TWO-DIMENSIONAL DRAFTING

   TWO-DIMENSIONAL DRAFTING 

Creating a drawing in the X and Y coordinates on a plane or paper is termed as two-dimensional drafting. In 2D drawing distance are measured from the origin of two axes namely X and Y. The axes could be fixed during the creation of elements (called absolute mode) or there may be an option for the automatic shifting of axes, so that distances are measured from the end of each successive element (called incremental mode). 

All the existing CAD software divides options into three main categories –  

1. Creation tools 

2. Modifying tools (Editing tools) 

3. Support tools (Aid tools)

Creation Tools 

All existing CAD systems provide users with curve entities, which can be divided into analytic and synthetic entities. Analytic entities are points, lines, arcs, circles, conics, rectangle and polygon. Synthetic entities include splines and Bezier curves. 

Creation Tools 

1. Points 

2. Line 

3. Arc 

4. Circle 

5. Rectangle 

6. Polygon  

7. Conics 

8. Splines  

9. Bezier Curves 

Points 

Points have two coordinates namely X and Y, measured from origin either by absolute mode or by incremental mode. 

Line 

Straight lines connecting two points 

Arc 

Arcs have three points. It can be made in different ways, e.g., start point, End point, and point on arc or Centre, start and end point. 

Circle 

Circles have either two or three points. It can be made in different ways, e.g., Centre and radius or Centre and diameter for two point method. Circle by three tangent lines for three-point method. 

Rectangle 

Rectangle can be created by either two-point method or three-point method. 

Polygon 

Polygon has two points. Polygon can be created in three ways (Centre and side of polygon, Centre and inscribed radius method and Centre and circumscribed radius method). It requires number of sides for all the three types.  

Conics 

Lines, circle, ellipses, parabolas and hyperbolas are all special forms of conic curves. They all can be generated when a right circular cone of revolution is cut by planes at different angles relative to the cone axis, thus the derivation of the name of conics. Circles when a cone is sectioned by a plane perpendicular to its axes. Ellipses, parabolas, and hyperbolas are generated when the plane is inclined to the axis by various angles. 

Splines  

Splines are synthetic entities. They are of two types – cubic spline and b-spline. They are formed by two methods.

a) Spline by points or curve interpolates 

b) Spline by poles or curve extrapolates. 

 

In spline by point’s method the spline touches all the defining points. In spline by poles method the spline touches only start and end points, and it forms a curvature between intermediate points.   

Bezier Curves 

It is a synthetic entity defined by a set of data points. It may interpolate or extrapolate the data points which are used to control the shape of the resulting curves.

Modifying Tools (Editing tools) 

Tools or option used to edit or modify the curves are called editing tools. Some of the commonly used editing tools are move, copy, cut, paste, offset, scale, mirror, array, fillet, chamfer, rotate, trim, extend, stretch, delete, divide, etc. 

Modifying Tools (Editing tools) 

1. Move 

2. Copy 

3. Cut 

4. Paste 

5. Offset 

6. Scale 

7. Mirror 

8. Array 

9. Fillet 

10.  Chamfer 

11.  Divide 

12.  Trim 

13.  Extend 

14.  Stretch 

15.  Delete  

16.  Rotate

Move 

This option moves an item from one location to another location. It is also called translate. 

Copy 

This option is otherwise called duplicate, because it duplicates the original one at another location. This copy function is similar to the move function except that it preserves a copy of the item at its original location.    

Cut 

This option is used to remove the drawing or drawing entity. 

Paste 

This option is used to paste or add the object which was already cut or copied. 

Offset 

This option offsets an item to the required distance. It differs from ‘move’, because a move translates an item from one point to another point, but offset transfers the curve in the normal direction as per the defined distance.   

Scale 

This option is used to increase or decrease the item to the required value. 

Scaling is of two types. 

a) Uniform scaling 

b) Non-uniform scaling.

  In uniform scaling an item is scaled in all directions equally. In non-uniform scaling an item is scaled to different values.   

Mirror 

This option creates a mirror image of the item about a specified plane. 

Array 

This option is also called ‘instancing’ or ‘pattern’. Using this option you can make an item into a number of instances or arrays. There are two types of arrays, rectangular array and circular array. 

Fillet 

This option is blending the corners of the curves. It is also called ‘blend’. 

Chamfer 

This option is bevelling the corners of the curves. It is also called ‘bevel’.   

Rotate 

This option is used to rotate an item through a specified angle from is original orientation. 

