Understanding Production Drawings and Mechanical Drawing Reading
Production drawings, also known as working drawings, provide essential information for manufacturing machines or structures. They include dimensions, material details, assembly instructions, and more. This legal document ensures manufacturing standards adherence and serves as a guide for production. Mechanical drawing reading involves interpreting details like tolerances, projections, and scales indicated in the title block. It is crucial for accurate manufacturing and assembly processes.
- Production Drawings
- Mechanical Drawing
- Manufacturing Standards
- Assembly Instructions
- Mechanical Drawing Reading
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1- INTRODUCTION A production drawing, also known as working drawing, supplies information and instructions for the manufacture or construction of machines or structures. A production drawing should provide all the dimensions, limits, special finishing processes, surface quality, etc. The particulars of material, the number of components required for the assembly, etc., are given in the title block.
The production drawing of a component should also indicate the sub-assembly or main assembly where it will be assembled. Since the working drawings may be sent to other companies to make or assemble the unit, the drawings should confirm with the standards followed in the country. For this reason, a production drawing becomes a legal document between the parties, in case of disputes in manufacturing. Working drawings may be classified into two groups: (i) detail or part drawings and (ii) assembly drawings.
Types of Production Drawing A detail or part drawing is nothing but a production or component drawing, furnishing complete information for the construction or manufacture of the part. This information may be classified as: 1. Shape description: this refers to the selection of number of views to describe the shape of the part. The part may be drawn in either pictorial or orthographic projection; the latter being used more frequently. Sectional views, auxiliary views and enlarged detailed views may be added to the drawing in order to provide a clear image of the part. 2. Size description Size and location of the shape features are shown by proper dimensioning. The manufacturing process will influence the selection of some dimensions, such as datum feature, tolerances, etc.
3. Specifications: this includes special notes, material, heat treatment, finish, general tolerances and number required. All this information is mostly located near the title block. 4. Additional information such as drawing number, scale, method of projection, date, names of the part, etc., come under additional information which is included in the title block. Since the craftsman will ordinarily make one component at a time, it is advisable to prepare the production drawing of each component, regardless of its size, on a separate sheet. Figures below show the detailed drawings of a template jig and gear.
Guide on how to read Mechanical Drawings 1. Always start with reading the details in the title block. This information is regarded as the context in which the drawing should be perceived. The details should give you the following information; o General tolerances o Projection details o Scale used in the drawing o Status of the drawing (Preliminary, Approved, etc.) o Name of the component or assembly o Contact details of the drawing owner o Mass o Units used in the drawing o Sheet number and number of sheets.
Guide on how to read Mechanical Drawings 2. The next step is to read the notes in the drawing (outside the title block). Any information in the notes that conflict with the title block should be considered as the correct information hence the notes will in all instances, supersede the title block information. 3. Read the Bill of Material (BOM). The bill of materials is a list of the components and the quantity that makes up the general assembly. The BOM is usually tabulated on the first page. 4. Make sure you have at hand all the relevant pages for the assembly drawings. Drawings could be part of series and hence the entire series should be present in order to be able to translate the information.
Guide on how to read Mechanical Drawings 5. Understand the difference between the visible lines, hidden lines and phantom lines. o Visible lines indicate an edge is visible in relevant view. o Hidden lines indicate the edge is behind a face o Phantom lines indicate edges of structure that are relevant but not included in the drawing or phantom lines could also mean a tangent line (where a curve starts or ends) o Centre lines indicate the geometric center of the assembly. 6. Understand the projections, sections and details. View the drawing itself disregarding the dimensions and try to visualize how and what the assembly looks like in 3D. Most new drawings will have an isometric view to assist. Use the sections and details as a start point and you will soon realize that the details and sections have been created to highlight important components or features.
7. Using the BOM try to find the components in the drawing in order to understand the role the component plays. 8. Look at the notes that have a leader (arrow) to the assembly, this information is usually vital to the assembly and its functionality. 9. If in doubt, ask. Drawings are essentially a transmittal of instructions and if you don t understand the instructions then it is likely that they may have been vague in order to prompt an enquiry with the owner of the drawing. This is common practice in highly elaborate assemblies that are not a mass produced. 10. Use the dimensions in the drawing to be able to grasp the size of the component/Assembly and even use a tape measure or ruler to gage the size.
Remember this process may take up to an hour or even more depending on the complexity of the assembly and on the experience of the reader. If the drawing is too much to absorb, then it is better to put the drawing down and resume after a few hours. This will allow a better perception of the lines and also allow the subconscious to mull over the details whilst the conscious is distracted.
Examples Rear tool post is generally used on capstan lathes, mainly for parting-off operations. It is fixed on the cross-slide in the slots, provided at the rear side of the lathe. Study the drawing shown in( Fig. 1)and answer the following: 1. What is the overall size of the tool post? 102mm 70mm 62mm 2. How many bolts are provided for fixing the tool, and what is the size of each bolt? 3, M10 3. What type of tool can be used with it? Parting tool 4.What is the maximum height of the tool holder? 25mm 5. How many screws are provided to locate the tool? 2
6. How is the tool holder fixed to the cross slide? By 2 Nos. of M6 Hex. socket headed set screws 7. What is the purpose of the threaded hole marked X ? For adjusting the tool height, by means of a screw 8. Explain the note 4 HOLES, M10. There are three tapped holes in the body to clamp the tool in position by screws and the fourth tapped hole is at the bottom of the base. The size of the tap is 10mm.
Example 2 2- Relating to drawing in figure (2) answer the following: 1-What is the tolerance of the 38 mm diameter spigot? 2-What is dimension (A)? 3-What is the angle of projection? 4-How many surfaces are machine finished? 5-How many holes require drilling? 6-What are the overall dimensions?
