Boss features

 
Fasteners are a common joining mechanism in plastic parts. To place and hold fasteners in place, model matched features on both parts. Model a boss for the head of the fastener and a post to receive the threaded portion of the fastener.
With the Boss feature, you can design both components of a fastener placement, called head and thread. You can also design fastening ribs. Ribs are useful when the length of the boss is greater than three times the diameter.

Placement

A Boss feature is placed at a point centered on the mating face of the head and the thread. The Boss is then extended to the next face of the target part body. To design the two mating components in the two opposite bodies, use the same placement elements with opposite directions.

 
You can select the following placement elements:
  • Points From Sketch (From Sketch option). Select placement points from the points defined in the same sketch. The sketch normal provides boss direction. To switch to the opposite direction, drag the boss direction preview arrow.
  • 3D Work points or sketch points (On Point option). Select placement points from different sketches or work points. In this case, the sketch normal is not used. To define the boss direction, select geometric or work elements .

This feature can exist only if it can extend to a face of the target part body that is opposite to the placement point in the boss direction. The feature automatically determines the closest face of the part body to which it can extend. You can also select a different target body and flip the direction.

Use manipulators to set the dimensions of the Boss feature. When precise dimension input is not required, the manipulators are available on the preview to define the geometric parameters interactively.

Preview manipulators

During preview, the cross section of the Boss is shown in a plane normal to the camera axis. Pause the cursor over the cross section to highlight the segments that you can drag. Pause the cursor on key points to displays additional dots that you can drag. Some dots remain hidden to prevent excessive clutter in the preview.

There are two types of manipulators:

  • Dot manipulators define some of the angular and linear parameters of the snap-fit. The following images show examples of how they work.
  • Profile manipulators define the linear parameters of the Boss, as shown in the following examples.

Stiffening ribs

 
When adding stiffening ribs on a From Sketch placement, the first rib alignment angle is measured from the sketch X axis.
For an On Point placement type, you can select a direction for the first rib alignment. Select a linear geometric element that projects onto the plane normal to the Boss direction.
You can select the number of ribs and the angle to fill around the Boss, beginning at the first rib alignment.

For stiffening ribs, use the manipulators to determine the dimensions interactively.

Front view:

Side view:

Boss fillets

The Boss feature includes an option for defining constant radius fillets at three different locations, as shown in the following images:

 
  • At the intersection edges of the entire Boss feature with the part body target.
 
  • At the intersection edges between the stiffening ribs and the boss.
 
  • On the edges of the ribs.

 

Procedures

Build a Boss feature (Head component) on a part using points of a 2D sketch

  1. Create or import a thin-walled part.
  2. Build a 2D sketch with a couple of points corresponding to the Boss placements.
  3. On the ribbon, click 3D Model tab Plastic Part panel Boss .
  4. Verify that the Placement method is From Sketch and the Boss type is Head .
  5. If this sketch is the only one with points, they are automatically selected. Otherwise, select the points for the placement (CTRL + click to cancel the selection). The closest part body in the direction of the sketch normal (both ways) is chosen as the target body. To select a different target, use the body selector on the main tab.
  6. Enter a value in the Offset From Sketch field to start the Boss above or below the sketch plane.
  7. Adjust the Boss head parameters or use the manipulators until the appropriate dimensions are reached.
  8. Add two stiffening ribs. Verify that they are oriented as shown in the image. If necessary, enter a 90-degree angle depending on the sketch X axis orientation. Use the manipulators or the dialog box input fields to adjust the dimensions of the ribs.
  9. Add fillets at the intersection boss-body, at the edges of the ribs, and at the ribs-boss intersection. Click OK to complete the mounting Boss.
     
     

Build a Boss feature (Thread component) on a part using On Point placement

The goal is to create a couple of thread bosses using one point from a sketch and one 3D work point. For example, the part has different boss heights.

  1. Create or import a thin-walled part. Place a Boss feature on the circular edge at a position that is not convenient for the “on sketch” positioning style. For example, choose a point on the edge where the hook direction is not likely to be aligned with a sketch X or Y axis.
  2. Build the construction elements. Create one sketch point and one 3D work feature where the bosses are needed.
  3. On the ribbon, click 3D Model tab Plastic Part panel Boss .
  4. Verify that the Boss type is Thread and that Placement method is On Point.
  5. Select the points defined in step 2 as the Centers. Select a vertical edge like the one in the image as the Direction.
  6. When the direction is defined (it is the same for all the bosses in the same feature), the preview displays.
  7. Verify that the bosses can extend to the target body, for example, their projection is completely within the part body boundary.
  8. Adjust the dimensions as necessary, and assign a fillet for the intersection boss-part body.
  9. Stiffening ribs are not necessary here. Click OK to complete the Boss.

