Limits and fits Flashcards
What are limits and fits?
A set of rules relating to the dimensions and tolerances of machined parts.
What is a clearance fit?
The maximum size of the shaft is always smaller than the minimum size of the hole.
Name the types of clearance fit.
- Loose running fits
- Free running fits
- Close running fits
- Sliding fits
- Locational clearance fits
What is an interference fit?
The maximum size of the shaft is always bigger than the minimum size of the hole.
Name the types of interference fit.
- Press fit
- Driving fit
- Forced fit
What is a transition fit?
The maximum size of the shaft is somewhat equal to the minimum size of the hole.
Name the types of transition fit.
- Similar fits
- Fixed fits
What standard is used for limits and fits?
BS4500 (now known as ISO limits and fits), included as an appendix in BS8888.
How are hole sizes allocated in limits and fits?
Each range of hole size is allocated a capital letter and a number.
How are shaft sizes allocated in limits and fits?
Each range of shaft size is allocated a lower case letter and a number.
What is the nominal size of the shaft hole for a precision running fit example?
25mm diameter.
What does ES stand for in common abbreviations?
Upper deviation for holes.
What does ei stand for in common abbreviations?
Lower deviation for shafts.
Fill in the blank: The maximum material condition (MMC) indicates when both the shaft and the hole are on _______.
[maximum material condition]
What is the upper limit of a hole size of 25mm in an H8 fit?
+0.033mm.
What is the lower limit of a shaft size of 25mm in an f7 fit?
-0.041mm.
What is the clearance for a shaft and hole at maximum material condition for a nominal size of 25mm?
0.020 mm.
True or False: Interference fits require the maximum size of the shaft to be smaller than the minimum size of the hole.
False.
What is the purpose of calculating fits?
To ensure proper interaction between machined parts.
What is the tolerance unit used in the tables for bores/holes?
0.001mm.
What is the abbreviation for lower deviation for holes?
EI.
What type of fit is suitable for a precision running fit?
H8 and f7 clearance fit.
What assembly method is used for a forced fit?
Heating the parts with a hole and freezing the shaft.
