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SHOP NOTES 473
SHOP NOTES
Standard Sizes of American Machinery Catalogs.
9 x 12 inches, largest size.
6 x 9 inches, regular size.
4X x 6 inches, medium size.
3 x \% inches, pocket size.
Shrink Fit.
The allowance to be made for a shrink fit will vary more or
less according to the nature of the work and the judgment of
the designer.
When shrinking a collar on a shaft or similar work, an
allowance of 0.002 inch to 0.003 incn wn*l do for a shaft of one
inch diameter, and as the shaft is larger in diameter add 0.0005
inch to the allowance for each inch the diameter is increased.
For instance, a shaft of 6 inches diameter may for a shrink
fit be made 0.007 i ncri larger than the hole. However, there may
be cases where it is better to allow less, because frequently a
shrink fit, in want of suitable tools, only is used instead of a
press fit.
Press Fit.
The force required to press a shaft into a hole made for a
press fit will depend not only on the allowance made on the fit,
but also on the kind of material, the length of the fit, the finish,
etc. Press fits are frequently made so that a pressure of 5 to 10
tons per inch diameter is required to force the shaft into its
hole.
When the length of the fit is from one to two times its
diameter, and the finish is good and smooth, an allowance of
three-quarters to one and one-quarter of a thousandth of an
inch may do well for pressing a one-inch shaft of machinery
steel into a hole in cast iron or machinery steel, and as the
shaft increases in size the allowance may be increased about
half of one-thousandth for each inch the shaft is increased in
diameter; but there is no hard and fast rule to go by, judgment
and experience are the best guides.
A shaft of machinery steel 4 inches diameter, 8 inches
long, straight fit, made 0.004 mc^ larger than the hole in the
cast iron gear required 40 tons to press it into place. White lead
mixed in machinery oil was used as a lubricant.
A shaft of machinery steel 2% inches diameter, 5 inches
long fit, pressed into a gear of machinery steel at a force of
about 10 tons, when the shaft was by actual measurement made
0.00 1 inch larger than the hole in the gear. White lead mixed
in machinery oil was used as a lubricant.
When pressing shafts into gears or similar things, the
strength of the hub must be considered and also the strength
of the shaft, because if the shaft is long it may buckle under
the pressure. The shaft is in this case under the same condi-
tion regarding strength as a long column, see page 224.
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