how to read 2d part drawings
How to gear up a technical drawing for CNC machining
Technical drawings are non necessary to request a quote, but they are still very important and widely used in the manufacture, as they improve the communication of technical requirements betwixt the designer/engineer and the machinist.
Why are technical drawings still important?
It is necessary to include a technical drawing to your gild when your 3D CAD model includes:
-
Threads (internal or external)
-
Features with tolerances that exceed the standard
-
Individual surfaces with specific finishing requirements (surface roughness etc)
These requirements cannot be conveyed in a 3D CAD file.
Even if your design does not include the above, it is generally a good practice to back-trail your 3D CAD file with a drawing when placing a CNC gild. Normally, the 3D CAD file is used for programming the CNC machine and the drawing is used as a reference throughout the machining process. Most CNC service providers tin can also industry parts directly from a technical drawing and they frequently prefer them over 3D CAD files, because:
- They are trained to interpret apace the geometry of a part from the 2nd cartoon
- Information technology is easier to identify the master dimensions, functions and the critical features of a part
- Information technology is easier to assess the cost of manufacturing the office
In that location are many different standards and best practices for drafting a technical drawing. Information technology does not matter which techniques yous utilize to draft your technical cartoon, as long as all the technical requirements are communicated clearly.
Pro Tip: In the instance cartoon of this commodity, the model is fully-dimensioned. This is recommended but not necessary, as the bones dimensions of the part are conveyed in the 3D CAD file. To save time, you can comment in your technical cartoon only the most important features that you want to exist measured and the threads.
A technical drawing is not required to get an instant CNC quote.
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The beefcake of a technical drawing
A typical technical drawing consists of the following parts:
- A title cake
- An isometric/pictorial view of the office
- The main orthographic views of the part
- Department views or detail views
- Notes to the manufacturer
The title block
The championship block contains bones data about the function, such as the function name, the textile, the finishing and color requirements, the proper noun of the designer and the visitor. It is important to fill up in this basic information, equally they inform the manufacturer about the role of the part.
The title block besides contains other technical information, such every bit the scale of the drawing, the standard used for dimensioning and tolerancing.
Some other chemical element that is usually present in or near the title block in the angle projection. The angle projection determines the way the views are arranged in the drawing. Typically, drawings drafted using ASME standards (U.s., Australia) use 3rd bending project and ISO/DIN standards (Europe), similar the drawing of this example, use 1st angle projection.
The pictorial (isometric) view
Adding one or more 3D pictorial view of the part to your drawing is recommended, as it makes the drawing easier to understand in a glance.
Isometric views are used for this purposes, equally they combine the illusion of depth with the undistorted presentation of the parts geometry (vertical lines remain vertical and horizontal lines are drawn at 30o).
The main orthographic views
Most information almost the geometry of the part is conveyed in the chief orthographic views.
These are two-dimensional depictions of the three-dimensional object, representing the exact shape of the part, equally seen from the outer side of a bounding box one side at a time. Only the edges of the parts are drawn this way to permit for the clearer communication of dimensions and features.
For most parts, 2 or three orthographic views are sufficient to accurately describe the whole geometry.
Department views
Department views tin can exist used to testify the internal details of a function. The cutting line in a chief orthographic view shows where the part is cross-sectioned and the cross-hatch pattern of the section view indicates regions where material has been removed.
Technical drawings tin take multiple section views with 2 messages linking each cutting line with each section view (for case A-A, B-B and so on). The arrows of the cut line bespeak the management you lot are looking at.
Usually department views are placed in-line with an orthographic view, simply they can also be placed elsewhere in the drawing if there is not enough infinite. The part can be sectioned forth its whole width (like in the example above), forth half its width or at an angle.
Note: The edges of hidden internal features can also exist represented in an orthographic using dashed lines, but section views add more clarity.
Detail views
Detail views are used to highlight complex or hard to dimension areas of a chief orthographic view.
They are typically circular in shape (placed offset to avoid defoliation) and are annotated with a single alphabetic character that links the detail view with the master drawing (for case A, B then on).
Particular views tin can be placed anywhere on the drawing and tin use a dissimilar scale than the residual of the drawing, as long as this is clearly communicated (like in the example).
Notes to the manufacturer
Notes to the manufacturer can exist added on the technical drawing to convey additional information that was not included in the technical drawing.
For example, instructions to intermission (deburr) all abrupt edges, specific overall surface finish requirements, and a reference to a CAD file or to an other component the role in the cartoon interacts with can all be added to the notes of your technical drawing.
Sometimes symbols are used instead of text. For instance, surface roughness is unremarkably annotated with a symbol.
Note: If only one surface requires a specific surface roughness finish, so it should be annotated on the drawing and not on the notes. The standard surface roughness of the parts machined on Hubs is Ra 3.2 μm (125 μinch). Finishes to a surface roughness of Ra 1.6 μm (64 μinch) and 0.8 μm (32 μinch) are as well bachelor.
Fix a technical drawing in 7 steps
Here is a summary of the steps yous should follow when drafting your technical drawing:
Step i. Define the most important views and place the relevant orthographic in the centre of the drawing, leaving plenty space betwixt them to add dimensions.
Footstep 2. If your part has internal features or complex and difficult to dimension areas, consider adding department views or particular view accordingly.
Stride 3. Add construction lines to all views. Construction lines include centerlines (to define planes or axes of symmetry), heart marks, and center mark patterns (to define the location of the middle of holes or of circular patterns).
