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 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.
• 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.
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.
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:
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.
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.
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.
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.
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.
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.
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.
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 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 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 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 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.
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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