DRIVING, FORCING AND TAPER FORCING FITS.

[Stanley]

DRIVING, FORCING AND TAPER FORCING FITS.

Taken from ‘TEXT BOOK OF ADVANCED MACHINE WORK’. By Robert H Smith of the Massachusetts Institute of Technology. Written in 1919 and published originally in 1925 by the Industrial Education Book Co and re-published by Lindsay Publications, Bradley, IL, in 1984.

[This publication, though it is eighty years old is still regarded as one of the most comprehensive manuals of fitting and machining ever published.]

Page 216

[The text refers to ‘shafts’ but applies equally to hollow bushes.]

37. Driving or drive fits, easy and hard are made by turning the shaft to size with allowance for filing. For easy fits, file, or grind until shaft will enter hole about two-thirds length of fit with hand pressure; for hard fits, one-third. The former are used for light-keyed fits and small work; the latter for ordinary work which may be removed for repair.

38. Forcing or force fits. In assembling and erecting machinery, nothing is more important than the proper fitting of the parts that have to be driven or forced together, or driven or forced apart, when making repairs. Examples of forcing fits are gears, couplings, locomotive driving wheels, crank pins, car axles, rod bushing, crank disks, various kinds of bushings, linings into cylinders, various parts of engines, generators and motors, iron bands on wagon-wheel hubs, crank shafts into automobile fly wheels, various parts of built-up cranks, or any two machine parts that have to be joined by forcing one into the other with sufficient power to prevent them ever becoming loose. Attention. To avoid abrasion and destruction of work lubricate both surfaces with machine oil. For heavy work use cylinder oil, white lead, or grease.

HOLE DIAM. SHAFT/BUSH DIAM LIMIT OF S/B DIAM + OR -

.00 to .49 .00075 .00025
.50 to .99 .0015 .0005
1.00 to 1.49 .0025 .0005
1.50 to 1. 99 .0035 .0005
2.00 to 2. 49 .0045 .0005
2.50 to 3.24 .0055 .0005
3.25 to 3. 99 .0065 .0005
4.00 to 4. 99 .0075 .0005
5.00 to 5.99 .0085 .0005
6.00 to 8. 00 .0095 .0005

39. Taper forcing fits. - For some classes of machinery. such as marine and engine work, taper forcing fits are used. The hole is bored to a taper of .060” to 1” and the shaft or bush ground or turned the same but large enough when put together by hand to stop about one-fourth to one-eighth of its length from the desired location, then forced to place. Large taper holes are often scraped true to gages before forcing the shaft into place. On some classes of work, the hole is made straight and the shaft ground or turned to a taper of about .001” to 1”, which makes an effective fit.

SCG/19 May 2005