Improvements in Keying Wheels and other Parts of Machinery to Shafts and Axles.
Year: 1888

page_text: Date of Application, 11th Aug., 1888
Complete Specification l'eft, 13th May 1889-Accented, 6th July. 1889
PROVISIONAL SPECIFICATION.
Improvements in Keying Wheels and other Parts of Machinery to
Shafts and Axles.
I, HENRY GRAFTON of 53, Chancery Lane in the County of Middlesex, Engineer,
do hereby declare the nature of this invention to be as follows:-
My Invention relates to the keying of wheels and other parts of machinery upon
circular shafts or axles; and it has for its objects to obviate the difficulty of fitting and
the defects in working inherent to the ordinary mode of keying whether by a driven
key or by a spline or feather.
In the ordinary mode of keying with a driven key, it is usual to make the key seat
in each of the parts in the forin of a three sided groove so that when the two grooves
coincide a rectangular opening is formed to receive the key, two opposite sides of such
opening-.e. the top and bottom-being parallel to, and the other two opposite sides
being perpendicular to, a radius of the shaft intersecting the axis of the key.
:
It is usual to make the key-seat in the wheel or other part to be keyed on the shaft
of gradually varying depth-known as the draft-the key being of wedge shape to
correspond, the key-seats being of uniform width and the sides of the key parallel.
In cutting such key-ways, it is rarely in practice that the key-ways in the two parts
to be keyed together are cut of equal width and in fitting a key thereto it is necessary
to make the key-ways as nearly as possible of equal width by filing which entails
trouble and necessitates skill. In fitting a key to such a key-way, it also requires
considerable skill to make the key a good fit between the parallel sides of the keyways,
such as is necessary to prevent the key working loose. In such a key a good fit in
this direction is moreover, of primary importance as it is through these sides that the
major part of the strain is transmitted when at work. A bad fit in this direction
being fatal, it is endeavored to avoid the defect by driving up the key, so that by its
wedge like action it bears excessively tight on the top and bottom, thereby bringing a
great bursting strain on the wheel etc. to be keyed without adding to the efficiency of
the sides, so that assuming the latter to bear no part of the strain the key is equivalent
to a key bearing on a flat only. A badly fitting key could not by any possibility
resist for any length of time frequently reversed strains to which the moving parts of
machinery are exposed in a greater or less degree, particularly cranks and rocking shafts.
Again, in a key fitted in the ordinary way the metal of the key is not compressed
in the direction in which the working strain comes upon it, and consequently even in
a well fitted key the key is not entirely free from shake in consequence of the metal
yielding to the strain, owing to its elasticity. It is well known that to avoid parts
transmitting varying or reverse strains from working loose, it is necessary to put the
metal under an initial strain not less than that of the working strain in order take up
the elasticity of the metal within the working limits. This cannot however, in practice
be done with the ordinary mode of keying on shafts. Although not perhaps generally
known it may be pointed out that this principle of subjecting to initial strain is given
effect to in cottering a cross-head to a piston rod for instance, such cotters never
working loose if properly driven up.
In the case of a spline or feather for permitting sliding motion on the shaft, there is
little or no bearing on the top of the feather and consequently practically the whole of
the work comes upon the side of the feather, and causes a strain that tends to give a
rolling motion to the feather, which tendency has the effect of sooner or later working
the feather loose in its bed on the shaft. If the feather is subjected to reverse strains,
this occurs very quickly; so much so that in some cases recourse has been had to the
costly expedient of planing the feather and shaft out of the solid. Moreover, the
feather if solid with or otherwise securely fixed to the shaft causes difficulty in passing
the shaft through other bearings, wheels, and side frames, and the like.

