So here’s a question; have ever assembled IKEA’s flat-pack furniture and thought that you could definitely do a better job at designing one yourself? If so, then keep on reading because today we’ll go through the steps of designing and building a DIY outdoor bench project. The design we’re using today is made up of two main elements – CNC cut plywood profiles and an inner timber structure. We’ll start by looking at the plywood panels first, then move onto the timber frame, before finally assembling it all together.
Full set of technical drawings for the seat assembly including DXF/DWG-files for CNC cutting are available to download from the link below.
Before we do any cutting, first we need to figure out the seat dimensions. A standard height for a seat is usually in the range of 450 – 500 mm with a depth of 400 – 500 mm. One thing to keep in mind is the thickness of the cushions, as we need to allow for these in our measurements. So, let’s assume the thickness of the seat cushions are 50 mm and the backrest cushions are 100 mm. This means if we want to end up with a depth of 450 mm, we need to offset the thickness of the backrest cushion and make it 550 mm. Likewise, for a finished seat height of 500 mm, the seat frame needs to be offset by 50 mm – as shown below.
1) PLYWOOD PROFILES
We’ll be using 18 mm thick plywood, which is a good robust thickness for this sort of work. Keeping in mind the plywood sheet size of 2440 mm x 1220 mm, we want to make use of most of the available material. Also, to make the assembly easier, we want to make sure all the profiles are cut nice and square. And what do I mean by nice and square? I mean that we’re going to make the panels slightly less than the sheet length, so that the CNC router can cut all the edges of the profile. In other words, we’re getting rid of all the factory edges, which can sometimes be a bit sub-par.
2) NESTING & CNC CUTTING
Once we know the panel sizes, we can send the dimensions to a CNC cutting service and they would do the rest. This is a useful way of outsourcing the cutting process, especially since most of us don’t have access to a workshop to do the cutting ourselves. However, it’s good practice to draw the profiles out on a piece of paper and try to fit them within the 2440 x 1220 mm sheet size area yourself. This is a process formally known as nesting. The aim is to fit the profiles into as few sheets as possible, which will then tell you how many sheets you need. If you’ve ever played Tetris, then this is where those skills should come in handy.
And how exactly does CNC cutting work? Well, CNC stands for Computer Numerical Control, which basically means converting a CAD drawing to coordinates for a machine to cut the plywood. You can see the machine (CNC router) in action in the video below. These machines are particularly brilliant when using complex profiles, round shapes, and other forms that would otherwise be difficult to cut by hand.
3) TIMBER FRAME
With the plywood panels ready to go, it’s time to cut some timber for the support frame. The purpose of this frame is twofold; to make the seat structurally sound and to provide a surface to screw the plywood panels onto. To build the frame we’ll be using some 50mm x 50mm treated and planed timber – which comes at a finished profile size of 44 mm x 44 mm.
To draw up the frame, all we need to do is take the overall dimensions of the seat and subtract the thickness of the plywood. So, given that the seat is 2400 mm long, and allowing 18 mm plywood on either side, then our timber section (A) comes out as 2364 mm. Frame sections such as (B) (D) and (C) that sit between two other frame sections will need to be trimmed down by not only the plywood thickness, but also twice the timber section.
Alternatively, you might find it easier to cut these as you go along, checking all dimensions in-situ. It’s all about personal preference really, and how confident you are in your own skills. That is, there’s no real set plan to assemble this frame – as long as it ends up being nice and sturdy. Before looking at how we might want to assembly it all together, let’s take a quick look at the tools we need to get the job done.
TOOLS & EQUIPMENT
Now, if you enjoy carpentry work on regular basis then you probably own a good set of tools already. Whereas if you only do a bit of DIY once every blue moon, then it’s probably not worth buying hundreds of pounds worth of new equipment. But regardless of where you fall on that scale, it’s still useful to go through the equipment you would need for a project like this – especially if you were to cut the plywood yourself.
DRILLING AND SCREWING
- Drill Bits (pilot holes)
- Cordless Combi Drill & Impact Driver
- Screw Bit Set
- Wood Screws for Frame (5 x 60mm)
- Wood Screws for Panels (4 x 57mm)
- Piano Hinge Screws (3 x 12mm)
- Piano Hinge (1000mm)
GLUING AND TREATING
PUTTING IT ALL TOGETHER
1) PILOT HOLES
While assembling the seat, we need to keep in mind one important technique – drilling pilot holes. This means using a drill bit with a smaller diameter than the screw, to drill a pilot hole into the work piece. The point being that this makes the plywood/timber a lot less likely to split. You can see these steps demonstrated in Figure 6 below.
2) SCREW DETAIL
When it comes to the screws, there are few different approaches you can take. If you are using plywood panels and want to preserve that plywood texture, then the screws can be hidden by driving them in from the inside face (see Figure 7 below). Alternatively the screws can be driven in through the top face and the hole filled with wood filler – just remember to countersink the holes first. The filler can then be sanded and the surface painted over.
Whichever approach you choose, don’t forget to apply wood glue while fixing the profiles. It’s the glue that does all the bonding – the screws only hold it in place. Also, once the bench has been completed you will need to treat the wood – especially if it will be standing outside. This will extend it’s life significantly. There are loads of options available from different shades of wood stain and different types of varnish.
3) ASSEMBLY STEPS
Once finished assembling one seat, you could easily repeat the design to make up a moduled seating area – like the one shown in Figure 1. Drawings for the corner piece can be found in the drawing package which you need to purchase through the PayPal link. The point here is that you don’t need have your own workshop to build a bench like this. In fact, some places, like B&Q for example, offer free cutting service on top of your MDF and plywood sheet purchase. Although the amount of cuts is limited, which-after you need to pay per cut.
So, to return to our original question. If you haven’t thought about making your own furniture before, then I hope this post has inspired you to have that moment of design-epiphany. Don’t forget to check out our Pinterest board for more DIY outdoor bench inspiration. Once you’ve found a design that you like and worked out the dimensions, head over to your local timber merchants for the materials and start building. Because remember; those summer evening drinks always taste better while sitting on a bench you’ve build yourself!