Chapter 4 - Shop Practices Flashcards
How is accuracy and reliability maintained during the service life of measuring tools?
- tools must be handled with care, kept clean, and used only for their specific purposes
- apply a thin coat of oil to any moving part
For best accuracy, how should the measuring tool be held in relation to the piece to be measured?
Figure 1
- the measuring instrument must be exactly in line with the axis of measurement
What is the accuracy limitation of a measuring tool?
- the accuracy limitation is determined by its smallest scale graduation
What are steel rules made of and what lengths are standard?
- made of hardened and tempered spring steel
- flexible, semi-flexible or ridged steel, graduates in metric or imperial, or both
- available in a variety of lengths: — 6” 150mm — 12” 300mm — 18” 450mm — 24” 600mm
How long is 1mm in inches?
- 1mm = 0.03937”
- 1” = 25.4mm
To what degree of accuracy are metric and imperial steel rules graduated?
- Metric — graduated in millimetres and half-millimetres
- Imperial — graduates in fractions or decimals of an inch - 1/8”, 1/16”, 1/32”, 1/64”
Describe the construction and purposes of a vernier caliper.
- a precision measuring instrument which can be used to measure a wide range of sizes rapidly
- consists of a main frame (beam) and a moveable jaw
Describe the operating principle of a vernier scale.
- a vernier caliper has a main scale on its beam and a vernier scale in the movable jaw
- the beam may be graduated in both of its sides or both of its edges
- May be used to measure inside and outside dimensions and depths
- May also be used as a layout instrument
Describe how to read a metric vernier scale.
1 - read the whole number (3cm = 30mm)
2 - read the number of graduations the moveable jaw has passed (2mm)
3 - read along the vernier scale to find the increment which lines up to a graduation on the beam (0.66 mm)
4 - Add these figures together to achieve the total reading (30.00+2.00+0.66=32.66mm)
Describe how to read imperial vernier scales in both 0.025” and 0.050” graduations
1- note the X” increment on the beam
2- note the 0.X” increment on the beam
3- note the 0.0XX increment on the vernier scale
4- Add together to get total reading
What is the principle of the micrometer based upon?
- based on the pitch and lead of a thread
- at a specific pitch of a thread, the lead is a set distance
List the parts of a micrometer.
- spindle — has a thread ground on its periphery and acts as a bolt
- thimble — has graduations around it and is attached to spindle
- sleeve — has an internal thread which acts as a nut in which the spindle and thimble assembly fit — also has a line along its axis which acts as a datum
- anvil — connected to the sleeve by means of the frame. Acts as a fixed position from which the spindle moves. This distance is calibrated by the graduations on the thimble to the datum line on the sleeve
- ratchet — the amount of torque applied to the thimble can be controlled and allow the user to maintain consistent readings regardless of feel
- lock nut — allows the the spindle to be locked to prevent movement after a measurement is taken
Describe the operating principles of a metric micrometer.
- the spindle thread has a pitch of 0.5mm which equates to a lead of 0.5mm. In one rotation of the spindle, it moves 0.5mm
- the sleeve of the micrometer is graduated in 0.5mm increments
- the thimble of the micrometer is divided into 50 increments around its periphery. Every increment represents 1/100th of a millimeter (0.01mm). Every fifth increment is numbered for easy reading
Describe how to read a metric micrometer.
- note the X mm reading on the sleeve
- note the upper or lower graduation on the sleeve
- note the graduation on the thimble in line with the datum
- Add together to get total reading
Describe the operating principle of an imperial micrometer.
- the spindle thread has a 40 threads per inch (tpi) which equates to a lead of 0.025”. In one rotation of the spindle, it moves 0.025”
- the sleeve of the micrometer is graduated in 0.025” increments
- the thimble of the micrometer is divided into 25 increments around its periphery. Every increment represents 0.001”. Every increment on the thimble is numbered and every fifth increment is numbered for easy reading
Describe how to read an imperial micrometer
- note the reading on the sleeve
- note the upper or lower graduation on the sleeve
- note the graduation on the thimble in line with the datum
- Add together to get total reading
What accuracy can be achieved using a mobile cornered with a vernier scale?
- this vernier scale divides each 0.001” into 10 equal increments which provides reading accuracy of 0.0001”
What are the applications for comparison measuring tools?
- used to measure or gauge variations or clearances
- have no capacity within themselves to show a measurement
- used to compare a size with a known measurement achieved from measuring tools
What are the uses for dial indicators?
- used to measure movements such as the run out of a shaft or to compare parts against each other
- continuous reading dial indicator is used to measure run-out of shafts and other rotary parts
- the back plunger is used to align and set up parts of equipment
What care should be taken to ensure accurate readings?
- take care to ensure that the axis of the indicator spindle is in line with the axis of measurement
Describe how to take a clearance measurement with feeler gauges.
- feeler gauges have each leaf marked with a size
- if a number of leaves are stacked together, the thickness should be checked with a micrometer
Describe how to duplicate shaft sizes and bores with outside and inside calipers.
- outside spring caliper
— the smallest size in which the caliper can pass over the shaft without resistance on its legs represents the size of the shaft - inside spring caliper
— the largest size in which the caliper can rock within the bore without resistance on its legs represents the size of the bore
Describe how to duplicate the size of a bore with a telescope gauge.
- insert the gauge into the bore
- move the handle slightly off the axis of the bore
- release the lock nut to allow the plunger to contact the bore
- snug the lock nut
- arc the handle through the axis of the bore (only once)
- remove the gauge and measure with a measuring tool
What are the purposes of layout tools?
- used to prepare the surface, and to scribe and mark lines, arcs, circles, angles and points
What substances are used to enable the millwright to see the layout lines more readily?
- layout dye or bluing is a blue dye which can be brushed or sprayed onto a surface to enable the layout lines to be seen more easily
- white latex paint or chalk can be used if dye not readily available
Describe the uses for the following:
- scribers
- pencil-like tool used to mark layout lines on the surface of the workpiece
- single or double-ended
Describe the uses for the following:
- straight edges
- used to lay out straight lines, and to check surfaces for flatness and alignment
Describe the uses for the following:
- spring dividers and trammels
Spring dividers
— used to scribe arcs and circles and to transfer measurements
— useful in dividing lines, arcs and circles into equal distances
Trammel
— used in the same manner as a spring divider except that the beam allows the points to be spread a larger distance
Describe the uses for the following:
- hermaphrodite calipers
- used to lay out lines parallel to an edge and to find the centre of round or irregular shaped objects
- by passing the bent leg past the point, they can also be used to scribe a line parallel to a flange
Describe the uses for all the main parts of a combination set.
- Steel rule
— allows for the attachment of the various heads - Square head
— used to lay or lines or measure parts on 90 and 45 degrees, lay out and measure surfaces parallel to an edge, or act as a depth gauge
— also has a spirit level parallel to the square edge and a scribe fitted into it - Protractor head
— used to lay out and measure angles (1 degree accuracy) - Centre head - used to find the centre of round stock