Читать книгу The Handyman's Book of Tools, Materials, and Processes Employed in Woodworking - Paul N. Hasluck - Страница 148

The grindstone, as a rule, is neglected except just when it is wanted for use; consequently, it is only with difficulty that tools can be ground on it at all. A good grindstone kept in proper order will save its own cost in twelve months. It should be selected of a light grey colour, even throughout. A dark streak through the centre, or a dark patch on one place, indicates that the stone is much harder at those places than elsewhere; consequently, it will wear away faster at the softer parts, and will never be truly round for long together. It will-wear lumpy, and at the dark places the tool that is being ground will glide over easily, and directly afterwards catch hold of the softer stone suddenly, and most likely “dig in.” A stone that shows flaws on the sides, such as little smooth places running into it with fine cracks showing away from the ends, should be rejected, as such a stone will not stand frosty weather; a thick stone, also, is undesirable—one 3 1/2-in. or 4 in. wide on the face being ample—as it will tend to wear hollow, and from that cause always be faulty. A smooth stone with a bluish tint should be avoided, as it will work harder and smoother till it becomes like a glass bottle, and of no use at all for proper work. Choose a stone of from 30 in. to 36 in. in diameter and 3 1/2 in. to 4 in. thick, of an even light grey colour, with a rough, gritty surface. Test it with the thumb-nail, and the stone should wear the nail down with a few rubs backwards and forwards and leave straight furrows on the nail; this shows a good free-cutting stone.

Fig. 432.—Half-round Wood Rasp.

Fig. 433.—Half-round Cabinet Rasp.