The chief uses of this tool are to strike circles, to lay off angles and arcs, to take off measurements from a rule or some object, to lay off measurements, and to "scribe" in places where a gauge can not be used (see Scribing). In using compasses, particularly those which are not set by a screw, hold them and swing them around by the top at the hinged joint, rather than grasp them near the points, which may cause them to move or slip.
Fig. 495.
Circles or circular arcs can be struck roughly, as you doubtless know, with a string and a nail at the centre, the string being loose around the nail. This method is not very accurate, for obvious reasons, and is only suitable for rough work. A more accurate way is to drive two nails through a strip of wood at a distance apart just equal to the radius of the required circle, one nail being driven into the wood to act as the centre, the other doing the marking (Fig. 495). Instead of the marking nail a hole can be bored for a pencil. You can use a stick of this sort repeatedly by changing the position of the centre nail, or of the marking point. The same can be done with a brad or stout pin and a pencil, using stiff paper, card-board, or zinc instead of a stick. By such expedients you can do a great deal of work without buying compasses.
Compass-Saw.—See Saw.
Fig. 496.
Corner-Blocks.—These are merely small pieces of pine, or other wood which holds glue well, with two adjacent surfaces at right angles. Hot glue is applied to them and they are rubbed into interior angles of cabinet-work, to strengthen and stiffen the work (Fig. 496), and are very useful for this purpose. They are got out in short pieces, lengthways of the grain, and can be freely used in places where they will not show, as inside of the base-board in Fig. 304. The shape can be varied according to the conditions of the joint. Apply hot glue plentifully, place the block where it is to go, and rub it back and forth several times, when it can be left for the glue to dry.
Corner-Chisel.—See Chisel.
