The rebate is 4mm wide by 5mm deep. To accurately measure it, set your marking gauge to 6mm. Hold it firmly and squarely against one face surface of the leg and score a line in the inside edge from the top down to the 600mm line (Fig.3). Score another line like it from the opposite face surface of the same leg, leaving 5mm in the middle for your rebate. Do the same on each leg. Then run a sharp pencil down each score line so it’s easier to see.
If you use a router, you can remove the waste timber in just one pass. Because of the narrowness of the timber, you may have to clamp on another piece or two of timber to support the router base and to allow you to use the guide attachment for a perfectly straight, accurate cut.
If using a circular saw, you’ll need to make two or three passes to remove the waste. But again, clamp on another piece of timber to support the saw’s base. Set the saw’s blade to 5mm deep, and if you have a fence for the saw, set this to match the gauge line, then make a cut on the inside of one score line from the top to the 600mm mark. Do the same on the inside of the opposite score line. Any waste remaining on the middle of the two cuts can be removed with a third pass of the saw or with a chisel.
The router or saw cuts will go beyond the 600mm line to give you the exact measurement but don’t worry – the bottom crosspiece covers it over and hides it. But check that the rebate stops at the same point on each leg before continuing.
Whether using a router or a saw, make sure all timber to be worked on is clamped (and never held by a person) to a rigid work surface.