1. Carefully locate the centers for the screw holes in the piece A (Fig. 34) thru which the screws are to pass.

2. Bore "body size" holes in piece A equal to or a little larger than the diameter of the screws just under the head.

3. Clamp the pieces in position - it is well to use center lines to determine the proper locations - and mark the centers in piece B.

4. Bore core size holes in piece B equal to the diameter of the screws at the root of the thread.

5. Countersink the body size hole if a flat head screw is to be used.

Notes:

(a) As with nails, paraffine or soap may be used as a lubricant on the threads of screws.

(b) If you do not wish the head of the screw to show, you may bore a hole large enough to receive the head of the screw and then plug the hole. The plug cutter is a handy tool to use in this connection.

Fig. 34.

Reference and Experimental Work: Look up "drive screws." Experiment as to the holding power of screws in end grain and cross grain of wood. Collect and mount all the different kinds and sizes of screws and bolts that you can find.

Use of Hand Screws Hand screws are used for a great variety of purposes, e. g.:

1. To force two or more pieces together while gluing.

2. To hold work on the bench top while cutting mortises, scraping, etc.

3. To clamp pieces in position for boring holes.

4. To hold, by means of two or more hand screws, pieces of work at almost any angle.

When using hand screws: 1. Keep the jaws parallel.

This is accomplished by turning first the center, and then the outside screw. (See A and B, Fig. 35.)

Fig. 36 shows what happens when the jaws are not kept parallel:

(1) The pieces are not held together properly and,

(2) The screws may be broken, due to excessive bending.

Fig. 35.

Fig. 36.

2. Keep the jaws free from hard lumps of glue and bad scars, otherwise they will often mar your work.

3. Before gluing parts together - so that time may be saved in gluing - it is always wise to clamp them together in their proper positions so as to be sure: (1) That everything is square and fitting properly, and (2) that the clamps will all work. The clamps and hand screws should then be taken off and piled so that they can be easily reached and adjusted after the glue is applied.

Reference Work:

1. Visit a woodworking shop and maek sketches of all the clamping devices used.

2. Collect and mount pictures of all the clamping devices that you can find. Trade catalogs will furnish you many examples. You can put a piece of tracing paper over any picture, and by tracing get a sketch that will do for your collection. You should in every such case give the name of the book and the page on which the illustration was found.

3. What is a caul? Make a sketch of one.