Improvements in Slide Rules.
Year: 1891

page_text: Date of Application, 18th Apr., 1891-Accepted, 23rd May, 1891
COMPLETE SPECIFICATION.
Improvements in Slide Rules.
CHARLES LOUIS HETT of Turbine Foundry Brigg in the County of Lincoln
Engineer do hereby declare the nature of this invention and in what manner the
same is to be performed, to be particularly described and ascertained in and by
the following statement :-
This invention has for its object the arrangement of a special and effective slide
rule which I call a belting calculator, by means of which calculations specially
required for finding the width and speed of a single or double leather bele used for
driving machinery may be much more readily made than by ordinary calculation or
by the use of the ordinary engineer's slide rule.
By the use of the belting calculator or improved slide rule it is possible, having
the diameter and revolutions of a pulley given, by a single setting of the rule to
read off the proper width for a single or double belt together with the speed such
belt would be run at, or conversely the horse power can be derived from the width,
diameter, and number of revolutions of a pulley. This slide rule may in common
with earlier arrangements be used for calculating the rates of speed of pullies of
different dimensions.
In this invention I use the ordinary logarithmic scales, usually employed on slide
rules but their arrangement or relation to one another is specially designed to
secure the answer to a problem with the least effort.
I am aware that slide rules have been used for a variety of engineering calcula-
tions including those required to find the widths of belting, and the speeds at which
it should be run.
I am also aware that special arrangements of the scales in relation to one another
have been designed for special purposes, and I therefore make no claim to the use
of slide rules for engineering calculations, including belting calculations, neither do
I claim any special arrangement of scales, hitherto in use for special calculations.
In the accompanying drawings I show two arrangements of the belting calculator.
Fig. 1. arranged to suit English measures and Fig. 2 arranged to suit metric
measurements.
As will be seen there are four logarithmic scales or lines a. b. c and d, of these,
a and d are on the fixed part of the rule, whilst and c are on the slide or movable
part of the rule. The method of using the rule is precisely similar to that employed
in all ordinary slide rules. A second scale is engraved above scale C suitable for
double belts having a range from 4 inches up to 36 inches.
In the arrangement of the English belting calculator, scale a, begins at 3,
scale b, begins at 2000, scale d begins at 6., these numbers all being arranged
exactly under one another.
When the slide is fully in, scale c, is arranged so that 18 is immediately
above 42-9 on d. A pointer for belt speed is cut on scale c, so as to
read 157.1 on d.
The method of using the belting calculator, may be best illustrated by an
example.
Taking the slide as being in the position shown, then a pulley 6 inches diameter,
running at 1000 revolutions per minute would have a speed of 1571 ft. per minute,
and with a single belt of 5 inches wide would give off 12 horse power, or with a
double belt 5 inches wide, 18 horse power.
To make the belting calculator more useful sometimes engrave on the back,
tabular information relating to belting generally, such as corrections for centrifugal
force. Thus for belt speed of 2100 feet per minute, the width obtained by the

page_text: calculator should be multiplied by 1·058, for a speed of 6000 feet, the corresponding
multiplier would be 1.8.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be used, I declare that what I
claim is :-
The particular arrangements of logarithmic scales forming a belting calculator or
slide rule as set forth and shewn in the drawings Fig. 1 and Fig. 2.
Dated this 4th day of April 1891.
CHAS. LOUIS HETT.