Year: 1887

page_text: Date of Application, 30th Mar., 1887
Complete Left, 30th Nov., 1887
Complete Accepted, 30th Dec., 1887
I THOMAS DAVID OGDEN of 274 Queens Road Miles Platting Manchester in the
County of Lancaster Engineer do hereby declare the nature of this invention to be as
follows:-
My invention relates to the instruments termed protractors which are used by
Draughtsmen, Engineers and others in obtaining angles or degrees of an angle as is
well understood and has for its object to increase and facilitate their usefulness.
Protractors are ordinarily made from a piece of sheet steel or other suitable
material and consists of half a circle with the degrees or angles marked on the outer
edge thereof and it is necessary that the person desiring to obtain any angle that may
be required to strike it from the centre of the protractor and the desired angle on the
outer edge thereof by means of a set square or straight-edge or other suitable
instrument.
By means of my invention I am enabled to obtain any desired angle by means of a
simple and inexpensive addition to the existing protractor. With this object I
construct a finger which can be moved along the outer edge of the protractor (with
one part of the finger always true to the centre of the protractor) to indicate any
desired angle. This finger is made by preference in three parts, the top plate or
finger which indicates the angles or quadrants and radiates from the centre of the
protractor, is cut from a piece of sheet steel and at the extreme end from the point of
the finger is formed an arm a portion of which runs on the surface of the outer edge
of the protractor and made to fit against this arm is a second plate which fits against
the outer edge of the protractor and is ground to the same angle. Underneath this
is a plate of exactly the same proportions as the arın formed on the finger. I bolt
these three plates together in the order described by means of four or a greater or less-
number of binding screws. It will thus be seen that by these means I am enabled to
form a groove between the top and bottoin plate, as the middle plate is not of so
great a width as the other two. I may vary the width of this groove according to the
thickness of the protractor and the said groove may be of any suitable formation. To
indicate the outside angles I make the finger projecting to any distance beyond the

page_text: centre or outer edge of the protractor. For inside angles I only make the finger
projecting to the exact centre. In some cases I form the protractor of an outer rim
with the exception of a piece projecting from one side to the centre thus effecting a
saving in material and at the same time adding to its lightness. In order to be able
to fix the finger at any angle it may be desired I pass a thumb screw with a milled
head through the plates on the finger thus tightening the edge of the top and bottom
plates on the edge of the protractor. I do not confine myself to the exact construction
I have described as I might modify the form of the finger and method of forming the
groove, for instance I might make the finger and groove from one piece of steel, and
although I have described my improved protractor as being made from steel I wish it
to be understood that I do not confine myself to this material. I might use wood
ebonite or any other suitable material.
Dated this Twenty ninth day of March One thousand eight hundred and
eighty seven.

page_text: I THOMAS DAVID OGDEN of 274 Queens Road, Miles Platting, Manchester, in the
County of Lancaster 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 and accompanying drawings:
My invention relates to the instruments termed Protractors which are used by
Draughtsinen, Engineers and others in obtaining angles or degrees of an angle as is
well understood and has for its object to increase and facilitate their usefulness.
Protractors are ordinarily made from a piece of Sheet Steel or other suitable
material and consists of half a circle with the degrees or angles marked on the outer
edge thereof and it is necessary that the person desiring to obtain any angle that may
be required to strike it from the centre of the Protractor and the desired angle on the
outer edge thereof by means of a set square or straight-edge or other suitable
instrument.
By means of my invention I am enabled to obtain any desired angle by means of a
simple and inexpensive addition to the existing protractor. With this object I
construct a finger which can be moved along the outer edge of the protractor (with
one part of the finger always true to the centre of the quadrant) to indicate any
desired angle.
In order that my invention may be fully understood I have attached hereunto a
sheet of drawings wherein,
Fig. 1. is a front view of the protractor with the finger for the obtainment of
outside angles shown in position.
Fig. 2. is also a front view with the finger used in the obtainment of the inside
angles shown in position and
Fig. 3. is a section of a finger on the line A. B.
It will be seen on reference to these drawings that the protractor is formed of an
outer rim a with the exception of a piece b projection from the side to the centre thus
effecting a saving in material and at the same time adding to its lightness.
Around the rim of the protractor are marked the degrees. The figures commencing
on the left hand side with "10" are for the short finger i shown in Fig. 2 and the
figures on the right hand are for the use of the long finger j shown in Fig. 1.
The drawings show the fingers indicating the inside and outside angles of
90 degrees.
These fingers are made by preference in three parts as already shown in Fig. 3.
The top plate or finger c which indicates the angles or quadrants and radiates from
the centre of the protractor and at the extreme end from the point of the finger is
formed an arm da portion of which runs on the surface of the outer edge of the
protractor and made to fit against this arm is a second plate e which fits against the
outer edge of the protractor and is ground or otherwise made to the same circle so as
to run true herewith. Underneath this is a plate fa portion of which runs on

page_text: the bottom of the protractor. I bolt these three plates together in the order described
by means of two or a greater or less number of binding screws g.
It will thus be seen that by these means I am enabled to form a groove between
the top and bottom plate as the middle plate is not of so great a width as the other
two. I may vary the width of this groove according to the thickness of the quadrant,
and the said groove may be of any suitable formation. To indicate the outside angles
I make the finger projecting to any distance beyond the centre or outer edge of the
protractor. For inside angles I only make the finger projecting to the exact centre.
The outer edge of the piece b and the inside edges of the fingers always forming the
angles. In order to be able to fix the finger at any angle desired
pass a thumb
screw n, with a milled head through the plates and the finger thus tightening the
edge of the top and bottom plates on the edge of the protractor. I do not confine
myself to the exact construction I have described as I might modify the form of the
finger and method of forming the groove, for instance I might make the finger and
groove from one piece of steel.
Although I have described my improved protractor as being made from steel I wish
it to be understood that I do not confine myself to this material I might use wood
ebonite or any other suitable material.
Having now fully set and indicated the nature of the said invention and in what
manner the same is to be performed I declare that what I claim is :-
1-The protractor substantially as set forth and indicated.
2-The protractor formed of an outer rim a with the piece projecting from one
side to the centre thereof substantially as and for the purpose set forth and indicated.
3-The fingers and j constructed and acting substantially in the manner set forth
and indicated.
Dated this 29th day of November 1887.