Modern Machine-Shop Practice Part 207

"Set a bevel square to an angle of 45. Take the halves of the branch apart, and rest the stock or back of the bevel against the end face, and let the blade lie on the joint face, and mark two lines A B in Fig.

2812, which lines must just meet in the centre of the branch at the end.

Cut away the angular pieces C and D down to the lines A B. This performed on each half will leave them when given a quarter turn as shown in Fig. 2812, and the curve shown by the junction of the horizontal with the vertical shading lines is the curve for the end; hence the surface covered with the horizontal lines requires to be cut away.

[Ill.u.s.tration: Fig. 2812.]

"When this is done on both halves the branch will fit to the body, as shown in Fig. 2813, in which A is the body and B C the two half branches. For a temporary pattern the branch may be fastened to the body with a few screws; but for a permanent pattern it should be glued also, which is done as follows:--

[Ill.u.s.tration: Fig. 2813.]

[Ill.u.s.tration: Fig. 2814.]

[Ill.u.s.tration: Fig. 2815.]

"Lay one half of the body A, Fig. 2813, on a board, with the f.l.a.n.g.e overhanging to be out of the way, and clamp it there; lay the branch also on the board, and draw it firmly up to the body by clamps, while also clamping it flat down to the board, as shown in Fig. 2814. This will insure that the joint faces are true with one another, that is, lie in the same plane. Paper should, however, be placed between the joint faces and the board to prevent them from becoming glued to the board, and the edges, therefore, from breaking away. The second half can be put together as the first one, paper being put between the two to prevent them from being glued together; and to further strengthen the joint, let into each half a piece of hard wood P, Fig. 2815, and put in the screw shown at A.

"Suppose now that the diameter of the branch had been smaller than that of the body of the pattern, then the length of curve necessary on the branch end to let it abut fairly against the cylindrical pattern body may be found as follows:--

[Ill.u.s.tration: Fig. 2816.]

[Ill.u.s.tration: Fig. 2817.]

[Ill.u.s.tration: Fig. 2818.]

"Draw on a piece of board the line A B, Fig. 2816, and from any point C mark a semicircle equal in radius to that of the radius of the body of the pattern, draw the line E parallel to A B, and distant from it to an amount equal to the radius of the branch, then from the junction of E with the semicircle as at D, mark the line F at a right angle to A B.

Let it now be noted that the semicircle A G represents half the pattern body, and E D F B the branch; hence from F to G is the length of the branch end that will require to be curved to fit the circ.u.mference of the body, while it is also the length to be added to the distance the branch requires to stand out from the body. To draw the curve on the end D F G of the branch the gauge or marking instrument, shown in Fig. 2817, is employed. The branch P is placed in [V]-blocks (Fig. 2818), resting upon a plane surface. The gauge consists of a stand E carrying a vertical bar A; upon A is the closely fitting cross-tube carrying the arm C, which in turn carries the marking pointer D, which is set distant from the centre of the bar A to the amount of the radius of the piece of work or the cylinder is to fit against.

[Ill.u.s.tration: Fig. 2819.]

"If the branch required to stand at an angle to the body, as in Fig.

2819, the marking may be performed by the same gauge and in the same manner, but the axial line of the branch must be set, when marking one side, at an acute angle to the axial line of A, and at an obtuse angle to A when turned over to mark the other side, which may be done in each case by raising one of the [V]-blocks until the branch lies in either case at the same angle to A as it will require to stand to the body on which it is to fit.

"When the body is much larger in diameter than the branch, a hole may be bored in the former to receive the end of the latter, by giving to the branch end a stem, as in Fig. 2820, and then cutting in the body a recess for the branch end and its additional stem. This recess may be cut out in the lathe, chucking the body as in Fig. 2821.

[Ill.u.s.tration: Fig. 2820.]

[Ill.u.s.tration: Fig. 2821.]

"Should it occur that one end of the [T] is of larger diameter than the other, one chucking [V] must be deeper than the other, and we may find their respective depths by the following process:--

[Ill.u.s.tration: Fig. 2822.]

"Draw line A B, Fig. 2822, which line represents the chuck face. Let point C represent the centre of the lathe. Mark line C E and set a pair of compa.s.ses to the radius of the body of the pattern at the centre of the branch location. Then take a radius from C and about 1/16 inch up from line A B, and with this radius we mark on the line C E the point E.

From this centre we mark the two arcs having radii corresponding to the unequal diameters of the pattern at the location where the chucking [V]'s are to be placed. We then draw tangent lines to each of these arcs, and thus obtain the correct depth of [V] necessary to hold the axial line of the pattern parallel to the lathe chuck.

[Ill.u.s.tration: Fig. 2823.]

