Improvements in Machines for Grinding Surfaces to a Parabolic Form.
Year: 1892

page_text: Date of Application, 19th Oct., 1892
Complete Specification Left, 19th July, 1893-Accepted, 14th Oct., 1893
PROVISIONAL SPECIFICATION.
[Communicated from abroad by Messrs. SCHUCKERT & Co., of Nürnberg,
Germany, Engineers.]
Improvements in Machines for Grinding Surfaces to a Parabolic
Form.
I, JOSEPH SINCLAIR FAIRFAX, of 433 Strand, in the County of London
Patent Agent and Consulting Engineer, do hereby declare the nature of this
invention to be as follows :—
In order to grind parabolic conoidal surfaces, it is necessary to give the grinding
tool passing over a rotating shell (for example) a kinematic guide, which produces
the parabolic shape. Reference is made to the annexed drawings which show (in
elevations) a machine for grinding the said surfaces, and diagrams relating thereto.
The geometric principle forming the basis for the machine, hereinafter described,
is stated by my foreign correspondents to be the following.
There is given, a fixed right angle K L M (Fig. 3) and a moveable right
angle A O B. If now through the cutting point a a line parallel to L M is drawn
until O B is cut in e, then the geometric point for e is a parabola.
The arrangement of the grinding machine is shown in the front elevation Fig. 1.
The object to be ground is carried by the vertical spindle a upon a horizontal face
plate brotated by the spindle working in a bracket bearing c, the lower end of the
spindle being carried in a step bearing. A horizontal pulley d is shown upon the
spindle for driving the same, in the well known manner.
On suitable standards a horizontal bed e is secured, like the bed of a lathe ; and
on the vertical face thereof is mounted a compound slide, the main portion f being
A vertical
moved horizontally by a leading screw in the well known manner.
slide 9 is fitted to work up and down on the main or horizontal slide f and the
leading screw is driven by a pulley fastened thereon. A fixed stud i is carried
on the top of the horizontal slide which engages in a slot formed in the upper
arm of a bell crank, and the lower arm similarly engages with a pink on the
vertical slide g, the position of the latter being controlled by the pink relatively to
its position in the lower slot. Consequently, under these conditions, and in
accordance with the geometrical principles referred to above, the pin k or any
other point on the slide will describe parabolic curves when the compound slide is
caused to move along the bed e.
A modification of the above described machine is shown in Fig. 2, wherein the
geometrical principles involved are based upon those indicated in the diagram
Fig. 4. In this, the equal divisions a, a', a² and a³ bear a desired proportion to
the divisions b, b1, 62, 63, and if the points of the machine corresponding to a and b
travel during their movement over corresponding distances, then parabolic curves
are likewise followed in this machine also. To obtain the requisite proportion, the
bevel bearing driven from the horizontal leading screw drives the vertical
screw g', at the required rate of progression, so that a pin carried by a nut on the
screw 9' moves at the corresponding rate, and its movement is communicated to
the pink, by the connecting rod j'. Suitable slots are provided at each end of the
rod for the engaging pins and to work in, similarly to those described with
reference to the bell crank ; and its corresponding pins i and k, in Fig. 1; and
both crank and rod j¹ are pivoted to a clamp bracket m, which can be secured at
any desired part of the bed e. It will be seen that the connecting rod j¹ determines
the place of the pin and its slide 9, so that all points of the slide describe
parabolic curves, as in Fig. 1; and also that the sweep or dimensions of the

page_text: parabolic curves so described may be varied either by the relative proportions of
the bevel wheels 1, or by the pitch of the screws f¹ and g¹.
It is further to be noted that other driving gear may be used as equivalent to
that described above. For example, wheel gearing engaging with a rack, may be
used as indicated by Fig. 5, so that with suitable change wheels parallel parabolas
may be described; while in Fig. 6 a worm f2 engaging with a worm wheel carrying
a cylinder n may be used, so that a cord o is wound on and off the said cylinder,
and being attached to a pin and block 2, working in guides, is capable of actuating
the rod . This arrangement may be adapted for the horizontal movement of
the compound slide; while the size of the cylinder will determine the proportionate
dimension of the parabola. The lower point of the slide is adapted to carry
any suitable means for grinding.
Dated this 19th day of October 1892.
FAIRFAX & WETTER,
433, Strand, London, Agents for the Applicant.
COMPLETE SPECIFICATION.
Improvements in Machines for Grinding Surfaces to a Parabolic
Form.
I, JOSEPH SINCLAIR FAIRFAX, of 433 Strand, in the County of London,
Patent Agent and Consulting 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 :-
In order to grind parabolic conoidal surfaces it is necessary to give the grinding
tool, passing over a rotating shell, (for example), a kinematic guide which produces
the parabolic shape. In the further description of this invention, reference is
made to the accompanying drawings, in which Figs. 1, 2, 5 and 6 show in elevations
the whole or part of machines or mechanical devices required for the above purpose
and Figs. 3 and 4 are geometrical diagrams.
The geometric principle forming the basis of the machine shown in Fig. 1
(hereinafter described) is stated by my foreign correspondents to be the following;
reference being made to the diagram Fig. 3.
There is given a fixed right angle KL M and a moveable right angle A O B.
If now, through the cutting point A a line parallel to L M is drawn until O B
is cut in e, then the geometric point for e is a parabola.
A modification of the machine shown in Fig. 1 is given in the part elevation
Fig. 2, the geometrical principles of which are based upon those indicated in the
diagram Fig. 4. In this diagram the equal divisions a¹, a, a³, bear a desired
proportion to the divisions 1, 2, 3; and if those points of the machine which
correspond to the said a and b travel during their movement over corresponding
distances, then parabolic curves are likewise followed in this case also.
One arrangement of a grinding machine is indicated by the front elevation
Fig. 1, wherein the object to be ground is carried by a face plate upon a vertical
spindle a, working in suitable bearings, and driven by a pulley as shown; or in
any other equivalent manner. A horizontal bed is mounted on standards, like the
bed of a lathe, and on the vertical face of the bed a compound slide is mounted;
a nute of the compound slide being moveable along the horizontal bed by means
of a nut and leading screw, (as shown), and the slide 9 moveable vertically.
Secured to the bed is a clamp bracket carrying a stud, the centre of which is
shown as being on the same horizontal plane as the leading screw, and vertically
coinciding with the axial line of the spindle a and this stud serves as a pivot for
a lever. This lever has two long slots at its extremities, one engaging with a
fixed stud e on the top of the compound slide c, and the other with a pin / fixed to
the moveable slide g. Thus far the description given applies equally to Figs. 1
and 2, but it is to be noted that in Fig. 1 the slotted leverf is of the bell crank

