Read Aloud the Text Content

This audio was created by Woord's Text to Speech service by content creators from all around the world.

Text Content or SSML code:

Re stack Take Down eve Down Bead. Shra FIGURE 10 .5451-0005 .5451+.0005 Tolerance of Mating Parts be applied to one part and a positive tolerance to the other. Figure 10 illustrates. Unilateral tolerances may be shown in several ways. Figure 11 illustrates a method of showing unilateral tol- erance. Whether bilateral or unilateral, tolerances on elevator layouts are usually designated in inch fractions. On esca- lator layouts tolerances are more apt to be shown in dec- imal form. In ANSI Standard dimensioning, parts of an inch are shown to three decimal places. In a previous example, 3/4" is shown as .750". The final zero has no numerical value, but serves to indicate the desired degree of accuracy. Adding tolerance figures to this dimension confirms the accuracy expected from the machinist. If greater accuracy is required, more decimal places are added. For example a tolerance of plus or minus .0005" is 5 ten-thousandths of an inch. Automotive crankshafts are machined this degree of accuracy. Metric Drawings Where engineering drawings are rendered in metric, the ANSI standard dimension is the millimeter. One inch equals 25.4 millimeters, so one millimeter is a rather large dimension - about 25% larger than 1/32". Accurate met- 7-5/8 +1/64 -0 FIGURE 11 Unilateral Tolerance ric dimensions are shown as a whole number and a deci- eight and one half millimeters to three place accuracy. mal. On a metric drawing, 8.500 indicates a dimension of Remember the earlier exercises in metric. Moving the decimal point three places right gives 8500 micrometers. One micrometer is one one-millionth of a meter-an accurate measurement indeed. Figure 12 shows several features of a metrically dimensioned detail drawing. Note that the dimensions are understood to be in millimeters, and the suffix mm does not appear after the numbers. ±0.05 30 10° ---- ±0.05 28 +0. 2 +0.6 0 FIGURE 12 Metric Detail Drawing SOOT 0 -20. Beginning at the left, the major diameter is shown as 30 millimeters plus or minus 0.05 millimeters. This tol- erance is plus or minus five one hundred-thousandths of a millimeter. Notice that a zero precedes the decimal point in decimal parts of a millimeter, unlike decimal inch parts which do not have the zero preceding. This convention serves to distinguish between metric decimal parts and inch decimal parts. The circle and slash, somewhat like the "NO" symbol used with NO SMOKING or NO PARKING signs indi- cates that the dimension shown is a diameter. Slope of the taper is shown as 10 degrees. Depth of the keyway is indi- cated as 2 millimeters, plus or minus 0.05. Length of the taper is 28 millimeters plus 0.6/minus 0.00 millimeters - an example of unilateral tolerance. Finally, the diameter of the small end of the taper is 20 millimeters plus or minus 0.05 mm. Diameter of the shaft extending beyond is not given on this drawing. Review Questions Check your answers on page 24 23. On a layout showing, for example, distance between guide rails, if the tolerance is not stated it is understood to be 24. Where the upper minus measurem 0125. Tolerances on el 26. On escalator la form. 27. To distinguish b placed ahead c system THREADS The most co tion is the threa guide rails to tin threaded faster In addition t used on adjust adjustable by large part adju braking mecha Another fun mission of po machine is a Simple me include the builders und object by roll building of th circling arou around the ra was probabl thread is a fo leap from th A spiral i it makes wit threads, hel a plane perp wheel, histo What is we standardiza Prior to threads for bolts and m interchang posed a sta of the thre worth thre In the U a standard was later of World ognized b 12