Maharashtra HSC Engineering Drawing (Technical Science) flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Isometric foreshortening factor

In isometric projection all three axes are equally foreshortened by a factor of 0.816, so an isometric length equals 0.816 times the true length. Isometric drawing uses true lengths instead.

Isometric ellipse axes

A circle of diameter d on an isometric face appears as an ellipse with major axis 1.22d and minor axis 0.71d; the major axis lies perpendicular to the axis normal to that face.

Cabinet oblique projection

An oblique projection in which the front face is drawn true shape and the receding edges are drawn at half scale, usually at 45 degrees, reducing the apparent distortion of depth.

Cavalier oblique projection

An oblique projection using full scale along the receding axis, usually drawn at 45 degrees. It exaggerates depth and is chosen when the object is short in the receding direction.

First-angle projection arrangement

The object lies between the observer and the plane. The top view is placed below the front view, and the view from the left is placed on the right of the front view.

True length of inclined line

True length squared equals front-view length squared plus the difference of end heights squared. Equivalently, the front view foreshortens by cos of the angle to the horizontal plane.

Horizontal trace of a line

The point where a line meets the horizontal plane. It is found by extending the front view to the XY line and projecting down onto the extended top view.

Point on both reference planes

A point lying in both the horizontal and vertical planes has its front view and top view coinciding on the XY line, since both distances are zero.

Development of a right cone

The development is a sector of radius equal to the slant height l, with sector angle 360 degrees times r divided by l, so the arc length equals the base circumference.

Development of a right cylinder

The lateral surface unfolds into a rectangle whose width equals the base circumference, 2 pi r, and whose height equals the cylinder height. Bases are added as separate circles.

Intersection by cutting planes

A series of parallel cutting planes is passed through both solids. Where each plane cuts both surfaces, points of the intersection curve are located and joined smoothly.

Equal-diameter cylinder intersection

When two cylinders of equal diameter intersect at right angles, the line of intersection appears in one view as two straight lines crossing at the axis intersection.

Section plane on a cone

A plane parallel to the base gives a circle, parallel to a generator gives a parabola, inclined more steeply than the generator gives an ellipse, and parallel to the axis gives a hyperbola.

Frustum volume formula

Volume of a frustum equals h/3 times the sum of the two base areas plus the square root of their product, where h is the perpendicular height between the parallel bases.

Polygon circumradius formula

For a regular polygon with n sides of length a, the circumradius equals a divided by twice the sine of 180 degrees divided by n. The apothem uses tangent instead.

Tangent length from external point

The length of a tangent drawn from an external point to a circle equals the square root of OP squared minus r squared, where OP is the centre distance.

Eccentricity of conic sections

Eccentricity equals the distance from a point to the focus divided by its distance to the directrix. It is 1 for a parabola, less than 1 for an ellipse, greater than 1 for a hyperbola.

Cycloid dimensions

A cycloid traced by a circle of radius r rolling along a straight line has an arch height of 2r and a base length equal to the circumference, 2 pi r.

Half section

A view in which one quarter of the object is removed, showing half the view in section and half as an outside view, separated by a chain thin centre line.

Offset section

A section using a cutting plane bent at right angles to pass through features that do not lie in one plane; the section is drawn as one continuous view.

Parts never sectioned

Shafts, bolts, nuts, screws, rivets, pins, keys, and the solid parts of ribs and webs cut lengthwise are drawn unsectioned by convention even when the cutting plane passes through them.

Hatching convention

Cut surfaces are hatched with continuous thin lines at 45 degrees to the outlines, spaced 2 to 4 mm apart; adjacent parts in an assembly are hatched in opposite directions.

Metric thread designation

M20 times 2.5 denotes an ISO metric thread of nominal diameter 20 mm and pitch 2.5 mm. Omitting the pitch, as in M20, indicates the coarse series.

Square thread proportions

A square thread has a depth equal to half the pitch, with square crests and roots. It gives high efficiency and low friction but is difficult to cut with a tap.

Saddle key

A key that bears on the shaft surface by friction without a keyway cut into the shaft. It is used only for light loads because it can slip.

Flange coupling

A coupling with two flanges, each keyed to one shaft end, bolted together. It transmits high torque and keeps the shafts accurately aligned during operation.

Tolerance calculation

Tolerance is the difference between the upper and lower limits. For a hole it equals ES minus EI; for a shaft it equals es minus ei. It is always positive.

Clearance fit

A fit in which the largest shaft is smaller than the smallest hole, so a gap always exists. Examples are H7/g6 and H7/h6 in the hole-basis system.

Interference fit

A fit in which the smallest shaft is larger than the largest hole, so the parts must be pressed or shrunk together. Examples are H7/p6 and H7/s6.

Maximum material condition

The condition where the shaft is at its largest permitted size or the hole at its smallest. It represents the tightest assembly condition for the mating parts.

Filing margin on drawing sheet

A 20 mm wide strip along the left edge of the drawing sheet, outside the frame, reserved for binding or filing. The other three margins are usually 10 mm.

Building plan cut height

A building plan is a horizontal section taken about 1.2 m above the floor, so that doors, windows, and walls are cut and visible in the plan view.