The element of cause and effect can become a powerful tool in the design process. Almost everything we do can be defined by a decision tree. If this, then that. With drawings, be they 2D or 3D, this can be used as a basis for automating simple and often repeated design tasks. A few minutes or hours saved by reducing the tedium can be better used to address some other issue.

When using CAD, there are several levels of design automation to consider.

Blocks & Templates

Why reinvent the wheel? Plan the parts and pieces you create so that you can use them over again. No need to redraw a bolt or nut each time you need one. Save a set of blocks that create a library of related parts. Organizing your library of parts requires some forethought into how you might name them and file them so they can be easily found. Nuts, bolts, & screws are a good starting point for a fastener library. Every time you need a nut you can go to a folder and retrieve one that is the correct size and insert it in the drawing.

Keyboard Macros:

Each program implements these differently, yet the results are the same: You record a series of key presses that perform some task, then save it for reuse. Some macro recorders will let you mix hard-coded commands (draw rectangle) with prompts for the user for width and height, while others may require / allow a fixed dimension to be set. Say you want a macro to draw a pipe batten – you could issue a rectangle command, followed by a prompt of the length, then automatically force the height to be 1.9” (for 1½” i.d. schedule 40 pipe anyway).

Scripts:

These are similar to Keyboard Macros except they are written-out in a text file that the computer program reads as if it was input from the keyboard. They are convenient in that you can edit them to meet your needs. You could write a script to draw a pipe batten, like above, save it as Pipe Batten 1.50 inch Sched 40, then open the file and modify it for drawing 1¼” Schedule 80 hand railing pipes and save it as Hand Railing 1.25” Sched 80.

Programming:

This can take many different forms depending upon the type of CAD program you are working with and the skill level you have as a programmer. Common programming languages like C, Basic, Lisp, and Diesel, can be written with specific ‘hooks’ into CAD software to facilitate elaborate operations and decision trees to define virtually every aspect of a drawing. The programming allows you to make selections of blocks to insert, how they might be scaled and/or rotated, and calculate the mathematical relationships for various elements. One example of this might be to define a Motor Control Center cabinet: The user could be prompted for the number of motors, the lift capacity of the hoists, and a few other items and the program could select the correct size and type of power contactors, safety relays, power supply, etc., which in-turn would define the standard cabinet size from a list of available devices.

Parametric Constraints:

This type of design automation can be useful in reducing the inventory of blocks you keep in a library. Rather than having separate drawing files for ½”, 1”, and 2” diameter bolts of 2”, 4”, and 6” length, it stores one generic bolt and prompts the user for the diameter and length and then inserts the part rendered to the size needed. This simple example may not seem much different than using a macro or script, however, more complex structures can be defined. Look at the complex relationships of an audience sightline development:

The elevation of each row of seats is dependent upon the elevation of the row of seats in front of it, the spacing between the rows, the elevation of the stage, the elevation of the ‘must see’ visual target, and the distance from the audience’s eyes to the visual target all affect the elevation of each row of seats.

This could be calculated with a spreadsheet and transferred to a script, or written as a Programming Application, or, you could define the constraints between all the control points in a parametric model:

• We can force Stage Height to be a vertical dimension.
• We can force Seated Eye Height to be a vertical dimension.
• We can force Target Height to be a vertical dimension.
• We can force Target Distance to be a horizontal dimension.
• We can force 1^st Row Distance to be a horizontal dimension.
• We can force Row-to-Row Distance to be a horizontal dimension.
• We can force the sightline to the target from the n+1 row to pass tangent to the top of the head of the person in the n^th row
• And we can link the common points together so that one entity can’t move without dragging its adjacent linked parts along with it.

The result is a drawing that completely reconfigures itself each time any of the defining parameters is changed. It takes a little time to initially build the list of constraints, but after the relationships are defined, you only need to edit the parameters of interest to see the program redraw the entire assembly.

What are your mind-numbing repetitive CAD tasks? How have you made them more convenient?