Wednesday 11 July 2018
In today's climate of falling bird numbers, like a lot of households, we spend a small fortune on bird feed and other bird-aid projects, like replanting hedgerows with berry-bearing shrubs, which have massive thorns to deter the cats from turning to birds as an alternative food source. However, cook draws the line at the birds helping themselves to her soft fruits and as a result, fruit cages are required. This design is based on easily procured 'standard' treated fencing materials, using 100mm x 100mm x 3m posts as uprights and 85mm x 38mm x 3m rails. The overall dimensions can be adjusted to suit your own requirements, but do bear in mind 'standard' lengths when planning things like bay lengths, as treated timber offcuts are not much use for other projects and are totally banned as firewood. Another factor to consider at the planning stage is the width of the netting you want to use – in my case, I planned on using 1m rolls with 13mm holes. With regard to uprights, my plans are based on the old adage that one-third of a post should be in the ground, which leaves 2m clear above ground. The best practice is to pack the posts with stones or gravel, to allow water to drain. Do not be tempted to resort to the 'builder's' trick of digging a short hole and setting the post in concrete â€“ this will only lead to early post failure along the top of the submerged concrete, as not only does the concrete actually eat into timber, but it also allows the ground water to pool round the post, accelerating decay. A treated timber post in gravel should last up to 10 years, but will fail at half that if bedded in concrete.
Before you begin the project, you will need to assess whether the ground – or your time/back – is up to digging down one metre. If not, then I would recommend that you resort to a drive-in metal post anchor rather than concrete.
Halving joints will suffice for the structure – two variations are shown here; these should be nailed or screwed through to the posts using galvanised nails or coated decking screws.
Jointwork and fixing
The mitred corner joints need some time and skill – or machinery – and will require the uprights to be true and square if the mitre ends are to meet accurately. If you have neither time nor wish to construct to this sort of accuracy, then the corner joints can be made as butt-joints, which is far more tolerant, as the first rail can be fitted into the post's rebate, marked and cut to fit, with the second rail now overlaid and fixed, then trimmed to length in-situ – the results are not much different.
The strongest joint is a mortise and tenon, but these will probably all have to be chopped in-situ by hand. All these joints are simple enough to undertake completely by hand, but I chose to use the bandsaw for post tops and a circular saw for kerfing rebates.
A wide Chinese chisel comes in handy to knock-out the waste.
The frame should be braced for stability, which can be achieved with the conventional corner braces…
… or the structure can borrow stability from being made as a lean-to on an existing wall, in which case the uprights will need to be drilled for washers, bolts, and nuts and then firmly secured to the 'host' before being plugged. I through-drilled the wall and secured the uprights with M6 rods locked tight with double nuts to make sure the frame would never move.
Roof and door construction
The 'roof' of the cage is formed from transverse joists, cut to length from the 85 x 38mm offcuts and as they are barely structural, they can be simply screwed through the top rail at a spacing to suit your wire netting. A bit of lateral rigidity can be found by screwing the centre joist to the relevant posts. Use a water level to ensure the structure is levelled right across the top.
The door is constructed with lapped joints where it is important to get the centre joint really tight, as the rigidity of the door depends on this joint. As the door is otherwise unsupported, judicious use of exterior glue may be appropriate to lock the halving joints solid, assisted by exterior grade screws in all the joints, to give it strength. The door could be positioned either in a long or short side, to suit your need for access and is hung from one of the upright posts using strap hinges that are two-thirds the width of the door, with a jam-post inserted at an appropriate distance. This can be either another main post or even a length of the 85 x 38mm rail let into the ground. With the construction complete, the netting can be stapled to the frame, and then you're done!