Tech Tip: Using Master Modeling Techniques in Onshape

Looking at a blank page is never easy. Everyone knows the first line is the hardest to write. Similarly, getting started on a new design can be just as daunting. You will likely revisit the first sketch to make changes and alterations. 

While the first sketch can create a lot of hardship, focusing on the end goal of the project and its high-level constraints can put a design on the right path. Creating a scalable and flexible sketch allows the design to grow in complexity over time without creating more obstacles. 

Remember, everything starts with a sketch.

Master Modeling Starts with a Plan

Ask some questions about the final design before starting a sketch: 

1. How many subsystems exist?
• Break down the problem into chunks.
2. What is the length, depth, and width of the general shape of the object?
• Create a bounding box.
3. Where are the main points of integration? 
• Consider relations between subsystems.

Source: bigrentz.com

Take this scissor lift as an example: 

1. There are three core systems: 
• Basket
• Scissor Mechanism
• Carriage/Base 
2. The bounding box of each system requires the following:
• The basket needs to fit 1-2 humans, plus some gear
• The scissor lift needs to support the basket and be stable
• The carriage needs to have everything folded into it and have a low center of gravity
3. The three subsystems need to integrate at two points:
• Basket-to-scissor mechanism
• Scissor mechanism to carrier 

Now that you have broken down the problem, you can start tackling each system independently and do the same exercise a level down. Take your time to understand and digest how each one of these subsystems works. The deeper you look, the more complexity is uncovered. Try to stick to the core systems so you are not overwhelmed. 

The Master Modeling Approach

Looking at the blank page again, consider this Master part approach: 

The video below shows how you can implement the Master part approach in the sheet metal design for the lift carriage: 

Using Sketches and Variables when Master Modeling

Using sketches is another excellent technique when master modeling. These can help drive the design parametrically through a derived sketch. There are multiple approaches to integrating sketches in your design workflows, such as using them in an assembly and deriving them into other Part Studios. 

Here is another example workflow, this time leveraging a sketch: 

In the lift example, we created the beams using a master sketch. This is useful down the line. If all parts of the design reference the same constraints, it will be easy to make subtle or drastic changes. 

Next, look at the construction of the sketch, and how it is moved upstream in the design. 

When doing this work, being smart about the variables created is crucial. Constructing extremely robust models is easy when using global variables. But if you are not careful, your variable list can grow fast. 

Mixing variables with some well-written equations can lead to great success. For example, look at this Tech Tip on Numeric Fields. Combining variables with some master modeling approaches results in top-level assemblies that are easily controlled, manipulated, and configured from a top level. 

In the following video, we can see the result of master modeling practice: 

In conclusion, using master modeling techniques is extremely powerful as we create complex systems and capture design intent into our models. 

As you become more familiar with master modeling, you will experience all the benefits of capturing your intent early on in a project as it flows downstream into a progressively more robust model.