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Marking Out Wooden Coffee Tables' Corner Joints.
MARKING OUT THE TENONS
MARKING THE TEST PIECE
The above illustration shows how your test piece should look after marking out the tenon. ( I've applied black lines to the image to make the gauge marks stand out more clearly ) Note, this tenon is slightly off-set, rather than being central to the rail: the reason being that, in this project, a rebate was to to be cut along the lenght of the back of the rail.
PROCESS FOR RAILS CUT BY HAND:If you've cut the coffee table rails to length by hand, unless you've got them pretty much identical in length, you should mark the tenons out in the traditional way. To do this, line them all up, side by side, edge down on the workbench, and cramp them all together with a pair of G-clamps: (this is assuming you are making a square coffee table, if it's oblong you need to do this separately for the two sets of rails). Mark the centre line of the rail nearest to you, and measure from that to mark the position of the shoulder of the tenons at either end, then use a square to strike a pencil line across the remaining rails. You can now uncramp them and use your square to strike the shoulder line all round the ends of the rails. The reason for doing it this, rather tedious, way is that your rails between the shoulders should turn out identical in length, with any discrepancy caused by inaccurate cutting of the total length now showing in the tenons themselves. This is no problem as the mortices are cut with bottom clearance, and also, if necessary, the length of the tenon can be trimmed with no untoward effects.
PROCESS FOR MACHINE CUT RAILS:If you've cut the coffee table rails to length using a cross cut or overhead saw using stops, they should be identical in length. In that case (assuming you've calculated how long your tenons should be to leave the correct length of rail between the shoulders) just set your marking gauge to the proposed length of your tenons, and, working from the ends of your test piece of rail, score a line round all four sides to show the shoulder line of the tenon.
- Set the width of the mortice gauge to the width of your mortiser's box chisel, or, if you are cutting the mortise by hand, to the width of your mortising chisel. If your tenon is to be central on the rail: using your test piece of rail, set the mortising gauge roughly by eye to central position, and semi tighten the stock. Working from the face, turn the gauge so that it makes two indents in the top of the test rail. Now apply the gauge to the back of the rail, turn it as above, and see if the two points line up exactly with the indents. If not, holding the gauge by the stock, tap one or other of the ends of the stem on the workbench according to which direction you need the stock to go. From the face, make a fresh pair of indents further along and try again. Repeat this whole procedure until you get the indents to coincide, and then fully tighten the stock. If your tenon is offset: measure in from the face and mark on your test piece how far in you want the tenon to be and set your mortise gauge to that mark.
- Next, working from the face, use your mortise gauge to mark out on your test piece the thickness of the tenon. If you are going to cut the tenons by hand, bad luck. You now have to repeat this step 16 times: i.e. mark out both ends of each rail in a similar fashion. If you are cutting by machine you only have to mark out the test piece, and set up the machine from that.
- When you've finished marking, run the point of a pencil down all the grooves cut by the gauges: this makes them easier to see when you are setting up for mortising or tenoning. When you are first starting out, or if you are making a complicated joint, hatching all the waste to be removed with a pencil can be advisable as a visual aid.
- That's it, all done (the haunch gets marked out later). You are now ready for the first part of the tenoning.
Researched & written by Nick at TheCoffeeTable.co.uk - Copyright © TheCoffeeTable.co.uk - Telephone: 01420 474862