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Measuring Large Bolt Circle Geometry Equations Review

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For bolt circles that are too large to measure using typical methods or the measuring tools. Measuring or determining distances for a bolt circle geometry can be facilitated using the following equations and methods.

Note: In general dimensional specification for circular pattern of features is best illustrated using cartesian (x and y) linear dimensional data rather radial and angle dimensional data (bolt circle). Current industry technologies enable or embrace measurement of linear dimensional data. Most most modern manufacturing equipment are equipped with linear displacement indicators or technology, as well, as coordinate measurement machines (CMM). All units shall be consistant and given in inches or mm. Angles (theta) are given in degrees.


Illustration A

Even Number of Holes Within Circle: To measure or determine the unknown distance x over opposite pins (largest gage pins that can fit into holes) within a bolt circle of holes (n or number of bolts holes must be even and greater than 4), as shown left in Illustration A, use the equation:

Where:

y = the distance over alternate pins
d = the diameter of the holes
θ = 360°/n or angle between adjacent holes.

Open:
Measuring Large Bolt Circle Even Number of Holes Calculator

Illustration B

Even Number of Holes Within Circle #2: To measure or determine the unknown distance c over adjacent hole or pins (largest gage pins that can fit into holes) within a bolt circle of holes (n or number of bolts holes must be even and greater than 4), as shown left in Illustration B, use the equation:

Where:

c = the distance over adjacent pins
d = the diameter of the holes
θ = 360°/n or angle between adjacent holes.

Open:
Measuring Large Bolt Circle Even Number of Holes Calculator #2

Illustration C

Odd Number of Holes in Circle: To measure the unknown distance x over semi-opposite holes using pins (largest gage pins that can fit into holes) and the number of holes n is odd and greater than 3, and the distance c between adjacent holes (pins) is known as shown left in Illustration C, use the equation:

Where:

c = the distance over adjacent pins
d = the diameter of the holes
θ = 360°/n or angle between adjacent holes.

Open:
Measuring Large Bolt Circle Odd Number of Holes Calculator #3

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