Planer Quick Return Mechanism

QUICK RETURN MECHANISMIN PLANING MACHINE

Mainly of 3 types

• Using open and crossed belt drive mechanism• Using a reversible motor• Using hydraulic systems

WHAT IS A PLANING MACHINE ?

• A machine for planing is any machine which produces plane surfaces.

• The piece of work to be planed shall move to and fro, but not the cutting-tool. The piece is thus moved by means of a moving table, to which the article is fastened with screw-bolts and plates.

• The tool horizontal feed is given during return or backward stroke of the worktable.

PLANING MACHINE

OPEN SIDE PLANER

DOUBLE HOUSING PLANER

QUICK RETURN MECHANISM???

BASIC WHITWORTH QUICK RETURN MECHANISM

• A mechanism which converts rotary motion into reciprocating motion.

• Characterized by slow cutting motion and a quick return.

• Essentially a four-bar chain.• In planer, the quick return mechanism is

implemented throughOpen and cross belt drive Reversible motor

OPEN AND CROSS BELTDRIVE MECHANISM

A - Crossed Belt D - Table G - 1 ST Intermediate

B - Crossed Belt E - Bull Gear H - Drive Pinion

C - Rack F - 2 ND Intermediate

OPEN DRIVE MECHANISM WITH

RACK AND SPUR GEARS

A - Counter Shaft E - Table I - 2 ND

Intermediate

B - Crossed Belt F - Rack J - 1 ST

Intermediate

C - Open Belt G - Drive pinion and Tight pulley Shaft K - Tight pulleys

D - Belt Shifter H - Bull Gear L - Loose Pulleys

CROSS BELT DRIVE MECHANISM WITH RACK

AND SPUR GEARS

OPEN AND CROSS BELT DRIVE MECHANISM

Open and crossed belt drive• In open and cross belt drive, the belts are alternatively

used as drivers to reciprocate the table.• The cross belt with a greater arc of contact on the

larger pulley is used to drive the table on the cutting stroke or forward stroke.

• Two belts, one open and one crossed operate on loose and tight pulleys. Crossed belt is used for forward or cutting stroke and the open belt for return motion.

• The open and Crossed belt making a greater arc of contact on the pulley is considered better for driving the table on the cutting stroke.

• crossed belt drive mechanism permits operation of the gear train in such a manner that the table will travel slowly on the cutting stroke and travel faster on the return stroke.

• Pulleys keyed to the drive pinion shaft are called tight pulleys and those which turn freely on the shaft are called loose pulleys. The larger tight pulley is used for the slower forward speed or cutting stroke drive and the smaller tight pulley is used for the quicker return stroke.

• During cutting stroke the crossed belt is on the tight pulley, the open belt is on the loose pulley and the position is reverse during the return stroke.

• Belt shifter reverse lever and the trip dogs*: are responsible for relative shifting of belt automatically at the end of each stroke without stopping the machine.

*Trip dogs are provided, one each at both ends of the planer table. At the end of each stroke, the trip dog meets against the reverse lever, actuates the belt shifter and thus the table movement is reversed.

REVERSIBLE MOTOR

A - Driving Motor E - Worm shaft entering machine bed at an angle

I - Worm

B - Flexible Coupling F - Table J - Bed of Machine

C - Worm G - Table Rack K - Worm wheel

D - Column H - Shaft supported in bearing both sides of worm

L - Box shown broken to expose drive

PLANER REVERSIBLE MECHANISM WITH RACK AND WORM

• Planers are driven direct by a coupled motor in place of the old method of open and crossed belt drive.

• The reciprocating motion of the planer table is obtained by driving through a worm on to a rack attached to the length of the underside of the table.

• The reversal of the drive for cutting and return strokes is obtained in most cases, by reversing the motor itself either by field or phase changing.

• The main driving motor may be fed with a variable voltage ,direct current of reversible polarity from a special motor-generator set which forms part of the equipment of the planer.

• Special types of motors and control gear are incorporated to ensure a rapid but controlled reversal, as well as a steady acceleration which is necessary in order to avoid a sudden impact upon the tools as they commence their cut.

• A control unit is present which is responsible for the automatic reversal.

The trip cams are carried on the table itself and are set to actuate the switch gear through a rocking lever. Trips are mounted on one side of the planer table with a gap between them equal to the stroke length.The trip cams are carried on the table itself and are set to actuate the switch gear through a rocking lever.

TWO TYPES OF CONTROL MECHANISM

Trips are mounted on one side of the planer table with a gap between them equal to the stroke length.

The other control mechanism employs the principle of attaching the trips to a circular flange whose revolving movement synchronises with the longitudinal motion of the table.

ADVANTAGES OF REVERSIBLE MOTOR MECHANISM

• Large number of cutting and return speeds can be obtained.

• Higher return speeds are possible.• The control is quick accurate and more

responsive.