Milling cutter head for making arcuate toothing

Milling cutter head for making arcuate toothing, comprising a substantially disk-shaped carrier body that is surrounded by a locking ring, the body having therein one or more pairs of grooves of a stepped cross-section, for receiving a corresponding number of pairs of removable, axial milling cutters, in each pair one being an inner and one an outer cutter. These cutters have head cutting and flank cutting edges, and optionally head and flank clearance surfaces. The head cutting edges are made of overlap partially; the cutting edges are formed at intersecting points between the clearance surfaces. Both kinds of cutters have cylindrical body surfaces that include chip bearing surfaces and associated limiting surfaces, as well as optional supporting surfaces. The inclination angle defined between the chip bearing and the limiting surfaces is smaller than 90.degree.. The cutters are preferably rod-shaped and have quadrilateral cross-sections. The receiving grooves are preferably include supporting and locating surfaces for the cutters. The invention defines and recommends various critical and useful parameters, such as a tilt angle by which the supporting groove surfaces are displaced with respect to the milling-cutter axis, a radial angle by which the locating groove surfaces are offset with respect to a tangent to the trajectory of the cutting points of the head cutting or the flank cutting edges of the cutters, and other useful constructional parameters.

The invention relates to a milling cutter head for making arcuate toothing, 
having therein removable inner and outer milling cutters that form one or 
more pairs. 
For producing bevel gears with arcuate toothing, face milling cutters are 
used with cutters inserted into a carrier body, the edges corresponding to 
the desired tooth profiles, and which cutters can be made in the form of 
inner or outer flank cutters. The milling tools are received in axial 
grooves of the body and secured therein by screws and the like. For radial 
adjustment of the edges to the desired cutter track circle, adjusting 
wedges are usually provided between the bottoms of the grooves and the 
tool shafts. 
The tools usually have a quadrilateral shaft cross-section with an 
adjoining head portion, the latter being usually profiled in accordance 
with the edge form. The cutting edges are constituted by the cutting 
planes of two flank clearance surfaces and a head clearance surface. In 
order to maintain the useful cutting profile, the edges have to be 
re-sharpened at the chip bearing surface, noting of course that each 
sharpening removes some of the tool material so that that surface is 
displaced parallel with its previous outlines and transversally to the 
clamping shaft axis. 
To allow such milling cutters to be sharpened as often as possible, the 
cutter head portions are made much wider than the clamping cross-section 
in the operating direction. This widening requires more room than is 
usually needed while it is not possible any more to accommodate a 
substantial number of the milling cutters, which is endeavored to increase 
production results. 
The over-dimensioning in the re-sharpening direction necessitates the use 
of substantially more, rather expensive material. The repeated sharpening 
has the further disadvantage that the changes at the chip bearing surfaces 
require the gear cutting or other machines to be repeatedly re-adjusted, 
resulting in their poor exploitation, and usually in a reduced quality of 
the gears produced thereon. 
To avoid these and other disadvantages one has already designed gear 
cutting milling heads where the cutters have rod shapes and a 
cross-section that is substantially uniform all along the cutter lengths. 
Both at the clamping and at the cutting portions these milling cutters 
have the same widths. In known arrangements using such cutters, usually 
three rod-shaped cutters are employed together, supplementing each other, 
namely in the respective roles of a rough cutter, an outer cutter and an 
inner cutter. The triple cutter set-up cooperates in making a single tooth 
or space between adjoining teeth. Special arrangements have to be provided 
for fixing the respective cutter portions in the head, which complicates 
the set-up, the adjustments and the milling operation itself. 
The purpose of using the rod-shaped cutters in a milling group or unit was 
to apply a relatively large number of milling cutters within a small space 
so as to increase productivity. 
In a further known arrangement, two cutters were used: the cutting edges 
were constituted by a chip bearing surface which is at an angle to the 
rod-shaped cutter axis, two flank clearance surfaces also inclined to the 
axis, and a head clearance surface transversal to the cutter axis. 
