Drilling Methods and Machines-Tech

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.

Simple drill press: A simple drill press, shown below, may be floor-mounted, 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 inches to 8 inches. Stops can be set to limit and regulate the depth.

Sensitive drill press: 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 below.

The drill press has the same motions as the previous one plus a telescoping screw for raisingand lowering the table and a sliding drill head. These two features allow easier handling of parts of varying heights.

Radial drill: For handling medium to very large castings, weldments, or forgings, radial drills are ideal; The length of the arm along which the spindle housing rides specifies the size. This arm can be from 3 feet to 12 feet long. The column that holds the arm may be from 10 inches to 30 inches in diameter.

For very large work, the arm may be rotated 180 degrees and work placed on the shopfloor. 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.

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 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 workholding 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. Speeds on a stepped V pulley drive are changed by changing the position of the V-belt. Speeds on a variable-speed drive mechanism are changed by a hand wheel on the head. The spindle must be revolving when this is done.

Quill assembly: The spindle rotates within the quill on bearings. The quill moves vertically by means of a rack and pinion. The quill assembly makes it possible to feed or withdraw the cutting tool from the work. Located on the lower end of the spindle is either a Morse tapered hole or a threaded stub where the drill chuck is mounted. For drilling larger holes, the drill chuck is removed and Morse tapered cutting tools are mounted.

Size classification: The size (capacity) of a drilling machine is determined by all the following features:
– Twice the distance from the center of 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.

Drilling systems 
Drilling systems are usually automated and computer controlled. Speeds, feeds and depth of cut are often pre-set. Such systems combine drilling operations with reaming, tapping, countersinking, etc.