Basic Modeling: Carrier Handle
As an example model, I pick one of the carrier handles used to carry multipack containers home from your supermarket. This particular model comes from PakTech in Oregon (P/N TP-135-325). It's made out of HDPE. The intention here is not to reverse engineer an exact copy, but to illustrate a particular approach. I've left out a lot of the difficult parts, such as draft, cosmetic fillets, extruded text that exists on the actual part.
Here are three views of the final part. How would you approach the model?
Overall we can follow these general steps:
A. Preplanning Hierachy
We can model this as a single part, so do not need to worry about a hierachy of assemblies and subassemblies. We also won't use multibody parts or surface parts to construct this, so there is just a single file name.
B. Origin and Orientation
The parts natural orientation is that it's largest mass lies flat in the X-Z plane (i.e. the hole axis is along Y). It is a symmetric part, both about Z and X. The gate for the injection molding is in the center of the part, it would be a good origin. Along Y the actual part has its parting line in the middle of the height. A good place for the origin is the center of the part.
C. Reference Planes and Auxiliary Geometry
This geometry is simple enough that we do not need to construct reference planes to help with the modelling.
D. Modelling Planning
Because the part is symmetric, we'll build the right side only. There's also a front to back symmetry, but there is little benefit to construct only a quarter of the part.
I will focus on the main "snapping" feature that attaches to the bottle to be carried and then will build the rest of the geometry around it. In this particular case, I am modeling this to avoid having to use multibody construction.
I start with an initial ring extrusion to position the part accurated, then do a revolve cut to cut the profile. We add reinforcement ribs, then cut the individual tabs, add additional ribs, build the center section, and the pry tab, and eventually mirror the whole body.
E. Modelling Steps
1. Extrude the base ring
2. Cut away material to create the snapping profile
3. Use a rib feature to add the reinforcement structure underneath. Notice how few dimensions are needed (and how inaccurately the rib lines are placed) for this to work.
4. Add the outside ring. Add material to bridge the two. Note that the outside bridge is too tall.
5. Use a ring to cut the bridge to its proper depth (up to surface).
6.. Cut the major tabs to create the basic shape. Note that the right tab is not the same as the upper and lower, so you cannot use a pattern here.
7. Build the first feature to create the individual tabs.
8. Circular pattern that feature at a 30 degree spacing. Make sure you skip the three instances that you don't need. Don't just leave them in.
9. Add the support ribs that connect the inner to the outer ring. Note that we don't need any dimensions for this feature.
10. Add the center handle section. Notice that with the tangency constraints (there are four tangency constraints) you only need a single dimension. Notice that there are two horizontal construction lines that the curves are made tangent to.
11. Use an offset to create the profile to cut. Notice that I had to use separate offsets for the top and bottom arc. A single offset for both would not have worked.
12. Mirror the cut to the underside of the part.
13. Add the pry tab as an extrusion. The top face of the tab is aligned to the partling plane (the "top" plane). Notice that I am including the fillet in the sketch.
14. Grab the outside edge and to a thin extrude to the top of the part. Steps 13. and 14. could have been done as an extrude to the top and then a cut in, but I preferred to locate the initial sketch at the parting line.
15. Add some basic cosmetic features (like full radius fillets), but don't go overboard.
16. The final step is to mirror the entire body. You end up with the part shown above.
F. Communication
It is good practice to rename your features to help you understand - later on - how this was constructed and how it could be modified. Here is my resulting feature manager.
I assigned the material HDPE to the part. The final calculated weight is 10.1 g. The measured weight is 10 g.
Basic Build Time: 2 hrs