CAD is slow
CAD is used to develop an idea once hand sketching stops being useful. (Don’t shortchange the sketching phase. CAD is slow and once you start modeling you often reduce the number of options you are considering. Doing that too early may set you on the wrong path.)
CAD is a means to an end
The CAD tool you choose is often interchangeable since the final output is something like a PDF (machining drawing or laser cutter) or an STL file (3D printer).
CAD is Hierarchical
There are many hierarchical relationships you will encounter in CAD. You often need to create reference geometry before you create functional geometry. A few of the key hierarchies include:
Make a Plane or Surface and then use it to draw a Sketch
Use your Sketch to create a Feature (like a cut or an extrusion)
Create Parts and then put them together into an Assembly
Create and accurately dimension Parts or Assembly and then add them to a Drawing
CAD can capture Design Intent
A good CAD model and drawing will properly convey design intent, “the intelligence built into the solid model to control the behavior of the part when subjected to changes or alteration” (such as changing a dimension). Here’s one example for how you create and dimension a hole in a block. The hole can be a certain distance from a corner or edge, or it can be in the middle of the face, for example. If the size of the block or the hole changes, the part rebuilds correctly if the design intent has been considered in the definition.
Parametric modelers (like SolidWorks and Onshape) capture the intent of a design, including relations, parameters, and model behavior. You can draw lines approximately, and later dimension them exactly. You can also change the sketch and feature dimensions at any time and rebuild the part.
In this example, one hole is fixed, one is driven by an equation, and the other two are mirrored. As the size of the hinge changes, the holes remain properly spaced along the length and width.
How will it be made?
As you design a part and assembly, you can consider how it will be made and create relationships and dimensioning schemes that communicate the manufacturing approach.
- Orient your part the way it makes sense in the world
- Use the origin and the starting planes
This sewing machine sits on a table. Consider using the table surface as the Top plane. You typically approach the long side of the sewing machine, so the Front would go through the long dimension of the sewing machine
Start from the ground up
- Build a strong foundation of reference geometry (Planes, surfaces, curves, axes and sketches)
- Avoid referencing edges and features that will change frequently when dimensioning or adding relations. Use those initial planes, surfaces, curves and sketches to drive the rest of the design.
Use symmetry and patterning whenever you can
Revolve instead of extrude round things
- Know when to start your model over. When you iterate over and over, your model tree gets full of junk. Now that your design is solidified, you should be able to quickly model it from scratch.
- If you are designing an injection molded part, you will need drafts and rounds (fillets) to help with the molding process. Add these features at the end of your model tree to simplify the modeling.
The best way to learn CAD is by using it for your own project. At our workshops we use the Design Hub Bambu 3D printer to make keychains / backpack hangers you design. Come to a workshop or just design your own.
- Your design should have at least two parts so you can think about the relationship between two bodies, figure out how to provide the proper clearance and once you build it, see what is working and what isn’t so you can iterate.
- Uses this steel cable key ring (provided). The cable is 2 mm in cross-section diameter.
- Here are a couple examples (fidget and a detachable spork)
- Once you have your design, download Bambu Studio here. Setup your plate, slice it, and export the plate to a *.gcode.3mf file.
- Put that file on a mini SD card, insert it into the Bambu, go to files, select your file and hit print.