Improvements in or relating to Rotary Cutting-tools, and the Methods of Manufacture of the same.
Year: 1896

page_text: Date of Application, 24th Feb., 1896-Accepted, 30th May, 1896
COMPLETE SPECIFICATION.
Improvements in or relating to Rotary Cutting-tools, and the
Methods of Manufacture of the same.
I, CHARLES LOUIS GOEHRING of Alleghany, in the County of Alleghany,
State of Pennsylvania, United States of America, Doctor of Medicine, 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 relates to rotary cutting-tools such as are used for planing wood,
producing wood mouldings, and for otherwise operating upon wood and metal, its
object being the production of improved cutters which when placed on a cutter-
head afford a helicoidal or spiral cutting-edge having clearance or vacant space
before and behind it and which have the grinding-surface in a plane lying aslant
across the axis about which they rotate. In rotary cutters as hitherto commonly
made the primary grinding operation requires considerable skill, care, and time;
moreover subsequent grindings, equally troublesome, are seldom effected without
so modifying the form of the cutter that it produces after being re-sharpened,
work which differs from that produced before the re-sharpening. An improved
cutter formed and arranged according to the present invention and distinguished
from milling and rotary cutters of the usual types, in respect of the features above
referred to possesses the additional advantage that its cutting edge (for either flat
or moulded work) can be produced by the simple operation of grinding a plane
surface upon the cutter, and fresh cutting edges can be produced from time to time
by a like operation, without altering the profile of the figure of revolution generated
by the cutting edge during the rotation of the cutter-head. Therefore such a
culter can readily be repeatedly ground without causing a difference between
the profile of the work produced before and that produced after each grinding.
To facilitate a proper comprehension of the form and arrangement of a cutter
made according to this invention, it is conveuient to refer first to the aforesaid
plane surface ground on the cutter; when the cutter is in place on the cutter-head
ready for work, this surface, hereinafter termed the "grinding-surface" is in a
plane which lies aslant across the axis of rotation of the cutter-head and is herein-
after termed the "reference-plane," and assumed to be stationary.
The cross-sectional profile of the work to be produced having been chosen, that
is to say a cross-section of the work in the plane of the axis of rotation of the
cutter-head, is geometrically projected on to the reference plane in such manner
that the resulting projected profile on that plane (which must be the profile of the
cutting edge) will generate, when rotated about the cutter-head axis, a figure of
revolution having a profile agreeing with that of 'the work to be produced. Con-
versely the profile of the cutter, in the reference-plane, can be considered as the
edge of a section taken aslant across the axis of the figure of revolution. The
cutter blank is turned in the lathe or otherwise given, throughout its length, a
preferably cylindrical or conical form or contour, although it may be made straight,
this contour being such that the outer surface of the cutter intersects the grinding-
surface, at any desired angle along the cutting-edge profile determined as aforesaid;
the contour of the cutter is a figure of rotation producible by rotating the profile,
produced by projection on to the reference plane as aforesaid, about any desired
axis not coincident with that of the cutter-head but preferably parallel to the

page_text: latter or approximately so. In other words, the intersection of the turned or
shaped contour and the grinding surface occurs at and constitutes the cutting edge.
In the actual process of manufacture the cutter blank is first turned to or other-
wise formed of the desired contour and the grinding surface is afterwards imparted
to it, the contour of the blank and the disposition of the grinding-surface having
been determined geometrically beforehand. The curvature of a curved cutter is
conveniently less than that of the circles described by the cutting-edge, and its axis
and that of the said circles do not coincide when the cutter is in use; the cutter lies
within those circles in such a position that a sufficient clearance is afforded for the
cutting edge.
If a cutter thus formed be adjusted about its own axis or in the direction of its
own length its cross section at any moment on any plane of section producible by
the reference plane as the cutter is moved therethrough will have precisely the
same profile as was projected from the work in the manner hereinbefore indicated
and this profile will maintain. its original situation relatively to the axis of the
cutter head, if as is assumed the axes of cutter and cutter head are maintained in
their original positions. Therefore to satisfactorily re-grind such cutters it is
only necessary to maintain the same coincidence between the reference-plane and
the grinding-surface as originally existed. This is done by making guide marks
on the cutters which enable new grinding-surfaces being flat, to be properly located
on the cutter with great facility, and by so forming the cutters and the cutter-
seats or other parts of the cutter-head as to prevent the cutter from being adjusted
otherwise than about its own axis, that is to say, in the direction of its length if
it be a straight cutter.
