Lab Report: To study different types of drilling machines and different drilling machine operations.

 Experiment Name: To study different types of drilling machines and different drilling machine operations.

Introduction: The drilling machine is defined as a machine that is used to make a circular hole, a tool used to drill holes of different sizes, and other related operations using a drill bit.

The drilling machine is one of the most important machines in a workshop. As regards its importance it is second only to the lathe machines. Holes were drilled by the Egyptians in 1200 B.C. about 3000 years ago by bow drills. The bow drill is the mother of the present-day metal-cutting drilling machine.

Objectives:

• To get familiar with the h drilling machine

• To get familiar with parts and types of drill machine

• To get familiar with operations performed on the drilling machine

Types of Drilling Machines

• Portable drilling machine 

• Bench drilling machine 

• Radial drilling machine 

• Pillar drilling machine 

• Gang drilling machine 

• Multiple drilling machine

Portable drilling machine 

These types of drilling machines are commonly used in all the workshops. Used to drill small-sized holes. It is operated by holding a hand. The workpiece where the hole is to be drilled is held in a vice.

Figure: Portable Drilling Machine

Bench drilling machine 

The bench drill is used for drilling holes through materials including a range of woods, plastics, and metals. It is normally bolted to a bench so that it cannot be pushed over and that larger pieces of material can be drilled safely. These are light-duty machines used in small workshops. Also called Sensitive drilling machines because of their accurate and well-balanced spindle. Holes of diameter 1 mm to 15 mm.

Figure: Bench Drilling Machine

Parts:

• Vertical main column 

• Base

• Moving drill head 

• Worktable

• Electric motor 

• Variable speed gearbox 

• spindle feed mechanism.

Working:

• The workpiece with the exact location marked on it with the center punch is clamped rigidly on the work table. 

• spindle axis and center punch indentation are in the same line. 

• The machine is started and the drill bit is lowered by rotating the feet d handle. 

• The drill bit touches the work and starts removing material.

Radial drilling machine 

The schematic diagram of the radial drilling machine is shown in the figure. It consists of the base, column radial arm, drill head, spindle speed, and feed mechanism. These are heavy-duty and versatile drilling machines used to perform drilling operations on large and heavy workpieces. Holes up to 7.5 cm.

Figure: Radial Drilling Machine

Parts:

• Heavy base 

• Vertical column 

• Horizontal arm 

• Drilling head

Working

• Workpieces are marked for exact location and mounted on the work table. 

• Drill bit is then located by moving the radial arm and drill to the marked location. 

• By starting the drill spindle motor holes are drilled.

Specification of a radial drilling machine

• Power capacity eg: 1.5 hp for drilling motor and 0.5 hp for elevating motor. 

• The range of speed of spindle eg: 50 to 2800 rpm. 

• Lengthen the h of the arm on which the drill head can traverse. eg: 600 mm.

• Vertical movement of the arm eg: 500 mm. 

• Angular swing of arm eg: 360˚ 

• Range to which drill bit can reach eg: 350 mm to 900 mm. 

• Drill depth eg: 32 mm for steel

Pillar drilling machine 

Pillar drills (also referred to as drill press machines) are versatile machines that can be used on a wide range of materials where single-hole drilling is required. The head is lowered vertically and plunges into the material using a hand lever and the table can be adjusted to suit varying sizes of material.

Gang drilling machine 

This machine consists of several drill heads placed side by side so that more than one hole of the same or different sizes can be drilled at a time on the same job or different jobs. The space between drill spindles is varied to suit the gap between the holes. This type of machine tool is used to drill a large number of holes in the same job at a faster rate. The main advantage of this type of machine tool is that the series of operations can be performed with different spindles mounted with different tool bits on the same workpiece by moving it from one position to another position.

Figure: Gang Drilling Machine

Multiple drilling machine

This machine tool is similar to a gang drilling machine in construction. It is used to drill several holes in the same workpiece simultaneously and to reproduce the same work in several similar jobs. All the spindles are driven by a single motor and fed continuously. During the feeding table, the workpiece is raised or lowered and the drill head position is not varied.