These milling cutters can be resharpened on both the flank clearance 
surfaces and the cutting surface. The former are sharpened to the extent 
that the cutting surface is shifted along the cutter axis while 
maintaining the geometry of the cutter set-up. 
The improved arrangement gave the possibility of applying a substantial 
number of cutters about the periphery of the head. Both the wear and the 
re-sharpening occur in the axial cutter direction so that subsequent 
readjustments are greatly simplified. It should be clear that much less 
valuable material is needed for these cutters since they are thinner and 
do not require portions thereof to have an excessive width or thickness. 
It is however a drawback of these cutters that the provision of several 
cutters behind one another does not leave sufficient space for the removed 
chips, resulting in chip stalling and premature deterioration of the 
cutters themselves. It has been attempted to remedy this by applying a 
spacer plate in the peripheral direction between the cutters which in turn 
resulted in a greater space requirement of the entire cutter head. It can 
be seen that the grouped arrangement of two or more milling cutters has 
given only partial results. 
The webs between the cutter receiving grooves have to be left sufficiently 
wide to withstand the encountered cutting forces during the milling 
operation. The gain in space that was accomplished with these known 
arrangements was consequently of a dubious value. The endeavored increased 
efficiency was only partly achieved in these known milling cutters. 
Finally it should be mentioned that the technology of re-sharpening also 
met with serious difficulties. The procedure has proven to be difficult 
and time-consuming because sharpening had to be performed on at least two, 
possibly three surfaces while strict rules had to be observed in view of 
the trigonometric relationships between the cutting angles. It became 
unavoidable to use precision-type, expensive re-sharpening devices that 
are relatively difficult to handle properly, so that further time and 
material expenditures were encountered. 
Re-sharpening, if performed on all four surfaces, results in a substantial 
volume of material being removed which further increases the expenditures. 
It is therefore one of the objects of the present invention to eliminate 
the disadvantages and drawbacks encountered with hitherto known milling 
cutter heads and cutters therefor. The invention aims at increasing the 
efficiency of the cutters, reducing the specific consumption of the 
cutting material, simplifying the re-sharpening procedure, and decreasing 
the maintenance costs. 
It is another object of the invention to provide a milling head in which 
several (or several pairs of) cutters can be accommodated, without 
impairing chip formation and removal, and which gives the 
earlier-explained advantages of a foolproof, less costly sharpening 
procedure. 
In accordance with major features of the invention, this is accomplished in 
the novel milling cutter head by providing one or more pairs of removably 
insertable, substantially axial outer and inner milling cutters inserted 
in stepped receiving grooves of a carrier body which is surrounded by a 
locking ring. Both cutters have head as well as flank cutting edges, the 
latter partially overlapping between cutters of a pair, wherein the 
cutters have cylindrical body surfaces that are substantially rectilinear 
along the entire cutter lengths and in both spatial directions; these 
surfaces include active chip bearing surfaces and limiting surfaces, the 
latter adjoining the flank cutting edges. 
In accordance with an important feature of the invention, the angle defined 
between the chip bearing and the limiting surfaces is smaller than 
90.degree.. The milling cutters are preferably rod-shaped and have 
quadrilateral cross-sections. 
Another important feature is constituted in that the receiving grooves have 
are stepped in their cross-section. Appropriate supporting and locating 
surfaces may be included in the stepped configuration for the milling 
cutters. 
The locating surfaces in the grooves are preferably offset with respect to 
a tangent to the trajectory of the cutting points of head cutting or flank 
cutting edges of the milling cutters by a specified radial clearance 
angle. 
As to the supporting surfaces in the grooves, they are displaced with 
respect to the axis of the milling cutter head, in the operating direction 
thereof, by a specified tilt or inclination angle.

The inventive milling cutter head generally designated by numeral 1 
comprises a disk-shaped carrier body 2 and a surrounding locking ring 3. 
