Optimizing the Shape of Milled Parts to Avoid Design Flaws

Sometimes, when working on a concept project, we can create our shape driven by its intended use or interactions with other mechanical components.

A usage-driven approach is perfect for achieving the most optimized geometry that will work the best. However, we may miss a few important details needed from a manufacturing point of view. These “minor details”, however, may be the key difference between a cheap component and a much more expensive one or even an impossible part to machine.

In this chapter, we will explain the most typical issues with milled parts, showing you a wide set of tricky geometries to be milled and the approach to achieving them successfully. This should give you the tools for a more aware and better approach to part design.

In this chapter, we will cover the following topics:

• Handling undercuts and accessibility
• Learning how to manage mill radius
• Solving a very bad...

Technical requirements

The main technical requirement for this chapter is having a basic knowledge of part design using any CAD software. Making sure you have read Chapter 6 is a great starting point since we will now dive deeper into milling, but this time from a design perspective. We will also discover a couple of commands from Fusion 360 that can help us during the design process; therefore, having access to the program is also recommended.

Handling undercuts and accessibility

There is a typical issue with milled parts that can be found in models designed without a clear understanding of manufacturing limitations: geometry undercuts.

What is this issue all about? The important thing to understand is that our machine can reach any point located inside its working boundaries, but the geometry we are trying to machine may restrict accessibility and impede tool movement. Areas not accessible to our tool are called undercuts.

The following diagram is an example of a badly designed part featuring an undercut:

Figure 7.1: Undercut

As you can see from the diagram, the highlighted area is inaccessible to our tool; therefore, it cannot be machined.

Before starting any milling setup, we should always analyze in detail part geometry and check for undercuts. If the shape to be machined is quite complex, there is a useful tool inside Fusion 360 that can spot undercuts. This command is called Accessibility...

Learning how to manage mill radius

Having worked with milled parts for years, I can assure you that another common issue you will encounter is the wrong management of the mill radius.

To overcome this, you need to understand the following concept: milling processes cannot perform squared slots, and the mill radius will always be imprinted on the part.

In the following diagram, we can better understand the problem:

Figure 7.14: Mill radius

As you can see from the diagram, there is no way for our flute to leave a rectangular-shaped slot. If the mill cutter has a 20 mm diameter, we will always leave a 10 mm radius on corners. But what if we really need a squared slot? There are a few techniques that can help overcome this intrinsic behavior of milling machines:

• Reducing the mill radius
• Tweaking our part geometry
• Changing the milling direction

Let’s look at these three options in more detail.

Reducing the mill radius

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Solving a very bad design

Now that we mentioned a few of the typical problems we may find with parts, we can review an example part to be machined from a squared stock. Let’s suppose that we are CAM operators and that a group of designers give us this part to realize:

Figure 7.21: Example part to machine

This part is most likely an April fool’s joke against us; there are a number of very big mistakes that not even a beginner can be excused for! But let’s imagine this is the real deal and that we have to somehow machine it with our milling machine.

Let’s review the mistakes one by one and try to find possible solutions with the design team.

Undercut face

There is a well-pronounced sloped face that cannot be machined at the moment. As we are about to discover, there are only three options available to us to achieve a similar shape, but all of them require minor changes to the design.

There is no correct one; picking...

Summary

That was the end of the chapter, let’s recap what we learned together. We introduced the basic concept of undercuts inside the geometry of the part and how undercuts are strictly related to tool orientation. Then we analyzed a couple of examples centered on how to machine undercuts if their presence is required by the part’s intended use.

After this introduction to accessibility issues, we learned what leftover radii are and how to get rid of them if they compromise our part coupling with other components. Then we introduced the concept of multiple machining placements, and we found how they can change radii patterns and undercuts machining.

And finally, we tried to apply all the described techniques to a very tricky part to be machined.

This introduction to typical errors found on milled parts is essential for approaching the design of a part to be realized by milling operations.

In the following chapter, we will move on from the theory discussed...