References

Boss

Creates a Boss feature using points of 2D sketches or 3D work points and direction elements.

Access:

Ribbon: 3D Model tab Plastic Part panel Boss
Type specification
 
Head type. It is where the head of the fastener stays.
.
 
Thread type. It is where the thread of the fastener engages.

Click the name of the dialog box tab to display definitions of the options.

Boss - Shape tab

Common to both types. It holds the controls for the Boss placement.

Access:

Ribbon: 3D Model tab Plastic Part panel Boss , and click the Shape tab.
  Placement
    Body selector, to select the target body.

From Sketch placement requires 2D points on the same sketch.

     
Centers selector, to select the points.
     
Flip, flips the direction. The direction is automatically set as the one to the closest distance with the part bodies along the sketch plane normal axis. You can also flip the direction by dragging the direction preview arrow.
      Offset From Sketch enter a value to start the boss above the sketch plane. Use a negative value to start below the sketch.
    On Point placement requires 3D work points or sketch points and one direction.
     
Centers selector, to select the points.

Direction selector defines the boss direction.

     
Flip flips the boss to the opposite direction.
 
Fillet defines the constant fillet radius at the intersection between the boss (and ribs) with the target part body.

Boss - Head tab (Head type, counterbore style)

 
Specifies the head parameters of the Boss feature for a counterbore style of fastener.

Access:

Ribbon: 3D Model tab Plastic Part panel Boss , and click the Head tab.
 
Wall thickness
 
Shank height
 
Clamp height
 
Head diameter
 
Shank diameter
 
Clamp diameter

Draft options

 
Outer draft angle
 
Inner draft angle
 
Shank draft angle
 
Clamp draft angle

Boss - Head tab (Head type, countersink style)

 
Specifies the head parameters of the Boss feature for a countersink style of fastener.

Access:

Ribbon: 3D Model tab Plastic Part panel Boss , and click the Head tab.
 
Countersink angle
 
Wall thickness
 
Shank height
 
Clamp height
 
Head diameter
 
Shank diameter
 
Clamp diameter

Draft options

 
Outer draft angle
 
Inner draft angle
 
Shank draft angle
 
Clamp draft angle

Boss - Thread tab (Thread type)

Specifies the thread boss parameters of the Boss feature.

Access:

Ribbon: 3D Model tab Plastic Part panel Boss , and click the Thread tab.
 
Thread boss diameter
 
Thread boss hole diameter
 
Thread boss inner draft angle
 
Thread boss outer draft angle

The thread boss offers three hole types (hole check mark on):

 
Depth Enter the hole depth.
 
Full Depth The hole is automatically extended to the internal wall face. The best practice is to avoid sink marks in molded plastic parts.
 
Through The hole cuts the entire part.
 
If the hole check mark is off, the thread boss can model an ejector pin.

Boss - Ribs tab

Stiffening ribs are optional. If the Stiffening Ribs check mark is on, all controls to input the Ribs parameters become active.

Access:

Ribbon: 3D Model tab Plastic Part panel Boss , and click the Ribs tab.
Number of stiffening ribs indicates the number of ribs surrounding each Boss.
 
Rib thickness
 
Rib draft
 
Shoulder length
 
Shoulder top offset
 
Shoulder radius
 
Shoulder flare angle
Rib Fillet options
 
Rib fillet radius on the edges of the rib.
 
Rib blend radius at the intersection between the ribs and the boss.
 
Start angle is the first rib inclination angle with respect to the sketch X axis (when Placement is On Sketch). When Placement is On Point, the rib start angle is determined by a projected line on a plane that is normal to the Boss direction.

Space angle is the angle to fill. This value is divided by the number of stiffening ribs to determine the angle between ribs.

 
Start Direction the selector is active when the Placement is On Point. Use this selector to define the reference direction of the first rib.
 
Flip is active when the Placement is On Point. Use to reverse the direction of the first rib reference axis.