Part 14 (1/2)

To secure accuracy, all gaging on the surface of wood, should be done from the ”working face” or ”working edge.”

[Ill.u.s.tration: Fig. 213. Setting a Marking-Gage.]

[Ill.u.s.tration: Fig. 214. Using the Marking-Gage.]

It is sometimes advisable, as in laying out chamfers, not to mark their edges with a marking-gage, because the marks will show after the chamfer is planed off. A pencil mark should be made instead. For this purpose a pencil-gage may be made by removing the spur of a marking-gage, and boring in its place a hole to receive a pencil stub with a blunt point, or a small notch may be cut in the back end of the beam, in which a pencil point is held while the gage is worked as usual except that its position is reversed. For work requiring less care, the pencil may be held in the manner usual in writing, the middle finger serving as a guide, or a pair of pencil compa.s.ses may be used, one leg serving as a guide. A special gage is made for gaging curved lines, Fig. 215.

[Ill.u.s.tration: Fig. 215. Marking-Gage for Curves.]

The _cutting-gage_, Fig. 216, is similar to a marking-gage, except that it has a knife-point inserted instead of a spur. It is very useful in cutting up soft, thin wood even as thick as 1/4”.

[Ill.u.s.tration: Fig. 216. Cutting-Gage.]

The _slitting-gage_ is used in a similar way, but is larger and has a handle.

The _mortise-gage_, Fig. 217, is a marking-gage with two spurs, with which two parallel lines can be drawn at once, as in laying out mortises. One form is made entirely of steel having, instead of spurs, discs with sharpened edges.

The _scratch-awl_, Fig. 218, has a long, slender point which is useful not only for marking lines, but for centering.

[Ill.u.s.tration: Fig. 217. Roller Mortise-Gage.]

The _auger-bit-gage_, Fig. 219, is a convenient tool for measuring the depth of holes bored, but for ordinary purposes a block of wood sawn to the proper length thru which a hole is bored, is a satisfactory subst.i.tute.

_Screw- and wire-gages_, Fig. 220, are useful in measuring the lengths and sizes of screws and wire when fitting or ordering.

The _spirit-level_, and the _plumb-line_ which it has largely replaced, are in constant use in carpentering, but are rarely needed in shopwork.

[Ill.u.s.tration: Fig. 218. Scratch-Awl.]

[Ill.u.s.tration: Fig. 219. Auger-Bit-Gage.] _Blackboard compa.s.ses_, _triangles_, etc., are convenient accessories in a woodworking cla.s.sroom.

[Ill.u.s.tration: Fig. 220. Screw- and Wire-Gages. a. Screw-Gage. b.

Wire-Gage. c. Twist-Drill-Gage.]

8. SHARPENING TOOLS.

The _grindstone_ for woodworking tools is best when rather fine and soft. The grinding surface should be straight and never concave. The stone should run as true as possible. It can be made true by using a piece of 1” gas pipe as a truing tool held against the stone when run dry. Power grindstones usually have truing devices attached to them, Fig. 221. A common form is a hardened steel screw, the thread of which, in working across the face of the grindstone, as they both revolve, shears off the face of the stone. The surface should always be wet when in use both to carry off the particles of stone and steel, and thus preserve the cutting quality of the stone, and to keep the tool cool, as otherwise, its temper would be drawn, which would show by its turning blue. But a grindstone should never stand in water or it would rot.

It is well to have the waste from the grindstone empty into a cisternlike box under it, Fig. 221. In this box the sediment will settle while the water overflows from it into the drain. Without such a box, the sediment will be carried into and may clog the drain. The box is to be emptied occasionally, before the sediment overflows.

[Ill.u.s.tration: Fig. 221. Power Grindstone.]

In order that the tool may be ground accurately, there are various devices for holding it firmly and steadily against the stone. A good one is shown in Figs. 221 and 222. This device is constructed as follows: A board A is made 2” thick, 6” wide, and long enough when in position to reach from the floor to a point above the level of the top of the stone. It is beveled at the lower end so as to rest snugly against a cleat nailed down at the proper place on the floor. The board is held in place by a loop of iron, B, which hooks into the holes in the trough of the grindstone. In the board a series of holes (say 1” in diameter) are bored. These run parallel to the floor when the board is in place, and receive the end of the tool-holder. The tool-holder consists of four parts: (1) a strip C, 1-1/2” thick, and as wide as the widest plane-bit to be ground. The forward end is beveled on one side; the back end is rounded to fit the holes in the main board A. Its length is determined by the distance from the edge of the tool being ground to the most convenient hole in A, into which the rear end is to be inserted. It is better to use as high a hole as convenient, so that as the grindstone wears down, the stick will still be serviceable; (2) a strip, D, of the same width as A and 7/8” thick, and 15” to 18” long; (3) a cleat, E, 5/8”3/4”, nailed across D; (4) a rectangular loop of wrought iron or bra.s.s, F, which pa.s.ses around the farther end of the two strips, C and D, and is fastened loosely to D by staples or screws.

[Ill.u.s.tration: Fig. 222. Grinding Device.]

[Ill.u.s.tration: Fig. 223. Holder for Grinding Chisels or Plane-Bits.]

The tool to be ground slips between this loop and the strip C, and is held firmly in place by the pressure applied to the back end of D, which thus acts as a lever on the fulcrum E.

Any desired bevel may be obtained on the tool to be sharpened, by choosing the proper hole in A for the back end of C or by adjusting the tool forward or backward in the clamp. As much pressure may be put on the tool as the driving belt will stand without slipping off.

A still simpler holder for the plane-bit only, is a strip of wood 1-1/2” thick and 2” wide, cut in the shape G shown in Fig. 223. The plane-bit fits into the saw-kerf K, and in grinding is easily held firmly in place by the hand. By inserting the rear end of the stick G into a higher or lower hole in the board A, any desired angle may be obtained. G is shown in position in Fig. 221.

[Ill.u.s.tration: Fig. 224. Agacite Grinder.]