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Activity 1.5.6 Bracket

 

Introduction

Studying how an object is fastened is not something you do every day. But, just for fun, consider looking at how your desk or your locker is held together. Most likely, you will notice that they are held in place by different types of screws. The same is true with doors and windows. When you look at stairs and other objects, you begin to realize that objects are held together in many different ways.

                                                                                                                                             

In this activity you will be introduced to a 3D model that includes counterbores and countersinks. These are two types of specialized holes used with fasteners. A countersink is used to recess the tapered head of a fastener below the surface of an object (e.g., a screw on your chair). A counterbore is a cylindrically enlarged hole, generally used to allow the head of a screw or bolt to be recessed below the surface of an object (e.g., the small holes for the screws on the back of a radio or television).

 

Equipment

  • PLTW Gateway notebook

  • Pencil

  • Computer with 3D modeling software

 

Procedure

Using the same procedures you learned in previous activities, create a 3D model of the bracket depicted in the orthographic and isometric views provided.

 

Figure 1. Bracket.

If you look at the orthographic drawings closely, you will see the difference in the profiles of the counterbore and countersink. They show up well in the right side view. This bracket might be used by being bolted to a solid surface through the counterbores and having a lighter piece attached to the back using the countersunk holes.

 

In order for you to know how to create the holes, counterbore, countersink, fillets, and rounds for this project, you will need to follow the instructions of your teacher or complete the tutorials regarding these topics.

 

Orthographic and Isometric Views of Bracket

 

 

 

Step-by-Step Procedure

 

NOTE: All measurements are in millimeters.

 

  1. Open a new Standard part file

  2. Go to the tools tab and click on document settings, change units to mm and click Apply.

  3. Create a 2D sketch on the XZ plane.

  4. Sketch a rectangle 50mm tall x 156mm wide.

  5. Finish the sketch.

  6. Extrude the sketch to a distance of 87mm.

  7. Save file as Bracket.

  8. The next step is to cut away the sides. Create a 2D sketch on the front of the part.

  9. Use the rectangle command to draw a shape similar to the sketch in Figure 2.

  10. Add dimensions shown and Finish the sketch

  11. Extrude the sketch.

 

 

 

 

 

 

 

 

    Figure 2. Rectangle

 

 

 

 

 

 

 

 

 

  1. In order to create the notch on the right side of the object, use the Cut operation and the All Extents. Make sure the arrow is pointing through your part.

  2. Repeat steps 8-12 for the notch on the other side. Your part should now look like Figure 3.

 

 

 

 

 

Figure 3. Bracket with notched sides & sketch

 

 

 

 

 

 

  1. Create a 2D sketch on the front for the notch in the middle of the part which will only go part way through the bracket.

  2. Create the rectangular sketch on the front of the part, 50mm x 58mm. Make sure the rectangle is in the correct location as shown in Figure 3 using Dimensions.

  3. Finish Sketch and Extrude the sketch into the part. Use the Cut operation similar to step 12, Distance extents, and a depth of 27mm.

  4. We will now add the 2 counterbore holes on each side of the bracket. Create a 2D sketch on one of the top side rectangles. Use the point command and place a point 23mm from the back edge and 16mm from the side, use dimension to find the correct location.

 

 

 

  1. Use the Hole Command and Counterbore hole. Enter 13mm for a hole diameter, 18mm for a counterbore diameter, and 10mm for a depth. Select OK.

 

 

 

 

 

  1. Repeat Step 17 and 18 for the other side. When the second hole appears, hit Enter and then Exit the hole function.

 

  1. Now it is time to put the countersink holes into the back surface. Create 2D sketch and select the front middle cutout portion of the bracket.

 

  1. You will place 2 points for holes. Dimension them to be 23mm from the left side, and 15mm and 42mm down from the top, as shown above.

  2. Use the Hole Function to place the countersink holes. Use 20mm for the counter sink diameter, 13mm for the diameter of the hole, and Through All for termination.

 

 

 

  1. Apply a 12mm radius fillets to the 6 corners shown below.

 

  1. Apply fillets to all remaining edges of the bracket. The radius is 3mm.