Common Details missed in a Model - Part 1, The Model

So you designed a part, and you are proud of it, only to be told it sucks and can’t be made. Design engineers know this feeling all too well. After learning the “proper” way to design machined components, even the most experienced design engineers find themselves choking back their tears when a machinist points out things they’ve missed.

Here are some of the most common things missed in the model

• Design engineer didn’t understand the thread callout they assigned

This is a major blunder and rookie mistake. Threads can be very frustrating when a designer doesn’t really know how they are made. They know they want some kind of threaded hole, but don’t really understand the geometry that makes threads work. As a result, they design surrounding geometry without considering these details.

Tip1: understand the thread geometry, terms and how they are represented in the model.

Tip2: It’s all about thread clearances. Make sure your features provide enough clearance for the thread tool

• Thin walls and part deflection

Even the experienced design engineer can struggle with this one. At times, it is tempting to design geometry very thin to fit everything you need into a desired space. It can be difficult to know when a wall section is too thin. Many machinists can create very thin walls with advanced techniques, but the designer needs to understand if requiring the machinist to do this is worth the pay off.

When wall sections get too thin, part deflection is another important consideration. The part may wander further from its origin more than expected.

Tip: You don’t need to be an expert in FEA to understand your part’s deflection when making chips. Consult with the machinist for the wall sections they are comfortable with and tooling options available to them.

• Radii

Many design engineers almost never consider radii (rads). “It’s a round corner, who cares, right?” The machinists care a lot. Machinists need to select the right tool to do the job. Ideally, every parts would be cut with a ½” end mill and spit parts out every 23 seconds. This would produce ¼” rads in every corner. If a design engineer models with random rad sizes, then the machinists had to change out tools very often, driving cycle time and cost up and frustrating the machinist.

Tip: Take the time to consider each corn in your model. Assign the largest rad you can allow and make it common to as many corners in your design as possible.

• Undercuts

Every design engineer uses them, machinist hate them. Machinists can do a lot of amazing things. Many have figured out techniques for getting at some deep and complex undercuts. Regardless, they are a cost driver and a source of frustration.

Tip 1: If an undercut is needed in a single part, give plenty of tool clearance. Consider the smallest depth and width you could live with.

Tip 2: If an undercut is too large, consider splitting the part into multiple parts that are assembled.

• Bunus! Consider designing work holding features into your part when needed. Check this guy’s video out. He has lots of great advise!

https://www.youtube.com/watch?v=TbWFRvMV3gw