SolidWorks 2011 Parts Bible - Matt Lombard [312]
• Using trimmed and thickened (again, boss or cut) surfaces can be effective but may also be more difficult.
• One of my favorite methods, especially for non-planar parting lines, is to combine a thin feature with an extrude up to an offset surface body.
• Using a sweep to cut or add material can be effective on either planar or non-planar parting lines.
Each of these is really a workaround technique and not a specific plastic modeling tool. I will not go into depth on these techniques here. On the DVD, you will find example parts that demonstrate each technique.
Using the Rib feature
The Rib feature is a flexible tool for creating ribs in a number of different situations. Ribs can be drawn in one of two different orientations, which the SolidWorks interface calls Parallel To Sketch and Normal To Sketch. The names appear only on tool tips when hovering over the icons. To be more precise, what they really mean is that the rib will be created either parallel or normal to the sketch plane. If the sketch is a single line, it can be very difficult to tell the difference between parallel and normal.
To me these names are not very descriptive. I call the two orientations plan view (view from the top, looking in the direction of draw, normal to the sketch plane) and skyline (looking from the side, perpendicular to the direction of draw, rib is parallel to the sketch plane). To me, these names are more intuitively descriptive, and better reflect the function of the rib.
Ribs can incorporate draft, extend, or trim the feature beyond the sketch automatically and break normal sketch rules (plan view ribs only).
Figure 24.6 shows a plan view rib that violates normal sketch rules. Also shown is the Rib PropertyManager. Several models on the DVD show examples of various rib techniques.
The Rib feature workflow should be self-explanatory:
1. Draw the sketch, either the plan view or skyline. The sketch represents the top of the Rib. Material can only be added between the sketch and the rest of the part. Remember that the sketch plane direction makes a difference.
2. Initiate the feature, and set the type of rib and the direction. Use the Flip Material Side toggle to change the direction of the gray arrow, which should point from the top of the rib toward the part.
3. Set the thickness and draft amount and direction.
Using draft in the Rib feature
When you create ribs, you almost always apply draft to them. You can apply draft as a separate feature, or you can apply draft as a part of the Rib feature. It is often easier to just do it as part of the Rib feature, but some people like to make all their drafts as separate Draft features to keep the part faces orthogonal for as long as possible, or they just like to organize all the Draft features into a folder at the end of the FeatureManager so that there is never any question about which feature controls the draft.
FIGURE 24.6
The Rib PropertyManager and a Rib feature
By default, when you apply draft as a part of the Rib feature, the draft is applied from the sketch end of the rib. This can cause rib thickness problems if you have created a skyline rib where the rib may have various heights. In this case, the top of the rib will vary in thickness, and it may cause the base of the rib to be too thick. When you work this way, sometimes you have to experiment with the proper thickness at the top of the rib in order to get a thickness at the bottom of the rib that will not cause sink marks on the outside face of the part. A solution to this is to use the At Wall Interface option, which only appears once you enable draft in the PropertyManager. Then you can specify the thickness and draft so that the base of the rib maintains a specified thickness.
Best Practice
When modeling plastic parts, it is best practice to model the part at maximum material, and use draft to remove material.
Understand the Rib feature and multi-bodies
The Rib feature is sensitive to changes in the number of solid bodies in the part. For