There are a great many modifications of this joint. It would be well to look up and make sketches of the thru mortise-and-tenon, the blind mortise-and-tenon, the keyed, the stub, the wedged, the fox, and the dove tail mortise-and-tenon.

Laying Out the Joint

Remember that you are not ready to cut joints until you have mastered the uses of the rule, the gage, and the try-square, for, if the lines are not where they belong no amount of skill with the cutting tools will produce good results.

In general, the lay-out of the joints should be made as follows:

1. Measure all distances lengthwise of the grain.

These measurements should all be made from a fixed starting point, either the center of the piece, or the end first squared. In case of duplicate parts, measure the lengths first on one piece and then transfer them to the others by means of the try-square and knife.

2. Scribe all cross-lines with knife and try-square.

Work always from the working faces, and stop all lines so that they will not show upon the finished surfaces. The graduations on the try-square make this possible.

3. Lay out the bevel cuts if there are any.

Bevel cuts are best laid out by means of a T-bevel, altho they can be laid out by measurement.

4. Run all gage lines.

Gage always from one of the face surfaces, and in case of duplicate parts gage all with one setting of the gage.

Pointers:

(1) Always lay out the work on both sides of the board, if the cut is to run thru.

(2) Plan the work so that the face sides will come together, and whenever possible bring the shoulders of the tenons against one of the face surfaces. Why?

Cutting the Mortise See that the ends of the mortise are laid out with a knife line, and in case of a thru mortise see that the work is laid out on both sides. There are, of course, a number of ways to cut out a mortise.

Some prefer to bore out the center, especially when the mortise is large and made in hard wood; and then, starting in the center, to pare out to the knife and gage lines, always taking thin shavings when near the lines.

A second method is to begin in the center of the mortise with a V-shaped cut, the cut being taken across the grain, and then continue to the ends of the mortise with vertical cuts. The flat side of the chisel is always kept toward the end that is being approached. This method is especially useful where the chisel is as wide as the mortise, and in the case of mortises that do not go thru.

Fig. 38.

Fig. 39.

There is, however, another method that is considered best practice among mechanics.

1. Set the chisel as at A (Fig. 38) and cut toward the end of the mortise.

Note that the edge of the chisel is cutting across the grain. After the cut has been made it will look as at B. If the mortise is wider than the chisel, as shown here, more than one cut must be made.

2. Set the chisel in a vertical position as shown at C (Fig. 39). Note that the flat side of the chisel is against the end of the mortise. Tap gently with the mallet, thus forcing the chisel into the wood as shown by the dotted lines.

Do not drive the chisel down deeply, for the wedge action of the chisel might crowd the flat of the chisel over beyond the line

3. Set the chisel as at D, and cut toward the end of the mortise, as indicated by the dotted lines.

4. Repeat these operations until the cut is of the required depth, or half way thru in case of a thru mortise.

5. Repeat at the other end of the mortise.

If the mortise is narrow and long it is probably best to work back with slanting cuts, prying out the core at each stroke of the chisel until within about 1/16" of the other end; then turn the chisel over so that the flat side is toward the end of the mortise and finish the cut.

6. Turn the piece over, if the mortise goes thru, and repeat.

When the ends of the mortise are cut thru, the core can be pared away with slanting cuts until it will crush thru.

7. Pare out the sides and, if necessary, the ends of the mortise until they are true planes. Test these surfaces with the straight edge of the chisel.

In all this work one must be careful not to mar the ends of the mortise by prying down over them.

In the case of a blind mortise devise some method for testing whether or not the sides of the mortise are at right angles to the surface. One might use a plug with parallel sides as a help in the solution of this problem.

Cutting the Tenon

In cutting tenons the mechanic aims to saw to the center of the knife and gage lines so that there will be little or no paring to do with the chisel.

1. Do all of the rip sawing first.

2. Crosscut to the shoulder lines.

Note: If the method were reversed some of the lines would be lost on a tenon that had four shoulders.

3. If necessary, pare to the lines with a chisel. Never use a file or sand paper for this purpose.

Reference and Experimental Work: Look up and make sketches of:

1. The plain miter and the splined miter joint.

2. The box dove tail and the lap or drawer dove tail joint.

3. A fished joint.

4. Draw bolted butt joint.

5. A matched and beaded joint.

The encyclopedias usually contain information along this line. Let each member of the class select a joint; inquire of some good mechanics how to make it; write up the method and then make a good joint. These joints, together with the written method used, can be mounted upon a large board. This is a typical illustration of the advantages gained by subdivision of labor and team work. No one has to look up the method of making more than one joint and yet, when the work is completed, all can easily learn how to make any of the joints by referring to the exhibit.