DOI Seite / Zitierlink:
https://doi.org/10.11588/diglit.25888#0082
66
ENGINEER AND MACHINIST’S DRAWING-BOOK.
Oblique Projection of a Bevil Pinion.—
Plate XXVII.
Let the pinion be, in the first instance, regarded as
situated in a position parallel to the vertical plane, and
construct accordingly its projections at Figs. 1 and 2.
Then transfer the edge view to Fig. 4, giving to the axis
S O' the required inclination to the ground line; and pro-
ject upon the horizontal centre line A B the vertices 0,
O', S', of the various cones employed to determine the
direction and construction of the teeth. The teeth them-
selves are then to be projected upon Fig. 3 in the manner
already described in reference to spur wheels, observing
that all their rectilinear edges converge towards the
point S, while the outlines of the planes (which are, in
this instance, radial lines) tend towards 0 and O' respec-
tively, according as they are situated upon the exterior
or interior cones, between which the length of the teeth
is comprised.
SECTION IV.
Drawing of the Steam Engine.
Details of a Steam Engine Beam.—Plate XXVIII.
The Beam (which constitutes the distinguishing feature
in a large class of steam engines) is a very strong cast-
iron lever A, adapted to move freely upon a fixed axis C,
called the main centre, and which passes transversely
through the beam, in most cases at the exact middle of
its length and breadth. One of its extremities, as E, is
attached to the piston rod of the steam engine, which
communicates to it an alternate rectilinear motion of
ascent and descent, while to the opposite extremity E' is
jointed a strong bar or rod, generally of cast-iron, called
the connecting-rod, by means of which the alternating
action of the beam is converted into a continuous rotatory
motion, through the intervention of a crank fixed immov-
ably upon the revolving shaft.
Fig. 1 represents an elevation, or vertical projection of
the beam, and Fig. 2 a plan or horizontal projection. Its
extremities are cast, and afterwards carefully turned into
a cylindrical form, upon which are fitted the crossheads
E E', each of which is furnished with two studs or bear-
ings, whose axes are perpendicular to the centre line of
the beam; these pieces are retained in their places by
means of snugs or ferrules F F', fixed to the beam by pins.
The main centre C, which is supported by two plummer-
blocks bolted to the framing of the engine, is fixed into
the beam by keys very accurately fitted and firmly
driven; the spaces between the keys is generally filled
with lead poured into the eye in a melted state, and
formed externally into some species of ornamental mould-
ing. In treating of the parallel motion (Plate XXXI.)
we shall have occasion to describe the mode in which the
air-pump rod is attached to the intermediate stud a,
which is, in the present instance, situated exactly midway
between the centre of the beam and that of the cross-
head E. On these figures may also be observed the
smaller studs o and c, which are intended to give motion
to the rods for working the cold water and feed pumps.
Figs. 3, 4, and 5 represent different views of one of the
cylindrical ends of the beam; they are drawn to a scale of
double the magnitude of the principal projections. Fig. 6
is a section upon the line XY, and shows the forms of
the strengthening ribs or feathers of the beam, the main
body, or iveb, having no greater thickness than that com-
prised between the lines b d and e f. Lastly, Fig. 7
exhibits enlarged views of one of the cross-heads E, and
Fig. 8 of one of the retaining ferrules.
The various figures above enumerated having been
examined, and the forms of the objects they represent
being thoroughly understood, the first step in the pro-
cess of delineating them is to lay down carefully all the
centre-lines and distances of the principal points, as indi-
cated in the Plate. Then describe the curve i h i (Fig. 1),
which is a portion of a parabola, whose vertex is at h, upon
the vertical line passing through the main centre C; but
since neither the focus nor directrix of this curve are
given, the following method may be resorted to for its
determination:—■
After setting off the distances C h and i t, at the middle
and ends of the beam, according to the dimensions marked,
draw through the point h a straight line h 4', parallel to
the centre line of the beam, and intersecting the vertical
line i t produced. Then divide the difference of these two
quantities, represented by the line i 4', and the distance
t C into the same number of equal parts, say four, and
draw through the points of division 1, 2, 3, perpendicular
to the centre line, and from the points 1', 2', 3', straight
lines converging to the vertex h; the intersections of these
lines respectively are points in the curve required. The
points 1, 2, 3 being, in like manner, set off on the right ot
the main centre, and perpendiculars drawn through them,
the portion h % of the curve lying towards that side may
be constructed by transferring the distances 11", 22", 33"
to the corresponding perpendiculars. The remaining
curves of the outline and the exterior feathers of the beam,
which are either symmetrical with or parallel to that
already described, may then obviously be drawn without
any difficulty.
It will be observed that the extremities of the beam,
immediately within the pieces E, E', are terminated by
portions of cones penetrated by various plane and cylin-
drical surfaces. It is principally for the purpose of
enabling the student to understand more clearly the mode
of drawing the curves resulting from these penetrations
that we have given the enlarged views, Figs. 3, 5 and 6,
where he will observe in the first place that the plane
surface e f, being parallel to the axis of the cone Ic p s, the
resulting curve of intersection will be a hyperbola q v s'
(Fig. 3), the nature of which curve and the mode of draw-
ing it have been shown elsewhere; the only parts of this
curve which are visible are obvious by the line q v, and
corresponding portion on the opposite side of the centre
line. The line to l (Fig. 5) is a portion of a hyperbola
ENGINEER AND MACHINIST’S DRAWING-BOOK.
