Space: the final frontier!
…at least that is how I am beginning to feel as design software and its features evolve. In this post, I want to talk about the basics – specifically the basics of component design.
The age-old question will arise at times: do I begin the design at 0,0,0 or do I design the component in its assembly position? Does it matter? Well, yes and no. With most CAD software packages, you have the ability to constrain or mate the feature to the component it is mating to. So technically, almost every component can be designed at 0,0,0 and then just assembled when you are done, as long as you have a mating condition to work with. This method is typically referred to as Bottom Up design. You see this most often in design of off-the-shelf items you would basically plug and play as needed, e.g. Fasteners, Tubing, Brackets, etc.
The alternative to this type of design is when you have a group of components that don’t necessarily mate together but need to come into the correct assembly position every time they are inserted. This method is typically referred to as Top Down design. In the Automotive realm of design, all of the body panels are designed using a top down method. Generally you will hear the term “designed in body position,” which indicates it is a top down design.
The key to working on a top down design is that every component is designed using a common axis system, aka common 0,0,0 location. The major systems in a vehicle that are used in other vehicles as well will be developed using a common axis system that won’t be the vehicle axis system. For example, an engine would maybe have an axis system built at the rear face of the block and the centerline of the crank.
Then you could design every single piece that is specific to that engine using the engine common axis system. Once the engine assembly is complete, you drop that assembly into the vehicle(s) at the determined coordinate for the centerline of crank and rear face of block and you are good to go! Things that attach to the engine and the body are typically designed using the vehicle axis system since they are most likely not going to be used in multiple vehicles as each one is unique to a specific vehicle.
Obviously this can get very tricky working with multiple axis systems when it comes to measurement of point coordinates. Luckily, in CATIA V5 it’s pretty easy. In a case when you may have multiple axis systems in a given model, the measurement tools have an option – Other Axis – that you can use and simply select the axis system from the tree you want to measure from.
It’s important to note that if nothing is selected here, the default measurement is from the model 0,0,0 which may not always be what you are looking for; it would be nice to instead automatically default to whatever the current active axis system in the tree is, but at present that is not how the system works.
At Tata Technologies we have helped many companies with their CATIA V5 needs. Bottom line, axis systems can come in handy for all types of designs and can be constrained together as needed to ensure your design intent is being captured, whether it’s a Top Down or Bottom Up approach. I hope this tip has been useful for you, but feel free to add your own thoughts or ask questions in the comments.
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