Cutters for producing plane surfaces can conveniently be given cutting edges
which are parts of an ellipse, such ellipse being a conic section and being also
the slant section of a cylinder; in such case accurate cutters can be readily
procured by dividing metal cones into segments, these latter being so disposed on
the cutter head that their elliptical edges lie in planes aslant to the axis and
generate in revolving with the cutter-head, a cylinder; they effect a shear cut in
like manner to that in which a helical cutter operates.
Reference will now be made by way of example, to the accompanying drawings,
wherein
Figure 1 is a longitudinal section taken through a cutter-head having cutters.
constructed in accordance with this invention applied thereto.
Figure 2 is a section at right-angles to Fig. 1.
Figure 3 is a sectional perspective view of the construction shown in Figures 1
and 2.
Figure 4 is a longitudinal section through a cutter head showing the contour of
a pair of cutters for forming mouldings.
Figure 5 is a diagrammatic view showing one method of developing the profile.
of the cutter from the profile of the work to be produced.
Figure 6 is an end elevation of one of the cutters for dressing a plane surface,
the outer and inner dotted circles showing the circles described by the cutting edge
and cutter head respectively.
Figures 7 and 8 are respectively side and end elevations of a cone from which
cutters can be formed, showing the cuts for dividing the cone into the desired
number of cutters.
Figure 9 is a longitudinal section through one side of the cone on the line -,
Figure 8.
Like letters indicate like parts throughout the drawings.
The cutter bead may be of any preferred kind; for convenience an ordinary
form is illustrated. A is the body of the cutter-head which is adapted to be
clamped on the driving spindle B by means of nuts a working on the split ends of
the head so as to always properly centre the same. At each side of the head are
formed seats A' for the reception of the dove-tails C¹ of the cutters C, which
may be beld in place by the ordinary set screw or by a clamping-sleeve such as A'

page_text: which is set up and retained in place by a lock nut A'. The cutters C are as
usual adapted to be carried by the head A and the seats A' are formed on a curve
co-axial with that of the contour of the cutters. Thus the cutters being formed
with a curvature of relatively large radius their forward or cutting edges C' are
advanced (when the cutters are mounted in their seats on the head) beyond the
circle described by the cutting head and at a proper angle to give a good cut and
at the same time to afford a sufficient clearance in front of and behind the cutting
edge; this arrangement however, is well-known in connection with straight-edge
cutters and except in its relation to the improved cutters herein described forms no
part of the present invention.
The cutters illustrated taper in thickness from the side at which the rear or
"following" portion C' of the cutting edge is situated down to the side at which
is situated the advance portion C of the cutting edge, that is to say, the body of
the cutter tapers in thickness as shown clearly in Figure 9, and the advanced' or
foremost corner C of the cutting edge is formed at the thinner end of the cutter.
Further, the intersection of the contour of the cutter shown in Figs. 2 and 6 with a
plane containing the axis of curvature and the axis of the cutter-head, occurs along
a straight line."
According to one method of forming these cutters a cone E is turned with the
desired external contour, that is to say, a regular taper as shown in Figures 7 and 8,
where the cutter is designed for cutting plane surfaces, or of an irregular contour
where the cutter is designed for cutting mouldings (as will be presently explained)
and this cone is then divided by plane diagonal cuts E' into the desired number of
cutters C, usually three or (as shown in Figure 8) four; said cutters are then in
approximately proper shape for grinding and completing the accurate formation of
the cutting edge; the dovetails C of the cutters are produced by suitably turning
the inside of the cone, as shown clearly in the said Figures 7 and 8.
When it is desired to produce a cutter for dressing plane surfaces it is
necessary of course that the cutting edge at every point shall be equidistant from
the axis of rotation of the cutter head and to secure this result with the form of
knife shown in Figures 1, 2 and 3 and 6, points which are equidistant from the
axis of rotation are carefully marked on each end of the knife at the cutting surface,
and these two points such as C C are united by a straight cut such as E, Figure 8,
through the body of the knife. Such a cut, at its intersection with the conical
surface gives the cutting edge of the entter and it is formed at an angle of
intersection with the contour at any one point depending somewhat upon the
character of the material to be operated upon by the cutter. A straight cut
between the points mentioned will give a good cutting edge which is somewhat
curved, the amount of curvature depending upon the angle between the grinding
surface and the contour as above, but no matter what the angle of such grinding
surface may be the cutter can readily be adjusted so that every point in the cutting
edge is equidistant from the axis of rotation and of the cutter-head; then the
surface dressed by the cutter will be a smooth plane surface.
