Shop Trig
The geometry that is a nuisance to do at the machine. Bolt circles with a drilling block, triangles, arc centres and I/J offsets, a radius from three measured points, plus sine bar stacks, tapers, dovetails over pins and chord and arc work. Angles are in degrees, coordinates are in the XY plane, and lengths carry whatever unit you type, so inch in gives inch out.
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| # | Angle | X | Y |
|---|
G81 drilling block
Fanuc style, absolute, and G98 so the drill clears back to the starting height between holes rather than to the retract plane. Read it before you run it. The tool change, spindle, coolant and tool length offset lines your machine expects are not in here, and G54 is assumed.
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Fill any three of the six and leave the rest blank. Each angle sits opposite the side of the same letter. The sketch shows the shape and which part is which, drawn to scale but not to the orientation on your part.
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Three points on the arc. Probed, indicated or taken off a print.
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Common references: 7/24 CAT/BT = 3.500 TPF · R8 = 16°51′ included · Morse tapers run ≈ 0.600–0.630 TPF (varies by number — check the spec for the one you have).
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Inputs — enter any two
Solves the third from whichever two are filled. The classic use: find a radius from a chord and a depth mic reading.