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Factors to Consider for Fixing a Wooden Coffee Table Top.
The main aspect to take into consideration when fixing a wooden coffee table top is movement related to moisture content. The boards for the top will have been air or kiln dried to a predetermined moisture content, but because wood can absorb moisture from a damp atmosphere, or lose it to a dry one, there is potential for expansion or contraction of the top. To some extent the sealing of the top with wood finish will help to minimise this effect, but it is good design practice to allow for some independent movement. Timber moves the most tangentially, about half that amount radially, and least of all in the direction of the grain.
This will create a slightly different effect in a top made from quarter sawn timber than in one made from plain sawn timber. However, from a practical point of view, the main movement to be accommodated for in both cases will be across the grain direction of the table top (see fig 8). The possible outcome if the coffee table top is screwed to the base all the way round with no room for movement is a split top. This is because the grain in the end rails is running at 90 degrees to the grain in the top and they will be trying to expand or contract different amounts.
Using Slotted Battens to Fix the Coffee Table Top.
SLOTTED ANGLE BRACKET
Fig 9 shows one method of allowing for movement in the top. After the base has been finished, machine up 18mm thick battens, cut them to length, and glue to the inside of the rails. Make slots in the battens on the side rails, (you can do this by drilling 3 or 4 holes in a line and then drilling at an angle to remove the solid wood in between the holes), and drill a hole central to the table width in the battens on the end rails. The holes should be at least a couple of drill sizes larger than the screws & the slots should be a couple of drill sizes wider than the screws. Lay the tabletop face down on a blanket on the workbench and position the base on it as shown in fig 9. Drill a pilot hole into the table top through the two end central clearance holes and screw the base to the top with pan head screws and washers. This keeps the table top fixed around the central length-wise axis of the table. Next drill pilot holes in the table top through the middle of the slotted holes in the side battens. Insert pan head screws and washers and tighten until the screws nip the washers against the battens. Then slacken off the screw just enough that the washer can be turned with your finger. Now, if the top needs to move, it can slide the screws in the slots provided and do so symmetrically around the central length-wise axis.
If the table is quite heavy and you don't want to add the extra weight of the battens, the same result can be obtained by using slotted metal angle brackets, (see picture on right) available at many hardwear stores or builders merchants.
Using Buttons to Fix the Coffee Table Top.
third way of tackling moveable fixings is to use "buttons" see fig 10.
This involves slotting the inside of the rails of the table and fixing the top by means of rebated pieces of timber two or three inches square. These are screwed to the underside of the coffee table top with the rebates fitted into the slots in the rails. This holds the top firm but allows the rebate to slide in and out of the slot if the top moves.
Researched & written by Nick at TheCoffeeTable.co.uk - Copyright © TheCoffeeTable.co.uk - Telephone: 01420 474862