AutoCAD 2010- (The times, they are a-changin' — and when it comes to new 2D parametric drawing, change can be very, very good.)

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AutoCAD 2010- (The times, they are a-changin' — and when it comes to new 2D parametric drawing, change can be very, very good.)

Post by Tracy on Mon Jun 08, 2009 12:28 pm

Your boss comes out of a meeting with an important new client. As the two pass your desk, your boss hands you a marked-up printout showing seven changes to the client’s design that must be implemented before they get back from lunch.


The boss wants a few changes to a client’s design.
Before the two can finish putting on their coats, the printer spits out a revised drawing.

Your boss looks at the printout and says, "How would you like to join us for lunch?" -- making a mental note that you had even picked up on the revisions to the R2.000 and 4.500 dimensions that were necessary to match the revised diameter.


Roughly 10 seconds later, you are finished with the changes.
Are you a magician or a time traveler? No, but you are smart enough to have updated to AutoCAD 2010. AutoCAD now includes 2D parametric drawing functionality so anatomically correct changes are made to the drawing pretty much as quickly as you can enter new dimension values.

In case you are unfamiliar with the terminology, let's start with a couple of explanations.

Parametrics involves two basic functionalities: geometric and dimensional constraints.

Geometric constraints. Geometric constraints effectively are sticky object snaps. Assume that you are drawing a line in standard AutoCAD, then object snap it to be tangent to an existing circle. The line only knows about the circle for the brief instant that it takes for AutoCAD to calculate the tangency point, and the circle never knows the line exists. On the other hand, if we apply a geometric constraint to the two objects, they both remember that the other object exists and that they must always remain tangential to each other. If you move the circle, the line will also move to remain tangent.

The twelve available geometric constraints include fun ones such as collinear, parallel, symmetrical, and equal. The equal constraint can be applied to line lengths or to circle or arc radii. Horizontal and vertical constraints can apply to points as well as lines, so the center of a circle will always be located vertically (same y coordinate) as the center of an arc or the end of a line.

Dimensional constraints. Dimensional constraints are the opposite of AutoCAD's associative dimensions. In regular AutoCAD, if you change the length of a line, the dimension will update to reflect the new size. On the other hand, if you change the value of a parametric dimension, the line will change length. Meanwhile, all the geometric constraints remain active so that changing a single width dimension will update all drawing views that appear or are related to the revised object. The changes reflected in the first two figures above took less that 10 seconds to complete, and most of that time was spent typing in the new values.

Believe it or not, there’s more, and it’s even better. A dimension isn't limited to containing a specific value but can contain a formula that links it to one or more parameters. The formulas can include a full range of mathematical operators such as logarithms, exponents, and trigonometric functions, so drawings can include intelligence and design intent. A single drawing can represent a full range of model variations. Simply enter a model number, and things such as wall thickness, shaft, and bearing diameters will update. My favorite mathematical operator for design work is the random number generator.

The first drawing above was created without using a single temporary construction line, turning line, or object-tracking snap point. I simply sketched the basic shapes quickly, then used collinear and equal length constraints to align and link the objects between views. The left edge of the front view always is collinear with the left edge of the top view, and the depth of the top view is always equal to the width of the side view, and so on. To further simplify things, you can elect to just select a set of objects and AutoCAD 2010 will automatically apply the most logical constraints.

Similarly, I didn't use any form of precise or direct distance entry while creating the objects. I just applied dimensional constraints, then added my precise values later.

I have observed that most design projects start out as a quick sketch on a coffee shop napkin -- which I call napkin-aided design (NAD). The new parametric functionality now lets us recreate this directly in AutoCAD. Simply do a quick sketch first, constrain and dimension it, then play with the dimension values. That first drawing took about 15 minutes to create.

In the design process, the most constant thing is change. Show me a designer who claims that nothing changed from the first sketch through to production, and I'll show you a liar or a fool. With parametrics, we can play what-if scenarios all through the design process.
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Tracy

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Job/hobbies : AutoCad Technician / Lecturer
Registration date : 2008-03-29

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