## OverviewNeeding a Flat Belt style Pulley transmission system for my turbine I found this book titled – A treatise on belts and pulleys By John Howard Cromwell published 1885. I was just wanting a general outline of the style and dimensions for a pulley and this book pretty much will answer any question I have. Like many book from the period it is very wordy – I think they were probably paid by how many words were in the book. This blog gives me a chance to winnow out the bits that I need. Geeze. Trying to make sense of this is fun – in a .. hitting your finger with a hammer feels better when you stop – kinda way. |

## Rim Dimensions
For isolated pulleys the face-width B is taken some-what greater than the width of the belt b; often we take – B = Face Width |

-Thickness-The thickness k of the edge of the rim, or the thickness at the ends of the face-width, may be easily calculated from the formula – k = Rim Thickness B = Face WidthThe thickness of the rim at the center is therefore the rounding + thickness at the rim. |

## Pulley-NaveThe thickness of a pulley-nave is given by the formula – The length of the nave should not be taken less than Often (in idle pulleys, for example) the length L is taken equal to the face-width B of the pulley. |

## Arms of PulleysOrdinarily the arms of pulleys have val cross-sections, the diameter in the plane of the pulley being twice the smaller diameter. Fig. 57 shows a cross-section of the arm but that was simply how to draw an oval that is half the width. |

The axes of pulley-arms may be straight as in Fig. 58, curved as in Fig. 59, or double curved in the form of a letter S. Single-curved arms may be drawn in the following manner: Take (Fig. 59) the arc AE equal to 2/8 the arc EF, determined by the centres of the arms at the rim of the pulley, and draw AO perpendicular to AO. From the centre D draw CD perpendicular to AO. From the centre D draw CD perpendicular to OE, and the point C of intersection of DC and OC is the centre for the curved axis of the arm. |

-Number of Arms-The number of arms (N) necessary for pulleys of different sizes may be determined by means of the formula – where N = Number of Arms R = Pulley Radius b = Belt Width |

- A treatise on belts and pulleys, By John Howard Cromwell, pub 1885[↩]