"The core box would, unless the pattern were a small one, be built up in courses, as shown in Fig. 2823. The box would be drawn in plan, and end and side views drawn as shown, so as to draw in the half circle representing the bore of the half-core box and mark off the courses as from 1 to 6. These courses need not be of equal or of any particular thickness, but may suit that of any suitable timber at hand. Courses 1 and 2 should extend over the whole outline of the box, while the pieces 3 and 4 are made in width to suit the curvature of the core as shown, and to extend the full length of the box. The pieces 7, 8, 9, and 10 are of the length of the branch, and are made in width to suit the curvature of the branch core. If the branch core were a short one it could be cut out of the solid; but in any event, the grain of the wood should be as shown, and the holding pieces at G and H should be employed."

CHAPTER x.x.xV.--WOOD WORKING MACHINERY.

The machines employed in wood working may be divided into 7 cla.s.ses as follows:

1. Those driving circular saws.

2. Those driving ribbon or band saws.

3. Those driving boring or piercing tools.

4. Those employing knives having straight edges for surfacing purposes and cutting the work to thickness.

5. Those employing knives or cutters for producing irregular surfaces upon the edges of the work.

6. Those employed to produce irregular surfaces on the broad surface of work.

7. Those employed to finish surfaces after they have been acted upon by the ordinary steel cutting tools.

CIRCULAR SAWS.

[Ill.u.s.tration: Fig. 3078.]

The thicknesses of circular saws is designated in terms of the Birmingham wire gauge, whose numbers and thicknesses are shown in Fig.

3078, where a Birmingham wire gauge is shown lying upon two circular saws, which show the various shapes of teeth employed upon saws used for different purposes.

The teeth numbered 1 are for large saws, as 36 inches in diameter, to be used on hard wood. Numbers 2 and 5 are for soft wood and a quick feed.

Numbers 3 and 4 are for slabbing or converting round logs into square timber. Number 6 is for quick feeds in large log sawing. Numbers 7, 8, 9 and 10 are for bench saws, or, in other words, saws fed by hand or self-feeding saws. Number 8 is known as the "London Tooth," because of being used in London, England, on hard and expensive woods. Number 9 is the regular rip-saw tooth for soft woods. Number 10 is the Scotch gullet tooth. Number 11 is for either cross-cutting or rip sawing by circular saws used on soft woods. Number 12, is for large cross-cut saws; the flat place at the bottom of the tooth prevents the teeth from being unnecessarily deep and weak. Number 13 is for cross-cutting purposes generally. Number 14 is for rip sawing on saws of small diameter. It is also used for tortoise-sh.e.l.l, having in that case a bevel or fleam on the front face, and no set to the teeth.

The following table gives the ordinary diameters and thicknesses of circular saws and the diameters of the mandrel hole:

---------+------------+------------------- Diameter.| Thickness. | Size Mandrel Hole.

---------+------------+------------------- 4 inch.| 19 gauge. | 3/4 5 " | 19 " | 3/4 6 " | 18 " | 3/4 7 " | 18 " | 3/4 8 " | 18 " | 7/8 9 " | 17 " | 7/8 10 " | 16 " | 1 12 " | 15 " | 1 14 " | 14 " | 1-1/8 16 " | 14 " | 1-1/8 18 " | 13 " | 1-1/4 20 " | 13 " | 1-5/16 22 " | 12 " | 1-5/16 24 " | 11 " | 1-3/8 26 " | 11 " | 1-3/8 28 " | 10 " | 1-1/2 30 " | 10 " | 1-1/2 32 " | 10 " | 1-5/8 34 " | 9 " | 1-5/8 36 " | 9 " | 1-5/8 38 " | 8 " | 1-5/8 40 " | 8 " | 2 42 " | 8 " | 2 44 " | 7 " | 2 46 " | 7 " | 2 48 " | 7 " | 2 50 " | 7 " | 2 52 " | 6 " | 2 54 " | 6 " | 2 56 " | 6 " | 2 58 " | 6 " | 2 60 " | 5 " | 2 62 " | 5 " | 2 64 " | 5 " | 2 66 " | 5 " | 2 68 " | 5 " | 2 70 " | 4 " | 2 72 " | 4 " | 2 ---------+------------+-------------------

Circular saws are sometimes hollow ground or ground thinner at the eye than at the rim, to make them clear in the saw kerf or slot with as little set as possible, and therefore produce smooth work while diminis.h.i.+ng the liability of the saw to become heated, which would impair its tension. They are also made thicker for a certain portion of the diameter and then bevelled off to the rim.

This is permissible when the work is thin enough to be easily opened from the log by means of a spreader or piece that opens out the sawn piece and prevents it binding against the saw.

The s.h.i.+ngle saw, shown in Fig. 3079, is an example of this kind, the saw bolting to a disc or f.l.a.n.g.e by means of countersink screws.

The concave saw shown in Fig. 3080, is employed for barrel heads. The three pieces for a barrel head are clamped together and fed in a circular path, so that the saw cuts out the head at the same time that it bevels the edge.

The advantage of the circular saw lies mainly in the rapidity of its action, whether used for ripping or cross-cutting purposes. In order, however, that it may perform a maximum of duty, it is necessary that the teeth be of the proper shape for the work, that they have the proper amount of set, that they be kept sharp, and that the tension of the saw is uniform throughout when running at its working speed.

[Ill.u.s.tration: Fig. 3079.]