Drilling machine operation

Drilling machine operation

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Drilling is the process of cutting holes in metals by using drilling machines as shown,which are the tools used to cut away fine shavings of material as the drill advances in a rotational motion through the material. It is done by forcing a rotating drill into stationary job as on a drilling machine or by forcing stationary drill in a rotating workpiece as on a lathe.

No.  Description
 1  Electric motor
 2  Spindle feed handwheel
 3  Vertical support column
 4  Spindle and tool
 5  Work table
 6  Support base

Drilling Machine Operation :

1.Drilling

2.Reaming

3.Boring

4.Counter boring

5.Counter sinking

6.Spot facing

7.Tapping

8.Trepanning

Drilling:

Drilling is the operation of producing circular holes in solid metal by rotating the drill and feeding it through the job. This is the main operation done on the this machine.

Before starting the drilling it is necessary to mark the position of the hole on the work piece.

Drilling process is dose not produce accurate hole. The center may not be accurate, the size of the hole is slightly larger than required.

Reaming:

Reaming is an operation of sizing and shaping a hole using a tool called reamer.

A reamer as shown on figure is multitoothed tool designed for remove relatively small amount of material from a previously drilled hole.

Reaming is done to achieve accurate hole dimension.

Initially a hole is drilled slightly smaller in size.

Boring: 

Boring is a process of aligning, sizing and finishing a cylindrical hole.

It uses single point cutting tool which rotates relative to the stationary work piece.

The hole can be aligned and sized with good surface finish.

Boring is often used to enlarge the drilled holes.

Counter boring

Counter boring is the operation of enlarging one end of an existing hole concentric with the original hole with a square bottom as shown in figure.

The counter tool known as counter bore has a pilot as shown in figure.

The pilot enters in previously drilled hole and align the tool so that the counter bored hole is concentric with the existing hole.

The tool has end cutting edges square with the axis to produce a flat bottom.

Counter boring is used to recess a bolt head or a nut below the surface to permit a mitting part to operate with obstruction.

Counter sinking

 A countersink tool  enlarges the top portion of an existing hole to a cone-shaped opening.

Countersinking is performed after drilling to provide space for the head of a fastener, such as a screw, to sit flush with the workpiece surface.

Common included angles for a countersink include 60, 82, 90, 100, 118, and 120 degrees.

Spot facing:

Spot facing shown in figure is the process of producing a flat machined surface generally around a hole perpendicular to the hole axis.

This flat surface allows the bottom of a  screw or bolt to seat squarely with the material.

Spot facing is commonly done on castings where irregular surfaces are found.

Spot facing may be performed on a drill press with a counter bore of suitable size for the operation.

Tapping:

Tapping is a thread cutting for producing internal threads.

Tapping uses multi- point cutting tool called taps may be done manually or on machine like drills.

The tapping attachment used with the drill permits forward rotation of the tap when it is cutting and fast reverse rotation for withdrawal.

Trepanning:

Trepanning is the process for making large holes in sheet metal.

A small diameter hole is drilled in center for drilling large diameter hole.

The pilot of trepanning tool is fitted into this hole and the length of the adjustable arm is set to the radius of the hole to be cut.

Holes up to a diameter of 350 mm can be cut by this arrangement.

Subland drills:

Combination drills known as Subland drills combine a number of operations in a single tool; for example …

drill and ream,

drill two diameters,

drill and chamfer,

drill and spot face,

drill and counter bore,

Each cutting edge has a separate land and flute, fig.  which enables cutting to take place and re-sharpening to be easily carried out.

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