BY GEOMETER

Wheel and shaft pullersTAPERS and light driving or

force fits are common waysof securing components f i r m-

ly to shafts and other parts-yetadmitting of dismantling whenrequired. Normally, no problemsare encountered in assembling, asthere is usually a nut, setscrew,or series of such, by which partscan be pulled together. It is theirdismantling which occasions diffi-culty-or even damage, if the rightmethods and tools are not em-ployed.

Tools with which dismantling iseffected are called pullers, drags, ordrawers: and take a variety of forms.Some components can be dismantledwith universal tools covering a rangeof sixes, while others demand specialtools for each purpose.

The common type of puller, A,consists of a beam carrying a pressurescrew and slotted for a pair of jawswhich can be adjusted to fit overcomponents-flywheels? pulleys,sprockets, gears. Adaptations of thispuller are those incorporating a three-armed beam with link and screwadjustment for three jaws; and thosein which the beam is a circular plate,slotted for jaw attachments to three,four, and five stud fittings-these fordrawing wheel hubs.

Out-of-the-ordinary pullersOn very heavy commercial pullers,

the screw is often of large diameterwith a fine thread and incorporates ahydraulic device which provides avery powerful extracting force. Onpullers intended for vee-belt pulleys,the jaws, instead of being square, aretapered to fit the vee-groove, thusobviating damage. Such jaws wouldbe incorrect for ordinary use becauseof a tendency to “ ride up ” underpressure.

When the component-usually aflywheel, sprocket or gear-hasthreaded holes for extractor studs, asimple puller can on occasion be usedwithout a pressure screw, as at B,employing the nuts on the studs fortightening, then freeing the componentby striking centrally on the bar withhammer and punch.

The shock of such a blow is generallysufficient to free the component andthe same is true when a pressure screw

22 MARCH 1956

is fitted-though in all cases it isnecessary to consider what may befurther along the shaft, so damage isnot done by the blow. If possible,levering behind the component beforestriking is advisable.

When there are special reasons,such as restriction by adjacent parts,slenderness in a pulley or hub flange,or other inherent weakness againstextraction force, the boss of the com-ponent is provided with a thread totake a screw on puller, C, a typewhich is straighforward to use, butwhich must be screwed up fully-not on just a few threads.

It will be seen the pullers describedare fairly straightforward to makefrom mild steel, using B.S.F. bolts incommercial sizes. Type B is particu-larly easy, requiring only two holesdrilled through the bar, and two studsfor attachment. Type C can be madewhere a lathe is available-andmaterial of sufficient size.

Other equally easy-to-construct pul-lers appear at D, E and F. That atD is intended particularly for small

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sprockets and consists simply of threesuitable bolts and a bar. The latteris drilled clearance, centrally for thepressure bolt, and at suitable spacingfor the bolts acting as jaws to lieholding firmly in the sprocket teeth.

The type at E, slightly more com-plicated, can be used with a pressurebolt like the other, or with a tapped

SPROCKET

hole for a screw as shown. Thispuller is intended for drawing innermembers of ball bearings, and holesare drilled in the top and bottomplates for the two bolts passingthrough to hug tightly in the semi-circular track of the race member.T WO bolts also attach the endplatefor the pressure screw or bolt.

The type at F, known as an impactpuller, is employed for drawing axleshafts and bearings, and differs fromthe others in functioning by shockinstead of pressure. It is threaded atthe end to screw on the shaft, and theweight is bumped to the oppositeend. q

MODEL ENGINEER