Obviously, it is a simple matter to preserve the accuracy of the cutting edge in
the grinding and sharpening operation because that surface is flat and therefore
readily producible with accuracy; and furthermore, it is a very simple matter to
restore the edge to its accurate relation to the axis of rotation by again indicating
at each end of the knife a point equidistant from said axis and making a straight
grinding surface between the two points at the desired angle with the contoured or
coned surface of the cutter at any one point, it being observed that the angle varies
from point to point along the cutting edge although the grinding-surface is flat.
In carrying this invention into practice, in the practical formation of cutters for
moulded work as distinct from plain work, the cone from which the cutters are
formed and which is thicker at one end than at the other, is turned to have an
exterior surface contour which will when the cutters are formed and the grinding
surface cut at a given angle give a cutting edge capable of cutting the moulding
to a proper cross-sectional shape or profile. In order to enhance the shearing

page_text: action throughout all the irregularities of the cutting edge the deepest depressions in
the profile of the cutter are formed preferably in the thinner and lower end of the
same although this is not absolutely essential."
Figure 5 shows diagrammatically one method of procedure used in obtaining a
cutter to produce a given section of work. In the said figure the letter D indicates
the centre of rotation or axis of the cutter head and the circular dotted line d the
circle within which the cutter head revolves. The point E indicates the centre
of the circular are to which the cutters in this example are curved, and the full lines
represent a cutter blank in end elevation.
The situation of the grinding surface and reference plane is then indicated by the
lines 9 and g extending in at the proper angle from the contour lines and 1
respectively and intersecting said lines f and f¹ at points equidistant from the
axis D as shown. Using the point D as a centre and beginning with an arc
passing through the points of intersection of the lines g and g with the lines
a series of parallel ares F are struck at a predetermined distance apart, which ares F
are developed into straight parallel lines F as shown at the right in said Figure 5,
hetween lines F3 F and F F" which latter are at a distance apart equal to the
width of the cutter measured in a direction parallel to the cutter-head axis.
In the parallel lines F the profile H of the desired moulding is drawn as
indicated and in order to give the proper valuation to the profile in a scale
corresponding to the cutter to be made, that is to say, in order to properly plot this
profile to give the desired section to the cutter on a plane perpendicular to the
contoured surface thereof, that is to say, the plane of the axis of a conical cutter
for instance, a complemental scale I' 1 1 1 is constructed as follows:-
Using the point E as a centre, a series of arcs h are struck to intersect the line g
at the points where the arcs F intersect the same, thus the arcs h are at such
distances apart that they divide the cutter at one end into parts of the same relative
values measured radially above the cutter axis as the spaces between the ares F
possess on the line g and in the complemental scale I 1 1 1 a series of marks are
made on the line I' I which are at distances apart equal to the distance between
the arcs h on a line radial to the point E such as h', these distances correspond to
the value to be given at the thicker end of the cutter for corresponding spaces
between the lines F and ares F; but said value is a constantly changing quantity
as the opposite end of the cutter is approached and in order to give a proper
valuation throughout the complemental scale a second series of arcs are struck with
the point E as a centre which intersect the line gl at the points where the arcs F
intersect the same as indicated by the arcs 2 and these arcs are at distances apart
which indicate the value which the spaces between the arcs F possess relatively
to the thinner end of the cutter. These reduced values are set off on the line 13 1³.
