09-07-2012, 04:32 PM
Drilling Machines and Their Static and Dynamic Analysis
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Introduction to Drilling Machine
The powered drill press was developed by James Nasmyth around 1846, which permitted drilling of accurate holes in metal. [1] Drilling is a machining operation used to create a round hole in a work-part. This contrast with boring, which can only be used to enlarge an existing hole. Drilling is usually performed with a rotating cylindrical tool that has two cutting edges on its working end. This tool is called a drill bit or drill. The rotating drill feeds into the stationary work-part to form a hole whose diameter is equal to the drill diameter. Drilling is customarily performed on a drill press, although other machining tools also perform this operation.
d) Counter-sinking
This is similar to counter-boring, except that the step in the hole is cone-shaped for flat head screws and bolts. [11] In other words, Countersinking is the tapering or beveling of the end of a hole with a conical cutter called a machine countersink. Often a hole is slightly countersunk to guide pins which are to be driven into the work-piece; but more commonly, countersinking is used to form recesses for flathead screws.
2) Power Driven Drilling Machine
The power-feed drilling machines (Figure-12) are usually larger and heavier than the hand-feed. They are equipped with the ability to feed the cutting tool into the work automatically, at a preset depth of cut per revolution of the spindle, usually in thousandths of an inch per revolution.
VI. Parts of Drilling Machine
• Base: The vertical column is mounted on the base, it supports whole machine.
• Column: It is a vertical member of the machine; it supports table head containing all the driving mechanisms. It should be rigid.
• Table: It may be round or rectangular in shape. It has T slots with which work is directly mounted on the table. Table can be adjusted vertically, horizontally and rastially.
Drilling Support Devices
These devices are important to keep the work-piece parallel while being supported above the worktable or vise surface and to keep the drill from cutting into the holding device or worktable. The following two devices are the most common used.
• Blocks are used with clamps to aid in securing and supporting the work. These blocks are usually precision ground of hard steel for long life.
• Parallels are precision ground rectangular bars are used to keep the work-piece parallel with the worktable when the work-piece must be raised above the worktable surface, such as when drilling completely through a work-piece as shown in Figure-21. Parallels come in matched sets and can be solid or adjustable as needed. [40]