In a peripheral surface of the body 2 there are receiving grooves 4 that 
run somewhat in an axial direction and that are preferably stepped in 
their cross-section, as can be seen. These grooves serve for holding 
therein removably insertable milling-cutter pairs 5, 6 of which the former 
is an outer cutter and the latter is an inner cutter. 
It can be seen in FIGS. 1, 2 and 4 that these cutters are disposed in pairs 
(one or more in a particular cutter head), constituting together active 
cutting profiles. In FIGS. 3 and 5 one can see head clearance surfaces 15, 
flank clearance surfaces 16, head cutting edges 17 as well as flank 
cutting edges 18, for both of the cutters 5, 6 (although FIGS. 5 to 9 
concentrate on the outer cutter 5). It can be seen in FIGS. 1 and 3 that 
the edges 17 of the two cutters in a pair partially overlap. 
The cutters 5, 6 are preferably made with a quadrilateral cross-section, 
with an elongated rod shape, so that all four cylindrical body surfaces of 
a cutter run substantially rectilinearly in both spatial directions along 
the entire cutter lengths. 
The body surfaces of the cutters are constituted as follows: outer cutters 
5 have a supporting surface 51, left- and right-hand limiting surfaces 52 
and 53, and a chip bearing or cutting surface 54. Similarly, the inner 
cutters 6 have a supporting surface 61, left and right limiting surfaces 
62 and 63, and a chip bearing surface 64. 
The cylindrical body surfaces are consequently all parallel with a 
longitudinal axis A of each cutter 5, 6. Their chip bearing or cutting 
surfaces 54, 64, which are rectilinear in both spatial directions along 
these cutters, are tilted with respect to the neighboring limiting 
surfaces 53, 62 by an angle .PSI. as can be seen in FIGS. 2, 3. 
The angle .PSI. is preferably less than 90.degree. in accordance with one 
of the important features of the invention. The earlier-mentioned head and 
flank clearance surfaces 15, 16 have intersecting points where the head 
and flank cutting edges 17, 18 are formed. 
The flank cutting edges 18 meet the limiting surfaces 52, 63, that run to 
the clearance surfaces 15, with a flank angle .alpha..sub.w, the value of 
which depends on the flank angle of the workpiece to be machined and also 
on the requirements of the toothing to be produced. 
Cutter geometry and relationships are shown in detail in FIGS. 3 through 9. 
It is preferred that the chip bearing surface 54 defines with a tool 
reference plane W a cutting angle .gamma..sub.n for the head cutting edge 
17 while a similar flank cutting angle .gamma..sub.w for the flank cutting 
edge 18 is defined between the same surface 54 and the plane W. 
The edge 17 has a head clearance angle .alpha..sub.fn assigned thereto 
while the edge 18 is associated with a flank clearance angle 
.alpha..sub.fw. 
As can be seen in FIG. 6, the latter flank cutting edge 18 may also define 
an angle .lambda..sub.w with respect to the tool reference plane W, but it 
has been found better to have the edge 18 located directly in the 
reference plane. 
The receiving grooves 4 in the carrier body 2 are stepped in the radial 
direction and include supporting surfaces 41, 42, as well as bearing or 
locating surfaces 43, 44, as shown in FIG. 2, for carrying the cutters 5, 
6 in their respective positions. 
In the operating direction of the milling cutter head 1, the surfaces 41, 
42 preferably define a tilt or inclination angle .lambda..sub.s with 
reference to the milling-cutter head axis M, to allow the cutting edges to 
be readily set up (see FIG. 4). 
The locating surfaces 43, 44 are offset by an acute angle with respect to 
the tangent T to the trajectory of the cutting points S of either the head 
cutting or the flank cutting edges 17, 18 so as to allow a radial 
clearance angle .alpha..sub.fr to become effective at the head cutting 
edge 17 with regard to the adjoining limiting surface 52. 
