1、INCH-POUNDA-A-5947830 September 1999SUPERSEDINGMIL-P-288B12 May 1982Beneficial comments, recommendations, additions, deletions, clarifications, etc. and any otherdata which may improve this document should be sent to: Defense Supply Center Richmond(DSCR), ATTN: DSCR-VBD, 8000 Jefferson Davis Highway
2、, Richmond, VA 23297-5610.AMSC N/A FSC 6675DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited.COMMERCIAL ITEM DESCRIPTIONPROTRACTOR, THREE ARMThe General Services Administration has authorized the use of thiscommercial item description as a replacement for MIL-P-288B fo
3、rall federal agencies.1. SCOPE. This commercial item description (CID) covers two types and three classes ofprotractors with three movable arms used in position, plotting, and hydrographic surveying.2. CLASSIFICATION. The types and classes of protractors provided shall be as follows (see7.2(b).Type
4、I - MetalClass 1 - Three arm, left hand, circularClass 2 - Three arm, right hand, circularType II - PlasticClass 1 - Three arm, bilateral, circular3. SALIENT CHARACTERISTICS3.1 Type I protractors. All materials and hardware used in the construction of type I protractorsshall be corrosion resistant.
5、The assembled protractor shall consist of a circle frame with aninlaid graduated circle and three arms, one of which shall be fixed and attached to the circleframe and two that shall be movable and attached to a pivot center. A tangent screw with vernierscale shall be attached to each of the two mov
6、able arms. A reading glass shall be hinged to arotatable collar, attached to the pivot center. Figure 1 is an example of an acceptable design ofthe ribs for the circle frame.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-A-A-59478210 0 10350350 3608
7、0901002602802701009080 280260270170180170170 170180THREE ARM PROTRACTORTYPE 1 CLASSNSN 6687 -MANUFACTURERSYM2010 2010FIGURE 1. Type I protractor.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-A-A-5947833.1.1 Accuracy. The graduations on the body of
8、the type I protractors shall be such that nograduation mark will vary from its true position by more than 2 minutes of arc. The movablearms shall be mounted in the assembled instrument so as to rotate on an axis at the center of thegraduated circle, with an accuracy such that the maximum error due t
9、o eccentricity shall notexceed 3 minutes of arc. The total error of the assembled protractor shall not exceed 5 minutesof arc.3.1.2 Circle frame. The circle frame shall have a numbered scale engraved on the top surface ofthe frame such that, when assembled with the graduated circle, numerals will ap
10、pear at every 10degree graduation starting at 360 degrees at the fiducial point and continue clockwise indecreasing increments of 10 to 180 degrees, then in increasing increments of 10 to 350 degrees.Numerals shall be 0.070 inch high and shall be filled with black enamel. The base of thenumerals sha
11、ll be toward the center of the circle. The frame shall have a circular groove on theundersurface to receive the guide pins of the clamps. The center of the circle frame shall be adisc not greater than 1-7/16 inches in outside diameter. It shall be connected to the outer circleof the frame by three r
12、adial ribs. The center, ribs, and outer circle of the frame shall befabricated as one integral piece and shall form a rigid support for the arms. The center of thecircle frame shall be fitted for the pivot center. The required identification information shall belocated on the top rib of the circle f
13、rame (see 6.2).3.1.3 Graduated circle. The graduated circle shall be not less than one-half inch wide, with theoutside diameter not less than 6-5/16 inches and the inside diameter not greater than 5-7/32inches. The entire circle shall be accurately graduated at the outer circumference, in degrees an
14、dhalf degrees. The graduated lines shall have a depth of 0.003 inch minimum to 0.005 inchmaximum, shall have a width of 0.005 0.001 inch and shall be filled with waterproof ink orenamel. The length of the graduated lines shall be as follows: 10 degree marks 0.19 inch, 5degree marks 0.15 inch, 1 degr
15、ee marks 0.11 inch, and 30 minute marks 0.07 inch. Numeralsshall be engraved every 10 degrees in both a clockwise and counter-clockwise direction, startingwith zero at the fiducial point and continuing to 180 degrees. The base of the numerals shall betoward the center of the circle.3.1.4 Pivot cente
16、r. The pivot center shall be secured to the center of the circle frame bycountersunk screws or other suitable means. The pivot center shall have a projection above thecenter disc of the frame for retaining the collar of the reading glass, and a projection beneath thecenter disc for retaining the col
17、lars of the two movable arms. The inside and outside surfaces ofthe pivot center shall be true cylinders, concentric with the circle of the instrument, and shall beground to an accurate fit for the collars. The pivot shall be free from imperfections and finishedsmooth.3.1.5 Pivot plugs. Four pivot p
