5 Unit 4: Offset Boring Head
OBJECTIVE
After completing this unit, you should be able to:
- Identify offset Boring head
- Explain how to correct set up for Rotary Table.
Offset Boring Head
The offset boring is an attachment that fits the milling machine spindle and permits most drilled holes to have a better finish and greater diameter accuracy.
Safety:
Be sure all set screws are tight before operation. Be sure offset boring head has a clearance to fit into hole when boring. Remove Allen wrench before turning the mill one. Double check mill speed before operation.
Figure 1. Offset Boring Head
OFFSET BORING HEAD AND TOOLS
Figure 1. shows an offset boring head. Note that the boring bar can be adjusted at a right angle axis. This feature makes it possible to position the boring cutter accurately to bore holes of varying diameters.
This adjustment is more convenient than adjusting the cutter in the boring bar holder or changing the boring bar. Another advantage of the offset boring head is the fact that graduated micrometer collar allows the tool to be moved accurately a specified amount usually in increments of (0.001) without the use of dial indicator or other measuring device.
The bar holder or insert holder (#1) has been satin chromed for wear resistance. The dial screw (#3) has been precision ground to give accurate movement of the bar holder/insert holder in the dove tail slide. The gib tension has been preset at the factory. The two gib screws (#5) should not be loosened to make size adjustments. These screws are for adjusting the gib pressure only and are filled with red wax to prevent accidental adjustment. The locking screw (#6) is the only screw used for making size changes to the boring head.
Diameter Adjustment
To adjust the diameter of an Allied Criterion standard boring head:
1. Loosen the locking screw (#6).
2. Turn the dial screw (#3) clockwise to increase the diameter and counterclockwise to decrease the diameter.
3. Tighten the locking screw (#6). Adjusting Standard Boring Heads
Procedure:
- Set up and carefully align the work parallel to the table travel.
2. Align the center of the Milling Machine spindle with the reference point on the work.
3. Spot the location of hole with a center drill or spotting tool.
4.
5. Install bore head into Milling Machine.
6.
7. Recheck the work alignment, as well as the alignment of the spindle with the reference point, to make sure it has not shifted. If any error is evident, it will necessary to repeat procedure 6 before processing.
8. Adjust Milling Machine speed for hole size and material.
9. Engage worm feed on Mill. Bring quill to material. Pull handle out to engage power feed. Remove boring head from hole.
10. Finish bore hole to the required size.
NOTE: Repeat Procedures 6-9 until hole is desired size.
Rotary Table
A rotary table can be used to make arcs and circles. For example, the circular T-slot in the swivel base for a vise can be made using a rotary table. Rotary tables can also