Drilling Operation and Methods
One of the most important and essential tools in any metalworking shop is the drilling machine or drill press. Although the drilling machine is used primarily for drilling holes, it is often used for reaming, boring, tapping, counterboring, countersinking, and spotfacing. All drilling machines operate on the same basic principle. The spindle turns the cutting tool, which is advanced either by hand or automatically into a workpiece that is mounted on the table or held in a drill press vise.
Successful operation of any drilling machine requires a good knowledge of the machine, proper set-up of the work, correct speed and feed, and proper use of cutting fluids applied to the cutting tool and work. 9. 2 Types of Drill Presses Many types and sizes of drilling machines are used in manufacturing. They range in size from a simple bench mounted sensitive drill press to the large multiple-spindle machines able to drive many drills at the same time. Figure 9. 1 shows a schematic diagram of a standard vertical drill press as well as a schematic diagram of a turret-drilling machine.
Schematic illustration of (a) vertical drill press, (b) CNC turret drilling machine. Chapter 9/Tooling & Production 1 www. toolingandproduction. com Chap. 9: Drilling Methods & Machines 9. 2. 1 Simple Drill Press A simple drill press (Fig. 9. 2) may be floor mounted as shown, or have a shorter main post and be mounted on a bench. The motions of this machine are very simple. The table on a floor model can be raised or lowered and rotated around the machine column. The spindle rotates and can be raised and lowered, with a stroke of 4 to 8 inches.
Stops can be set to limit and regulate the depth. castings, weldments, or forgings, radial drills are ideal. The length of the arm along which the spindle housing rides specifies their size. This arm can be from 3 to 12 feet long. The column that holds the arm may be from 10 to 30 inches in diameter. A radial drill is shown in Figure 9. 4. For very large work, the arm may be rotated 180 degrees and work placed on the shop floor. Speeds and feeds are dialed in by the machine operator and are the same as for other drill presses. Drilling is either hand or power feed.
The name ‘sensitive’ is used to indicate that the feed is hand operated and that the spindle and drilling head are counterbalanced so that the operator can ‘feel’ the pressure needed for efficient cutting. A table mounted sensitive drill press is shown in Figure 9. 3. The drill press has the same motions as the previous one plus a telescoping screw for raising and lowering the table and a sliding ‘drill head’. These two features allow easier handling of parts of varying heights. 9. 3 Drilling Machine Components
Rigid and accurate construction of drilling machines is important to obtain proper results with the various cutting tools used. The sensitive drilling machine construction features are discussed in this section because its features are common to most other drilling machines. Base: The base is the main supporting member of the machine. It is heavy gray iron or ductile iron casting with slots to support and hold work that is too large for the table Column: The round column may be FIGURE 9. 3: A table mounted sensitive drill used for drilling small holes. (Courtesy Clausing Industries, Inc. ) 9. 2. 3 Radial Drill
For handling medium to very large size FIGURE 9. 2: a) a sensitive drill press is used for drilling holes; b) speeds on a stepped V pulley drive are changed by hanging the position of the V belt; c) speeds on a variablespeed drive mechanism are changed by the handwheel on the head. (Courtesy Clausing Industries, Inc. ) 2 Tooling & Production/Chapter 9 made of gray cast iron or ductile iron for larger machines, or steel tubing for smaller bench drill presses. It supports the table and the head of the drilling machine. The outer surface is machined to function as a precision way of aligning the spindle with the table.
Table: The table can be adjusted up or down the column to the proper height. It can also be swiveled around the column to the desired working position. Most worktables have slots and holes for mounting vises and other work-holding accessories. Some tables are semi universal, meaning that they can be swiveled about the horizontal axis. Head: The head houses the spindle, quill, pulleys, motor, and feed mechanism. The V-belt from the motor drives a pulley in the front part of the head, which in turn drives the spindle. The spindle turns the drill. Two head assemblies are shown in Figure 9. 2 b and c.
Speeds on a stepped V pulley drive are changed by changing the position of the V-belt (Fig. 9. 2b) Speeds on a variablespeed drive mechanism are changed by a hand wheel on the head. (Fig. 9. 2c) The spindle must be revolving when this is done. Quill assembly: The spindle rotates within the Quill (Fig. 9. 5) on bearings. www. toolingandproduction. com Chap. 9: Drilling Methods & Machines the spindle to the inner face of the column • The maximum length of quill travel • The size of the Morse taper in the spindle • The horsepower of the motor. 9. 4 Drilling Systems Drilling systems are usually automated and computer controlled.
It is extremely important that the overload limits be set no more than 10 – 13 percent above the actual drill pressure for each drill diameter and feed. The feed will then be able to stop before the drill is damaged. Machine Types: The design of deep hole drilling machines varies. The lengths of the machines are adapted to the special diameter ranges and lengths of the workpiece. A special very long machine is shown in Figure 9. 22 Deep hole drilling machines are often designed to permit a choice between a rotating workpiece, a rotating tool or both rotating workpiece and rotating tool.
In the machining of asymmetric workpieces, the machine works with a rotating drill and a non-rotating workpiece, since the workpiece cannot rotate at sufficient speed. In the machining of long, slender workpieces, a non-rotating. Special gun drilling machine is shown drilling six camshafts simultaneously. This machine includes automatic loading and unloading of parts.