Project 7: Fan Blades

This project teaches the following skills:

• Making and using soft jaws.
• Create feature to locate part for subsequent operation.
• 3D Roughing.
• 3D Finishing.

Figure A.19: Project-7, Fan

1. Create Job-1 Soft Jaws Fixture

Cut a pocket into the aluminum jaws as shown in Figure A.20. This is used to grip the sawed raw stock while machining the top side (G54).

Soft jaws for this part require advanced planning. Round stock is usually slightly larger than the size ordered, so either first turn it down on to the desired size on a lathe, or cut the jaws to match the actual material size. The jaws have to be cut deep enough to grip the part securely during machining. Cutting forces in Delrin are small, so a grip depth of .30 inches is adequate to secure this part.

Figure A.20: Job-1 Soft Jaws

The XY datum is established by the pocket machined into the jaws. In other words, soft jaws both grip and set the datum for the part.

Before machining the jaws, place a bar (a vise hard jaw works well) between the vise jaws about 2.00 inches wide. This stabilizes the jaws during machining and sets the grip width.

One way to find the approximate location of the pocket center is to mark the center of the stock with a pencil, and set the stock on the top of the jaws. Load a small drill in the tool holder and jog the machine over the XY center of the stock and set this as the G54 X0Y0 position.

Machine the pocket using a spring pass to ensure the walls are straight. De-burr the top edge of the pocket by creating a .05 in chamfer.

2. Set G54 Z Position

It is safest to shift the G54 Z upward so all rapid moves are +Z values. Because sawed stock varies in length typically by .02-.05 in, set the G54 position to the top surface of the shortest stock material to be machined.

3. Machine Job 1 (Top Side)

Tighten the jaws firmly with a toque wrench, or mark the vise handle location after closing so the vise can always be tightened to the same pressure. Machine the blade using the processes in Table A.6.

4. Create Job-2 Soft Jaws Fixture

Replace the soft jaws with new blanks or re-cut the previous jaws. Set up and cut the jaw pockets for Job-2 exactly like for Job-1. De-burr the top edge of the pocket by creating a .01 in chamfer.

These jaws include a .125 in diameter hole used to set the rotary index position of the part for the second operation. This hole should extend about .25 in into the soft jaw step.

Figure A.21: Soft Jaws for Job-2

5. Set G55 Z Position

Set the G55 Z Position off the floor of the soft jaw pocket, then shift it upward .944 in above this surface (distance from face of fan ring to bottom of the part).

G55 Z could be set to the face of the soft jaw pocket as long as the top face of the ring is set as the G55 datum in the CAM system. Just be sure to set the clearance, rapid, and feed heights so the tools clear the part and stock during machining.

6. Load Part into Job-2 Fixture

Lightly tighten the vise jaws so part still rotates in fixture.

Next, insert a .125 in diameter gage pin (or a 1/8 in drill upside-down) through the locating hole in the stock (drilled in Job 1), and into the hole in the fixture. Use this to align the part so the surfaces machined in Job 1 line up perfectly with the surfaces machine in Job 2. Securely clamp the jaws. Remove the pin or drill before machining.

Figure A.22: Use Drill or gage pin to Align Part

7. Machine Job-2 (Bottom)

Machine the bottom of the fan using the operations listed in Table A.7. Select the appropriate tools and machining parameters.