Drilling machine: Types, Operation, Working, Parts & Accessories

Construction of Simple Drilling Machine:

Simple Drilling Machine
Simple Drilling Machine


The main component of the drilling machine are as follow:

(1) Base: It is a cast iron heavy solid body or little bit hollow body carrying bolts to be grouted on the floor. It carries a vertical column and a motor on the side of the base. In the heavy machines, the base and table may become the same. In such cases, the base and table are heavy and rigid and usually used for heavy work. The base may also support pulleys and motor for spindle driving.

(2) Column: It is a vertical column of cast iron (round or box section) and supports the table and head or arm. It is very heavy (little bit hollow) and rigid and should be able to withstand the entire load of cutting process. The head or arm can move vertically up and down along the column on rack teeth cut on the face of the column with the help of handwheel. The box sections column has got the accurate guideways on which the table can go up and down for vertical adjustments.

(3) Drill head: Usually the head is mounted on column and is housing the spindle driving and feeding mechanisms. In universal and radial drilling machines, the head is mounted on a radial arm extending over the base and can move along the guideways provided on the arm. The head or arm can move up or down according to the job, and can be locked at a desired position.

(4) Table: It is a heavy casting of round or rectangular shape. For quick and accurate clamping, T-slots are cut on the table face. The table can move up and down to accommodate variety of work sizes. Further, other work holding devices (vice and jigs) can also be clamped on the table. The table movement can be locked in any position.

(5) Spindle drive and feed mechanism: This mechanism is housed in the drill head. Basically, it consists of (i) spindle, (ii) spindle rotation and (iii) feed mechanism.

Spindle is vertical shaft which can hold the drill firmly. The lower end of the spindle carries a Morse taper hole with a slot at its end for accommodating taper shank drill and tang of the drill. With the help of a key, the drill can be pushed down through the slot, to take the drill out. Sometimes for holding smaller diameter drills morse taper socket or chuck is provided on the spindle.

The spindle gets the motion from motor or pulleys through bevel gears and is able to rotate at desired speeds. The spindle rotates in a non-rotating sleeve carrying rack teeth at its outer surface. The sleeve can be moved up and down by rotating a pinion with the help of hand wheel which meshes the rack teeth.

The spindle is provided with a multiple speed driving mechanisms. This mechanism may be constituted of step cone pulley drive; step cone pulley drives with one or more back gears; or complete gear driving mechanism. Modern heavy-duty machines are generally carrying motor mounted on the frame. The multiple speeds may be obtained by sliding gears and sliding clutch.

The feed mechanism consists of vertical movement of the drill into the work, and this movement may be controlled by hand or power. The automatic feed is applied while drilling larger diameter holes, so that the cutting pressure can be maintained uniform.


Types of Drilling Machine:

Drilling machine is classified in two different ways:

(1) According to construction
(2) According to application

There are nine types of drilling machines in use such as:


  1. Portable drilling machine
  2. Sensitive drilling machine
  3. Upright drilling machine
  4. Radial drilling machine
  5. Gang drilling machine
  6. Multi spindle machine
  7. Turret type drilling machine
  8. Automatic drilling machine
  9. NC drilling machine

We will now study them in brief:


(1) Portable drilling machine: Hand drill, electrical drill, and pneumatic drill are portable drilling machines. They are smaller in size and compact in construction and hence they are handy. They are used on very large workpieces which are either difficult to mount on machine table or to carry to the machine. They are either manually operated or by an electric motor or by compressed air.

(2) Sensitive machine: It is similar to bench drill but its spindle and bearing are more accurate. It runs at a very high speed approximately 30,000 rpm. It has a hand-feeding mechanism and it is used for dolling small holes particularly in tool and die work.

(3) Upright Machine: It is similar to a sensitive machine but it is heavy in construction and is capable of varieties of operations. It has a power feed and a gear-driven mechanism so that many different spindle speeds and feeds can be obtained. Therefore, suitable for drilling holes in different workpiece material. A universal table can also be used with this machine. Column drilling machines and pillar drilling machine are upright drilling machines.

