Techniques for Effective Analysis of CNC Mechanical Drawings

There are five standard paper formats, each designated by a letter and a number: A0, A1, A2, A3, and A4. In the lower right corner of the drawing frame, a title bar must be included, and the text within the title bar should align with the viewing direction.

 

There are eight types of drawing lines: thick solid line, thin solid line, wavy line, double fold line, dotted line, thin dash line, thick dash line, and double dash line.

 

In a drawing, the visible contour of a machine part should be drawn using a thick solid line, while the invisible contour should be drawn using a dotted line. Dimension lines and dimension boundaries should be drawn with a thin solid line, and the symmetry center line and axis should be drawn with a thin dash line. The width of the dotted line, thin solid line, and thin dash line should be approximately 1/3 of the thick solid line. Paper formats can be divided into five types according to their size, and the drawing format codes are A0, A1, A2, A3, and A4. There must be a title bar in the lower right corner of the drawing frame, and the direction of the text in the title bar is consistent with the viewing direction.

 

There are eight types of drawing lines: thick solid line, thin solid line, wavy line, double fold line, dotted line, thin dash line, thick dash line, and double dash line.

 

In the drawing, the visible contour of the machine part is drawn with a thick, solid line. The invisible contour is drawn with a dotted line. The dimension line and dimension boundary are drawn with a thin solid line. The symmetry center line and axis are drawn with a thin dash line. The width of the dotted line, thin solid line, and thin dash line is about 1/3 of the thick solid line.

 

The ratio refers to the ratio of the size of the figure in the figure to the actual size.

 

The ratio of 1:2 means that the actual size is twice the size of the figure, which is a reduction ratio.

 

The ratio of 2:1 means that the size of the figure is twice the actual size, which is an enlargement ratio.

 

When creating a drawing, it’s important to use the original value ratio as much as possible. If needed, you can use a reduced ratio of 1:2 or an enlarged ratio of 2:1. Regardless of the ratio used, the actual size of the machine part should be indicated on the drawing.

 

All Chinese characters, numbers, and letters on the drawing should be neatly written with clear strokes, uniform spacing, and tidy arrangement. Chinese characters should be written in the long Fangsong font.

 

The three elements of dimensioning are dimension limit, dimension line, and dimension number.

 

Symbols in dimensioning: R represents the radius of a circle, ф represents the diameter of a circle, and Sф represents the diameter of a sphere.

Actual dimensions of parts should be used on the drawing. When dimensions are in millimeters, there’s no need to mark the code or name.

 

When horizontal dimensions are used, the dimension number should be placed upward; for vertical dimensions, the number should be placed to the left. Angular dimension numbers should be written horizontally. If any drawing line intersects the dimension number, it must be disconnected.

 

The slope, which is the degree of inclination of an oblique line to the horizontal line, is represented by the symbol ∠. When marking, the inclination direction of the symbol should be consistent with the slope’s inclination direction. The marked taper direction should also be consistent.

 

The symbol “∠1:10″ indicates a slope of 1:10, while “1:5″ indicates a taper of 1:5.

 

Line segments in a plane figure can be classified into three types: known line segments, intermediate line segments, and connecting line segments. Draw the known line segments first, followed by the intermediate line segments, and finally, the connecting line segments.

 

A line segment with known shape and positioning dimensions is called a known line segment. An intermediate line segment has shape dimensions but incomplete positioning dimensions, and a connecting line segment only has shape dimensions but no positioning dimensions.

 

The projection plane containing the main view is called the orthographic projection plane (represented by the letter V). The plane containing the top view is called the horizontal projection plane (represented by the letter H), and the plane containing the left view is called the side projection plane (represented by the letter W).

 

The three projection views rule states that the main view and the top view have equal lengths, the main view and the left view have equal heights, and the top view and the left view have equal widths.

 

Parts have dimensions in three directions: length, width, and height. The main view can show the length and height of the part, the top view can only show the length and width, and the left view can only show the height and width.

 

Parts have six directions: up, down, left, right, front, and back. The main view can only show the up, down, left, and right directions of the part; the top view can only show the front, back, left, and right directions, and the left view can only show the up, down, front, and back directions.

 

The basic views are the main view, the top view, and the left view. Additionally, there are three additional views: the bottom view, the right view, and the back view.

 

The section view can be divided into three types based on the cutting range: full section view, half section view, and partial section view.

 

The sectioning methods of the section view can be divided into five types: full section, half section, partial section, step section, and combined section.

 

The annotation of the sectional view includes three parts: ① The symbol (section line) indicating the position of the section plane, and letters marked at both ends ② The arrow indicating the projection direction ③ The words “×——×” are written above the sectional view.

 

A sectional view with all annotations omitted indicates that its section plane is drawn after cutting through the symmetry plane of the machine part.

 

The sectional view is used to show the internal shape of the part. There are two types of sections: solid parts and hollow parts.

 

The difference between the removed section and the coincident section is that the removed section is drawn outside the view outline, and the coincident section is drawn inside the view outline.

 

The graphics in the drawing only represent the structural shape of the part. The actual size of the part should be based on the dimensions marked on the drawing.

 

The number of the dimension is called the dimension basis. In the three directions of length, width, and height of the CNC machinery parts, there is at least one basis for dimension in each direction.

The five elements of a thread are thread profile, diameter, pitch, lead, number of threads, and direction of rotation.

For internal and external threads to be screwed together, their profile, diameter, pitch, number of threads, and rotation direction must be consistent.

Threads that meet national standards for profile, diameter, and pitch are called standard threads. Threads that do not meet national standards for the profile are called non-standard threads, and threads that meet the profile standard but not the diameter and pitch standards are called special threads.

The prescribed drawing method for external threads is as follows: the major diameter is represented by ＿d＿, the minor diameter is represented by ＿d1＿, and the termination line is represented by a thick solid line.

In the cross-sectional view, the major diameter of the internal thread is represented by ＿D＿, the minor diameter is represented by ＿D1＿, and the termination line is represented by a thick solid line. For invisible threaded holes, the major diameter, minor diameter, and termination line are all represented by thick solid lines.

Common threaded connection forms include bolt connection, stud connection, and screw connection.

Common types of keys include ordinary flat keys, semicircular keys, hook wedge keys, and splines.

Cylindrical gears can be classified into straight teeth, helical teeth, and herringbone teeth based on the direction of the gear.

The prescribed drawing method for the gear tooth part is as follows:
– The top circle should be drawn with a thick, solid line.
– The pitch circle should be drawn with a thin dotted line.
– The root circle should be drawn with a thin solid line, which can also be omitted.
– In the sectional view, the root circle should be drawn with a thick solid line.

When all surfaces of a machined metal parts have the same surface roughness requirements, they can be uniformly marked in the upper right corner of the drawing. If most of the surface roughness of the part is the same, the same roughness code can be marked in the upper right corner, and the remaining two words can be added in front.

A complete assembly drawing should consist of the following four CNC auto parts:
1. A set of views
2. Necessary dimensions
3. Technical requirements
4. Part number and detail column

The types of dimensions in the assembly drawing are:
1. Specification dimensions
2. Assembly dimensions
3. Installation dimensions
4. External dimensions
5. Other important dimensions.

 

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