Story and photos by David Howlett
Carry out a particular operation enough times and chances are you’ll become quite good at it. More than anything else, this project is a great exercise in producing mortise and tenon joints. There are 44 of them in this bench. You may not be particularly interested in building a garden bench but I hope the processes I’ve outlined in this article will help you to create better joinery projects more efficiently whatever they may be.
This bench has a nice mix of straightforward joints and tasks, with a few more challenging details that involve very precise marking and shaping. Look at it as two end frames consisting of legs, seat rail and armrest, joined by two long seat rails and a backrest.
Full size working drawings
I always draw new projects out full size on a piece of 3mm MDF. This gives me an accurate measured plan to work from and also gets me thinking of all the tasks that need to be done, and the order in which they need to be carried out. Once happy with all the proportions and angle of the backrest recline (here 113°), a template of the back leg was made using 9mm MDF.
Selecting your timber
In Perth we have an abundance of jarrah which is right up there with the most durable timber species in the world for exterior use. Over the years I’ve built various benches in jarrah, but with lots of American white oak stored in my timber racks I liked the idea of making a fairly traditional oak bench. This piece will last a long time so it is worth selecting high quality timber. The total bill of materials for this bench came in just over $600. Whatever timber you choose, do a little research and make sure you go for a species that is suitable for exterior use. Most species that tick the durability box are also quite hard so unless you invest in some nice Huon pine the mortises will require a fair bit of effort.
Nesting the legs
Large 250 x 50mm boards allowed for nesting of front and back legs for efficient use of materials. The back leg needs to be marked out hard up against the edge of the timber so the seat rail mortise can be positioned on a flat vertical facet. It is critical that the seat rail mortises on the front and back legs are at exactly the same height from the bottom of the legs. Nesting the legs on one wide piece of timber makes this easier to mark out. Waste-out all mortises before separating legs from the timber blank.
Chopping mortises
Many woodworking teachers encourage students to remove all of the timber from a mortise by chisel alone. This is a completely pointless exercise unless you are said teacher and wanting to keep your students occupied. It’s quicker to remove waste material with either a drill slightly smaller than the width of the mortise, or with a plunge router.
For fast and accurate mortises in a home workshop a plunge router is hard to beat. Chopping endgrain square in a hard timber is a punishing task on your nice bench chisels honed at 25°. Save your bench chisels for paring the sides of the mortises. A mortise chisel is specifically designed for the purpose. I like to keep mine honed at 35° as we often chop out very hard jarrah.
Shaping the back legs
Bandsaw the back legs from their timber blanks leaving 1–2mm all around. The 9mm MDF leg template is then attached to the leg with at least three small panel pins. Carefully align the template so it is flush with the bottom of the leg and the front area or facet where the seat rail mortise is located. Once the template is securely attached a 50mm pattern following router bit is just the trick for producing two identical legs on the router table.
A router bit with guide bearings top and bottom allows you to flip the leg over so you are never routing against the grain. Once the back legs are shaped to match their template you can then mark out and cut the mortises for the armrest and the upper and lower backrest rails. Your full size drawing will help ensure the armrest joins the back leg at the height dictated by its join at the front leg. The front legs on my bench are straight so I simply ripped them from the blank on the tablesaw.
Many ways to produce tenons
Something I love about woodworking is there are often many ways to achieve the same result. Tenons need to be produced on the seat rails, rear of the armrests and at the top of the front leg. While it’s fun to hand saw tenons, it can be a little tricky on the 1.6m long seat rails. Dropping the height of the blade on your tablesaw and using the crosscut method is slow but works well. I produced the larger tenons for the seat and backrest rails using this method on my 3.8m panel saw. A crosscut sled with dado blades produced fast accurate results. A dedicated tenoning jig is fantastic for smaller parts but is not great for long or large parts. Tenons on shorter lengths can also be produced very quickly and accurately on the router table. Of course a well tuned bandsaw with a carefully aligned fence is yet another option.