Divide 

This option is used to divide the entities into: a) Number of elements b) Between two entities c) A percentage of entities, etc. 

Trim 

This option is also called ‘break’. It trims a line or other component by removing the unwanted portions which extend beyond the required limit.   

Extend 

This option extends the line or curve to the required limit. 

Stretch 

This option is also called ‘dragging’. This is used to move the particular geometry along with adjacent geometries also. 

Delete 

It is also called ‘remove’ or ‘erase’. This function causes the selected segment of the drawing to be removed from the screen and from the database. 

Support Tools (Aid Tools) 

Tools which support the geometric modelling or curve creation are called aid or support tools. Some of the common aid tools are Undo, Redo, Hatching or area filling, Grids, Layers, Limits, Snap, Boolean, Grouping, User Defined Features, Macros, Selection Methods, Colours, Relations or Expressions and drawing tree. 

Some of the common tools which support graphical display are visualization, Boundary setting or windowing, Fit, Zoom, Pan, and rotating the screen. Some tools support the 2D geometry in adding dimension, text annotation, symbols, notes and labels, and bill of material or part list to the geometry.   

Support Tools (Aid Tools) 

1. Undo 

2. Redo 

3. Hatching 

4. Grids 

5. Layers 

6. Limits 

7. Snap 

8. Boolean 

9. Grouping 

10. User Defined Features (UDF) 

11. Visualization 

12. Colour 

13. Drawing tree 

14. Pan 

15. Zoom 

16. Rotate 

17. Fit 

18. Macros 

19. Entity Selection Methods 

20. Relations or Expressions 

Undo 

It helps the user to get back to the previous step that was made by mistake.  

Redo 

It helps the user to get back to the ‘undo’ step. 

Hatching 

This option is used to fill the closed areas of a sectional portions or geometry. It is also called ‘area filling’. 

Grids 

This forms points at regular intervals in X and Y coordinates, so that the user can easily understand the positions of the geometry. Grid points will not affect the geometry output.  

Layers 

This option is used to organize the objects in different layers so that the user can easily activate the required layer. The unwanted or other geometries will not be shown. Thus, it reduces the complexity in the display.  

Limits 

This option is used to set the size for drawing sheet. 

Snap 

This option helps to pick the required point of the existing geometry. Some of the snap options are, end point, midpoint, tangent point, intersection point, quadrant point, circle Centre point, etc. this option is also called ‘geometric modifiers’.  

Boolean 

This helps us to use the Boolean operations such as unit, subtract, and intersect in the geometry.  

Grouping 

This option is used to organize the similar type of geometry and to name it. This helps the user to identify and group the similar type geometry, e.g., dimensions, text, curves, etc. 

User Defined Features (UDF) 

This option is useful when making a same geometry with different values or data. In this the user has to make a UDF with the value that ranges from lower limit to upper limit and stores it in a UDF library. When the geometry requires a specific value, it can be taken from UDF library and set the required value for the geometry. Thus, UDF reduces the time in creating the same parts with different values, e.g., parts like nuts, bolts, etc. 

Visualization 

This option is used to set background and foreground for the geometry. 

Colour 

It helps the user to differentiate geometry for a set of entities according to its purpose or use, e.g., differentiate dimension, texts, drawings, etc. 

Drawing Tree 

It is used to quickly view the options used to make the drawing. Thus, it helps in modifying or editing the drawing entities. 

Pan 

This option is used to move the drawing in the screen or display without changing its original location.  

Zoom 

This option is used to see the drawing closer by enlarging the portion of the drawing in display without changing its original size. 

Rotate 

This option is used to rotate the drawing in display without rotating the original position. 

Fit 

This option is used to bring the entire geometry into the display window. 

Macros 

This option is used to repeat the steps of geometry creation to the parts which are similar in shape and size. Instead of drawing it again we can record the geometry creation of the first entity and store it and macros. We can play the recorded macro which will do the same operations done in first one. Thus, it reduces design time for similar geometry creation using similar operations.  

Entity Selection Methods 

Entity selection methods help the user to pick the entity as per the user’s wish. The user can select: 

(a) Individual entity 

(b) Group of entity 

(c) Select the entity which comes inside a closed boundary

 (d) Selecting the entity by its colour, etc. 

Relations or Expressions 

This option is used to make a drawing with relationship to other entities so that each can be adjusted when the user updates a particular value. This option helps to make geometries like gears.

Thank You.