(4) Radial drilling machine: It is a heavy-duty machine and used for heavy and large workpieces. It has a radial arm that can move up and down and also, can be rotated on the column. This facilitates drilling at any location on the workpiece by sliding the drill head suitably on the radial arm. It has a reversible motor which makes possible the use of power tapping attachment.

There are three varieties of radial drilling machines:

(i) Plain radial drilling machine which can be used for drilling only in vertical plane.

(ii) The semi-universal machine in which the head can be swiveled at any angle. Hole can be drilled in a vertical plane.

(iii) The universal radial machine in which in addition to head, the arm can also be swiveled.

(5) Gang drilling machine: It is similar to arranging single spindle drilling head in line. It has a long table. It is used mostly for mass production for drilling different operations such as drilling, reaming, countersinking, etc. Different tools as required are fitted on different head and the operations are performed by shifting the workpiece from one head to another.

(6) Multi spindle machine: In this machine many parallel holes can be drilled in the workpiece. It needs drilled jig to guide the tools properly either the drill head can be moved down or the table can be raised for drilling holes. The latter arrangement is more common. Rake and pinion, lead screw, rotating plate cam mechanisms are generally used for the movement of table.

(7) Turret type radial machine: It is similar to single-spindle power fed drill press but here spindle is mounted on every phase of indexing turret. The spindle can be either manually or automatically indexed. Different tools are mounted on the turret and operations can be performed in the required sequence.

(8) Automatic drilling machine: It is used for high production work. Here a special type of base is used on which single spindle /multi-spindle unit head is arranged in different positions such as horizontal, vertical, and inclined. Use is also made of indexing table and drill jigs.

(9) NC drilling machines: In this machine the movement of the table and drill spindle is controlled by numerical tape. The operator job is only to load and unload the workpiece.




Construction of Radial drilling machine:


Radial drilling machine is very much versatile machine for product repair and maintenance work. Large size workpieces which cannot be accommodated on pillar drilling machine are conveniently used for drilling holes on radial drilling machines. The radial arm which can be rotated 360* is provided on the vertical column of the drilling machine. The drilling head can be slide forward or backward on a horizontal radial arm. The radial arm can be moved up or down on the vertical post of the drilling machine.


Radial drilling machine
Radial drilling machine


Important parts of radial drilling machine are as under:

            1. Electric motor for elevating the radial arm.
            2. Vertical column or post
            3. Elevating screw or rack
            4. Radial arm
            5. Spindle drive motor
            6. Spindle
            7. Base of drilling machine
            8. Table
            9. Handwheel
           
1. Electric motor for elevating radial arm: This motor raises or lowers the radial arm. It is mounted on the top of the column.

2. Vertical column or post: It is a strong steel column mounted on the base of the drilling machine. The radial arm moves up and down by sliding motion on this column. It is capable to take up the load of a radial arm as well as force developed during a drilling operation.

3. Elevating screw or rake: Nut or pinion provided in a radial arm give the drive to the radial arm due to which it can be raised or lowered.

4. Radial arm: It is a strong horizontal forged steel beam on which the drilling head is mounted and can be slide forward or backward.

5. Spindle drive motor: This motor gives drive to the spindle and is mounted on drill head.

6. Spindle: It is the main drilling spindle and receives drive motion from the spindle drive motor. The drill chuck or collet is provided on the lower end of the spindle.

7. Base of drilling machine: It is a strong heavy-duty cast-iron base with enough weight to provide stability to the machine.

8. Table: It is a heavy-duty and strong structure of table shape provided on the base of drilling machine.

9. Handwheel: It provides feed during the drilling operation. It is used for raising or lowering the drill.



Accessories of drilling machine and work holding devices:

During drilling operations, the workpiece is subjected to forces and torque. It is therefore required that the workpiece must behold firmly on the machine table to avoid breakage of the tool, injury to operator, and spoilage of operation. The devices used for this purpose are known as work holding devices. The following are commonly used work holding devices:

            1. Machine vice
            2. T-bolt
            3. Step block
            4. Parallels
            5. V-block
            6. Angle plates
            7. Step clamp
            8. Drill jig

Machine vice and parallels

Fig shows the use of machine vice and parallels is shown. The vice is fitted on the drill table.