I like to cut tenons just slightly too thick then use my 3/4” HNT Gordon shoulder plane to tune them for a perfect fit. I want to be able to push joints together without having to force with a mallet or clamp. All of the mortise and tenon joints in the end frames were around 20mm deep, 20mm wide and 50mm long. Even the slightest chamfer on the ends of tenons makes them easier to fit.
Angled tenons
The trickiest tenons to produce in this project are the ones at the back of the armrests as they are not 90°. Any errors here will result in unsightly gaps where armrests meet backrests. Very accurately setting the required angles on a mitre gauge and using the crosscut method on a tablesaw is probably the best way to go at home. I highly recommend producing at least one perfect tenon on a test piece before cutting tenons on your armrests.
Assembling end frames
Once all joints have been tested for fit, each of the components for my end frames was sanded in preparation for the glue-up. A gentle curve was cut into the top edges of the seat rails to create a curved seat.
A 3mm or 6mm radius round over bit in a trimmer router will be used to treat most edges after assembling and gluing. Outdoor furniture is often fully exposed to the elements so an appropriate adhesive is very important. Waterproof PVA could work but I would always opt for an epoxy gel for this type of furniture.
Accuracy for backrest and seat rails
Both long seat rails and the upper and lower backrest rails were docked to length and tenoned at the same time on my tablesaw to ensure accuracy. The distance from shoulders at one end to the other must be identical on all four rails.
For perfect alignment, mortises in the upper and lower backrest rails were marked out with the rails clamped together. With 14 backrest splats installed the whole frame must measure up perfectly square. A plunge router makes very fast and accurate work of 28 mortises. When it comes to gluing up the backrest frame you will be very glad of the long open time afforded by an epoxy. Take your time, do a dry fit and get it right before you apply any glue.
Getting it all together
Attend to any details such as treating edges of legs and armrests before going ahead with the final assembly. Once you’re ready to put the whole bench together, ask for some assistance for the glue up. If this isn’t the kind of work you do every day this will really help to make everything come together smoothly.
If your backrest frame is perfectly square then it should square up your end frames nicely on the vertical but you will still need to check the horizontal seat slat section of the frame. Measure the diagonals from the inside corner of the front legs to the inside corner of the back legs and adjust the clamps if required. After gluing up the entire bench frame install a middle seat slat rail between the front and back seat rails.
Attaching seat slats
You can screw seat slats directly to the seat rails individually or fasten them together as a frame that can be inserted with cross braces that fit perfectly between the inside faces of the seat rails. The latter makes it easy to replace the slats and also eliminates screw holes in the top surface that would pool rainwater. For both methods, only use solid brass or stainless steel screws.
Design variations
There are plenty of simple changes you could make to completely alter the style of this bench to suit your tastes. Shape the legs a little more, curve the top backrest rail, and perhaps add some lower rails. This bench has a rail length of 1500mm but you could beef up the long rails a little and make it longer.
On other benches I’ve included lower rails between front and back legs, more for appearance than structural necessity.
Applying a finish
I always recommend to our students to think about surface finishes during the planning stage rather than deciding what to use as an afterthought. If a varnished finish is what you’re after then be sure to use oil-based marine grade polyurethane. While you’re applying several coats of varnish you can think about how much work it will be stripping it all back in a few years time.
I would only use a varnish if my bench was going to stay under cover.
In planning this bench I visualised it in an oil finish right from the start. Head down to any hardware store and you’ll find all kinds of oil products for exterior use all boasting remarkable durability. I think one of the oldest and cheapest oils is still one of the very best. A couple of coats of raw linseed oil brings out the rich colour and contrast in the grain, but I’m really looking forward to watching the oak age to a nice weathered silvery grey.
David Howlett is a furniture designer/maker and director of the Perth Wood School.
Diagram: Graham Sands
Click on the photos to see a larger view and captions.