7.6: Fits and Clearances Flashcards
What does the number system in drill sizes range from?
From 1 to 80
What are the three types of fit?
Clearance fit
Transition fit
Interference fit
What is an inteference fit?
When there is no possible movement after the assembly because the inner part is larger than the part it fits into
What are the three classes of interference fit?
Driving fit
Force fit
Shrink fit
What is the driving fit?
When the shaft is slightly larger than the hole and the allowance is such that the parts can be assembled by driving, like hammer taps
What is a force fit?
When the parts are forced together, usually by presses and the interference is larger than that for a driving fit
What is a shrink fit?
When the parts are joined permanently, with the outer member heated or the shaft cooled. The interference is greater than the force fit
What is a transition fit?
When the mating parts are almost the same size
What are allowances?
The difference in dimension that is necessary to give a particular class of fit between two parts
What are tolerances?
The total amount of variation in the size of the part, which is the smallest size subtracted from the largest size
What are the British Standard System divided into?
21 Hole classifications with a capital letter
21 shaft classifications with a small letter
16 grades of accuracy with a number
What are the ISO standards divided into?
28 hole and shaft classifications
20 grades of accuracy
What is the Newall system?
Provides a range of clearance, transition and interference fits for sizes up to 12 in
What is hole basis?
A system of fits relating to basic or nomial hole size with fundamental deviation being H
What is shaft basis?
A system of fits relating to basic or nominal shaft size with fundamental deviation being h