Step 4. Add dimensions to your cartoon, starting with the most important dimensions showtime (more tips on this are given in the side by side section).
Step v. Specify the location, size and length of all threads.
Step six. Add together tolerances to features that need higher accurateness than the standard tolerance (in Hubs this is ±.125 mm or ±.005'').
Pace 7. Make full in the title block and brand sure that all relevant information and requirements that exceed the standard practices (surface terminate, deburring etc.) are mentioned in the notes.
When your cartoon is fix, consign is as a PDF file and adhere it to your order.
Now that you lot are familiar with the basic structure of a technical drawing, let's delve deeper into the specifics of adding dimensions, annotations and tolerances.
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Tips for calculation dimensions, tolerances & annotations
Adding critical dimensions
If your part is accompanied with a 3D CAD file, the dimensions that you lot add on the technical drawing are the dimensions that will be checked past the manufacturer. Information technology is recommended to dimension all important features on your drawings though to avert errors.
Hither are some tips to aid you lot dimension your models:
- Start past placing the overall dimensions of the part.
- Side by side, add the dimensions that are well-nigh critical for functional purposes. For example, the distance between the ii holes in the example drawing are the most of import.
- Then, add together dimensions to other features. A good practice is to identify all dimension starting from the same baseline (likewise known as datum), as shown in the example.
- The dimensions should exist placed on the view that describes the feature most clearly. For case, the dimensions of the threaded holes are non included in this view, as they are more clearly described in the detail view A.
- For repeated features, add dimensions to only one of them, indicating the total number the characteristic is repeated on the current view. In the example, two identical holes with a counterbore are specified using a 2x in the callout.
More information on calculation dimensions to your cartoon can be plant in this commodity by MIT.
Hole callouts
Holes are common features in CNC machined parts. They are usually machined with a drill sot they take standardized dimensions.
They often also include secondary features, such every bit counterbores (⌴) and countersinks (⌵). Adding a callout instead of dimensioning each private characteristic is recommended.
In the example below, the callout defines ii identical though holes with a counterbore. The depth symbol (↧) tin can be used instead of calculation an additional dimension to the cartoon.
Adding Threads
If your parts contain threads, then these must be clearly specified on the technical drawing. Threads tin be defined by merely indicating a standard thread size (for example M4) instead of a diameter dimension.
The recommended manner to define a thread though is past using a callout, as callouts add clarity to the drawing and permit the specification of pilot holes and threads with different length.
In this case, the commencement operation should define the dimensions of the airplane pilot pigsty (the advisable diameter tin can exist establish in standard tables), and the second operation the dimension (and tolerance) of the thread.
Important: Ever add a "cosmetic" thread to your 3D CAD files instead of a "modelled" thread.
Specifying tolerances
Tolerances divers using different formats on a master orthographic view
Tolerances define a range of acceptable values for a sure dimension of the part. Tolerances tell a "story" about the function of the part and are especially important for features that interfere with other components.
Tolerances come up in many different formats and tin can be applied to whatsoever dimension on a drawing (both linear or athwart).
The simplest tolerances are the bilateral tolerances, which are symmetrical around the base of operations dimension (for example, ± 0.1 mm). At that place are also unilateral tolerances (with different upper and lower limit) and interference tolerances that are defined in technical table (for example, 6H).
Note: Tolerances are only required on a technical drawing when they must exceed the standard value. When y'all place an club with Hubs, the standard tolerance is ±.125 mm (or ±.005'').
A more advanced style to define a tolerance is GD&T (Geometric Dimensioning & Tolerancing). A flatness tolerance (⏥) was defined in the example to a higher place. Here is a brusk introduction to GD&T:
Geometric Dimensioning & Tolerancing (GD&T)
The Geometric Dimensioning & Tolerancing (GD&T) system is more difficult to use than standard dimensioning and tolerancing, but is considered superior, as it communicates technology intent more conspicuously. Using GD&T overall looser tolerances tin can be defined, while still fulfilling the main design requirements, improving quality and reducing price.
In the above instance, true position (⌖) was used to define the tolerance of this pattern of holes. Other common geometric tolerances include flatness (⏥) and concentricity (◎).
It is out of the scope of this commodity to describe in depth how yous can apply GD&T to your designs, as it is a very complex field of study. An excellent introduction to the topic can be found here.
We will requite you though the basic noesis you need to read them in case you ever meet them in a drawing. Hither is an example:
This callout defines eight holes with a nominal diameter of 10 mm and a tolerance of ± 0.1 mm to their diameter. This ways that no matter where you measure out this diameter, the upshot of the measurement must exist between 9.ix and 10.1 mm.
The true position tolerance defines the location of the center of the hole in respect to the 3 main baseline edges (datum) of the part. This ways that the centre axis of the hole must always be within an platonic cylinder that has a middle at the location defined by the theoretically exact dimensions in the drawing and a diameter equal to 0.one mm.
This practically means that the center of the hole will non drift abroad from its designed location, guaranteeing that the part can fit to the rest of the associates.
On Hubs, we encourage the addition of GD&T to your parts, just it is recommended to use them simply for critical assemblies and at after stages of the design procedure (for example, during full-calibration production), as they have higher metrology requirements, increasing the cost of a one-off prototype.
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Source: https://www.hubs.com/knowledge-base/how-prepare-technical-drawing-cnc-machining/
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