It should again be mentioned that the contemplated partial overlap between 
the edges 17 of the adjoining cutters 5 and 6 in each pair is shown in 
FIG. 3. The active track circles of the outer and inner cutters 5, 6 are 
respectively identified by .rho..sub.sa and .rho..sub.si. 
As a practical expedient the invention also provides clamping screws 31, 32 
and clamping blocks 33, 34 (see FIG. 2) with which the cutters 5, 6 can be 
inserted, fixed and immobilized in the carrier body 2. Upon the 
application of these elements in the receiving grooves 4, the milling 
operation can be started. 
It is particularly advantageous in the inventive milling cutter head that a 
greater number of cutter pairs 5, 6 can be accommodated on a body 2 than 
ever before, in part due to the radially offset arrangement, as was 
explained before, in respect of certain inner surfaces of the grooves 4. 
The following important features of the inventive milling cutter head can 
be summarized. The head comprises a substantially disk-shaped carrier body 
with a locking ring surrounding the same, these being the parts 2 and 3 
shown in the drawings. The body has at least one pair of the grooves 4, of 
a stepped cross-section, for a corresponding number of pairs of removably 
inserted, substantially axially extending outer and inner milling cutter 5 
and 6, respectively. It is important that the grooves 4 have different 
distances from the main axis M of the cutter head. 
The cutters have head cutting edges 17 in head regions thereof, that 
partially overlap between the adjoining cutters of a pair, and 
corresponding flank cutting edges 18. Both cutters 5, 6 have cylindrical 
body surfaces 51 . . . 54 and 61 . . . 64 that are substantially 
rectilinear along the entire cutter lengths. These body surfaces include 
the chip bearing surfaces 54, 64 and the associated limiting surfaces 53, 
62, which latter adjoin the flank cutting edges. 
It is most important that the inclination angle defined between the chip 
bearing and the limiting surfaces is smaller than 90.degree.. In fact, at 
least one of the chip bearing surfaces (54, 64) is substantially planar 
along the entire cutter length, and constitutes a main acting cutting 
surface from the outer end of the respective cutter (5 or 6) to its 
cutting edge, within the range of the head and flank cutting edges 17 and 
18. 
According to yet another important feature of the invention, the outer and 
the inner milling cutters 5, 6 are in direct contact with the carrier body 
2 in both radial and tangential directions, as can readily be seen from 
FIGS. 1, 2 and 4 of the drawings. 
A greater chip removal and hence an increased productivity is achieved. 
This is more and more important since attempts are generally made to 
reduce the unit time needed per workpiece in respect of machine running 
times. 
The arrangement of the milling cutters in pairs leaves sufficient room for 
chip removal, thereby further increasing tool life, and improving machine 
performance. The invention retains the expedient of re-sharpening in the 
direction of the cutter axis, which greatly simplifies these procedures 
and reduces costs. As it was explained before, several (usually three or 
four) surfaces had to be re-sharpened, the inventive cutters require such 
work to be performed merely on the flank and the head clearance surfaces. 
The geometric requirements can be easily fulfilled when re-sharpening the 
milling cutters of this invention. 
The technology of sharpening two remaining surfaces is much simpler than 
those used so far, a detail which has a decidedly favorable effect on the 
obtained gears and other produced articles. 
Less material has to be removed when sharpening, which results in further 
material savings. It has been established with actual shop tests that only 
about one-third of the costly tool material is lost, as compared to the 
hitherto applied re-sharpening processes on four surfaces, not to mention 
the unavoidable subsequent adjustments which can be dispensed with 
according to the invention. 
Both the head and the cutters themselves can be dimensioned much smaller, 
while maintaining the same safety and performance values, because less 
space is required for the inventive pairs of cutters while they even 
provide positive cutting angles in the milling process. 
It should be understood, of course, that the foregoing disclosure relates 
to only to a preferred embodiment of the invention, and that it is 
intended to cover all changes, modifications and possible additions of the 
described example which do not constitute departures from the spirit and 
scope of the invention.