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ROAD AND WORKSHOP by Handyman

17th July 1964, Page 41
17th July 1964
Page 41
Page 41, 17th July 1964 — ROAD AND WORKSHOP by Handyman
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Keys and Tapers

A REGULAR feature of vehicle repair is the loose companion flange or drive coupling. As on most vehicles a taper seating and key will be found a quick repair is not always an easy matter without fitting experience. All too often the worn key is hurriedly replaced and the flange bumped home on the, shaft with little thought to the condition or fit of what should be three mated items. Perfect mat:ng of the tapered shaft and coupling is most, important, both to security and true running. Also, with true mated tapers, little or no strain is placed on the key.

Proof of the grin of a sood tamer fit is well known in the motorcycle world, where most flywheels are mounted on tapered shafts with no key required. This also applies to other items, magneto drives in particular. Where the mating is satisfactory, trouble-free operation is assured. In commercial vehicle repair, however, where a key is used inside many types of coupling, damage is often found on the taper faces, and the coupling can never be truly secure unless the damage is removed.

In dealing with light damage to the taper surfaces, lapping in with grinding paste can often re-mate the shaft and flange, and lapping should continue until a full seat is indicated by marker blue. In worse situations, however, metal can have been transferred from one face to the other, and as the cause of this is a sheared key, both flange and shaft may

need machine shop attention. After machin:ng it is still a wise plan to hand lap the male and female items until a good fit is assured. It is also necessary to fit a new key. Again, this is a task needing a little experience, as mistakes can be made—a key only one or two thousandths of an inch too tall can cause the flange to ride on the key instead of the true taper.

In fitting a key, the keyway should be cleared of scars or burring, and the key should be a good, tight fit in the shaft keyway. In the flange, the key should

be a firm, sliding fit with no trace of side play. It should be determined by measurement that with key in situ, and flange mounted fully on the taper, there is a clearance between the top of the key and the flange keyway bed of between 0.015 in, and 0.025 in. max. This can be determined either by a lead wire reading or by a narrow feeler blade. The final task is to fully tighten and pin the retaining nut.

One important point should be borne in Mind when dealing with keys in nitrided shafts. Extra care is needed in removing and replacing keys, as any force or rough treatment can remove chips of metal from the keyway wall and edges.


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