Machine Designers Reference. J. Marrs
BSI PD 5304 (Section 9), EN 1088, ISO 14119, and in the book Product Safety Management and Engineering (Chapter 11). Be aware, also, that the interlocking part of interlocking guards are a part of the machine’s “safety-related control system,” discussed in some detail in a footnote later in this chapter.
7 Although customarily this information and instructions has been in manual form, increasingly, it is becoming more and more common to find electronic media used as well. The book Writing and Designing Manuals provides further information on writing machine manuals (cited in Section 2.5).
8 These being: “3. Instruct and warn the user,” “4. Describe requirements for training the user,” and “5. Recommend personal protective equipment.”
9 In manufacturing settings, tags are normally attached to lockout devices identifying the person who placed the lockout on the machine. In cases where multiple persons are working on a machine simultaneously, it is not uncommon for there to be multiple identifying tags placed on a lockout device. This prevents communication errors between work crews from jeopardizing the lockout.
10 Plug-connected electric machinery for which exposure to hazards is controlled by unplugging the machine and by the plug and cord being under the exclusive control of the employee performing the maintenance work is exempted from OSHA’s lockout/tagout standards.
11 Emergency Stops and their associated parts are components of a part of a machine’s control system identified as the machine’s “safety-related control system”, or SRCS. A machine’s safety-related control system is that part of the machine’s control system that prevents a hazardous condition from occurring, either (1) by preventing the initiation of a hazardous situation (e.g., two-hand controls), or (2) by detecting the onset of a hazard (e.g., emergency stop switches). Safety-related control systems are designed to perform safety functions. A machine’s SRCS must continue to operate correctly under all foreseeable conditions, and because they perform a safety function, the components in the system must be verifiably reliable. Industry standards ISO 138491-1 “Safety Related Parts of Control Systems” (ISO 13849-1 replaces EN 849-1), EN 62061 “Safety of Machinery — Functional Safety of Safety-Related Electrical, Electronic and Programmable Electronic Control Systems,” and, related to control reliability of pneumatic and hydraulic systems, ANSI B 155.1 “Safety Requirements for Packaging Machinery and Packaging-Related Converting Machinery” address requirements of machine safety-related control systems and their components.
12 BSI, The British Standards Institution, another significant standards development and distribution organization, is the National Standards Body (NSB) of the U.K. (BSI organized the first Commonwealth Standards Conference in 1946, which led to the establishment of the International Organization for Standardization (ISO).) CEN includes BSI transpositions of EN standards.
13 CSA is not a part of the Canadian government. CSA is a not-for-profit organization that represents Canada on various ISO committees.
14 ASABE, ASME, and SAE are engineering societies that, among other things, develop safety standards applicable to the design and construction of machines associated with their industry.
15 UL is an independent organization, not a part of any government, that, among other things, develops (and provides testing services for) safety standards applicable to products and machines.
16 (as observed in ANSI B11-2008)
17 The IEC (International Electrotechnical Commission) is a non-governmental internationally recognized standards organization that develops and issues standards for electrical and electronic technologies and related equipment, including componentry often used in machinery.
Contents
3.1LIMITS, FITS, AND TOLERANCE GRADES
3.2TOLERANCES ON DRAWINGS, AND GD&T
Tables
3-1Commonly Used Limits and Fits
3-2Selected ANSI Tolerance Grades
3-3Selected International Tolerance (IT) Grades
3-4Manufacturing Process Average Tolerance Grades
3-5Selected Limits of Size, Holes (Inch)
3-6Selected Limits of Size, Shafts (Inch)
3-7Additional Selected Limits of Size (Inch)
3-8Selected Limits of Size, Holes (Metric)
3-9Selected Limits of Size, Shafts (Metric)
3-10Additional Selected Limits of Size (Metric)
3-11Common Implied Tolerances (Inch)
3-12Common Implied Tolerances (Metric)
3-13ANSI and ISO Geometric Symbols
3-14Area Under the Standard Normal Curve
3-15Effect of Material Modifier on Stack-Up
3-16Effect of Least Material Condition Modifier on Stack-Up
3-17Boundary Calculations for Positioned Features of Size
3-18Stack-Up Method Application Matrix
LIMITS, FITS, AND TOLERANCE GRADES
All parts and features have some variation from ideal size, and this variation is controlled by the designer through the application of dimensional tolerances. The system of limits and fits allows the designer to quickly tolerance parts that fit together with a predetermined clearance or interference. Limits of size refer to the two tolerances or deviations applied to a dimension that set the upper and lower limits for that dimension. These tolerances are meant to be applied to nominal parts that were designed ‘line to line’ (without clearance when nominal size)