Technical Drawing Basics

• In technical drawing, a numerical linear dimension specified without a unit signifies millimeters (mm).
• A conically sharpened wooden pencil should be rotated while drawing because it ensures a sharp and clear line.
• On a wooden pencil, "3H" signifies the hardest lead.
• The recommended ratio of thin lines to thick lines for standard drawings is 1:2.
• A 60/30 and 45 Set-square cannot qualify as a template.
• All title blocks must contain all of these pieces of information: title of drawing, names and dates, checker and designer, dimensions, & scale

Scale

• The ratio of the size of the drawing of a part to its actual size is called the scale.
• A circle is a plane figure bounded by a circumference equidistant from the center.
• A Continuous Thick Line has precedence over all other types of lines.
• A cycloid is created by the motion of a point on a circle as the circle rolls along a straight line.
• If 1 meter is represented by 2cm, the scale used is 1:50 (1 m = 100 cm, so 2 cm represents 100 cm, therefore the ratio is 2:100 which simplifies to 1:50).
• A circumscribed circle is one where a circle is drawn around a polygon such that each vertex of the polygon lies on the circle.

Orthographic Projection

• The orthographic projection involves projecting views of an object onto planes perpendicular to each other to represent the object in 2D.
• The orthographic projection shown is in Third Angle Projection.
• The diagram shows a center line.

Hexagon

• There are 3 pairs of parallel lines in a regular hexagon.

Elevation and Plan

• Front elevation is a view of an object from the front.
• The plan view is a view of an object from above.

Geometric Statements

• Dashed lines should meet at corners and tangent points with dashes.
• Where visible and invisible lines coincide, the visible line takes precedence.
• Where an invisible line and center line coincide, the center line takes precedence.
• Tools required for geometric construction include a drawing board, T-square, and pair of compasses.
• The meeting of two invisible edges can be best represented by a dashed line.
• Cones are not plane figures.
• Use thin constructional lines, use large radii, consider accuracy, and ensure neat work for constructional purposes.
• The intersection of the perpendicular bisectors of two chords of a circle gives the center.
• A line is tangential to another line if it touches the line but does not cross it.
• External tangency that involves the distance between the centers of two circles, R being the radius of the larger circle, and r being the radius of the smaller circle, is R + r.
• Internal tangency that involves the distance between the centers of two circles, R being the radius of the larger circle, and r being the radius of the smaller circle, is R - r.
• For an external tangential relationship between two circles, the point of tangency and the centers of the two circles must lie on a straight line.
• An epicycloid is not a conic section.
• For an accurate ellipse, the concentric circle method should be applied.
• The semi-circle (Right-triangle) theorem is applied to construct a tangent to a circle through a point on the circle/arc.
• The semi-circle theorem can construct a common exterior tangent to two unequal circles.
• In cases with what is the distance between the centers of two circles (R=50, r =20) that are externally tangential the answer is 70.
• In cases with what is the distance between the centres of two circles (R= 70, r = 20) that intersect one another the answer is 50.
• Cycloidal Curves are types of plane curves.
• A cycloid is generated by a point on the circumference of a circle that rolls along a fixed straight line.
• An epicycloid is generated by a point on the circumference of a rolling circle which rolls outside a directing circle.
• A trochoid is generated by a point within or outside a circle that rolls along a straight line.
• An involute is a curve traced out by a point on a piece of string when unwound from any geometrical object.
• A spiral is created by a point moving continuously in one direction along a rotating line
• An hypotrochoid is generated by a point within or outside a circle which rolls on the inside of the directing circle.
• Selection of views in Orthographic Projection are guided by the following rules that is considered first: The rule of the longest side.
• In the first angle orthographic projection, the object is imagined to be placed above the HP and in front of the VP.
• A point has been projected onto the VP-Vertical plane and HP-Horizontal plane as shown in Figure Q58.
• Orthographic projection has been of prior importance because it can be dimensioned.
• Figure Q60 shows a pictorial view of a block.
• The first most important view of an object during Orthographic Projection is captured on the Vertical plane.
• The view i represents third angle orthographic projection Right Side View.
• The view ii represents first angle orthographic projection Bottom View.
• The view iii represents First angle orthographic projection Right Side View.
• The view iv represents First angle orthographic projection Bottom View.

Properties of Orthographic Projection

• Properties of Orthographic projection EXCEPT: It is a single-view projection.
• The most important view (Front View) is shown.
• In a reduction scale drawing, the drawing is of a reduced size of the object.
• A student is requested to purchase clutch (mechanical) pencils for producing engineering drawings. The combination sizes of pencils will suit this purpose, 0.7 and 0.35.
• The correct FRONT View of the figure is shown.