Starting from point O, draw the bending angle B = 90 (2 rays), and then press with point O as the center.

bend radius

Draw an arc ...

2.

It should be pointed out that:

Shrimp waist

The angles of each part of the elbow are inconsistent.

Total angle

Be divided by ...

Pitch number

, this is wrong! No matter how many joints there are in shrimp waist elbow. ...

3.

along with

point to

Draw the diameter of the elbow (377) as the midpoint, and

At both ends

Dot draw two lines perpendicular to the diameter line; Intersect in the first part ...

4.

Draw the third section in the same step, connect the intersection points, and complete the elbow dimension drawing;

5.

If it is an elbow with more than three sections, the angle of the middle section must be twice that of the first and last sections. Then take it. ...