Читать книгу The Handyman's Book of Tools, Materials, and Processes Employed in Woodworking - Paul N. Hasluck - Страница 33

The spirit level is used for determining the plane of the horizon, that is the plane forming a right angle to the vertical plane. A frame firmly holds a closed glass tube nearly filled with anhydrous ether, or with a mixture of ether and alcohol. Good spirit levels are provided with a graduated scale engraved on the glass tube or on a brass or steel rule fastened to the frame beside it, so as to mark the position of the bubble, the tube being so shaped that when the level is lying on a flat and horizontal surface the bubble occupies the centre of the tube. Many levels have provision for altering the length of the bubble. Fig. 77 is a view of an ordinary spirit level, and its construction is made quite clear by the sectional view, Fig. 78. In use the level is applied to the work twice, it being reversed at the second application, and the mean of the two indications then is adopted. Spirit levels are made in many sizes and shapes, but the method of construction always is the same. A serviceable tool is of the narrow shape, about 10 in. long, its greatest breadth being 11/16., and diminishing to 1/2 in. at the ends. The frame is of any hard, tough wood, such as box, ebony, lignum-vitæ, birch, beech, walnut, or oak. At the back of the tube should be silvering, which shows up the bubble and enables side lights to be dispensed with. The tube is set in plaster-of-paris, and has a brass cover. Shop-bought spirit levels are constructed generally in ebony or rosewood, better qualities having a metal protection for the edges and faces. This protection preserves the truth of the instruments for a long time, and is very desirable. A serviceable American level has a mount entirely of steel, which is hexagonal in section, and has rounded ends. Another handy form is the one mounted wholly in brass; this has a revolving protector over the bulb opening, and there is provision for adjustment should the level after a time wear out of truth. A very convenient form of level is the one with a graduated screw slide, by means of which the fall per foot is shown at a glance.

Fig. 75.—Application of Mitre Template.

Fig. 76.—Using Chisel with Mitre Template.

Fig. 77.—Spirit Level.

Fig. 78.—Section of Spirit Level.