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Marking Out Wooden Coffee Tables' Corner Joints.
This is an important process and needs to be done carefully as the final joint will only be as accurate as your marking out.
You will need the following tools: a marking gauge and a mortise gauge (shown on the right), a try or combination square, and possibly, a roofers' square. The mortise gauge differs from the marking gauge only in that it has two spurs rather than one: one of which is adjustable to the width of the tenon/mortise.
Marking out to cut mortise and tenons by hand is an extremely time consuming process as every component has to be marked up. In the case of machined joints, full marking for the tenon needs only to be applied to one component, (or preferably to a test piece: see top tip below) and, if you are using a mortiser that can be set up with stops, the same may apply for marking up the mortises.
TOP TIP: It is normal in joinery, when rough cutting components to length, to make them 50mm longer than the finished length required. When I rough cut the coffee table rails to length, I make a couple of them about 150mm longer than required. This leaves me, when I cut them to final length, with two offcuts which I then mark up and use as test pieces in setting up for tenoning on the bandsaw, allowing fine adjustments to be made before making the final cuts on the tenons to get a really snug fitting tenon.
The first thing to do before you start, if you haven't already done so, is to choose the best face and edge of each bit of stock, mark them with a pencil line, and and stack them so the good faces and the good edges are all aligned in the same direction. All marking up should be from these faces and edges. If you are using test pieces, make sure you mark them up in the same way.
WHY MARK OUT FROM THE FACE ONLY?
Because when you cut the tenon, you will work always with the face side against the fence of the bandsaw. You might think that, as your tenon is central, you could set the fence once only, make the first cut with the face against the fence, and then turn the stock and make your second cut with the back face against the fence. This is inadvisable for several reasons. Firstly, if you were making a contemporary design of coffee table, you might have the rails lined up with the face of the legs rather than inset slightly like a more traditional design. Obviously that would mean marking and cutting the tenon from the face of the rails, and the mortice from the face of the legs, to ensure that the two faces are exactly in line when the joint is fitted. Secondly, if your stock varies by the slightest amount in thickness (which is quite possible, thicknessers are not micro precision machines: the blades can get worn unevenly for instance) you will end up with different thicknesses of tenon. And lastly, the tenon may not be a central tenon, but may be offset to one side, with a different amount of waste wood to be removed on each side. As a rule, it is generally more accurate to work from the face, turning the stock from end to end when cutting tenons.
In some of the methods described for tenoning on the previous page, (cross cut on circular saw, or using a router) it is necessary to turn the stock and cut from the back face as well. The marking out should still be done from the face, and the face cuts performed first on all the rails. When the back cuts are to be performed, it may then be necessary to make some slight adjustments to the height of the cutter/saw blade. As this method is less accurate, it is probably wiser to make the back cuts to leave a slightly oversized tenon, and then hand fit them, (as is the case with hand cut tenons) by making any adjustment necessary to the back side of the tenon with a shoulder plane.
Researched & written by Nick at TheCoffeeTable.co.uk - Copyright © TheCoffeeTable.co.uk - Telephone: 01420 474862