Have you ever run across a part file that, for some odd reason the model isn’t fitting up as it was designed? More often than not, it’s a simple fix of a parameter that may have been missed in the revision process. Or as we’ll discuss here, a sketch isn’t fully constrained.
In a nutshell, the easiest way to build a stable part is to build off a solid foundation. Nothing, NOTHING in Inventor is more stable than a file’s origin point, axis or planes.
Figure 1 - Part Origin Entities
No matter how hard you try, you can’t delete or modify these items. User-created points, axis, or planes can not only be deleted, but depending on how they were created and what they are tied to, these items can “shift” ever so slightly while you are modifying other features.
Rule number 1 is to fully constrain your sketch. All too often I see users sketching out in space:
Figure 2 - Unconstrained Sketch
Notice the color of the entities. As a visual aide a lot of users tend to overlook, depending on the color scheme you have active, Constrained and Unconstrained entities will show in different colors to assist the user in quickly identifying what is or what isn’t constrained. Note the few examples below of the very same sketch, but with different color schemes. Choose the scheme that works best for you.
Now, don’t get me wrong, you’re more than welcome to continue doing this, I’m just attempting to help you avoid extra work and errors.
Always keep in mind the design intent of your component. Knowing how the component is used/assembled, placed, and even how it could change. “Design for change” is a common phrase I’ve seen over the years.
For example: Let’s say you have a cylindrical post to model. Knowing this post is always used in the vertical position, model it as such, with the Y-axis as its spine. Keep in mind the component’s origin point. By default, this point is where the component inserts into an assembly. Following this train of thought will pay off later in the process. In this case, the cylinder comes in vertically, eliminating the extra positional constraint command to make it vertical in the assembly you are placing it into. That makes sense, right? You wouldn’t model a floor in 3D on its edge.
Back to fully constraining your sketches, I have personally witnessed unconstrained sketch lines “shifting” slightly when other sketch lines were being modified. It’s basically common sense when you think about it. The entities are floating there in 3D space, they are not constrained or partially constrained and thus they can move freely until constrained.
In the very same manner when you are working in an assembly, you insert a part or sub-assembly and add constraints or joints to “constrain” the component from moving.
Not constraining your sketch entities and thus allowing them to freely move, you are risking a major setback at some point and depending on when it happens, determines the costs involved. “An Engineering change costs $10, Shop Floor change costs $100, Field change $1000”.
This simply proves best practice is to fully constrain your sketches and tie them to the part origin features when possible. Yes, there are rare occasions where you may need something unconstrained, but that should always be due to design intent.
Please constrain your sketches.
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