Rob continues with his coffee table project
The joints in the side rails need some holes cut and there are a multitude of different ways to chop them out. Over the years I’ve tried nearly all them from early attempts with a big ‘pig sticker’ chisel and lignum maul through to a dedicated morticing machine.
They all work and they all produce nice, reasonably rectangular, oblong holes in fairly smart time. The catchword here though is ‘reasonable’ because no matter how hard I tried, the edges were always a bit ragged, like a series of drunken saw teeth that have had a night on the tiles, which is fine in most cases as the edge is going to be covered by the tenon shoulder.
The ragged edge, where it’s going to be seen, as in this particular application, causes a bit of an issue as it’s got to be as smooth as the first time you ever saw Sean Connery in Dr. No!
The only way to get round this ticklish little problem is to cut the mortices with a router, which is easy enough and then square out the holes with chisels, which takes a lot longer. There have been loads of methods developed to cut mortices with a router, using all sorts of fancy jigs and double fences but they’re all a waste of time because all you really need are a few packing pieces and a couple of decent cramps.
The set-up needed is shown in the pic above.
The real problem is the dreaded ‘router wobble’, where the base hasn’t got enough area to rest on. The piece being mortised is placed along the edge of the bench and an identical piece (usually another leg or rail, as in this case) is placed parallel to it. Note that as the mortise is going straight through, there’s a packing piece underneath, otherwise the bench top is going to look like a Swiss cheese. Then get hold of two biggish lumps of ply which act not only as cramping blocks, but also as ‘stops’ for the router travel. Set the router up, plunge in and traverse a few times. Always taking shallow cuts and the first mortise is shown, with the second one arrowed.
Reset for another cut and it doesn’t take too long to cut them all out.
The tenons finish just shy of the line and they’re then made square with chisels, which is a bit of a time-consuming palaver. The outside rectangles are also made longer by around 2mm to allow the wedges to expand into the joint, meaning that the end grain slopes inwards.
Sounds complicated? Worry not, it is, but all will be explained.