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Choosing & Preparing the Timber for a Wooden Coffee Table Top.
timber used to be planked using the quarter sawn method. This meant
that the planks to some degree all radiated outwards from the core of
the trunk as opposed to the present through & through method where
only the middle planks do.
If possible, it is best to choose planks that are quarter sawn, (look at the end of the plank, the grain lines should run roughly vertically). This not only reduces the risk of cupping, but maximises the figure (medullary rays) on your coffee table top.
One of the woods I use is English oak which is cut through & through, and I consequently usually have to sift through a whole stack of planks to select the central (quarter sawn) planks. (See figs 1 & 2 below.) If you cannot obtain quarter sawn timber you should use opposing grain directions on alternate planks, this allows any slight tendency to cup to be balanced out over the width of the coffee table instead of the whole top trying to bend in one direction. (See fig 3.)
Once you have selected your timber cross cut the slabs of oak to 50mm longer than your finished coffee table top length, rip off the sapwood and splits to produce sawn planks, (I generally use between 175mm / 200mm wide), or if your timber is already planked simply cross cut them to 50mm longer than your required finished coffee table top size. Make sure that the total combined widths of your planks is about a minimum 100mm wider than the finished width of your table top, remember that you will loose width when you plane the edges of the boards and if any of them have bows in you may loose quite a lot.
Now plane the
edges of the boards on a planer thicknesser, if you find any board with
wind (twist) in it discard it and cut yourself a new board, if you
attempt to plane out the wind you will loose a lot of your required
Lay the boards out on a flat surface edge to edge. If you are using quarter sawn boards you will be able to select all the best faces to be upmost, otherwise you will have to lay them out as in fig 3 which may mean some of the planks having best face down.
Mark the top face of each board and number the planks so you know which go next to each other. Look at how well the board edges fit to each other and replane the edges of any that need it with the infeed table set for shallow cut, making sure that your fence is set at exactly 90 degrees to the outfeed table. Check each plank with a square to make sure the face & edges are at 90 degrees.
If your planer is
set up, you should be able to get a perfectly straight joint between
each board which is the ideal situation.
Some cabinet makers advocate planing a very slight inward bow on each plank so that when the table top is cramped up the ends are under positive inwards pressure. This helps to avoid splitting which is most likely at the ends. (see fig 4).
The one thing you must avoid is an outward bow on the planks, leaving a slight gap at the ends. Although you may be able to close this through cramping it will be constantly under pressure to spring apart and will cause the ends of the planks to split - the grain is weaker at the ends, having been cut, and not being continuous which it is in the middle of length of the top. (see fig 5).
Researched & written by Nick at TheCoffeeTable.co.uk - Copyright © TheCoffeeTable.co.uk - Telephone: 01420 474862