The Inspection of External Screw Threads is sequential, and satisfies the dimensional requirements of FED STD H-28 or ASME B1 as applicable. The following Inspection Procedures are specific, and should be followed without deviation or changes in sequence. For information regarding specific dimensional Limits of Size and the criteria for the acceptance or rejection of an individual element or characteristic, please refer to the actual specification, standard, or product print. To preserve the integrity and reliability of the following Inspection Methods, periodically verify the proper setting of all thread comparators by engaging the appropriate Setting Master. For further information regarding these procedures, please refer to the appropriate Setting Instructions for each Individual Comparator.
External Inspection Procedures
Sequence for differential gaging analysis
- Inspect the Minimum Material – Pitch Diameter. Rotate the product to properly seat the Gaging Elements and also to detect any three (3) point out-of-round conditions. As the part is rotated, note the indicator variations. Engage the product thread in several locations along its axis to detect any taper. Note the extreme high-low indicator variations. Any portion of the full thread which exceeds the Pitch Diameter Limits of Size is cause for rejection.
- Inspect the Maximum Material – Functional Size. Oscillate the part approximately two revolutions to properly seat the gaging elements and to detect any out-of-round conditions. As the length of the thread on the part may exceed segment length of thread engagement, inspect the part in two locations along its axis, verifying that the Pitch Diameter Limits of Size meets the required Limits of Size at any point along the thread axis. Any portion of the full thread which exceeds the Pitch Diameter Limits of Size is cause for rejection.
- Utilizing standard Measurement Equipment such as Digital Calipers, inspect the Major Diameter. The Major Diameter should not exceed the Standard or Specification requirements.
- Lead Error is isolated by comparing the first full thread of the Functional Size Thread Comparator with the full engagement of the same Functional Size Thread Comparator. Any difference is Lead Error (including Uniformity of Helix). When performing Thread Lead Analysis, perform all inspection operations in the same plane. Be sure to eliminate the effect of taper
- Angle Error is isolated by comparing the indicated value of the first full thread of the Pitch Diameter Thread Comparator and the first full thread of the Functional Size Thread Comparator taken in the same position and plane. Any difference is Angle Error.
Without question or exception, it is necessary that all parts and gaging elements are thoroughly cleaned prior to inspection. In addition, a periodic cleaning and inspection of the gaging elements is recommended. For further recommendations regarding gage maintenance and care, please refer to the individual Gage Setting Instructions