Figure: Multiple Drilling Machine

Drilling machine operation

• Reaming

• Boring 

• Counter boring 

• Counter sinking

• Spot facing

• Tapping

Reaming

Reaming is an accurate way of sizing and finishing a hole that has been previously drilled. To finish a hole and to bring it to the accurate size, the hole is drilled slightly undersize.

It is a process of smoothing the surface of drilled holes with a tool. The tool is called a reamer. Initially, a hole is drilled slightly smaller in size. The drill is replaced by a reamer. Speed is reduced to half that of the drilling. Reamer cannot originate a hole. It simply follows the path which has been previously drilled and removes a very small amount of metal. For this reason, a reamer cannot correct a hole location. The material removed by this process is around 0-375mm and for accurate work, this should not exceed 0-125mm.

Figure: Reaming

Boring 

Boring is performed in a drilling machine for the reasons stated below:

• To enlarge a housing of an adjustable cutting tool with only one cutting edge. This is necessary where a suitable-sized drill is not available or where the hole diameter is so large that it cannot be ordinarily drilled.

• Used to finish a hole accurately and to bring it to the required size.

• To machine the internal surface of a hole already produced in casting.

• Used to act out of the roundness of the hole.

• To correct the location of the hole as the boring tool follows an independent path concerning the hole.

The cutter is held in a boring bar which has a tapered shank to fit into the spindle socket. For perfect finishing, a hole, in the job is drilled slightly undersize. In precision machines, the accuracy is as high as +0.00125mm. It is a slow process than reaming and requires several passes of the toll.

Figure: Boring

Counter boring 

Counterboring is the operation of enlarging the end of a hole cylindrically. The enlarged hole forms a square shoulder with the original hole. This is necessary in some cases to accommodate the heads of bolts, studs, and pins. A tool used for counterboring is called a counterbore. The counterbores are made with a straight or tapered shank to fit in the drill spindle. The cutting edges may have straight or spiral teeth. The tool is guided by a pilot which extends beyond the end of the cutting edges. The pilot fits into the small-diameter hole running clearance and maintains the alignment of the tool. 

These pilots may be interchanged for enlarging different sizes of holes. Counterboring can give an accuracy of about +0.005mm. The cutting speed for counterboring is 25% less than that of drilling operations.

• This process involves increasing the size of a hole at only one end. 

• Cutting tool will have a small cylindrical portion called the pilot. 

• Cutting speed = two-thirds of the drilling speed for the same hole

Figure: Counterboring

Counter sinking

Countersinking is the operation of making a cone-shaped enlargement of the end of a hole to provide a recess for a flat-head screw or countersunk rivet fitted into the hole. The tool used for countersinking is called a countersink. Standard countersinks have 60, 82, or 90 inclined angles and the cutting edges of the tool are formed at the conical surface. The cutting speed in countersinking is 25% less than that of drilling.

• This is an operation of making the end of a hole into a conical shape. 

• Cutting speed = half of the cutting speed of drilling for the same hole.

Figure: Countersinking

Spot facing

Spot facing is the operation of smoothing and squaring the surface around a hole for the seat for a nut or the head of a screw. A counterbore or a special spot-facing tool may be employed for this purpose.

• It is a finishing operation to produce a flat round surface usually around a drilled hole, for proper seating of bolt head or nut. 

• It is done using a special spot-facing tool.

Figure: Spot Facing

Tapping

It is the operation of cutting internal threads using a cutting tool called a tap. Tapping in a drilling machine may be performed by hand or by machine. A tap may be considered as a bolt with accurate threads cut on it. The threads act as cutting edges which are hardened and ground. When the tap is screwed into the hole it removes metal and cuts internal threads which will fit into external threads of the same size.

• Process of cutting internal threads with a threading tool called a tap.

• Tap is a fluted threaded tool used for cutting internal thread 

• Cutting speed is very slow.

Figure: Tapping

Course: ME Workshop (1.2)

Credit to Mohammad Mithun

Submitted by Mohammad Mithun