18、lugs shall be furnished for use in marking positions. They shallbe free from imperfections and finished smooth. The outside diameter of the plugs shall allowfor a sliding fit in the pivot center. The four kinds of plugs shall be as follows:a. A cylindrical hollow plug, with a glass or clear plastic
19、bottom, having a hole in thecenter to receive a pencil point and marked with cross lines at right angles on the bottom plasticProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-A-A-594784surface. The glass or plastic bottom shall be set flush in the hol
20、low plug. The hollow plug shallbe painted with white enamel on the inside.b. A solid cylindrical plug with a plunger having a point on its lower end, fitted with aspring to hold the point clear of the bottom when not pressed from above.c. A cylindrical plug, with a glass or clear plastic bottom havi
21、ng cross lines on theundersurface, at right angles and intersecting accurately at the center on the bottom surface. Theglass or plastic bottom shall be set flush in the hollow plug to avoid parallax. The hollow plugshall be painted with white enamel on the inside.d. A solid cylindrical plug having a
22、 short needle point in the center of the base.3.1.6 Arms. The arms shall be flat bars having a length of 18 inches minimum to 18-3/4 inchesmaximum from the center point of the instrument. Each arm shall be one-eighth inch inthickness with a top-edge bevel angle of 20 to 45 degrees along the radial s
23、traightedge and a facewidth of one thirty-second to one-sixteenth of an inch. Each arm shall be 0.6 inch in width at itsouter extremity and shall be tapered to accomplish the following construction. The fixed armshall be secured, by means of screws and pins, to a rib of the circle frame in such a po
24、sition thatthe beveled edge will lie on the radius of the circle, which passes through the fiducial point onthe graduated circle. The two movable arms shall be secured to collars which rotate about thepivot center. Each movable arm shall be fitted with a vernier, clamp, and tangent screw. Thecollars
25、 shall be reduced in thickness, so that when the arms are secured in place they will comeflush with the bottom of the pivot center and lie on the same plane.3.1.7 Straightedges, type I, class 1. Using the center point as datum, the straightedge of the leftmovable arm for the type I, class 1 protract
26、or shall lie on a radius of the circle and shall passthrough the fiducial point of the graduated circle when the left arm of the protractor is closed.The straightedge of the right movable arm for the type I, class 1 protractor shall lie on a radius ofthe circle and shall be at an angle not greater t
27、han 11 degrees, 30 minutes from the fiducial point,when the right arm of the protractor is closed.3.1.8 Straightedges, type I, class 2. Using the center point as datum, the straightedge of the rightmovable arm for the type I, class 2 protractor shall lie on a radius of the circle and shall passthrou
28、gh the fiducial point of the graduated circle when the right arm of the protractor is closed.The straightedge of the left movable arm for the type I, class 2 protractor shall lie on a radius ofthe circle and shall be at an angle not greater than 11 degrees, 30 minutes from the fiducial pointwhen the
29、 left arm of the protractor is closed.3.1.9 Angle range, 260 degrees. The straightedge of the left movable arm for the type I, class 1protractor and the straightedge of the right movable arm for the type I, class 2 protractor shall becapable of laying off angles up to 260 degrees.3.1.10 Angle range,
30、 270 degrees. The straightedge of the right movable arm for the type I, class1 protractor and the straightedge of the left movable arm for the type I, class 2 protractor shall becapable of laying off angles up to 270 degrees.Provided by IHSNot for ResaleNo reproduction or networking permitted withou
31、t license from IHS-,-,-A-A-5947853.1.11 Extension arms. Three extension arms shall be provided. Each extension arm shall be13-1/2 inches long, tapering in width from 0.6 to 0.4 inch at the outer end, and shall be joined tothe permanent arms by scarfing pieces. The scarfing pieces shall be permanentl
32、y attached to theextension arms and secured, when needed, to the permanent arms by means of a threadedthumbscrew and two dowel pins affixed to the scarfing pieces. Extension arms shall be match-marked to the mating arm.3.1.12 Vernier scales. The upper surface of the vernier scales shall be flush wit
33、h the surface ofthe graduated circle. The vernier of each movable arm shall have its zero graduation positionedover the straightedge of the arm. Each vernier shall embrace 14 degrees, 30 minutes of thegraduated circle and shall be so graduated as to permit reading of the scale to l minute of arc.Eac