In the complemental scale I' 12 13 1 lines are drawn which at one end are a
distance apart corresponding to the distance apart of the ares (measured on a
radius from E) and at the opposite end are a distance apart corresponding to the
distance apart of the arcs 2 on a like radius. In order to determine the proper
angular position of these lines the inner surface of the cutter at its heel is
represented by the line I' 13 and the values determined as aforesaid are set off on
the lines 11 and 13 1 downward, in the same order as that in which they succeed
each other in successively increasing radii from the point E. Thus the proper
indications being made at each end of the complemental scale, lines drawn through
them will be at the proper angle, and it is a simple matter then with these lines
giving the valuation in the radial thickness of the cutter corresponding to the
valuation of the profile in the plotting F F F F, to transform said plotting into
the complemental profile by drawing vertical parallel lines K to indicate the points
of intersection of the "complemental profile" with the complemental scale, and then
drawing said profile as indicated in Figure 5 by the line H.
The line so drawn in the complemental scale indicates the exact profile of the
outer surface or contour of the cutters which when ground at the angle indicated by
the lines gg will give a cut on the work corresponding to the profile H.

page_text: The angle at i (Figure 5) (i.e. the angle between the grinding surface and a.
tangent to the contour at one end of the cutter) is different from the angle j at the
other end because the grinding surface is aslant across the cutter axis. In order
that the greater of these angles may be sufficiently acute it is only necessary to
suitably dispose the grinding surface relatively to the contour which will enable the
angle to be given any desired value.
0
To recapitulate, broadly, the complemental scale may be considered as being
produced by turning a plane work-profile scale-about the axis D of the cutter-
head to generate cylindrical surfaces; these surfaces are represented in end'
elevation by the ares F and produce at their intersection with the slant grinding-
surface elliptic arcs-which if then turned about the axis E of the cutter itself
will generate a series of concentric figures of revolution (concentric cones in the
present example). A section in the plane of their common axis E (which is also
the axis about which the operation of turning the cutter in a lathe for instance
is to be performed) will be represented by the complemental scale, which has the
same width as the work and can have the various widths directly projected.
upon it from the work-profile as by the lines K in Figure 5 but which will have
the several depths of the work-profile H modified in some such manner as is
indicated by the transformation of the lines F in the work-profile by means of
successive projections into equivalent but different lines in the complemental scale..
The cutter blanks and cutters may be so formed and the latter so disposed on
the cutter head that the cutting edge is part of a "left-hand " helicoidal thread
instead of the right-hand thread illustrated in the drawings. Right-band and
left-hand cutters may be used on the same cutter head.
Mouldings of any desired contour may be plotted in this manner and the
exact contour or conformation of the outer surface of the cutter determined ;.
thus it is a simple matter to produce cutters and to maintain their cutting edges.
by grinding and sharpening without in anywise altering the contour of the work
produced, a result which will be at once appreciated by those skilled in this art,.
and while one mode of plotting the contour of the outer surface of the knife to give
a specific result has been herein described, it will be understood that this invention.
is not limited in this respect as other methods may be devised for producing a like-
result in like cutters having a plane grinding surface.
Having now particularly described and ascertained the nature of the said inven-
tion ecd in what manner the same is to be performed, I declare that what.
I claim is :-
1. A rotary cutter combining a helicoidal or spiral cutting edge and a plane
grinding surface.
2. A rotary cutter such as C having a plane grinding-surface and so shaped or
so disposable upon a cutter-head as to afford a helicoidal or spiral cutting edge.
3. A rotary cutter such as C having a plane grinding-surface and so shaped or
so disposable upon a cutter-head as to afford a belicoidal or spiral cutting edge and
a clearance for the cutting edge substantially as described.
4. The combination of a rotary cutter such as described and a cutter-head so
formed or constructed that the cutter in its adjustment upon the head is guided
about its own axis of curvature in order that as it is moved through the aforesaid
"reference-plane" its cross section thereon shall not vary.
5. A rotary cutter which is a segment or portion of a cone, has a plane grinding-
surface, and is so disposable upon a cutter-head as to afford a helicoidal or spiral
cutting edge substantially as described.
6. A rotary cutter combining a helicoidal cutting-edge and plane grinding-
surface, and so formed that the intersection of its contour with a plane containing
the axis of curvature and the axis of the cutter-head, occurs along a straight
line.
7. A rotary cutter such as C tapered in cross section substantially as described.

page_text: 8. A rotary cutter having a cutting edge which is an elliptical curve situated in
a plane "aslant" the intended axis of rotation for the purpose described.
9. Producing rotary cutters by forming a cone or other circular body and dividing
it into sections substantially as described.
Dated this 24th day of February 1896.
BOULT & WADE,
Agents for the Applicant.