Many people have great technical ideas in their minds, but can’t express them to others. Technical drawings are the standard way to present a technical idea to your manager, investor, or manufacturer with all the necessary details.
In this article, you’ll learn how to make a general technical drawing and get tips on specific technical drawings for CNC machining, sheet metal fabrication, injection molding, and extrusion.
You’ll also find a concise 10-step guide to help you create a standard technical drawing for a part or product.
If you have an idea you want to express, or if you want to work as a mechanical engineer in a company, this brief article will improve your technical drawing skills.
Why Are Technical Drawings Important?
When you design a new concept, you have an idea made in your mind with most of the details.
However, you must present your idea on paper to check possible problems and errors before manufacturing. So technical drawings can save you time and money.
You can also represent your idea to your manager or investor to recognize what you mean in detail.
A technical drawing is a well-known method and common language of conveying the details of a concept, including the shape of the parts, the number of parts to be assembled, the dimensions and their required accuracies, the distances of the parts, the material of the parts, and all the information needed to demonstrate the concept to the manufacturers.
After manufacturing a part, the quality inspector inspects the finished parts based on the technical drawings.
Standards for Technical Drawings
As mentioned in the previous sections, the technical drawing should be used as a common language between a designer, a manager or investor, a manufacturer, and an inspector. So you need some agreed rules or templates on how to create a technical drawing.
Large companies have created some standards to ensure the uniformity of the technical drawings.
These standards tell you what information should be included in the technical drawings and how the information should be presented, including common points of view and the appearance of the information, such as font, line style, and thickness.
Here some of these standards are investigated briefly.
ISO 128 deals mainly with the appearance of the information, including font sizes and symbols. ASME14.5 tells you how to show geometric and dimensional tolerances in your technical drawings, and ANSI/ASME Y14.100 gives some guidance on creating a good technical drawing.
Some other standards deal with specifications for technical drawings in specific regions. For example, BS 8888 is used for technical drawings with British units, and JIS B 0001 is used mainly by Japanese companies.
By using these standards, you can be sure that you have a common and standardized language for presenting your idea to any manufacturer or inspector.
Technical Drawing Views and Other Features
You can represent the information of a part by looking at the part from different angles. This section reviews the 5 different views you can use in technical drawing and their applications.
Orthographic views are the most common views used in technical drawings. These views are orthogonal projections of the part and can represent most of the information needed for manufacturing a part.
You can use the front view, top view, and left view, which are commonly used orthographic views to show the most important information about your part or product.
Sometimes, some details inside the part may not be displayed correctly in orthographic views. In these cases, you can cut out the main part in Cartesian or radial lines and then project the part perpendicular to the section line.
These views are called section views and are used in many technical drawings. The cut-out material is represented by a hatch.
If the part contains some details that need to be shown at different scales, you can use the detail view to show them at a different scale.
All the views mentioned above are 2D projections of the part. The isometric view, on the other hand, looks at the part from a 3D perspective where all three axes can be seen. You can use these views to give the manufacturer a 3D insight into the part or product.
Another 3D view you can use in technical drawings is the exploded view, which is used to show products that are composed of multiple parts. In these views, you can see which parts will be used and how they will be assembled.
How to Quickly Prepare a Technical Drawing
From Model:
Technical drawings are typically used to tell a manufacturer the shape and dimensions of a 3D model. You can easily create a technical drawing from a 3D model. Most 3D modeling software can also perform drawing tasks for you, and the resulting technical drawings are linked to the model.
You should select only the views you need, including orthographic views, section views, detail views, and isometric views, and then choose the dimensions you want to represent.
Since the technical drawing is linked to the 3D model, the software simply inserts the dimensions from the 3D model.
Another option you can use with this method is to update your technical drawing.
If you need to change your 3D model after you have created a linked technical drawing, you can update the technical drawing with just one or two clicks in the drawing window and all dimensions and shapes will be updated based on the new model.
From Scratch:
Sometimes you have an idea in your mind that you want to show to others using technical drawings. In these cases, you don’t have a 3D model of your idea. That’s not a problem!
You can create the technical drawing using basic drawing elements such as points, lines, arcs, etc.
In this way, you can use the basic elements to create the shape you want, and then use constraints to apply the dimensions and geometric features you need. You can also include the required dimensions in these drawings.
AutoCAD is the most popular software for this purpose, which allows you to create your technical drawings from scratch.
What to Include on a CNC Machining Technical Drawing
When you send a technical drawing to a CNC manufacturer, you can use precise geometric and dimensional tolerances to express which dimensions of your part require the greatest accuracy.
You can also specify the areas to be machined using machining symbols. In addition, the machinist can define machining parameters based on the roughness values you have assigned to a surface.
Geometric tolerances and reference lines can specify the machining sequence and the reference points for mounting the part on the table. In addition, some dimensions can directly affect the tools the machinist will use to produce a part.
For example, corners with a small radius require a special tool for fabrication. However, you can also specify the required machining progress, tools, and other machining parameters directly in your drawing by making some notes.
