Metrology Flashcards
What’s the purpose of calibration?
Provide confidence about a measurement instruments accuracy and repeatability
What is a gauge block
Very accurately machined steel alloy or ceramic block.
Used to calibrate callipers and other measurement instruments
What is a gauge bar
Used to calibrate measuring equipment
What is a CMM
Coordinate measuring machine
What does a cmm do
Uses discrete points on an objects surface to measure it
How does a non contact cmm machine work, and where might it be used
Uses video technology to measure discrete points.
Used in application where contact would deform object
What type of cmm machine is portable
Multi axis measurement arm cmm
Which part of a cmm contacts the object being measured?
Touch trigger probe
What is a key problem with cmm’s that is often overlooked
They need a skilled operator to be used
What properties would a good touch trigger probe stylus have?
Stylus should be as short and stiff as possible.
The stylus ball should be as large as possible
Why is good surface texture important?
Can improve:
- fatigue resistance
-bearing properties
-wear resistance
What properties should a bearing surface have?
Contact area should have valleys to hold lubrication.
Perfect surface would bond with other surface
Would a larger or smaller surface area suffer more wear?
Smaller
What is the definition of roughness?
Irregularities from cutting processes
What is the definition of waviness?
Irregularities produced by machine vibration and deflections under cutting force
What is the definition of errors of form
Departure from geometrical shape
Out’ve waviness and roughness, which is primary and which is secondary?
Primary - Roughness
Secondary - Waviness
How many measurements are taken to determine surface texture
5
What is the equation for roughness?
Roughness = (Z1+Z2+Z3+Z4+Z5)/5
What errors can influence calibration?
- Temperature
- Pressure
- humidity
- vibration
- electrostatic fields
- electromagnetic fields
- human interaction
What shaft property will increase bearing wear?
If the shaft is not round
What is the first step in measuring roundness?
Find the centre point of the shaft using a vblock
What are the 2 types of roundness measuring machines?
Rotating workpiece
Fixed workpiece
What are the advantages and disadvantages of the fixed workpiece machine? (Roundness)
- precision spindle carries light load, high accuracy with low cost
- work table can be large, allowing for large parts
- computer aided cantering
- Internal and external measurements possible
