Tolerance Dimensioning Interchangeable Manufacturing Tolerancing Nominal Size Basic Size Actual Size Allowance By B. Cowan & R. Cash

Mass Production Interchangeable manufacturing allows parts made in widely separated localities to be brought together for assembly. That the parts all fit together properly is an essential element of mass production. Without interchangeable manufacturing, modern industry could not exist, and without effective size control by the engineer, interchangeable manufacturing could not be achieved. Dimensions should be given to as large a tolerance as possible without interfering with the function of the part to reduce production cost. Manufacturing to close tolerance is expensive.

Basic Dimension Toleranced Dimension

Unilateral Tolerance Bilateral Tolerance Unilateral Tolerance allows variation in only one direction. From basic size. Bilateral Tolerance Bilateral Tolerance allow variation in either direction from basic size.

Other Methods Of Positioning and Indicating Tolerances Bilateral and Unilateral

Specify Tolerance By Note NOTE: All dimensions Plus or Minus 1/16 Inch

Tolerance

Tolerance

Glossary Of Terms Mating Parts are parts that fit together within a degree of Accuracy. Tolerance is the difference between the limits prescribed for a single part. Allowance is the tightest fit between two mating parts. Nominal Size is an approximate size that is usually expressed with common fractions. Basic Size is the exact theoretical size from which limits are derived. The basic size expressed as a decimal

Shaft Hole Tolerance is the difference between the limits prescribed for a single part. The Tolerance for the Shaft is .002 Hole

Allowance is the tightest fit between two mating parts. The smallest hole and the largest shaft. The Allowance for the Shaft and Hole is .003

2 1/2 Inch Shaft Nominal Size Basic Size

Type of fits between mating parts when assembled. Clearance Fit is a fit that gives a clearance between two assembled mating parts. Interference Fit is a fit that results in an interference between the two assembled parts. The Shaft is larger than the hole. Transition Fit can result in either an interference fit or a clearance fit. The shaft can be either larger or smaller than the hole. Line Fit can result in a contact of surfaces or a clearance fit between shaft and hole. Page 389

American National Standard of Limits and Fits RC Running or Sliding Clearance Fits - Intended to provide a similar running performance with suitable lubrication allowance. Piston in a car. LC Locational Clearance Fits - Intended to determine only the location of the mating parts. FN Force Fits or shrink fits constitute a special type of interference fit, normally characterized by maintenance of constant bore pressure throughout the range of sizes. Page 393

Example: Specify a RC3 Fit for the 1 1/4 Inch Shaft and Hole See Page a25 in the Appendix

Nominal Size Range Hole Shaft Basic Size 1.2500 Nominal Size Range Hole Shaft 1.19 - 1.97 +1.0 -1.0 -0 -1.6

Nominal Size Range Hole Shaft 1.19 - 1.97 +1.0 -1.0 -0 -1.6 Multiply by .001 Nominal Size Range Hole Shaft 1.19 - 1.97 +.0010 -.0010 -0 -.0016

Nominal Size Range Hole Shaft 1.19 - 1.97 +.0010 -.0010 -0 -.0016 Add or Subtract From Basic Size To Calculate Tolerance.

Nominal Size Range Hole Shaft 1.19 - 1.97 +.0010 -.0010 -0 -.0016 Hole 1.25 + .0010 = 1.2510 1.25 - 0 = 1.2500 Shaft 1.25 - .0010 = 1.2490 1.25 - .0016 = 1.2484

Hole 1.25 + .0010 = 1.2510 1.25 - 0 = 1.2500 Shaft 1.25 - .0010 = 1.2490 1.25 - .0016 = 1.2484