Computer Studies
 Knot Making

Before starting a drawing

Setting the units

Before we start a new drawing we need to make sure that ACAD is set up to work the way we wish it to. For a start we will check that the units are set to Metric or Imperial, whichever is desired.

In the command line type the command ‘ddunits’:

Command: ddunits

A dialogue box ‘Drawing Units’ will appear where you are asked to select your preferences for ‘Length’ units ‘Angle’ units and their precision. If you are not sure which ones you should use then just stick to the default settings. You can also define in which direction ACAD increments angles. By default the base angle (zero degrees) points towards east and angles increment as you turn anticlockwise. If you wish to set ACAD so that angles increment as you turn clockwise, you have to tick the ‘clockwise’ option provided. If you wish to set the base angle, i.e. the direction which ACAD considers to be zero degrees, then click the ‘Direction’ button. A further dialogue box named ‘Direction Control’ appears. Select your preference through the radio buttons provided and click ‘Ok’. Back at the ‘Drawing Units’ dialogue box, under ‘Insertion Scale’ select the units of preference and click ‘ok’.

Setting the limits

The limits are a rectangular area that encloses all of your drawing. Limits are defined by specifying the lower left hand corner’s coordinates, and the upper right hand corners’. The default limits are 0,0 to 420,297 which is the size in millimetres of an A3 paper. Let us assume that you wish to set the limits to reflect the size of an A4 paper which is 297mm by 210mm. Type ‘limits’ in the command line and follow the command prompts as shown:

Command: limits
Reset Model space limits:
Specify lower left corner or [ON/OFF] <0.0000,0.0000>: press enter
Specify upper right corner <420.0000,297.0000>: 297,210

Now the limits of your drawing have been set to these dimensions. Try to zoom ‘All’, move your cursor to the upper right hand corner of the drawing area and watch the coordinates in the status bar. They should reflect this, apart from some variation between the proportions of your screen and those of the A4 paper specified.

Grid and Snap

At times, you may wish to draw in certain specified increments. The grid and snap modes at the status bar are very useful for such a purpose. Try to click the ‘Grid’ mode. A grid is displayed over your drawing area. Move your cursor over it, and notice that you can still move freely no matter if the grid is displayed or not. Now click the ‘Snap’ mode and try moving the cursor over the drawing area again. The cursor is now restricted to move only from one point of the grid on to the next. You can toggle the snap mode by pressing F9 and the grid by pressing F7.

In ACAD08 the snap and grid are recognisable as the words are written on the button itself. For ACAD09 the symbols are shown below:

Further to this, you can also adjust the settings for the snap and grid. Move the cursor over the snap or grid modes, right click and choose ‘Settings’. This will display the ‘Drafting settings’ dialogue box where you can define the x and y spacing of both the snap and the grid. Try to change the values but leave all other options to their default settings and press ‘Ok’.

We are almost ready to start drafting!

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