Planing Machine or Planer

Planer Machine, Principle of Operation of Planer, Classification of Planers, Construction Details of Planer Machine, Quick Return Motion Mechanism in Planer, Planer Operations

Planer Machine

Planer Machine
Planer Machine
Planer Machine

             Planer is a machine tool used for machining the heavy and rigid workpieces. Cutting too] is not moved while maching instead of this, the workpiece is fixed on the table and moved to and front. Single point cutting tool is used in this machine for machining the workpiece.  Workpiece surfaces can be machined in horizontally, vertically or inclined position.

Planer - Working Principle

Principle of Operation of Planer:

Planer is a very large reciprocating machine tool.
Principle of Operation of Planer
The work is rigidly held on the work table or platen of the machine.
The tool is held vertically in the tool head mounted on the cross-rail.
The work table with the job moves to and fro past the vertically held tool.
The cross feed is given by moving the tool head along the cross rail and the vertical feed is given by moving down the tool.
The feed can be given by manually or automatically.
Feed is given after each cut during the idle stroke of the table.

Classification of Planers

Types of Planer:

Standard or double housing planer.
Open side planer.
Pit planer.
Edge or plate planer.
Divided table planer.

Double Housing Planer:

This is the Standard model & most widely used for very heavy work.
The bed and two vertical housings are fixed.
Table moves along the guide ways of the bed.
Housing supports cross rail 81 tool heads.
Cross rail carries two tool heads.
Tool head carries tools.
• The standard or double housing planer is most widely used in workshops.
Double housing planer

The principal parts of this type of planer are;
Bed
Table
Columns
Cross rail
Tool head.

Open Side Planer:

             Only difference in this type is that it has only one vertical column or housing on which the cross rail is mounted.
Open side planer
Open side planer

Pit Planer:

The working principle of this planer is same as that of other types of planer.
The table of the planer is kept in a pit as the floor coincides with the top surface of the table.
The uprights and the cross rail are made sufficiently rigid to take up the forces while cutting.

Edge or Plate Planer:

This is used wherever the edges of the plates have to be machined.
The carriage can be moved longitudinally on guide ways.
The blade edge is located between the handgrips in order to plane an edge portion of a workpiece.

Divided Table Planer:

The planer has two tables, which may be reciprocated together or separately.
This types of design saves much of idle time while setting the work in continuous production work, when small workpieces clamped on one table are being machined and another table in operation.

Construction Details of Planer Machine:

Planer machine — construction details

Bed:
Bed is made of box shaped casting.
It is strong and rigid.
The length of bed is twice that of the table.
V guides ways are made on the bed.
Table is placed on the bed.
Cross ribs are provided in the bed to increase its strength.
bed of planer
Table:
Table is a box shaped casting part which moves on the guide ways of the bed also called platen.
Top surface has T-slots.
Work is clamped on T-slots.
‘T’ Slots are made on the table to hold the workpiece.
table of planer
Housing or Column:
Column is a part with guide ways.
Columns are mounted on both sides of the bed.
The two columns are connected at the top by a cross beam.
Cross rail slides on the guide-ways of the column.
There are two side tool heads mounted on the column.
Feed mechanism and power transmission links are provided at the end of the column.
column of planer
Cross Rail:
Cross rail connects the two columns.
It can be clamped on any place of column.
The cross rail carries vertical tool head.
This is moved up & down by elevating screw.
crossrail of planer
Tool Heads:
Generally, four too] heads are fixed on the planer.
The cross rail carries two too] heads and the column carries other two tool heads.
Double housing planer table is driven by a quick return mechanism.
It is used for machining heavy and large castings.
During return stroke cutting tool will be lifted.
Tool heads can be swiveled through 60° on either side of its vertical position.
tool head of planer

Specifications of Planer:

Planers are specified by the following important sizes;
Horizontal distance between the two vertical housing [maximum width of job]
Dimensions of the table.
Power of the motor.
Types of drives required.
Range of speed and feed available.