T-bolt, Clamp and step block

By using angular vice inclined holes can also be drilled. Fig shows the use of T-bolt, step block, V-block, clamp, etc.

Tool holding devices:

Tool holding devices used on drilling machine:

The following 3 types of devices are used to hold the tool:

(1) Drill chuck
(2) Sleeve and socket
(3) Spindle in which the tool is fitted directly.


(1) Drill chuck: It is used to hold small drills of the straight shank. The drill chuck shank is provided suitable tapper such that it can be fitted in the machine spindle. A self-centering jaw is provided to hold different sizes of drill tools as per its capacity. The jaws can be opened or close with the help of a key.

Drill chuck

(2) Sleeve: The sank of the larger size drill is a stepper. When such drills cannot be fitted directly into the machine spindle i.e. when the sank is smaller in size, the drill is first fitted in the sleeve and then the sleeve is fitted inside the machine spindle. A tang is provided at the end of the sleeve so that the drill may not slip during rotation. A drill drift is used to remove the drill sleeve.

(3) Socket: When the drill sleeve is larger in size then a socket is used to hold the drill which is inserted in the machine spindle.

Drilling Machine operations:

By using different types of tools different operations can be performed on drilling machine. The operations are:


  1. Drilling
  2. Reaming
  3. Boring
  4. Counter boring
  5. Counter sinking
  6. Spot facing
  7. Tapping
  8. Grinding
  9. Trepanning

We will now study these operations with a simple diagram and in brief.

(1) Drilling: The tool used is a twist drill with a straight shank or taper shank. The drill of the required size is fitted in the machine spindle directly or with an appropriate tool holding device. Then a center is indented on the workpiece and then by holding the workpiece properly it is aligned with the drill point manually. The next step is to select the cutting speed and feed considering the workpiece material. And the operation is performed in one or more steps to get the required depth. Use cutting fluid and after the hole is over remove the drill and cut-off power. Clean the chip with the help of a brush. Remove the job from the wise and file out any burr from the workpiece surface.

(2) Reaming: The tool used is called reamer. It has many cutting edges. This operation is performed in a drilled hole to get the accurate size and good finish. Reaming is completed at half the speed without disturbing the setup but removing the drill and using the automatic field.

(3) Boring: Boring is enlarging the hole to remove drilling defects such as inclined excess, out of roundness, etc. Boring is a more accurate operation. A single point tool is fitted in a boring bar which in turn is fitted in the machine spindle.

(4) Counter boring: Fig. 2.42. It can be seen from the figure that counterboring is performed only along a certain length of a hole. To facilitate the sitting of the head of blot of pin, a counterboring cutter is used for the purpose. A pilot is provided on the tool for alignment. The tool is fitted in the socket and then fitted inside the machine spindle.

(5) Countersinking: 


Countersinking

Fig shows this operation. A countersink tool is used. This operation is performed to carry out bevelling at the inlet of the hole to get a conical shape. The cone angle varies from 60 to 120 degrees and it is provided for the sitting of the head of screw or rivet.

(6) Spot facing:


Spot Facing
Spot Facing

Spot facing shows the operation. The tool used is called spot facing tool. A counterboring tool can also be used. Spot facing operation is used to prepare a surface for a correct sitting of bolt or nut head.

(7) Tapping: 
Tapping
Tapping

The tool used is called machine tap. Taping is performed in a drilled hole to get threads. To avoid damage to tap some type of slipping device is necessary. After taping operation is over spindle must be rotated in the opposite direction. When the taping attachment has used the machine spindle is rotated in the same direction but the tap will rotate in the opposite direction. The tap is held in a drill chuck.

(8) Trepanning: 


Trepanning
Trepanning

This operation is used to get a large hole in a thin workpiece. This is not possible with any kind of twist drill.

Drilling machine: Types, Operation, Working, Parts & Accessories Drilling machine: Types, Operation, Working, Parts & Accessories Reviewed by Harish on May 28, 2020 Rating: 5

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