7.6 Flashcards
Clearance fit
Always some play after assembly.
Subdivided:
- running = light hand pressure
- free running = without any force
Interference fit
No movement is possible after assembly as inner part is larger then the outer part.
3 subcategories:
- driving fit
Tapped together by hammer for example
- force fit
Forced together by presses, tighter
- shrink fit
Parts are either cooled or heated to shrink or expand parts, tightest.
Transition fit
In between clearance and interference
Parts are nearly same size
Info only :
Basic size of dimensions are given by tolerances.
Allowances
The difference in dimensions that is necessary to give a particular class of fit
Hole based system is. Most commonly used
Tolerance
The total amount of variation in the size of a part
Hole based and shaft based systems
Hole based is designated by a capital letter
Shaft based is designated by a lower case letter
British standard 4500
Based on standard sized holes with the various fits obtained bu using varying sized shafts.
H7 and K6 is a slight interference fit.
What is deviation
The difference between a size and the corresponding basic or nominal size.
Limits and characteristics of wear on shafts and holes
Ovality of a hole
Bow of shaft
Twist of shaft
Limits for bow
Considerable risk of vibration in a bowed shaft.
Limits for twist
Square shafts can be checked using a flat surface
Limits for wear
Can be checked by comparing dimensions to a new component.
Refer to wearable charts for permissible clearance , wear and dime n’envions/clearance when new.
Checking for bow
Set of feeler gauges and a flat surface.
Checking for twist
Witness marks
Strain gauges
