WORKSHOP DRAWING & DESIGN STANDARDS

Size: px

Start display at page:

Download "WORKSHOP DRAWING & DESIGN STANDARDS"

Angel Wade
5 years ago
Views:

1 WORKSHOP DRAWING & DESIGN STANDARDS Purpose: Function: Content: This handout is intended to provide a summary of basic drawing guidelines which will: a) enhance communication between you and the workshop technicians, b) improve the project outcomes by improving product quality while reducing manufacturing costs (and frustration). The manufacturing drawing allows for precise communication between the designer and the manufacturer of a part. As such it provides excellent opportunities for either efficient communication or a complete lack thereof. The effectiveness of a manufacturing drawing will be enhanced when both the drafter and the interpreter of the drawing have the same understanding of all the elements which appear there. It is very important, then, that standard drawing and manufacturing practices be employed wherever appropriate. The manufacturing drawing is generally thought of as primarily providing information about the shape of the part being produced. To this end, a variety of views such as orthographic, sectional, auxiliary, etc. are used. While pictorial views can convey a good impression of the general appearance of an object, orthographic views can more easily convey the detailed information needed to manufacture the part. The drawing also conveys non-graphic (textual) information which is equally important. Much of this information conveys essential design information. Important examples include: 1. Dimensions, units and standard sizes 2. Tolerances on locations, sizes and geometrical characteristics such as straightness, flatness, squareness perpendicularity), and roundness (circularity) 3. Material specification 4. Surface finish, condition 5. Special processing specifications Other information is required for the management of the different aspects of the design and manufacture and includes information normally included in the title block such as: 6. Part identification 7. Project identification 8. Personnel identification and responsibilities 9. Drawing control information such as drawing no. version, revisions, dates etc. The following notes are intended to address some specific items noted above.

2 Projections: Since different orthographic standards prevail in different areas of the world, it should be noted that third-angle projection is normal practice in N. America. The symbol for third angle projection is shown alongside and should be shown on the drawing to minimise potential for confusion. Units: Imperial units of measure are almost always more cost effective due to the nature of the local manufacturing infrastructure in place. Materials, machines, cutting and other tools, and measuring instruments are predominantly available in inch sizes. Standard sheets of metallic and non-metallic materials are typically measured in feet (e.g. 4 Η 8, 4 Η 12) as are full lengths of bar, structural sections, and hollow stock. Most stock materials of this type are purchased and brought into Engineering Stores as 20 foot lengths. Dimensions and Tolerances and standard sizes: Imperial units of measure may be based upon either fractional inch or decimal inch sizes. - The fractional scale is based on a normal minimum increment of 1/64" (0.0156"). Thus, standard fractional drill sizes (for example) include: 17/64", 23/", 11/16", 5/8", 3/4", and 1/2". - The decimal scale is based upon a normal minimum increment of 0.001" (often referred to as one "thou"). The choice of appropriate dimension and tolerance will clearly reflect the manufacturing process to be used and the accuracy which can be achieved by that process. For example, from Table 15.5 in the textbook, it can be noted that a turning process (on a lathe) can typically achieve a tolerance of from to inches (2-10 'thou') without undue expenditure of time and effort. Use of standard sizes will very often result in reduced manufacturing costs. Therefore whenever possible, dimensioning should reflect this whether applied to material stock sizes or tooling sizes. Some standard sizes deviate from the above outline. The important instances to note are as follows: - Sheet and wire products are often specified by referring to a gauge number. The table shown below provides some sample gauge information applicable to sheet thicknesses.

3 ENMF Workshop Dwg. Stds. P. 3 of 4 GAUGE CHART - Some Sample Values (inches) Galvanized Steel Sheet Stainless Steel Sheet Aluminum, Brass, Copper, Steel Tube; Copper Sheet Cold & Hot Rolled Steel Sheet Brass & Aluminum Sheet Gauge No. Brown & Manuf'r's. Birming'm U.S. Galvanized Sharpe Standard Wire Gauge Standard Sheet Gauge Note that while fractional sizes have equal-sized increments (as for an arithmetic series), gauge numbers increments represent a progression which is closer to a geometric series such that increments approximate to a constant percentage of an adjacent size. Similar considerations apply to some other standard sizing systems such as the drill size systems outlined below. - Machine Screw Sizes: Small threaded fasteners (smaller than 1/4" major dia.) are specified by using a size number ranging from 00 to 12 and a thread designated as a threads per inch (TPI) number. A 6- fastener has a size of '6' and TPI. Thread forms typically conforming to the Unified National Coarse (UNC) or Unified National Fine (UNF) should be used wherever possible. Some common examples are outlined in the following table. Further information is presented in Machinery's Handbook. Size No. Major Dia. (In.) Coarse UNC (TPI) Fine UNF (TPI) Number & Letter Drill Sizes: It should be noted that in addition to fractional drill sizes there exists a series of drill sizes denoted by letters A - Z and another series designated by numbers Letter drill diameters are shown in the table below.

4 ENMF Workshop Dwg. Stds. P. 4 of 6 Letter Dia. in. Letter Dia. in. Letter Dia. in. Letter Dia. in. A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A complete list of number drill sizes may be found in Machinery's Handbook but a sample of sizes is presented in the following table. Drill No. Dia. in. Drill No. Dia. in. Drill No. Dia. in. Drill No. Dia. in Pipe sizes "The size of all pipe is identified by the 'nominal' pipe size. The manufacture of pipe in the nominal sizes of 1/8 inch to 12 inches, inclusive, is based on a standardized outside diameter (OD). This OD was originally selected so that pipe with a standard OD and having a wall thickness typical of the period would have an inside diameter (ID) approximately equal to the nominal size." (Machinery's Hdbk. 22nd ed.) Wall thickness for pipe is usually conveyed by means of a 'Schedule Number'. Size and weight data for some sample pipe sizes and schedule numbers are outlined in the following table. PIPE SIZE CHART - Some Sample Values (Imperial sizes) (Information extracted trom ANSI B as presented in Machinery's Hdbk. 22nd ed.) Nominal Size (in.) O.D. (in) Wall Thickness (in.) Schedule No. Commercial Designation* Weight/foot (lb/ft) 1/

5 ENMF Workshop Dwg. Stds. P. 5 of 4 1/ / / X / X X / X / X

6 ENMF Workshop Dwg. Stds. P. 6 of * = Standard; = Extra Strong; X = Double Extra Strong

BOLTS AND NUTS Square Bolts( Table 1 ) Hex Nuts ( Table 7 ) Heavy Hex Nuts (Table 7) Heavy Hex Structural Bolts ( Table 2 )

BOLTS AND NUTS Square Bolts( Table 1 ) Hex Nuts ( Table 7 ) Heavy Hex Nuts (Table 7) Heavy Hex Structural Bolts ( Table 2 ) BOLTS AND NUTS 1493 An externally threaded fastener that must be assembled with a nut to perform its intended service is a bolt. (Example: heavy hex structural bolt.) An externally threaded fastener that