Steel Belt and Wheel Gearing.
Year: 1898

page_text: Date of Application, 19th Apr., 1898
Complete Specification Left, 19th Jan., 1899-Accepted, 25th Mar., 1899
PROVISIONAL SPECIFICATION.
Steel Belt and Wheel Gearing.
I, ROBERT HENRY SMITH, of 53, Victoria Street, Westminster, in the County
of London, and of Ellerslie, Sutton, in the County of Surrey, Professor of
Engineering and Consulting Engineer, do hereby declare the nature of this in-
vention to be as follows:
A band made of pen or other suitable quality of steel sheet such as is used for
band saws, except that it is made thinner in proportion to its width and is tem-
pered to a slightly different grade of hardness, is used to transmit motion and
power between a pair of toothed pulleys or wheels or between a toothed wheel
and a toothed pinion, the band passing round the peripheries of the wheels or
pinions in the same manner as leather, cotton or other belts or ropes used for
similar transmission pass.
The steel band or belt, however, has teeth formed upon its inner surface, that
is, the surface which is made to lie next the wheel or pinion.
These teeth are
of small depth and the pitch from one to the next is also small. The correspond-
ing teeth on wheel or pinion are formed by casting or cutting transverse grooves
of similarly shallow depth and of the same pitch.
Each tooth on the steel belt is formed by cutting two short parallel slits in the
thin steel' sheet, each slit being parallel to the edge of the belt and the two being
distant from each other a length equal to the desired width of the tooth. The
piece of steel sheet between the slits, which is still attached at both its ends to
the body of the sheet, is then pressed or stamped into a suitably shaped mould or
bottom tool" by a corresponding "top tool," thus forming a loop-shaped pro-
jection on the surface of the sheet. The steel sheet is well annealed before these
slitting and pressing processes are performed and is afterwards rehardened and
tempered to a mild spring. temper or such other degree as is suitable for the
particular work to be done by the belt.
The projection so formed may be of any desired shape, breadth & depth in
longitudinal section.
Being cut away from the sheet along its two edges parallel to the length of the
belt, the tooth is flexible in this direction. This flexibility of the tooth prevents
its attachment to the main uncut body of the belt interfering with the flexibility
of this main body or causing hindrance or resistance of important amount to
the close laying down of the belt upon the curved surfaces of the wheel and
pinion.
There may be one, two or many such teeth in the width of the belt, all those
lying in one transverse row engaging with one wheel or pinion tooth. Longi-
tudinally the belt teeth may be arranged in straight rows or may be staggered.
The general inclination of the side of a wheel or pinion tooth to the tangent
at the periphery is less than that to which the side of the belt tooth is pressed or
stamped from the plane of the belt; so that, when the belt tooth is laid down

page_text: closely upon the wheel or pinion tooth, the belt tooth is bent to one side out of
its unstrained position and shape. Thus all the belt teeth engaged at any one
moment with the periphery of the wheel or pinion exert each a fair share of the
driving pressure as between belt and wheel or pinion. The shapes of the two
teeth are so designed as to ensure that this straining of the belt tooth lies always
well below the elastic limit.
In driving by pin-link chains the distribution of the driving effort over the
wheel or pinion teeth in gear at any one moment depends upon the exactitude
of the equality between the pitches in chain and wheel; a minute want of equality
between these duc either to inexact workmanship or to wear, resulting in the
teeth affected by this irregularity doing no share of the work. In ordinary
practice the whole work is done by the first two or three teeth in gear.
The flexibility of the teeth of my steel belt results in all the teeth in gear
doing each a fair share of the work. If the pitches be exactly equal each tooth
does precisely the same amount of work but if there be small irregularities and
inequalities each tooth still does nearly although not quite, a share of the whole
work equal to the exact average of that done by all the teeth in gear. Thus,
for example, if in one pitch of a chain there be an excess of one five hundredth
of an inch over that of the pair of wheel teeth it gears. with, this is sufficient to
throw the wheel tooth thus affected out of gear altogether, that is, it does no
share of the driving work. If the flexible tooth of my steel belt, on the other
hand, be designed to be bent one fiftieth of an inch out of its unstrained position
in the process of being laid down on the wheel periphery, then the same above
irregularity of one five hundredth of an inch between the pitches, diminishes
the driving effort exerted between the particular wheel and belt teeth affected
only by ten per cent.
The steel belt herein described also allows the belt to overrun the wheel with-
out breakage in case of abnormal dangerous resistance being suddenly applied,
and in this respect retains (in a less degree) this important advantage of "slip-
ping" and "
creeping" inherent in leather, cotton and other untoothed flexible
belts and ropes. But except when such special danger arises, the driving is
positive there being no slip or creep" as with these last mentioned means of
transmission, and the speed ratio between the wheels or pinions is strictly governed
by the ratio of the numbers of grooves or teeth on the two wheels or wheel and
pinion.
$6
The driving is also more silent than chain or spur tooth driving.
I may sometimes fill up the external hollow of the belt tooth with a block of
india rubber, cork or other elastic substance, or by a thin steel tube, or by a turned
steel rod or wire passed through the loops forming one transverse row of teeth;
the object being to diminish the flexibility and increase the strength of the belt
tooth when the gear is used for heavy driving.
I may also sometimes omit the preliminary slitting process and form the tooth
by stamping or pressing alone without cutting any of its edges apart from the
body of the plate, each end of the tooth then assuming a globular form more or
less approximating to a quarter sphere. Teeth so formed are stronger and stiffer
than those above described, and their formation on the belt weakens the tensive
strength of the belt in a less degree. At the same time they reduce the flexibility
of the belt as a whole and result in its offering greater resistance to being laid
close down upon a curved pulley surface. One form of this kind of tooth is
nearly hemispherical a transverse row of many such small hemispherical pro-
jections entering one groove between a pair of wheel teeth. When the power
to be transmitted is very small as in clock work, or generally in indicating
mechanism, one such small hemispherical tooth in the breadth of the belt is
sufficient for the purpose of maintaining a positive" drive.
"
The ends of the steel belt are either brazed together as in circular saw bands;
or rivetted together with butt joint and outside covering strip; or jointed by
cutting rectangular tangs on each end of the belt, passing these through rect-