Quick Return Motion Mechanism in Planer:

             A planer machine produces flat surfaces. The table reciprocates with holding the work. There should be some mechanism to move the table in reciprocating motion. Table is to be moved quickly during idle stroke.
Mechanisms to drive the table [QRM]:
Open & cross belt drive
Reversible motor drive
Hydraulic drive.

Open and Cross Belt Drive Mechanism:

             Planer mechanism requires providing to and fro motion to the machine table. Quick return mechanism is also employed to give faster movement during the idle stroke.
Open and cross belt drive mechanism of planer
             Most planers carry this system of open and cross belt drive for the quick return of the tables. This mechanism consists of two belts, one open and one cross operating on two loose and fast pulleys. The main driving shaft is provided below the bed. One end carries the pinion which meshes with the rack provided under the table of the machine. Cross belt is used for forward or cutting stroke and the open belt is for return motion. Cross belt is connected to fast pulley and open belt is connected to loose pulley and it enables slow movement of the table during forward stroke. Trip dogs are mounted at each end of the table indicate the end of the stroke and belt shifter shifts the belts to the different pulleys. Now open belt is connected to the fast pulley and the cross belt is connected to the loose pulley. This enables faster movement and provides quick return motion for the machine table.

Reversible Motor Drive Mechanism:

             Electric motor drives the bull gear through gear trains. Motor is coupled to D.C. generator. When motor is started, generator supplies power to reversible motor. Reversible motor causes the planer table to move. At the end of stroke, trip dog operates the switch which reverses the direction of table. Speed of cutting stroke is reduced by regulating the field current of the generator.
Reversible motor drive mechanism of planer

Operations on Planer Machine

             Planer operations are similar to those performed on shaper, with a difference that the workpieces are much larger in size.

Planer Operations:

Planing horizontal surfaces.
Planing vertical surfaces
Planing angular surfaces / dovetails
Planing curved surfaces
Planing slots & grooves.

Planing Horizontal Surfaces:

Fix the work properly on the table.
Set the required cutting speed.
Give required feed of the tool.
Give suitable depth of cut for rough cuts.
Finishing the job by giving less depth of cut.
Planing horizontal surfaces

Planing Vertical Surfaces:

Fix the job on the table firmly.
Align the surface to be machined properly.
Vertical slide is adjusted perpendicular to the table
Swivel the apron away from the job.
Switch on the machine.
Rotate down feed screw by hand to give down feed.
Planing vertical surfaces

Planing angular surfaces:

Main angular planing is to make dove tails & V grooves.
Set the work on the table.
Swivel the tool head to the required angle.
Set apron away from work.
Give down feed as per requirement.
Planing angular surfaces

Planing Formed Surfaces:

Fix up a square nose tool in tool head.
Required form is obtained by feeding the tool simultaneously in both horizontal
and vertical directions.
Give suitable depth of cut.
Set apron away from work.
This can also be done with the aid of a special fixture.
Planing formed surfaces

Planing Slots and Grooves:

Fix up the job on the table suitably.
Fix slotter tools in tool heads.
Give feed using down feed screw.
Move the tool by the required amount to get uniform slots / grooves.
Planing slots and grooves

Cutting speed, Feed and Depth of Cut

Cutting Speed:

             As in a shaper, the cutting speed of a planer is the rate at which the metal is removed during the forward cutting stroke. The formula, for shaper holds good for a planer also. This is expressed in m/min.
Where,
L = Length of cutting stroke in mm.
m = Ratio between return time to cutting time
n = No of double strokes of the ram/min.

Feed:

             The feed in a planing machine is the distance the tool head travels at the beginning of each cutting stroke. It is expressed in mm/double stroke.

Depth of Cut:

             It is the thickness of metal removed in one cut and is measured by the perpendicular distance between the machined and non machined surface. It is expressed in mm.

Machining Time:

             If the cutting speed, feed, length of cutting stroke, breadth of the job and number of double strokes per minute for a planer operation are known, the machining time required for one complete cut may be calculated by using the formula.
The ratio of cutting time to return time usually varies from 2: 1 to 4:1.


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