Tolerances And Fits Flashcards
What is basic hole size in terms of tolerance?
The hole is your size, your shaft is what is adjusted to mate parts
Describe basic shaft size in terms of tolerances
Your shaft is your “basic size” and your hole is the part being adjusted
What does unilateral tolerance mean?
That all tolerances and dimensions are applied in only 1 direction
What does bilateral tolerance mean?
That the tolerances and dimensions are applied in both directions
What is a class 3 fit?
Interference
What causes fatigue failure?
Repeated stress has work hardened it
What is the main characteristic of stainless steel?
Corrosion resistance
What is the approximate percent of medium carbon steel?
.30-.50 percent
What form of tolerance does +/- 0.002 represent?
Bilateral
What part of a dimension is the total permissible variation in its size?
Tolerance
Twisting forces put what sort of stress on a key?
Shear
Where should a millwright place the bearing on a shaft if he has a choice?
As close to the loaded components as possible
What is the best tool for determining radial runout?
Dial indicator
Sliding fit is an example of what allowance?
Positive allowance
What is Prussian blue used for?
Identifying contact patterns for fitting and adjusting
What will improve with carful attention to surface finish, large fillets, runout keys, sharp edges, and closer diameter reduction ratios?
Fewer stress fractures
What is tolerance?
Total permissible deviation of a dimension on a part
What is the difference between the max and min limits of size called?
Tolerance
What are the two systems for applying tolerances to the dimensions of a mating part called?
Basic hole
Basic shaft
“The design size of the hole is basic the allowance is on the shaft” is what tolerance system?
Basic hole
What is the excess material on a part called?
Allowance
Define allowance
Excess material on a part
“The design size of the shaft is the basic size and the allowance is in the bore of the mating part” is what tolerance system?
Basic shaft
What is unilateral tolerance?
When all tolerance for the drawing is applied in one direction only
What is bilateral tolerance?
When the tolerance for the drawing dimensions are applied in both directions.
When the drawing tolerance dimensions go in both directions what is it called?
Bilateral
When the drawing dimension tolerances go in 1 direction what is it called?
Unilateral tolerance
What is another word for allowance?
Fit
What does “positive allowance” refer to?
The minimum clearance between mating parts.
What does “negative allowance” refer to?
The maximum interference between parts
The maximum interference between parts is called what?
Negative allowance
The minimum clearance between parts is called what?
Positive allowance
What is the degree of fit?
Result specifying a tolerance to each mating part
What are the two basic types of fit?
Clearance
Interference
What is clearance fit?
When mating parts maintain some clearance between them
What is interference fit?
When there is some resistance between mating parts
What are the 5 main classes of fit?
Running/sliding clearance fit
Locational clearance fit
Transition fit
Locational interference fit
Force/shrink fit
What class of fit provides room between mating parts for lubrication?
Running/sliding fit
What does running fit refer to?
Rotating parts
What does sliding fit refer to?
To parts the slide on each other
In sliding fit what does the clearance refer to?
The surface above
How is a gib used with a dove tail?
To adjust the clearance between the mating parts
Where is locational clearance fit used?
Normally stationary parts which can be freely assembled or disassembled
Where is transition fits used?
On mating parts
What is transition fit?
When the tolerance on mating parts partially overlaps so either a clearance or interference fit can occur
Where is locational interference fits used?
Situations where accurate location and rigid alignment is of utmost importance
What is locational fit NOT meant to do?
Transmit frictional loads from one part to another
What is force/shrink fits?
When the tolerance of mating parts fully overlaps causing an interference fit
How is the method of assembly determined? (3)
By the amount of interference
Availability of equipment
Size of the parts to be assembled
What are the three common methods of assembling mating parts?
Forced fitting
Shrink fitting
Expansion fitting
What is forced fitting?
One part is pressed onto another part
What is shrink fitting?
The hub is heated to expand to allow it to be easily assembled onto the shaft
What is expansion fitting?
The shaft is cooled so the part may be easily slipped onto the shaft
What is the best method for force fitting?
Hydraulic press with a manual lever preferably
What are the heat sources that can be used for shrink fitting? (6)
Hot water/oil bath
Steam
Torch
Furnace
Electric resistance heating
Electric induction heating
What are the 4 methods for expansion fitting
Industrial refrigerator
Liquid air
Liquid nitrogen
Alcohol/dry ice
What are the 4 main types of presses?
Fixed in place hydraulic
Mechanical arbor
Free standing hydraulic
Portable hydraulic press
What are manual pullers used for?
Light pulling jobs that don’t require large forces
What are the 3 situations where a manual puller would be used
Pulling a component off a shaft
Pulling a component out of a hole
Pulling a shaft out of a component
What are the two most common styles of manual pullers?
Jaw
Rod
How would you choose a manual puller?
The diameter of the adjusting screw should be at least 1/2 the size of the shaft
In a hydraulic application how would you choose a puller?
A puller that can withstand a force exerted in tons 7-10x the diameter of the shaft in inches
A minimum bore diameter and maximum shaft diameter is what fit?
Interference
A maximum bore diameter and minimum shaft diameter is what fit?
Clearance fit
Each group of fits breaks down into grades. What are the grades?
RC 1 - RC 9
What is a RC 1 fit?
Close sliding fit
What is RC 9 fit?
Loose running fit
What type of allowance is sliding fit?
Positive