page_text: angular slots stamped in an outside covering strip and bending the tangs over
outwards and backwards.
Dated this 10th day of A 1900
ROBERT H. SMITH,
I, ROBERT HENRY SMITH, Civil Engineer, of 53, Victoria Street, Westminster,
in the County of London, do hereby declare the nature of this invention and in
what manner the same is to be performed, to be particularly described and ascer-
tained in and by the following statement:-
A band, made of pen or other suitable quality of thin steel sheet and tem-
pered to a grade of hardness nearly the same as that of band-saws, or made of
other tough elastic metal, transmits motion and power between a pair of toothed
pulleys or wheels, or between a toothed wheel and a toothed pinion, the band
passing round the peripheries of the wheels or pinions in the same manner as
leather, cotton or other belts or ropes used for similar transmission pass.
The steel or other metal band or belt has teeth formed upon its surface, which
teeth engage with those of the wheel or pinion, and thus give a "positive" drive
between these. The depth and the pitch of the teeth are both made small, so
that in the semi-periphery in contact at any one moment, even in the case of a
pinion of small diameter, a comparatively large number of teeth are engaged.
One, two or several of such teeth are formed in a transverse row across the belt,
the uncut part of the belt lying between successive teeth in a row being generally
made of the same breadth as the tooth itself, but also sometimes smaller. In
the successive transverse rows the teeth may be arranged in longitudinal lines,
this arrangement giving the belt greater pulling strength per inch of width
than would a staggered arrangement. But when even wear of the faces of the
teeth on wheel and pinion is of paramount importance, the staggered arrange-
ment is preferred. The corresponding teeth on wheel or pinion are formed by
casting or cutting transverse grooves of similarly shallow depth, due allowance
for clearance being made, and of the same pitch measured over the tips of the
teeth. No clearance is allowed between the point of the wheel tooth and the
root of the belt tooth.
.
The teeth on the belt are formed by a process of slitting and stamping. For
each tooth two slits parallel to each other and to the length of the belt are made
through the substance of the belt. These slits may be from 1/8th inch to ½ inch
long and from th. inch to th. inch or more apart. The metal between these
slits is left attached to the body of the belt either at one or at both ends. In
one form of tooth it is sheared from the body of the belt at one end in a second
form it is sheared through at the middle of its length so as to leave two tangs
of equal length attached to the body at the two ends of the slits and in a third
form there is no cross shear.
The first form is illustrated in Figs. 1 and 2, which shew it in elevation and
plan. The tang formed by the two slits and the cross shear, is bent over at right
angles to the length of the belt and remains flat. It thus presents symmetrical
surfaces each way suitable for being driven on one side by the driving wheel
or pinion, and for driving on the other side the driven wheel or pinion. This
first form of tooth is suitable when only light working pulls are to be transmitted,
and when the main object is the transmission of motion and not of power as in
the case of clocks and other recording apparatus. The belt tooth may be given