page_text: type, and the stud e is fixed to c above the moveable slide g at an invariable height
above the axial line of the leading screw; while in Fig. 2 the lever is straight,
like a connecting rod, and the stud e on the nut c is moveable vertically by the
vertical screw as driven by bevel gearing, and actuates the lever f.
To obtain the requisite proportion indicated by the diagram Fig. 4,on the machine
indicated by Fig. 2, a bevel wheel b is mounted on one end of the horizontal leading
screw a and it drives by another bevel wheel b' a vertical screw at the required
rate of progression, so that the stud e carried on the nut c of the vertical screw
moves at the corresponding rate, while its movement is communicated to the pin /
on the moveable slide g by the slotted lever f, which is pivoted on a stud fixed to a
clamp bracket in a similar manner to that of Fig. 1. The leverf being pivoted
at one end and moveable upon, and driven by, the pin e at the other end, determines
the place of the pin and its vertical slide g; so that all parts of the slide describe
parabolic curves, (as in the case of Fig. 1), and also, the sweep or dimensions of
the parabolic curves, so described, may be varied by the relative proportions of
the bevel wheels i, or by the pitch of the horizontal and vertical screws shown.
It will be understood that the lower part of the slide g, in both Fig. 1 and Fig. 2,
must be adapted to carry a suitable tool for application to the required parabolic
surface.
It is also to be noted that other driving gear may be used as equivalent to that
described above, and examples are given in Figs. 5 and 6. In Fig. 5 a worm
wheel and cylinder g is driven by the screw or worm a so that a cord his wound
on or off the cylinder g, and being attached to the pin and block e working in
vertical guides, is capable of actuating the lever fin a similar manner to that
shown in Fig. 2; the size of the cylinder determining the proportionate
dimensions of the parabola. In Fig. 6 a toothed wheel on a, actuating wheel
gearing engaging with a rack, is made to slide a pin e up or down in vertical
guides, the pine being fitted to work in the slotted end of the lever, as before.
With suitable change wheels for the wheel gearing, parallel parabolas may be
described; and in the examples given suitable driving gear, such as the driving
pulleys d in Figs. 1, 2, and 5, is provided for working the compound slide.
Having now particularly described and ascertained the nature of the said
invention, and in what manner the same is to be performed, I declare that
what I claim is ;-
1. A machine for grinding parabolic surfaces of revolution having in combina-
tion à bed, a compound slide mounted upon and moveable thereon, a pivoted
bell crank lever having slotted arms, a pin engaging with one of the said arms and
fixed to a part of the slide moveable only in parallel relation to the bed, and a pin
engaging with the other arm and secured to a part of the slide moveable at
right angles to the line of the bed whereby a tool is made to describe parabolic
curves, means for traversing the compound slide along the bed, and a rotatable
apparatus adapted to hold the material to be acted upon by the said tool, sub-
stantially as and for the purpose described with reference to Fig. 1.
2. A machine for grinding parabolic surfaces of revolution having in combination
a bed, a compound slide mounted upon and moveable thereon, a pivoted lever
having slotted ends, a pin engaging with one slotted end of the lever and moveable
at right angles to the line of the bed, and a pin engaging with the other slotted
end of the lever and secured to a part of the slide moveable also at right angles
to the bed whereby a tool is made to describe parabolic curves, means for traversing
the compound slide along the bed, and the first named pin at right angles thereto,
and a rotatable apparatus adapted to hold the material to be acted upon by the
said tool, substantially as and for the purpose described with reference to Fig. 2.
Dated this 10th day of T.1. 1902
FAIRFAX & WETTER,
433, Strand, London, Agents for the Applicant.
FAIRFAX & WETTER,
433, Strand, London, Agents for the Applicant.