9 Unit 4: Turning
OBJECTIVE
After completing this unit, you should be able to:
• Describe the rough and finishing turning.
• Describe the turning shoulder.
• Describe the facing cut.
• Explain how to set up for center/spot drill.
• Explain how to set up for boring.
• Explain how to set up for knurling.
• Correctly set up a workpiece for parting/grooving.
• Determine the taper calculation.
• Correctly set up workpiece in a 4-jaw chuck.
Workpiece is generally machined on a lathe for two reasons: to cut it to size and to produce a true diameter. Work that must be cut to size and have the same diameter along the entire length of the workpiece involves the operation of parallel turning. Many factors determine the amount of materials which can be removed on a lathe. A diameter should be cut to size in two cuts: an roughing cut and finishing cut.
To have the same diameter at each end of the workpiece, the lathe centers must be in line.
To set an accurate depth of cut
Procedure:
1. Set the compound rest at 30 degrees.
2. Attach a roughing or finishing tool. Use a right-handed turning tool if feeding the saddle in the direction of the headstock.
3. Move the tool post to the left hand side of the compound rest and set the tool bit to right height center.
4. Set the lathe to the correct speed and feed for the diameter and type of material being cut.
5. Start the lathe and take a light cut about .005 inch and .250 inch long at the right hand end of the workpiece.
6. Stop the lathe, but do not move the crossfeed screw handle.
7. Move the cutting tool to the end of the workpiece (to the right side) by turning the carriage hand wheel.
8. Measure the work and calculate the amount of material to be removed.
9. Turn the graduated collar half the amount of material to be removed. For example, if .060 inch to be removed, the graduated collar should be turned in .030 inch, since the cut is taken off the circumference of the workpiece.
10. Remember, for each thousandth depth of cut, the diameter of the stock is reduced by two thousandths.
Rough Turning
The operation of rough turning is used to remove as much metal as possible in the shortest length of time. Accuracy and surface finish are not important in this operation. Therefore, max depth of .030 inch and a .020 to .030 inch feed is recommended. Workpiece is generally rough turned to within about .030 inch of the finished size in a few cuts as possible.
Procedure:
1. Set the lathe to the correct speed and feedrate for the type and size of the material being cut.
2. Adjust the quick change gear box for a .010 to .030 inch feed, depending on the depth of cut and condition of the machine.
3. For Example: .010
4. Move the tool holder to the left hand side of the compound rest and set the tool bit to right height to center.
5. Tighten the tool post securely to prevent the toolholder from moving during the machining operation.
6. Take a light trial cut at the right hand end of the workpiece for about .250 inch length.
7.