- A treatise on belts and pulleys, By John Howard Cromwell, pub 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.
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
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.
The 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 Pulleys
Ordinarily 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