that was miraculously
free of damage from chainsaws and harvesting equipment.
Turns out the slabs were free for the taking so I took
several slabs back to my shop to dry.

For months I kept wondering what to make with the
slabs. Other than a few wormholes, the grain and natural
edge were quite interesting. The undulating line where the
flatsawn surface met the natural edge of the log intrigued
me. From some angles, the plank’s thickness was almost
invisible. Eventually, I decided a bench would be the best
way to retain the natural look of the slab and highlight its
best features. The slab’s 14-in. width was wide enough to
provide sufficient stability, and at over 1-1/2-in. thick, it was plenty strong. That inherent strength and a unique joint I
came up with allowed me to eliminate the typical stretcher
between the legs and help keep the design as clean and natural
looking as possible.

I still had to figure out how to orient the legs to the slab.
I chose to turn the natural sides of the legs inward. That
kept all of the natural surfaces facing one another.

Leg position was another big decision. I once had a bad
experience with a cantilevered bench like this. There were
three of us on a bench, two got up and guess who ended up
on the floor? The lesson was that there are limits to how far
you can safely cantilever a bench seat. I wanted to avoid the
“teeter-totter” effect I fell victim to. I’m sure there’s a formula
somewhere for finding the point of stability, but I’m
no engineer, so I used trial and error. I adjusted the legs on
a prototype bench and made some test sittings until I found
a point where the legs were offset enough to look visually
pleasing without making the bench tippy or unstable.

 

Prep the slab

The first step is to flatten and smooth the sawn face of the
slab (Photo 1). You can use a hand plane to remove milling
marks and any twist or warp. If there’s a lot of material to
remove, a handheld power plane is easier. Sand to 180-grit,
using a random orbit sander. This provides a flat reference
surface and establishes the plank’s final thickness.

The next step is to cut the legs off the slab. I turn the
plank flat side down on my radial arm saw to make the cuts.
Due to the curvature of the log’s edge you’ll have to
approximate a square cut. This first cut doesn’t need to be
perfect. Once the legs are removed, fine-tune the cut until
each leg stands square (Photo 2). Next, make a 20-degree
angle cut on either end of the seat blank (Fig. A). If you
don’t own a radial arm saw, you can make all these with a
circular saw or jigsaw and a straightedge.

Lightly sand the bark side of the slabs by hand with 100-
grit sandpaper. Sand just enough to remove the oxidation
on the surface and smooth any rough edges. Sand up to
about 150-grit. Then switch to a flap sander chucked in an
electric drill (Photo 3).

 

Cut the joints

Cutting a stepped mortise in a natural edge sounds
daunting. I found a pretty easy way to get the job done
using a simple router jig and some chisels. First, build a simple
jig to bridge the width of the seat plank and provide a
level platform for your router to ride on (Photo 4). Then
lay out the location of the legs on the plank with a paper
pattern of the leg’s top (Photo 5). Set the jig to remove
most of the wood in the first step of the mortise (Photo 6).
Stop routing short of the natural edge of the mortise and
use a chisel to pare to the pencil line.

Next, tap the leg into the mortise until it bottoms out.
Then calculate how deep the notch must be to bring the
outside edges of the leg flush with the top of the seat (Photo 7).

A crosscut sled on a tablesaw
works well to cut the notch (Photo
8). By tapping the leg into the seat
plank once again, you can see where
to begin the second and third steps
of the mortise. Use a chisel to chop
the steps in the seat plank. Return to
the tablesaw and sled to finish the
notches in the leg.

 

Attach the legs

Lay out and drill holes in the mortises for the 3/4-in.
dowels. Insert dowel centers in the holes and tap the leg in
place (inset Photo 9). The centers transfer the hole locations
to the top of the leg. Drill dowel holes in the legs and
the joint is ready to assemble (Photo 9).

Use epoxy to glue the bench together. Epoxy is gap-filling
and slow-setting, perfect for a glue-up like this. First,
glue the dowels into the legs, then the legs in the seat. Tap
the legs in place with a mallet until they bottom out.
Carefully rotate the bench upright and use two cauls and
four clamps to apply clamp pressure (Photo 10). Allow the
epoxy to dry overnight.

Finish sanding the flat portions of the bench to about
220-grit.Apply your favorite finish. I used four coats of Sam
Maloof’s Poly/Oil Finish on the flat surfaces to give these
surfaces a satin finish. I used one coat of paste wax on the
natural surfaces to give them a flat finish.

Fig. A: Joinery

This story originally appeared in American Woodworker May 2008, issue #135.

May 2008, issue #135

Purchase this back issue.

Click any image to view a larger version.

1. The first step is to create a smooth, flat surface on
the roughsawn face of the log. I used a hand plane
and power sanders.

2. Saw the legs from the plank. Then fine-tune the
cuts until each leg stands on its own at 90 degrees.

3. A flap sander quickly removes oxidation and loose
debris from the slab’s bark side. Don’t try for a perfect
surface. Just sand smooth to about 180-grit.

4. Build a bridge over the seat to rout the mortises.
The bridge acts as a straightedge to guide the cut
and a platform to support the router.

5. Use a template to lay out the mortise for each leg
on the seat plank. Make the template by tracing
the top of the leg onto a piece of paper.

6. Rout the center portion of the mortise with a topbearing
flush-trim bit. The stepped ends of the mortise
will be finished later. Use the edge of the bridge to
guide the bit along the mortise’s straightedge. Move
the bridge slightly to rout the rest of the mortise.

7. The next step in fitting the joint is to cut a corresponding
notch in the leg. With the leg set in the mortise, mark the
notch’s length. Then determine the notch’s depth by measuring
the gap between the leg and the curved surface.

8. Cut the stepped notch at the top of each leg using a
tablesaw sled. Secure the leg to the fence with
clamps and wedges. Use your marks to position the
leg and set blade height.

9. Use dowel centers to transfer the hole locations to
the leg. Drill the dowel holes in the leg and glue
them in. Now you’re ready for the final glue-up.

10. Glue the bench together on a flat surface, so it
sits properly. Use cauls to transfer light clamping
pressure.