In recent years, a new type of space frame structure has rapidly gained popularity in the construction industry. Its characteristics include easy component processing, flexible and convenient installation, and unique design. The space frame structure applies mechanical principles to distribute gravity at specific angles, achieved through connections between steel pipes and bolted ball joints. The bolted ball is a crucial component of this structure, and its processing quality directly affects the mechanical properties of the space frame. The quality control of the bolted ball involves six indicators: 1. Ball blank diameter; 2. Ball roundness; 3. Distance between the bolted ball's threaded hole end face and the ball's center; 4. Parallelism of the threaded hole end faces on the same axis; 5. Angle between the axes of two adjacent threaded holes; 6. Perpendicularity of the threaded hole end face to the axis. We can see that the angle between the axes of two adjacent threaded holes requires ±30°. This parameter is very important, but measuring it using traditional methods is cumbersome. Therefore, we designed a bolted ball angle measuring instrument. In addition to measuring angles, this instrument, when used with some tools, can also measure other parameters of the bolted ball. In national standards, the diameter specifications for bolted balls are generally from 100mm to 260mm. The number of screw holes varies, generally 3-9 holes. The axis of each screw hole passes through the center of the ball. The position of the screw holes on the bolt ball is marked in angular coordinate space on the drawing. The bolt ball angle measuring instrument also uses the angular coordinate method to read the value. The two coordinates of the measuring instrument are respectively through the horizontal coordinate (X coordinate) and the vertical coordinate (Z coordinate) of the center of the ball, and the instrument is positioned by moving the positioning rod to read the rotation angle of the measuring instrument to achieve measurement. The structural principle of the measuring instrument is shown in the figure. [align=center]Schematic diagram of bolt ball angle measuring instrument[/align] A turntable 2 is set on the base 1 of the measuring instrument. The function of these two components is to form a planar angle rotation system. The rotation shaft system can adopt a ball bearing structure, which has high rotation accuracy and can meet the load-bearing capacity requirements. At the same time, a vernier 3 with a graduation value of 2' is installed on the base, and a locking handwheel 5 is also provided. A 360° scale with a graduation value of 30' is inlaid on the outer circumference of the horizontal turntable 2. The accuracy index of the entire horizontal turntable system is controlled within 3' to 4'. An arc-shaped boom 6 is fixed on a horizontal turntable 2. Gears and racks are inlaid on the boom. Rotating the guide handwheel 8, through the action of the gears and racks, drives the positioning rod component 7 to move together on the arc-shaped boom. Additionally, a dial 4 and a vernier 3 are inlaid on the arc-shaped boom and the positioning rod component. The horizontal axis passing through the center of the bolt ball is the 0 mark, upward is the positive mark, and downward is the negative mark, with a measurement range of ±75° and an accuracy controlled within 3' to 4'. The upper and lower threaded core rods 9 can be pulled inward and outward on the arc-shaped boom and the base respectively, and can also be fixed. The two threaded core rods are required to be on the same axis, and the axis direction of the core rods is marked with a circumferential indicator line in millimeters. During measurement, first screw the bolt ball 10 onto the lower threaded core rod and fix it, then screw in the upper core rod, and adjust the indicating scale of the upper and lower core rods to be the same size. The purpose of this is to position the bolt ball through the end face of the standard core rod so that its horizontal axis passes through the actual 0 mark line of the arc-shaped boom. Under the same batch measurement specifications, this adjustment means the lower core rod can remain stationary and requires no further adjustment. For specific readings, first rotate the turntable and the positioning rod component on the arc-shaped arm to insert the positioning rod into the first screw hole A1. This positioning rod has a 1:10 taper at its front end and is positioned by contact with the crest of the internal thread; this positioning method has a given accuracy specification. At this point, the horizontal rotation angle α1 and the Z-direction rotation angle β1 can be read. Then, using the same method, insert the positioning core rod into the second screw hole A2 adjacent to the first screw hole for positioning. Then, read the horizontal rotation angle α2 and the Z-direction rotation angle β2. |α2-α1|=α, and the result α is the projection angle of the axis of the first screw hole and the axis of the second screw hole on the horizontal plane. This angle is also the angle marked on the drawing. If α, β1, and β2 are the same as those marked on the drawing, then the measured angle can be considered acceptable. If there is a deviation, further calculation is required. Calculate the spatial angle value of the measured angle and the spatial angle value γ marked on the drawing, requiring it to not exceed ±30'. The calculation formula is γ = arccosα. cosβ, where α is the projection angle of the two screw hole axes onto the horizontal plane; β is the projection angle onto a plane perpendicular to the horizontal plane (β = |β2 - β1|). The overall design error of the bolt ball angle measuring instrument is 6' to 8', which fully meets the measurement accuracy requirements. If conditions permit, additional devices can be added to achieve automatic measurement and microcomputer data processing. This not only makes data processing faster and more accurate but also allows for the recording of measurement data for future reference. Editor: He Shiping