Page 311 - CITS - ED - Mechanical

ENGINEERING DRAWING - CITS

Key terms

Term Description

Absolute coordinates Distance measured from a fixed reference point.
Aperture Effective diameter of the cursor on the screen.

Cartesian coordinates A rectangular system of measurement to locate points in the drawing area.
Object snaps A method for indicating point locations using existing drawing objects
as a reference.

Origin point The 0,0 location of the coordinate system.
Polar coordinates A system to locate of the coordinate system.
Prototype drawing A template drawing that has a last location of the cursor.
Relative coordinates Distance measured from the last location of the cursor
User-defined co-ordinates A mode of measurement that allows the user to set up a customized coordi
nate System system.
Angular measurement (Fig 4)

Fig 4

AutoCAD measures angles in a particular way also. Look at the diagram below and then place your mouse on it
to see how this is
Degrees are measured counterclockwise starting at 3 O’CLOCK

When drawing lines at an angle, you have to begin measuring the angle from 0 degrees, Which is at the 3 O’clock
position. If you drew a line at 90 degrees, it would go straight up. The example above (When you move your mouse
over it) shows a line drawn at+300 degrees (270+30), or-60 degrees.
Your might not always have an obvious reference point for 0 degrees. Look at the example below and place your
mouse on the image to find out the angle in question.

In this example, you are given information about the lines, but not the angle AutoCAD needs to draw the line from
the start point. What you are given though, is (a) the knowledge that 0°is at the 3 o’clock position (b) the knowledge
that180° is at the 9 o’clock position and (c) the angle between 180° and the line you want to draw is 150°. With this
information, you can figure out what angle you need. Here is a fool-proof way of getting the angle you need (Fig 5)
1 Start at the 0° position and measure counter-closkwise (+) to 180°
2 From 180°, measure clockwise 150°(-)
3 Consider that you just went+180-150 and use that as an equation:+180-150=30 (Fig 5)

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CITS : Engineering Drawing (Mechanical) - Exercise 12