SolidWorks 2011 Parts Bible - Matt Lombard [117]
FIGURE 7.33
The Keep Feature option, both selected and unselected
Creating variable radius fillets
Variable radius fillets are another powerful weapon in the fight against boring designs; they also double as a useful tool to solve certain problems that arise. Although it is difficult to define exactly when to use the variable radius fillet, you can use it when you need a fillet to round an edge, and it has to change in size to fit the available geometry.
Best Practice
It may be easier to identify when not to use a variable radius fillet. Fillets are generally used to round or break edges, not to sculpt a part. If you are using fillets to sculpt blocky parts and are not actively trying to make blocky parts with big fillets, you may want to consider another approach and use complex modeling, which gives the part a better shape and makes it more controllable. Other options exist that give you a different type of control, such as the double hold line fillet.
In some ways, variable radius fillets function like other fillets. For example, they offer propagation to tangent edges and preview options.
Applying the values
When you first select an edge for the variable radius fillet, the endpoints are identified by callout flags with the value unassigned. A preview does not display until at least one of the points has a radius value in the box. You can also apply radius values in the PropertyManager, but they are easier to keep track of using the callouts. Figure 7.34 shows a variable radius fillet after the edge selection, after one value has been applied, and after three values have been applied. To apply a radius value that is not at the endpoint of an edge, you can select one of the three colored dots along the selected edge. The preview should show you how the fillet will look in wireframe display.
FIGURE 7.34
Assigning values to a variable radius fillet
By default, the variable radius fillet puts five points on an edge, one at each endpoint, one at the midpoint, and one each halfway between the ends and middle. If you want to create an additional control point, there are three ways to do it:
• Ctrl+drag an existing point.
• Select the callout of an existing point and change the P (percentage) value.
• Change the Number of Instances value in the Variable Radius Parameters panel of the PropertyManager.
If you have selected several edges, and several unassigned values are on the screen, then you can use the Set Unassigned option in the PropertyManager to set them all to the same value. The Set All option sets all radius values to the same number, including any values that you may have changed to be different than the rest. Figure 7.35 shows the Variable Radius Parameters panel.
FIGURE 7.35
The Variable Radius Parameters panel of the Fillet PropertyManager
Another available option with the variable radius fillet is that you can set a value of zero at an end of the fillet. You need to be careful about using a zero radius, because it is likely to cause downstream problems with other fillets, shells, offsets, and even machining operations. You cannot assign a zero radius in the middle of an edge, only at the end. If you need to end a fillet at a particular location, you can use a split line to split the edge and apply a zero radius at that point. (Chapter 8 covers split lines.) Figure 7.36 shows a part with two zero-radius values.
The image on the right shows Instant3D being used to edit a variable radius fillet. Select the face of the fillet with Instant3D turned on, and blue dots appear where ever radius values are assigned. You can move these dots to dynamically edit the corresponding value of the variable radius.
FIGURE 7.36
Zero-radius values in the variable radius fillet
Using straight versus smooth transitions
Variable radius fillets have an