NAVIGATION SYSTEMS Number: P079 Date: 08-25-2000 METROLOGY & CALIBRATION CALIBRATION/SERVICE PROCEDURE THREAD MEASURING WIRES GENERAL PROCEDURE PREPARED BY: R.E. Etter APPROVED BY: REVISIONS DATE REV BY PAGE AFFECTED REMARKS 08-08-90 REE all Original 07-17-96 CB all Convert to Word 08-25-00 JPS all Format Update FORM 963-E REV. 5-74 Page 1 I010P079.DOC
SECTION 1 INTRODUCTION 1.1 Thread Measuring Wires come three wires in a set, sized to measure the pitch diameter of an external thread of a given pitch. 1.2 Thread Measuring Wires are utilized with the three wire technique of measuring pitch diameter. With this technique, the wires of correct size are placed in the thread groove, two on one side and one on the opposite side. The contact face of the measuring machine must be sufficiently large to touch both wires. The size wire that touches exactly at the mid-slope of a thread of a given pitch is termed the the best sized wire for that pitch. SECTION 2 REFERENCE 2.1 Applicable Manufacture s Manual or brochures. 2.2 Calibration Recall and Information System (CRIS) New CRIS Users Guide. 2.3 Environmental Requirements for Calibration Operation are per Manufacturers Process Manual AH-MFG-24.06. 2.4 Screw Thread Standard Handbook H28, with change notices dated May 28, 1986. SECTION 3 SPECIFICATIONS 3.1 The specifications are listed in the CRIS by applicable Metrology number. The Specifications may be displayed from the Equipment screen by selecting Show Specification per the New CRIS Users Guide. 3.2 Range: 0.00722 to 0.14434 inch diameter. 3.3 Accuracy: Diameter within 0.000020 inch. Variations in diameter: Not to exceed 0.000010 inch. Out of roundness: Not to exceed 0.000010 inch. 3.4 Straightness will be checked by rolling the wires on a surface plate. Form 963-E Rev. 5-74 Page 2 I010P079.DOC
3.5 Wires that measure 48 to 80 threads per inch are permitted slight bends. Wires that measure 4 to 44 threads per inch must be replaced if they are bent. SECTION 4 PRELIMINARY NOTES 4.1 For service required use General Service Procedure, Mechanical Test Equipment, number 2000. 4.2 Calibration shall be performed in an environment that conforms to REFERENCE item 2.3 or to Manufactures Specifications. 4.3 If any of the requirements cannot be met refer to the Manufacturers Manual for corrective action. 4.4 The Thread wires shall hereafter be referred to as the TI. SECTION 5 STANDARDS REQUIRED 5.1 The Standards listed below have been selected on the bases of their higher accuracy level when compared to the unit under test. Equivalent Standards must be equal to or better than the Minimum- Use-Specification. 5.2 Minimum-Use-Specifications for Standards listed are 1/4 the accuracy required by the TI. STANDARDS USED MINIMUM-USE-SPECIFICATIONS MANUFACTURER/MODEL Surface Plate Grade A Collins Microflat Thread Wires* Diameter Within 0.000005 Inch Deltronic or Van Kuren Steel Cylinder Ground and Lapped Size : 0.125 and 0.750 Inch Deltronic Precision Measuring Machine Tolerance: ± 0.000010 Inch Used as a Transfer Standard * Note: Use corrections when required. Pratt & Whitney 24 Inch Form 963-E Rev. 5-74 Page 3 I010P079.DOC
SECTION 6 PRELIMINARY INSTRUCTIONS 6.1 Visually inspect the TI for any damage that would affect the operation or accuracy. 6.2 Clean the TI with alcohol prior to calibration. 6.3 Allow wires to temperature stabilize prior to calibration. 6.4 Roll the wires across the surface plate to ascertain the wires are not bent. Remove any wires that do not meet the requirements of the specification section of this procedure. 6.5 Calibration of the TI consists of comparing the measurement of each wire with a standard wire of the same nominal size. 6.6 Read the entire procedure before beginning the calibration. SECTION 7 DETAILED PROCEDURE 7.1 Select a standard wire of the same dimension as the three wire set to be calibrated. 7.2 Adjust the gaging force of the standard measuring machine in accordance with the following table. GAGING FORCE THREADS per INCH MEASURING FORCE 20 or LESS 2.5 POUNDS above 20 through 40 1.0 POUNDS above 40 through 80 0.5 POUNDS above 80 through 140 0.25 POUNDS above 140 0.125 POUNDS 7.3 Select the 0.125 inch cylinder for thread pitches above 40 threads per inch or the 0.750 inch cylinder for thread pitches of 40 threads per inch or less. 7.4 Place the cylinder selected perpendicular on the movable platform of the measuring machine. Form 963-E Rev. 5-74 Page 4 I010P079.DOC
7.5 Center the steel cylinder between the gaging anvils of the measuring machine. 7.6 Place the standard wire selected in step 7.1 along the side of the cylinder and adjust the measuring machine until zero null is achieve. Note the reading on the digital readout. 7.7 Replace the standard wire with one of the wires to be calibrated then repeat the measuring process in step 7.5. Note:Each wire is to be measured at three different locations, approximately 0.2 inch from each end and in the middle. 7.8 Repeat step 7.6 for the remaining two wires. 7.9 Calculate the common diameter of the three wire set by averaging the readings obtained in step 7.6 and 7.7. The average diameter equals the total of all measurements divided by the number of measurements. 7.10 Repeat steps 7.1 through 7.8 for the remaining three wire sets to be calibrated. 7.11 If the calculated diameter for any of the three wire sets exceed the tolerance specified in step 3.3 of this procedure, replace the low sized wire of the set and repeat steps 7.1 through 7.8. SECTION 8 DOCUMENTATION INSTRUCTIONS 8.1 Enter pertinent information into CRIS using Work performed screen. 8.2 Affix Calibration/Service due decal to TI container per New SRIS USERS guide. 8.3 Bag/Seal TI as required. NOTE:By sealing each three wire set container individually, minimum calibration time will be necessary for the next calibration. Form 963-E Rev. 5-74 Page 5 I010P079.DOC