It’s how you make it real. It’s how you know it might stick. It’s that time when you step up and decide, as a team, to switch to CAD.

Switching to a Computer Aided Design (CAD) method is a big step in moving forward from a brainstormed idea into an engineered concept. It makes a concept truly come to life and feel real for the first time. But sometimes designers can get overeager and invest in a computer model too early, only to have to scrap it down the road.

Here are some Pros and Cons that will help you determine when the timing is right.

The Good

CAD modelling a design has a number of positive benefits, such as revealing ‘real life’ issues like assembly, wiring, and volume or fit issues that can appear when a 2D drawing becomes a three-dimensional object. It might also require the designer to actually start specifying hardware, for better or for worse.

This can result in findings if it turns out that no one actually makes the off-the-shelf part you need for a reasonable price. The earlier these are caught the better for the project, which is a big check mark in the “switch to CAD sooner” column.

The other modern use for modelling a prototype is printing it. Now that 3D printers and virtual reality tools are becoming more and more available, the step from a model to an  object is just a few clicks away.

Tied in with all the great reasons listed above are the benefits of an early proof of concept model. Multiple CAD concepts that the engineer will know are possible to make and fit together can be presented neatly to decision makers in an understandable fashion. The concepts can then easily be tweaked and adjusted as needed, without starting all over again.

This is where things start to get dangerous, which leads us to the cons.

The Bad

The more tweaks and changes done to an early model, the more likely the team is going to want to keep it. “We did invest all that time, didn’t we?”… This can be a bad idea if it was originally built for a different reason. The ‘just one more modification’ attitude can result in a patchwork CAD model that is more trouble than it’s worth.  It may even need to be redone from the scratch, requiring a comparatively large time investment that isn’t always possible mid-project.

The later on in the project that the CAD model is done, the less of a risk this is.  

So, How Do I Decide?

Typically, the decision to switch to CAD should follow from a decision to commit a certain amount of engineering time to a particular design.

Another factor is the importance of size. It is easy to get lost in a model’s true size. The problem (or perhaps the beauty) of CAD software, is that the object is always the size of your computer monitor. Where size is important, an earlier switch is better.

It can be quite a shock to get a part in your hand and finally understand the true size was quite a bit different than you had envisioned.  

Alternatives and Intermediate Steps:

A lot of these concerns can be mediated by using intermediary steps between mental ideas and detailed CAD:

• A simple 1:1 scale paper print off can tell you how large an object will truly be for 60 seconds of effort, or a general paper calculation will tell you if a component is likely to fail prior to fabricating it.
• A cardboard shaping model, or taping out a rectangle on a desk to show the silhouette, can be a useful tool for non-handheld objects.
• It can also be easy to mock up a simple shape on a mill or lathe for flat or round objects.
• CAD can also be used to block out shapes without hardware. The key is to resist adding more and more detail and to remember that block CAD should probably be scrapped once a concept is chosen. These block models can then be 3D printed.
• AI can also be used to add detail to sketches to kind of leap frog a lot of a the intermediary work but use caution: just because an AI can shape it doesn’t mean anyone can build it.

The risk of throwing good money after bad can be minimized by keeping a designated amount of time aside to rebuild the model from scratch when it’s time to move to the final prototype.

So What Should You Do?

In reality, there is no golden rule to know when to switch to CAD from concept sketches: the pros must be weighed with the cons on a case-by-case basis. Ask yourself how likely the current revision is to stick around, whether or not resources are available to re-do it, consider intermediary steps, and then plan from there. Just be sure to do some planning before taking the big leap!