What to Include on a Sheet Metal Technical Drawing
In technical drawings of metal sheets, the most important parameter is the sheet thickness. You can insert it as a dimension in the drawing and also in the drawing table. You should also insert an unfolded view in your technical drawing. It shows the raw sheet before any processing.
You must specify the shape and dimensions of the raw sheet, as well as the location of the bend lines and bend angles in this view. In addition, you can specify the bending radius to get a precise bend in your drawings.
What to Include on an Injection Molding Technical Drawing
The manufacturer needs some special information to produce a part by injection molding. Some of these are essential and must be included in your engineering drawing.
Most of this information is needed for the specifications of the final part, such as the shape and dimensions of the part, the material, the surface roughness, the color, the wall thickness, and any required ribs on the final part.
There are also some other parameters related to the molding process that can be specified in the engineering drawing. These include the position of the gate for injecting the material into the mold and the position and number of ejector pins.
This information can be specified by the manufacturer and is not essential in an engineering drawing, but it would be good if you could specify it in your engineering drawing.
What to Include on a Plastic/aluminum Extrusion Technical Drawing
The extruded parts usually have a constant cross-section in long lengths. Therefore, the cross-section information for your part is essential in your technical drawing. You should specify the dimensional and geometrical accuracy you expect from the finished part.
You should also specify the surface finish, the material, and possibly the specific mechanical properties.
10 Steps to Prepare a Perfect Technical Drawing and What to Include in It
Here you can find a 10 step instruction that guides you to make an applicable technical drawing.
Step 1: Select Your Template
First of all, you should choose or design your template based on the standard that your company or customer need. This template will ensure consistency in all your technical drawings.
Also, using the template, you can adjust all of your standards such as line size, fonts, etc. only one time and there is no need to adjust them for each drawing.
Step 2: Place Your Orthographic Views, Centering Them as Much as Possible
Orthographic views are the most important part of your technical drawing and contain the most information about the shape and geometry of your part.
Therefore, you should place these views in the center of your drawing to attract more attention. Also, you should have enough space around these views to add auxiliary views such as section or detail views.
On the other hand, it is important to choose the right orthographic views that can show the most information about your part.
While the most common orthographic views are the front view, the left view, and the top view, you should use at least two of these views in your drawing.
Step 3: Add Detail and/or Section Views Accordingly
After you have selected the correct orthogonal views, you can add some axillary views to show more detailed information about your part. If there are some details inside your part, you can use section views to show them.
Also, detail drawings are usually used for some features that need a larger scale to show their details.
Step 4: Add the Isometric View
Isometric views show the 3D shape of the part or product and give the user a better insight into its shape. These views help the manufacturer to better realize other views.
Step5: Add Dimensions to Your Drawings
Use dimensions to indicate the overall size of each part, product, or feature in your technical drawing. You should also indicate the position of each part in an assembly.
Cartesian dimensions are mostly used by machinists, while inspectors usually use the shortest distance between two points.
Step 6: Specify the Location, Length, and Size of All Holes and Thread
You must specify the location, diameter, and length of all holes in the technical drawings. You should also specify the thread standard, including the thread type and pitch, and length.
Step 7: Add Tolerances to Critical Features
Fixed dimensions are impossible to achieve when manufacturing a part. Therefore, you must define some acceptable ranges for all dimensions and insert them into the technical drawing by geometric and dimensional tolerances.
The manufacturer and also the inspectors use these tolerances to make and then inspect the parts.
There are some standards for general tolerances that you can specify in your drawing table to consider for your general dimensions. If you use these, you will not have to include a variety of tolerances for all dimensions which would confuse the manufacturer.
However, for features that require different tolerances, or for critical dimensions that require special attention and accuracy, you will need to insert the appropriate geometric and dimensional tolerances.
On the other hand, the geometric tolerances can determine the order of machining progress and also the reference points for mounting the workpiece on the table.
Step 8: Fill the Drawing Table
One of the most important parts of any technical drawing is the drawing table. It must contain the part number, name, revision and quantity of the part as reference information.
In the drawing table, you can insert some characteristics of the part such as material, sheet thickness, mass, area, surface hardness, and so on. You should also include the standards used in the drawing and information about the company that designed or will use the part.
Other information you can include in your engineering drawing is the name of the designer, the reviewer, and the date of design and approval.
For assembly products, you can also indicate in the drawing tables in which product the part is used or which parts are involved in this product.
Step 9: Include All Notes and Additional Instructions to the Manufacturer
The technical drawing is the only information that is provided by you to the manufacturer, the inspector, or any other user. Therefore, they must contain all the necessary information or notes required for the manufacture, testing, or assembly of the part.
The notes may include the manufacturing instructions, test procedure, required surface finish or color, assembly or welding sequence, and so on.
Step 10: Always Check the Drawing Before Publishing
The manufacturer produces the parts or products only on the basis of the information contained in your technical drawing.
If the technical drawing contains any misunderstanding, unclear or wrong information, it can be very time consuming and costly to modify the part, or he may even have to manufacture it again, which is much more expensive.
So remember to check and review all your technical drawings before you publish them. It would be better to have someone else check your drawing to find any unclear or incorrect information.
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