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Finish marks (Y') used on machine drawings show surfaces to be finished by machining (fig. 1-6). Machining provides a better surface appearance and a better fit with closely mated parts. Machined finishes are NOT the same as finishes of paint, enamel, grease, chromium plating, and similar coatings. NOTES AND SPECIFICATIONS Blueprints show all of the information about an object or part graphically. However, supervisors, contractors, manufacturers, and craftsmen need more information that is not adaptable to the graphic form of presentation. Such information is shown on the drawings as notes or as a set of specifications attached to the drawings. NOTES are placed on drawings to give additional information to clarify the object on the blueprint (fig. 1-2). Leader lines show the precise part notated. A SPECIFICATION is a statement or document containing a description such as the terms of a contract or details of an object or objects not shown on a blue print or drawing (fig. 1-2). Specifications describe items so they can be manufactured, assembled, and maintained according to their performance requirements. They furnish enough information to show that the item conforms to the description and that it can be made without the need for research, development, design engineering, or other help from the preparing organization. Federal specifications cover the characteristics of material and supplies used jointly by the Navy and other government departments. LEGENDS AND SYMBOLS A legend, if used, is placed in the upper right corner of a blueprint below the revision block. The legend explains or defines a symbol or special mark placed on the blueprint. Figure 1-2 shows a legend for an electrical plan. THE MEANING OF LINES To read blueprints, you must understand the use of lines. The alphabet of lines is the common language of the technician and the engineer. In drawing an object, a draftsman arranges the different views in a certain way, and then uses different types of lines to convey information. Figure 1-6 shows the use of standard lines in a simple drawing. Line characteristics
Figure 1-6.-Use of standard lines. such as width, breaks in the line, and zigzags have meaning, as shown in figure 1-7. SHIPBOARD BLUEPRINTS Blueprints are usually called plans. Some common types used in the construction, operation, and maintenance of Navy ships are described in the following paragraphs. PRELIMINARY PLANS are submitted with bids or other plans before a contract is awarded. CONTRACT PLANS illustrate mandatory design features of the ship. CONTRACT GUIDANCE PLANS illustrate design features of the ship subject to development. STANDARD PLANS illustrate arrangement or details of equipment, systems, or parts where specific requirements are mandatory. TYPE PLANS illustrate the general arrangement of equipment, systems, or parts that do not require strict compliance to details as long as the work gets the required results. WORKING PLANS are those the contractor uses to construct the ship. CORRECTED PLANS are those that have been corrected to illustrate the final ship and system arrangement, fabrication, and installation.
Figure 1-7.-Line characteristics and conventions for MIL-STD drawings. ONBOARD PLANS are those considered necessary as reference materials in the operation of a ship. A shipbuilder furnishes a completed Navy ship with copies of all plans needed to operate and maintain the ship (onboard plans), and a ship's plan index (SPI). The SPI lists all plans that apply to the ship except those for certain miscellaneous items covered by standard or type plans. Onboard plans include only those plans NAVSHIPS or the supervisor of ship building consider necessary for shipboard reference. The SPI is NOT a check list for the sole purpose of getting a complete set of all plans. When there is a need for other plans or additional copies of onboard plans, you should get them from your ship's home yard or the concerned system command. Chapter 9001 of the Naval Ships' Technical Manual (NSTM) contains a guide for the selection of onboard plans. |
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