This page gives a method of assessing the difference between the size of a parallel bore, ** x**, and the size of a shaft,

In the example of the wheel shown, the wheel is first tipped to one side so that the extremities of its bore touch the surface of the shaft, and then tipped to the other side, and a measurement is made, at the diameter of the wheel, of the distance ** a**, the extent of the tip over the outer surfaces of the wheel.

Triangles OPR and OST are similar, therefore the ratio of ST to OT is equal to the ratio of OR to PR, i.e. ST ∕ OT = OR ∕ PR

- If the angle of the tipped wheel is very small:

ST = (–*a*) ∕ 2*w* - If OR is very small compared to PR:

OR =–*x*; and*y*= PR*b* - If OR is very small compared to OT:

OT = (–*d*) ∕ 2*y*

whereis the diameter of the wheel*d*

Re-expressing the congruency, ** x** –

** x** –

© Russ Elliott

July 2001

nomenclature for style of triangles clarified 4 August 2008

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