34、h vernier shall have one additional mark on each end of the scale. The graduationrequirements shall be the same as those of the graduated circle (see 3.1.3). The engravednumerals shall be numbered 0, 10, 20, and 30.3.1.13 Clamps. Each clamp shall be secured to the circle frame by a thumbscrew and gu
35、ided inmotion by a tongue which slides in the circular groove in the underside of the circle frame.3.1.14 Tangent screws. The tangent screws shall be of an appropriate size and have knurled orotherwise slip-resistant heads. Each tangent screw shall be attached to its clamp by a fixed ballworking in
36、a socket joint, and to the movable arm by a ball nut working in a socket joint.3.1.15 Reading glass. The reading glass shall be a 3.0X single-lens magnifier having a focallength of 1-1/2 inches and a clear aperture of five-eighths inch. It shall be hinged to a collarwhich rotates around the pivot ce
37、nter so as to have motion parallel to the plane of the instrument.The field of view of the reading glass, when the glass is parallel to the plane of the instrument,shall be centered over the graduated edge of the graduated circle and the vernier scale.3.1.16 Magnifying glass. A pocket magnifying gla
38、ss of 3.0X magnifying power shall befurnished with each type I protractor.3.1.17 Screwdriver. A screwdriver of good commercial quality, of a size fitting the screws onthe instrument, shall be furnished with each type I protractor.3.2 Construction, type II protractor.3.2.1 Assembly. All materials and
39、 hardware used in the construction of type II protractors shallbe corrosion resistant. The assembled protractor shall consist of a body having a graduated circlewith a fixed integral arm, a pivot center, two movable arms with vernier scales, and thumb nutclamps on each movable arm (see figure 2).3.2
40、.2 Accuracy. The total error of the assembled protractor shall not exceed 6 minutes of arc.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-A-A-5947867/163/64No. 60 Drill7/16 5/16Fiducial line3/64No. 60 DrillVenierClamp0 34020330 3010 350350 10110 250
41、100 26040 32030 33020 3400 Plastic washer50 310210 150200 160180 180 190 170 170 190 160 200 150 210140 220130 230120 240260 100230 1300 10 20 30 220 140THREE ARM PROTRACTORTYPE IISTOCK NUMBERMANUFACTURERCONTRACTINSP. _ U. S.Pivot center280 80290 70270 9050 60 40 320 40310 50300 6050 20 10 40 30 60
42、90 27080 28070 29060 300713-1/2 1/1613-1/2 1/1673/64No. 60 Drill7/165/165-1/2R 1/326-3/32R 1/32 250 110240 120All dimensions are in inchesFIGURE 2. Type II protractor.3.2.3 Body. The body shall be made of a high-polish finished plastic 0.040 inch (nominal)thick. The body shall be a circle 12-3/16 in
43、ches in diameter (plus or minus one-sixteenth inch)with a fixed integral arm extending 13-1/2 inches (plus or minus one-sixteenth inch) from thecenter of the circle. The arm shall taper from a width of 2-1/2 inches measured on thecircumference of the circle to a width of approximately 1-inch at the
44、rounded end. A fiducialProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-A-A-594787line shall extend from the pivot center through the center of the fixed arm for the full length ofthe arm. Two holes, three sixty-fourths inch in diameter, shall be dril
45、led through the fiducialline, one at seven-sixteenths of an inch from the outer end, and the other at 7 inches from theouter end of the arm. The circle shall be accurately graduated on the upper surface (see 3.2.5).The required identification information shall be located on the underside of the body
46、 (see 6.2).3.2.4 Movable arms. There shall be two movable arms made of a high-polish finished plastic0.030 inch (nominal) thick, which shall pivot about the center of the body. Both movable armsshall be the same length as the fixed arm and shall be rounded on the outer ends. Each movablearm shall ha
47、ve a fiducial line extending radially from the pivot center through the greatest lengthof the arm. Each arm shall have a smooth straightedge parallel to and five-sixteenths of an inchdistance from the fiducial line. The smooth parallel edge of one arm shall be to the left of thefiducial line and on
48、the other arm, to the right of the fiducial line, when the two fiducial lines arein coincidence. The shape of each arm on the opposite side to the smooth parallel edge shall besuch that the arm covers approximately 33 degrees of the protractor graduations, when thefiducial lines of the movable arms
49、are in coincidence with the fiducial line of the fixed arm. Thisside of the arms shall extend past the periphery of the protractor body a distance of three-eighthsof an inch, to accommodate a clamp (see 3.2.7), and shall taper toward the outer end at such anangle that the total width of the arm at the outer end is approximately 1 inch. Two holes, threesixty-fourths inch in diameter, shall be drilled through the fiducial line, on
