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From Chess Group Quality Management System
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Calipers

Diameter of a Cylinder

  1. Measure multiple places on the cylinder
    • Measure at the 3 locations on the cylinder which would be cut if you were cutting the cylinder into fourths.
    • Should the part be less than 0.5", measure in the 2 locations that would divide the cylinder into thirds.
    • Measurements should be taken from the head of the part down (non differentiated parts such as pins have no control on initial side)
  2. If all three measurements are within a 1/10-of-the-dimension-tolerance range (ex. for a dimension with a 0.005 tolerance, 3 recorded measurements on the same part are within 0.005 of each other), record the last measurement
  3. If all three measurements are outside this range, record the last measurement, write a note
  4. If this happens 3 or more times during an inspection, perform a capability index analysis on the difference between the upper and lower measurement for 30 parts.

Length of a Cylinder

  1. If the cylinder is less than 6" it can be measured with a caliper, if it is greater than 12" it must be measured with the CMM. Between here is at the discretion of the quality inspector and must be recorded in the Gage Review
  2. Place the part long-ways in the measuring teeth of the caliper
  3. Turn the part 90 degrees to measure again
  4. If both measurements are within a 1/10-of-the-dimension-tolerance range (ex. for a dimension with a 0.005 tolerance, 3 recorded measurements on the same part are within 0.005 of each other), record the last measurement
  5. If both measurements are outside this range, record the last measurement, write a note
  6. If this happens 3 or more times during an inspection, perform a capability index analysis on the perpendicularity of the head to the cylinder (using the cylinder as a datum) for 30 parts.

Thread Depth

  1. Obtain a threaded bolt at least 5x larger than the expected thread depth
  2. Make sure bolt is threaded all the way to both sides
  3. Screw bolt in until stops
  4. Measure head height to threaded surface
  5. Thread depth = Total Bolt Length - Measured Bolt Length

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Inside Diameter of a Rubber O-Ring

  1. Cut the o-ring so that it may be straightened
  2. Lay the rubber the groove of the ruler and line up with the edge
  3. Lightly lay the rubber in the groove without stretching
  4. Once straight, mark it final point or leave in if it remains straight
  5. Use the calipers to measure from the start of the ruler to where the o-ring (now cut into a line) ends
  6. Take the length and divide by 3.142
  7. Subtract out the width of the rubber itself
  8. This is the inside diameter of the o-ring

Optical Comparator

Chamfer Angle

  1. Hit crosshairs at two points on the shaft side of the part
  2. Hit crosshairs at two points on the base side of the part
  3. Obtain angle from the read-out

Chamfer Length

  1. Hit crosshairs at the exact intersection of the shaft and the chamfer
  2. Hit crosshairs at the exact intersection of the base and the chamfer
  3. Read off only the axis that is stated should be measured from the print
    • If the print measures length of chamfer from starting to base, then only the axis which runs the length of the part is recorded.

Head Radius

  1. The part is setup with a profile view on the optical comparator
  2. Three different points are hit with the crosshairs, between the edge nearest the under-side of the head and the apex of the head. These three different positions should be as equally spaced as possible, cutting the quarter circle into fourths.
  3. Record the measurement radius
  4. Do the same for the other side of the head
  5. If the differentiation is off by more than 1/10 of the dimension tolerance, make a note.
  6. Should this occur on more than 3 parts during the sample, a capability analysis must be done.
    • The preferred method is to use the head of the part to create a virtual sphere on the CMM [However, size may prohibit this]
    • This spherical feature should be extracted using spiral techniques rather than point techniques.

Pins

Drive & Drill Depth

When drive depth differs from drill depth, the most accurate measurement method entails using a cross-sectioned part. Using a pin when measuring drive depth can lead to a deeper reading with the hole. Likewise, using a pin with a conical drilled hole can lead to a reading which is too shallow for drill depth.

These inspection instructions may be followed when measuring an internal drive depth:

Drive Depth
  1. Choose a gauge pin that fits the internal circumcircle of the drive
  2. Place the pin upright on the optical comparator and focus the comparator on the top tip of the pin
  3. Place the crosshairs at the tip of the pin
    1. 20151203 111939.jpg
  4. Zero out the comparator
  5. Place the part, drive down, on the top of the erected pin. 
    1. 20151203 112020.jpg
  6. Move the crosshairs down to the top-most visible part of the pin (as per step 5, the part should now be covering the tip of the pin). 
  7. This is the reading for the drive depth.
Drill Depth
  1. Goto http://www.trianglecalculator.net/
  2. Enter the drill angle into the "A" angle
  3. Enter the pin diameter into "a" side length
  4. Take the result of [180-"A"]/2 and place in for degree  "C"
    1. Screenshot 2015-12-03 08.50.48.png
  5. Look at the Height calculation to the right (not the side length of "b" or "c")
  6. Add the result of step 5 to the Drive depth obtained in part 1.

Repro Rubber

  1. Room temperature must be between 70 and 75 degrees F
  2. Get Base formula (Blue)
  3. Get Catalyst formula (Yellow)
  4. Place equal quantities on a paper pad and mix together with a flat knife. Keep turning over until green
    • For larger cavities: Scoop it into the cavity containing internal measurements
    • For smaller cavities: Insert mixture into a plastic syringe. Place a push rod in the syringe and inject into smaller cavity
  5. Wait for 15 - 17 minutes
  6. Remove rubber and use for measurements
Authors
Aphrodite Rose