ISE 370 TOLERANCES

Performance Factors Performance Factors > Dimensions Linear Angular > Surfaces

Tolerance Tolerance Allowable Variation from the Dimension Difference Between the Maximum & Minimum Limits

Tolerances Techniques Tolerances Techniques > Bilateral > Unilateral > Limit Dimension

Geometric Attributes Geometric Attributes > Straightness > Flatness > Parallelism > Roundness, Circularity > Concentricity > Squareness > Angularity

Straightness: Straightness: The degree to which a part feature such as a line of axis is a straight line. Symbol

Flatness: Flatness: The extent to which all points on a surface lie in a single plane. Symbol

Parallelism: Parallelism: The degree to which all points such as a surface are equidistant from a reference plane or line. Symbol

Roundness, Circularity: Roundness, Circularity: The degree to which all points on the intersection of a hole & a plane perpendicular to the axis of revolution are equidistant from the axis. Symbol

Concentricity: Concentricity: The degree which 2 or more part features, such as a cylindrical surface & a circular hole have a common axis. Symbol

Perpendicularity: Perpendicularity: The degree which all points on a surface or line are 90 degrees from a reference plane or line. Symbol

Angularity: Angularity: The extent to which a surface is at a specified angle relative to a reference surface. Symbol

Three Types of Fits: Three Types of Fits: > Clearance > Interference Force > Transition

Surface Texture Surface Texture Defined By: > Roughness > Waviness > Lay > Flaw

Surface Texture Max Waviness Height – Max Waviness Width – (Cutoff Length) 63 Lay Symbol (Max Roughness Spacing) Max Average Roughness – Min Average Roughness (Micro-Inches) Surface Texture

Loss of Quality Represents Loss of Quality Represents Loss to Producer >Cost of Repairs >Cost of Rejects >Cost of Customer Dissatisfaction Loss to Society >Cost of Repairs >Cost of Operation >Cost of Maintenance

Quadratic Loss Function Quadratic Loss Function LSLUSL Loss Target x (Value) Loss = k (x – Target) 2 k = Cost Coefficient = Loss site / (Tolerance old ) 2

Window Frame Example Window Frame Example Find “width” tolerance… d 1 = fall out dimension d 2 = too long dimension d (target) = mean of d 1 + d 2 = ½ (d 1 + d 2 ) Convention Tolerance T 0 = ½ (d 2 - d 1 ) Customer Tolerance Range: w = d +/- T 0 Slatsd d 1 d 2

Loss Function Loss Function L(width) = k (width – d) 2 k = Cost(site) / T 0 2 (New Tolerance) T N = |width – d| Cost(mfg) = [Cost(site)/T 0 2 ] * T N 2 New Tolerances: T N = √ Cost(mfg) / Cost(site) * T 0

Tolerance Summary Tolerance Summary > Products & processes should be designed so that they are robust to external sources of variability. > Experimental design methods are an engineering tool to help accomplish this objective. > Operation on-target is more important than conformance to specifications.