page_text: a depth as small as 1/16th inch, or still less for clock work, and similar mechanisms,.
with a pitch of 1/8th inch. Fig. 3 illustrates the shape of the wheel tooth in this case,
the flank being best cut concave, but the theoretically correct concavity is so small'
that practically it may be cut straight. It is slightly inclined to the radius so that the
belt tooth requires to bend slightly before lying close to the flank of the wheel
tooth. When the thickness of metal employed is sufficient to allow of this being
done, the edge of the belt tooth is rounded off by grinding or otherwise in
order to minimise scraping action between it and the wheel tooth. Sometimes
it is possible to bend over this edge so as to form a bead, which effectually pre-
vents sharp scraping.
Fig. 4 shews the second form of belt tooth. In this the two tangs are pressed
down into two curved shapes precisely the reverse of each other, so that the two
together form a tooth suitable for being driven on one side or tang by the driver
and for driving the driven wheel or pinion by the other side or tang. This tooth
avoids the sharp scraping extremity or edge of the first design and is therefore
suitable for heavier driving. To strengthen it a small oval thin steel tube is
sometimes inserted between the tangs, as shewn in Fig. 5. The lower ends of
the tangs being curved towards each other, they clasp the tube and hold it in
place. To prevent the tube being displaced laterally, the top of the tube is cut
away between the teeth. forming one transverse row, the uncut part of the belt
entering the recesses so formed in the top of the tube, while the uncut parts of
the tube rise into the gaps in the belt formed by the slitting and stamping of
the teeth. The depth to which the tube is so cut need only be equal to the thick-
ness of the belt. In place of this tube a piece of wood, leather, cork, or rubber
of the same outside form may be used. In this form of tooth the depth may be
made th. inch with a pitch of sth. inch.
Fig. 6 shews in elevation and Fig. 7 in plan the third form of belt tooth. Here
the strip slit at its two sides from the body of the belt remains attached at each
end and also uncut across. It is pressed down to the shape shewn, the lower
part of the tooth being semi-circular and this part being joined to the body of
the belt by small curves. In the pressing of this tooth the metal is elongated
in a ratio of nearly 1. In the two previously described forms no elongation
takes place and the process of manufacture is therefore simpler and less costly.
This third form, however, offers a superior combination of strength and smooth
quiet gearing with the wheel and pinion teeth. It can be made of a depth
from th. inch upwards with a pitch equal to about three times the depth.
Fig. 8 shews the form of wheel tooth suitable for the second and third forms
of belt tooth. Other forms of tooth suitable to special requirements may be
stamped or pressed in the steel belt.
In all these forms the wheel tooth is so made that the belt tooth needs to be
bent slightly in the line of driving before it can lie close down on the flank of
the wheel tooth, and the belt teeth are all given a suitable degree of flexibility
so that the driving forces do actually bend them in this way.
This flexibility of the belt tooth has two objects. The first of these is to pre-
vent the tooth interfering by its attachment to the main uncut body of the belt
with the flexibility of this main body or causing hindrance or resistance of im-
portant amount to the close laying down of the belt upon the curved surfaces
of the wheel and pinion.
The second is to effect a fairly even distribution of the whole working pressure
over all the teeth in gear. In driving by pin-link chains a minute want of
equality between the pitches in chain and wheel results in the teeth affected by
this irregularity either doing all or most of the work or else doing none at all.
In ordinary practice the whole work is done by the first one, two or at most three
teeth in gear. But each flexible tooth in my steel belt exerts a pressure strictly
proportional to the degree in which it is bent elastically from its unstrained
shape. If the pitches be all exactly equal each tooth therefore does precisely
the same amount of work; but if there be small irregularities and inequalities,

page_text: each tooth still does nearly, although not quite, a share of the whole work equal
to the exact average of that done by all the teeth in gear. If the flexible teeth
be designed, for example, to be bent one fiftieth of an inch in the process of
being laid down on the wheel periphery, then an irregularity in pitch of one five
hundredth of an inch diminishes or increases the driving effort exerted between
the particular wheel and belt teeth affected by only ten per cent.
The steel belt herein described allows the belt to overrun the wheel without
breakage in case of abnormal dangerous resistance being suddenly applied.
Except when such special danger arises, however, the driving is positive, the speed
ratio being strictly governed by the ratio of the numbers of teeth on the two
wheels or wheel and pinion.
The driving is also more silent than chain or spur tooth gearing.
The ends of the steel belt are either brazed together as in band-saws; or riveted
together with butt joint and outside covering strip; or joined by cutting rect-
angular tangs on each end of the belt, passing these through rectangular slots
stamped in an outside covering strip, and bending the tangs over outwards and
backwards. This last form of joint is illustrated in Figs. 9 and 10, where Fig. 9
shews separately in plan and elevation the punched covering strip.
Having now particularly described and ascertained the nature of my said in-
vention and in what manner the same is to be performed I declare that what I
claim is
1. For the transmission of motion and power between rotating shafts the use
of a flexible belt of steel or other tough elastic metal with teeth formed upon its
surface by a process of slitting and stamping or pressing, these teeth gearing
with other suitably shaped teeth upon the peripheries of pulleys, wheels or pinions
fixed upon the shafts.
2. Upon such a flexible steel or other metal belt the formation of the teeth in
such a manner that each tooth shall be separately flexible substantially as herein-
before described and illustrated.
3. The use of such flexible teeth upon a steel or other metal belt so as to pre-
vent the attachment of the teeth interfering with the flexibility of the main body
of the belt.
4. The use of such flexible teeth upon a steel or other metal belt so as to fairly
and approximately equalise and distribute the driving pressure over all the teeth
at any one moment in gear with the wheel or pinion.
5. On the wheels, pulleys or pinions used in conjunction with such flexible
belts, the use of such forms of teeth as shall compel the belt-tooth to bend before
it can lie close against the flank of the tooth upon wheel, pulley or pinion sub-
stantially as hereinbefore described and illustrated.
6. The jointing of the ends of such flexible metal belts by notching each end
so as to form rectangular tangs or projections, passing these tangs through rect-
angular slots punched in a joint-covering strip, and bending the tangs over out-
wards and backwards substantially as hereinbefore described and illustrated in
Figs. 9 and 10.