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Spaghetti CAD

Updated: Jul 6, 2021

I love Spaghetti…but I hate Spaghetti CAD

Last week, I listened to an interesting podcast from Jeff Gable called the Agile Embedded Podcast.

Jeff discussed embedded medical device firmware development, and how he uses a Test Driven Development (TDD) process.

It was interesting to hear about his testing philosophy in Agile development.

Inexperienced engineers can unintentionally create testing problems by creating unstable code.

In software they call this ‘spaghetti-code’ that loops back and forth.

It’s very difficult to debug.

This spaghetti-code causes issues with functional testing because of the unexpected dependencies.

Changing one part of the code changes other code input, which can cause unexpected results.

Senior-level engineers often start with the end in mind. They can recognize errors before they happen.

They know that code will need testing to be validated for use in medical devices.

We see the same issues in mechanical device development.

Inexperienced designers will create CAD models with undefined dimensional schemes, circular references, and model recursion.

I think of it as spaghetti-CAD.

They add sketches at the part level, and then modify the part at the assembly level.

Parts with assembly references also have Master Model references.

Mates in the assembly override the mates at the subassembly.

Challenging models to debug, and nearly impossible to test.

There’s nothing wrong with Spaghetti-CAD in prototyping development.

I agree with Jeff, it’s the best way to test and learn quickly.

I am guilty of slapping a few crude cut/extrude/moveface commands to the end of a Feature Tree just to get some parts on the printer for a nightly run. But I also know that those features need to be fixed.

Shipping a clean production CAD model should be the end goal.

Before you ship production CAD to your manufacturing vendor, start a clean CAD model without the accumulated cruft of 6-months of development.

Let’s go! Make it a great week!

Solidworks Quick Tips:

  1. Feature/Body Patterns are more stable (and faster rebuild times) than Sketch Patterns link

  2. Master Models are a good way to ensure A-side surface continuity; see linkedin discussion here

  3. S-key is your friend. Use “S” to bring up quick-access toolbar (pro tip: It also brings up the search bar, so hit “S” and start typing)


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