page_text: .. "
My Invention consists in principle (and considering the cross-section of the shaft
and key as a geometric figure in which the key has an even number of sides) in so
placing the key with regard to the parts to be connected that the circle representing
the circumference of the shaft shall intersect diametrically opposite angles of the key,
and preferably that the opposite faces of the key which transmit the strain shall be
parallel, and perpendicular, to the direction in which the strain passes from the shaft
to the wheel etc., or vice versa. This principle would, for ordinary purposes, be carried
out in practice by fitting a key of square section in key beds of V groove form so that
the key is placed cornerwise, that is to say, two of its angles are met by the circum-
ference of the shaft whilst its other two angles are on the same radius, slight deviations
from accuracy in the latter respect consequent on variations in the sectional form of
the key being permissible. Thus, instead of being of square section, the 'key may be of
oblong form in section in which case two opposite angles would be met by the circle
of the shaft whilst the other two angles would not be on the same radius. Such a key
would be better adapted for transmitting strains in one direction than in the other; at
all events so far as regards bursting strain, on the boss of the wheel, and if reverse
strains are to be transmitted two such keys would be used, adapted to act oppositely
and to mutually tighten each other in their seats.
The key although preferably of rectangular section is not necessarily so and
is not necessarily four-sided, although only four sides would be effective.
For instance, it might be pentagonal or hexagonal. In either case the key would
only fit the seats on the sides adjacent to the angles intersected by the circle of
the shaft.
In cases where two keys placed at an angle to one another round the shaft are
ordinarily required, the same effect may be obtained with a single key by hollowing
the hub of the wheel etc., at the opposite side to the key to the extent of about a
quarter the circumference, whereby, three bearing points (two in the bore of the wheel
and one at the key) are obtained.
Generally, the key seat in the shaft would be of uniform depth and the seat in the
hub of the wheel etc. would be of gradually varying depth, the key being tapered in
the direction of its length, or having the usual amount of draft on all of its acting
sides.
Among the advantages of this improved mode of keying may be mentioned that
only half the usual amount of metal requires to be removed to form the key seats as the
key would, other things being equal, be of the same dimensions measured diametrically
from corner to corner as the ordinary key is measured across its sides. The same tool
will cut grooves of various sizes. AV groove is much more easily cut and the key
may be fitted with much greater facility and it must necessarily bear on four sides
thereby necessarily putting an initial strain on the metal in the direction in which
the working strain will come upon it.
With this mode of keying it is necessary to file one side of the key only in order to
adjust the wheel etc. in the circular direction around the shaft with the utmost degree
of nicety which is important where a certain relation is to be preserved between two
parts keyed on the same shaft.
0
In the case of a spline or feather, it is simply dropped into its seat in the shaft
without any caulking at the sides, as usual, end wise motion being prevented by the
ends of the groove.
Dated this 11th
C
I 1000

page_text: COMPLETE SPECIFICATION.
Improvements in Keying Wheels and other Parts of Machinery to
Shafts and Axles.
I HENRY GRAFTON, of 53 Chancery Lane in the County of Middlesex, 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:-
My Invention relates to the keying of wheels and other parts of machinery upon
circular shafts or axles; and it has for its object to obviate the difficulty of fitting, and
the defects in working, inherent to the ordinary inode of keying.
g
Reference is to be had to the accompanying drawings forming part of this specification,
in which figure 1 represents a cross-section of a shaft and key, with a portion of the
surrounding hub or boss of the wheel or other part to be keyed, the key being of the
ordinary form and in the usual position. Figure 2 is a similar view, illustrating the
improved mode of keying of this invention. Figure 3 is a similar view, shewing a
modification of the form of key. Figure 4 is a perspective view of a taper key of
square section, the amount of taper relatively to the length of the key being greatly
magnified. The same letters of reference indicate the same parts in all the figures.
In the ordinary mode of keying with a driven key, as represented in figure 1, it is
usual to make the key seat in the shaft A and the key seat in the hub or boss B (of the
wheel or other part to be keyed) each in the form of a three-sided groove ba c, e
edf,
the sides a d being perpendicular to, and the sides e b and ƒ°c parallel to, afradius 9 li
of the shaft intersecting the axis of the key. It is usual to make the key seat b a c in
the hub or boss of gradually varying depth and the key C of wedge shape to
correspond thereto (this tapering of the key in the direction of its length on its top
and bottom sides being known as the "draft") whilst the key seats are of uniform
width, that is to say the sides e.b are parallel to the sides fc, the sides of the key being
also parallel. The fitting of a key to such a key-way requires considerable skill to
make the key a good fit between the parallel sides e b,fc, of the key-ways such as is
necessary to prevent the key working loose, for such key-ways are in practice rarely
cut of equal width in the shaft and boss and it is therefore usually necessary to make the
key-ways as nearly as possible of equal width by filing. This entails much trouble
and necessitates skill and care. In such a key a good fit at the sides is of primary
importance if the sides of the key are to transmit, as they should do, any part of the
strain when at work. It is commonly endeavored to parry the defect of a bad fit
between the sides by driving up the key so tightly that by its wedge-like action it
bears excessively. on the top and bottom faces a and d thereby bringing a great
bursting strain on the hub or boss without, however, making a tight fit at the sides of
the key so that, assuming the latter to hear no part of the strain, the key is equivalent
to a key bearing on a flat only. A badly-fitting key, unless it be disproportionately
wide and driven up excessively tight on the top and bottom faces a and d, could not
by any possibility resist, for any length of time, the frequently reversed strains to
which the moving parts of machinery particularly cranks and rocking shafts are
exposed in a greater or less degree.
Assuming, however, the ordinary key to be well fitted and not driven up excessively
and assuming the shaft A to be driving the hub B in the direction of the arrow,
figure 1, it will be obvious that the whole of the driving strain transmitted through
the key will lie between the two lines i i, kk, the diagonal between the opposite
corners representing the line of force. But, as the sides of the key and key ways are
parallel it is impossible to make the key fit as tightly on the sides as it does on the top
and botton and therefore in a key so fitted the metal of the key is not compressed in
the direction in which the working strain comes, or should come, upon it and conse-
quently even in a well fitted key the key is not entirely free from shake in consequence
of the elasticity of the metal permitting it to yield to the strain. It is well known
that to avoid the working loose of parts which transmit varying or reverse strains it is

