Sketches, Simple is Better…

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Modeling in 3d is a quick and easy way to complete a design, however, many new users will have a tendency to over complicate sketches. Either the initial or any additional sketches as shown in the figure below…

We will review two different modeling processes and end up with two very different looking browser feature trees. Will see a completely different picture of the flexibility differences associated to the related modeling process shown  in this text…

Complicated_sketch

One can see that several dimension and constraints have been placed to control the Engineering behavior of this part sketch, Note, “I said Part Sketch…”. In this case almost the entire part has been defined by this single sketch. Advantage: at first thought it seems to be an easy method to design the part. Disadvantage: every time a change is made to the part-sketch all the dimensions must be re-evaluated by the sketching system. Sketches such as the one above will become difficult to mange because of the number of dimensions that can be affected. Imagine if you had 50 or more dimensions, the part change performance could and will be affected.

Revolving the sketch above creates this part…

part_1

Looking at another approach; start with a simple sketch defining the general shape of the part, for example, just the rough outside shape as shown here…

Simple_Sketch

With the simple sketch, one can easily identify any dimension requiring a change and only a few additional dimensions need to be evaluated by the sketching system each time a sketch change is made. Users can take advantage of simple sketching and utilize placed features such as, radius, chamfer and hole tools  to refine the part design later in the design process.

The resulting revolved part is from the sketch above…

part_2

Features can be added to the part shown above to complete the design as a series of simple sketches making part modification easier to track and manage. Let’s add some additional features to this part to achieve the design we need.

How about the grooves on the right end…

Let’s define the sketch plane as the XY plane…

part_2_A

Sketch the grooves…

part_2_B

Revolve the grooves as a cut to finish…

part_2_C

We can continue this process using independent Simple Sketches to complete the design. TIP! – with Simple Sketches defining the part it becomes easier to modify, remove  or temporally suppress a feature due to the availability of features in the browser…

Finishing the part using the Simple Sketch method will complete the design as shown below…

Another Groove…

part_2_D

Then finish up of the outside shape…

part_2_E

Working on the interior configuration can be approached by two different methods.

One – The revolve process: Advantage: ability to control depth and diameter. from a single simple sketch. Disadvantage: sketching must be done with slice graphics on, and a line representing the center line of the part must be projected or created then constrained during sketch creation, not difficult but needed…

and

Two –  The stacked or wedding cake process: Advantage: single circle will define base hole diameter while the extrusion will provide the hole depth control. Disadvantage: chamfers and rounds will need to be added as placed or sketched features. Sometimes this hinders the design process…

Both processes fit the Simple sketch concept…

The Revolve method sketch…

part_2_F

part_2_G

and the wedding cake (stacked) method…

the first hole diameter…

part_2_H

adding the drill point or chamfer feature…

part_2_I

Finishing part result…

part_2_J

Either way, the part ends up looking the same. The Simple Sketch method will have additional features present in the browser tree and those features  can be suppress or deleted without editing the sketch. The Complex Sketch method requires the sketch to be edited and changed each time to suppress, modify or remove an element (part feature shape) of the part. A complex sketch containing the shape definitions and defining dimensions can be difficult to modify. Incorrect editing can result in sketched geometry and/or dimensions that prevent proper part re-generation after modifications, resulting in a time consuming trouble shooting process to repair the sketch…

Complex sketched part:

complex     Complex_tree

Simple sketched part:

simple simple_tree

Note that the browser for the Simple Sketch method has more exposed features in the tree and thus provides greater flexibility in part modification. Whereas the browser tree for the Complex Sketch method looks far simpler, it does not provide as much flexibility in the event one needs to roll back the end of part or modify a feature on the part, it’s simply not in the browser to work with…!

Happy Part Modeling…

Mike

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