The basices of fits
Clearance Fits
A clearance fit always has a gap between the two mating parts.
The diagram below shows a clearance fit between a shaft and a hole
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Transitional Fits
This type of fit may result in interference, or clearance
This type of fit can be used for items such as snap fits
The figure below illustrates this condition for a hole shaft pair
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Interference fits always overlap and are used mainly for press fits where the two parts are pushed together, and require no other fasteners
The figure below shows an interference fit for a hole shaft pair
PRACTICE PROBLEMS
1. On a ferris wheel we have a 3.5" running journal that is to be pressure lubricated. The fit selected for this application is RC4. Use a tolerance diagram to determine the tolerances required on a final drawing. Sketch the hole, and shaft using appropriate drafting techniques.2. Do complete drawings for a 3.000" hole shaft pair if they have a RC3 fit.
3. Clearance fits are found in,
a) fitted assembly.
b) interchangeable assembly.
c) selective assembly.
d) all of the above.
4. Which statement is more true?
a) production errors cause tolerances.
b) there are no standard tolerances.
c) both a) and b) are completely true.
d) neither a) or b) is true.
5. Given the diagram below, what will the average interference/clearance be?
a) 0.008"
b) 0.020"
c) 0.032"
d) none of the above
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7. A hole shaft pair uses a bushing. We know that the fit between the shaft and bushing is LC5, with a nominal diameter of 7" and the fit between the bushing and outer hole is 8" with an FN3 fit. (8%)
a) Draw the tolerance diagrams.
b) Draw the final parts with dimensions and tolerances.
8. What will the gap between the shaft and the bushing be?