page_text: necessary to put the metal under an initial strain not less than and coinciding in
direction with, that of the working strain in order to take up the elasticity of the
metal within the working limits. This cannot however, in practice, be done with the
ordinary mode of keying except the whole of the working strain be transmitted
through the top and bottom faces a and d of the key which as above mentioned is only
equivalent to keying on a flat and imposes an excessive bursting strain on the hub
or boss.
or
My Invention consists in the combination with a shaft or axle and with a hub or boss
each having a key-seat of semi-square or semi-hexagonal form, of a key of square or
hexagonal section but of tapered or pyramidal form or having what is technically
known as "draft" on all of its sides, or acting sides. In consequence of the form of the
key grooves which corresponds to that of a square or hexagon (as the case may be)
divided diagonally the key is necessarily so placed with regard to the parts to be
keyed that the circumference of the shaft will meet opposite angles of the key. It is
essential that the opposite sides of the key which transinit the strain shall be parallel in
the transverse direction and shall be perpendicular to, and be bisected transversely by, the
centre line of strain passing from the shaft to the hub or boss or vice-versa. The preferred
-because the simplest-sectional form of the key is therefore square, and in practice, a
key of square section would consequently generally be used in key-beds of semi-square
form, as represented in figure 2, two of its angles being met at one point in its length by
the eircumference of the shaft, this coincidence of the circumference with the angles of
the key being true only at one point in the length of the key owing to the "draft"
taper form of the key and this preferably at or about the middle of its length. A square
key fitted as above described is obviously equally well adapted to transmit strains in
either direction of rotation as it fits equally tight on all four sides, as above mentioned.
The key although preferably of square section is not necessarily so and is not
necessarily four-sided although only four sides would be effective. For instance, it
might be hexagonal, as in figure 3. The key would only fit the seats in the sides
adjacent to the angles intersected by the circumference of the shaft (a slight amount
of clearance being left at the two remaining sides) both of the seats being therefore of
approximately semi-hexagonal form, as shewn, their divergence from a mathe-
matically-true figure being due to the clearance allowed. Generally, the key seat in
the shaft would be of uniform depth and the seat in the hub or boss would be of
gradually-varying depth but, under certain circumstances, these conditions might be
reversed the key being, however, in any case tapered in the direction of its length or
having "draft" on all of its sides. The amount of "draft" necessary will therefore,
be less than usual.
Among the advantages of this improved mode of keying over the ordinary mode,
illustrated in figure 1, may be mentioned that it is only requisite in cutting the key
seats to remove half the usual amount of metal as the key would (other things being
equal) be of the same dimensions measured diametrically from corner to corner as the
ordinary key is measured across its sides. This is shewn in figure 2 in which the
dotted lines represent the seats for the ordinary key. The same tool will cut various
sizes of grooves of the forms shewn, and such grooves are much more easily cut and
the key may be fitted thereto with much greater facility than when made of the
ordinary form, shewn in figure 1. The key when driven up must necessarily bear on
four sides and consequently an initial strain will be put on the metal in whichever
direction the working strain may come upon it, and the key will therefore not be liable
to work loose when subjected to reverse strains.
Having now particularly described and ascertained the nature of the said inven-
tion, and in what manner the same is to be performed, I declare that what
I claim is
The combination with the shaft or axle and the hub or boss to be keyed together-
each having a key seat or groove of semi-square or semi-hexagonal form in cross-
section and one or both said grooves being of gradually varying depth as described-
of a driven key of square or hexagonal section but of pyramidal or tapered form or

page_text: baving "draft" on all four of its acting sides and fitting tightly on all four of those
sides between the sides of the key seats, the opposite sides of said key which transmit
the strain being parallel in the transverse direction of the key and being perpendicular
to, and bisected transversely by, the centre line of strain passing from or to the shaft
or axle to or from the hub or boss, as specified.
Dated this loth day of May 10OD.
HENRY GRAFTON.
By A. M. & Wm. Clark,
53, Chancery Lane, London, Patent Agents.