Oblique Projection of a Bevil Pinion.—
Plate XXVII.
Let the pinion be, in the first instance, regarded as
situated in a position parallel to the vertical plane, and
construct accordingly its projections at Figs. 1 and 2.
Then transfer the edge view to Fig. 4, giving to the axis
S O' the required inclination to the ground line; and pro-
ject upon the horizontal centre line A B the vertices 0,
O', S', of the various cones employed to determine the
direction and construction of the teeth. The teeth them-
selves are then to be projected upon Fig. 3 in the manner
already described in reference to spur wheels, observing
that all their rectilinear edges converge towards the
point S, while the outlines of the planes (which are, in
this instance, radial lines) tend towards 0 and O' respec-
tively, according as they are situated upon the exterior
or interior cones, between which the length of the teeth
is comprised.
SECTION IV.
Drawing of the Steam Engine.
Details of a Steam Engine Beam.—Plate XXVIII.
The Beam (which constitutes the distinguishing feature
in a large class of steam engines) is a very strong cast-
iron lever A, adapted to move freely upon a fixed axis C,
called the main centre, and which passes transversely
through the beam, in most cases at the exact middle of
its length and breadth. One of its extremities, as E, is
attached to the piston rod of the steam engine, which
communicates to it an alternate rectilinear motion of
ascent and descent, while to the opposite extremity E' is
jointed a strong bar or rod, generally of cast-iron, called
the connecting-rod, by means of which the alternating
action of the beam is converted into a continuous rotatory
motion, through the intervention of a crank fixed immov-
ably upon the revolving shaft.
Fig. 1 represents an elevation, or vertical projection of
the beam, and Fig. 2 a plan or horizontal projection. Its
extremities are cast, and afterwards carefully turned into
a cylindrical form, upon which are fitted the crossheads
E E', each of which is furnished with two studs or bear-
ings, whose axes are perpendicular to the centre line of
the beam; these pieces are retained in their places by
means of snugs or ferrules F F', fixed to the beam by pins.
The main centre C, which is supported by two plummer-
blocks bolted to the framing of the engine, is fixed into
the beam by keys very accurately fitted and firmly
driven; the spaces between the keys is generally filled
with lead poured into the eye in a melted state, and
formed externally into some species of ornamental mould-
ing. In treating of the parallel motion (Plate XXXI.)
we shall have occasion to describe the mode in which the
air-pump rod is attached to the intermediate stud a,
which is, in the present instance, situated exactly midway
between the centre of the beam and that of the cross-
head E. On these figures may also be observed the
smaller studs o and c, which are intended to give motion
to the rods for working the cold water and feed pumps.
Figs. 3, 4, and 5 represent different views of one of the
cylindrical ends of the beam; they are drawn to a scale of
double the magnitude of the principal projections. Fig. 6
is a section upon the line XY, and shows the forms of
the strengthening ribs or feathers of the beam, the main
body, or iveb, having no greater thickness than that com-
prised between the lines b d and e f. Lastly, Fig. 7
exhibits enlarged views of one of the cross-heads E, and
Fig. 8 of one of the retaining ferrules.
The various figures above enumerated having been
examined, and the forms of the objects they represent
being thoroughly understood, the first step in the pro-
cess of delineating them is to lay down carefully all the
centre-lines and distances of the principal points, as indi-
cated in the Plate. Then describe the curve i h i (Fig. 1),
which is a portion of a parabola, whose vertex is at h, upon
the vertical line passing through the main centre C; but
since neither the focus nor directrix of this curve are
given, the following method may be resorted to for its
determination:—■
After setting off the distances C h and i t, at the middle
and ends of the beam, according to the dimensions marked,
draw through the point h a straight line h 4', parallel to
the centre line of the beam, and intersecting the vertical
line i t produced. Then divide the difference of these two
quantities, represented by the line i 4', and the distance
t C into the same number of equal parts, say four, and
draw through the points of division 1, 2, 3, perpendicular
to the centre line, and from the points 1', 2', 3', straight
lines converging to the vertex h; the intersections of these
lines respectively are points in the curve required. The
points 1, 2, 3 being, in like manner, set off on the right ot
the main centre, and perpendiculars drawn through them,
the portion h % of the curve lying towards that side may
be constructed by transferring the distances 11", 22", 33"
to the corresponding perpendiculars. The remaining
curves of the outline and the exterior feathers of the beam,
which are either symmetrical with or parallel to that
already described, may then obviously be drawn without
any difficulty.
It will be observed that the extremities of the beam,
immediately within the pieces E, E', are terminated by
portions of cones penetrated by various plane and cylin-
drical surfaces. It is principally for the purpose of
enabling the student to understand more clearly the mode
of drawing the curves resulting from these penetrations
that we have given the enlarged views, Figs. 3, 5 and 6,
where he will observe in the first place that the plane
surface e f, being parallel to the axis of the cone Ic p s, the
resulting curve of intersection will be a hyperbola q v s'
(Fig. 3), the nature of which curve and the mode of draw-
ing it have been shown elsewhere; the only parts of this
curve which are visible are obvious by the line q v, and
corresponding portion on the opposite side of the centre
line. The line to l (Fig. 5) is a portion of a hyperbola