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Nov. 5,- 1946.
' A. MACKM'ANN
¿M0544
METHOD OF AN D A_PPABATUS FOR FORMING GEAR TEETH
'
Filed April 4, 1942A
2 sheets-sheet 1
MM5
Patented Nom-.5, 1946l
nutren STATES iPartant ortie4
2,410,544 v
Mn'rnon oF Ann arraan'rus Foa
romvmrc enen 'rns'rn
Arthur Mackmann, Chicago, nl., assignor 'to
Foote Bros. Gear ,and Machine Corporation,
Chicago, lill., a corporationof‘Delaware
Application April 4, 1942, Serial No. 437,645
io claims. (ol. zio-1.6)
.
i
This invention relates to a method of and tool
for forming gear teeth and more particularly to
the iinishlng of gear teeth to provide a'smooth
very accurate surface thereon.
,
v
In the art of forming gear teeth it is the usual C21
practice at the present time to cut the teeth in
.
ä
Figure 6 is an elevation looking from the bot
tom of Figure 5;
'
in. ‘re 'l- is an end view of an alternative tœl
cons"`
Action;
,
Figure 8 is a side view of the tool of Figure ’lì
and
Figure 9 is a section illustrating engagement of
blanks by the use of toothed hobs or cutters. It
is extremely difficult -to form the cutting teeth on
the tool of Figures 'l and 8 with a gear.
such hobs accurately and is impossible Ato-keep
them accurate in use, particularly as any regrind
in a blank are first formed as accurately as pos-
mg or sharpening changes their size or configura
.,tion due to the necessity of relieving the teeth
behind their cutting edges.
'
.
Therefore, to obtain accurate gear teeth, it has
been necessary to use a shaving or finishing oper
ation after hobbing the blanks.
'
Shaving or finishing tools _for straight spur
According to the present invention,
sible either by form cutting or hobbing or by any
other one of the known conventional gear cut
ting processes to approximately their final shape
and size and are then adapted to be finished to
provide accurate tooth surfaces according .to the
method of and with the tool of the present inven
tion. The invention isillustrated in connection
with involute or approximately involute gear
gear teeth have been employed which are moved
teeth although it is Vapplicable also to other tooth Y
back and forth along the length of the teeth vand
forms.
20
withA which very satisfactory results can be ob
The tool employed constitutes in effect a master ‘
tained. Such tools, however, are expensive and
worm which is formed as-accurately as possible
have a short life, sharpening being 'very diiiicult
and more than a very few resharpenings being
impossible.
-
-
Finishing of> Worm gears where a high degree
of accuracy is required has heretofore been pos
sible only by hand and this is a very tedious and
expensive operation.>
-
The present invention has for one of its objects _
and which will tend to reproduce in the gear per
fect mating surfaces.
Since the worm tends to
produce a constant velocity in the gear, its cutting
or shaving action on the gear teeth willremove
any irregularities in the gear teeth as to tooth >
size, shape and eccentricity. Thus a gear may
be finished on its working shaft and will be per
concentric therewith.
to provide a method of and a to'ol for finishing 30 fectly
In order that the tool may cut or scrape the
gear teeth by which either worm or spur type
gear to remove material therefrom the flanks of
gears can be finished quickly and erliciently with
the-teeth thereon are provided with one or more
_
a high degree of accuracy.
cutting edges lying along lines tangent to a cyl
Another object of the invention is to >provide a
inde'r coaxial with the tool. If such cutting edges
tool for forming gear teeth which is relatively 35 were radial to the tool it would be necessary to
simple and inexpensive to manufacture and
relieve the tool body behind them in order to cut
which will have a long useful life. According to
-but I have foundthat by cutting grooves or slotsone important feature the tool requires no reliev
in the ñanks of the teeth _along lines tangent tc a
ing back of its cutting edges and can therefore be
circle concentric with the tool no relief is neces
resharpened _an indeñnite number of times until 40 sary. In one preferred form the cutting edges are
itis almost completely worn away.
formed to lie in planes tangent to the base cyl
Still another object of the invention is to pro
inder of the tool but this is not essential, it being
Y vide a method of and tool for forming gear teeth
suflicient that the cutting edges lie in planes
in which a cutting edge tangent to a base circle
tangent to any cylinder coaxial with the tool
45
is moved about the center of the circle across the
whether ofthe same size as or smaller'than the
sides or faces of the teeth- to be formed.
_
base cylinder of the tool. Another way ofex
The above and other objects advantages and
pressing the location of the cutting edges is that
desirable features of the invention will be more
they “lle in planes subtending chords less than
readily apparent from the following description
a semi-cylinder in a cylinder circumscribing the
50
when read in connection with the accompanying
outside diameter of the worm.
'
drawings, in whìch'
-Figures '_l, 8 and 9 illustrate one form of tool
Figure l is an end view of a tool embodying the
invention;
Figure 2 is a side elevation of the tool;
Figure 3 is a top plan view_illustratingthe cut
ting of a blank with the tool;
embodying the invention, which comprises a
cylindrical body lll having formed thereon heli
'
~
Figure 4 is a side elevation ,looking from the
bottom of Figure 3;
Figure 5 is a view_similar to Figure 3 illus
trating the cutting of straight spur gear teeth;
55 coidal teeth il. As shown, in Figure 8, the tool
is in the' form of a >double worm but it will be
understood that a worm form having one-or more
helical teeth thereon can be utilized equally well.
The surfaces of the helical teeth on their oppo
site faces are formed with a series of gashes or
2,410,544
Y slots i 2 each lying substantially tangent to the
cylindrical body I0 and extending throughout the Y
~
_surface of the teeth to the outer ends thereof. >
These gashes form cutting edges in the surface
of the teeth which edges lie- in the plane of the
tooth surface in the helicoidal line of action
thereof. Since no relieving of the teeth behind.
the cutting edges is necessary it will be apparent
that the tool can be sharpened an indeñnite num
y ber oi' times‘simply by enlarging the-grooves or
slots I2 on one or both sides thereof to renew the
cutting edges.
v
‘
Figures‘l and 2 illustrate another type of tooll
which'is somewhat simpler and less expensive to
manufacture than that of Figures 7 and 8 but
4
the tool formation. To form a worm gear these`
three movements, namely, rotation of the tool,
feeding of the tool radially into the gear, and
' relative movement along the tool, are all that are
-
found that the result
gear will have highly accurate and
smoothV surface showing asubstantially
>no tool
marks.
'I'he operation ask just 'described will form a
`worm gear with a zero back lash relative to the
tool and if a worm corresponding exactly in size>
to the tool is used with the gear, the lback lash
will be substantially zero. If it is desired that
somebback lash. should he obtained to provide a
which functions in substantially the same Way. 16 greater freedom of movement, the teeth on the
This tool comprises a cylindrical body Il having l
a double helical thread i5 thereon. Instead of
or slots in the opposite thread
result is to provide a load on the shaft 23 tending
faces, in this instance a plurality of elongated
g'ashes or slots I 6 are cut throughout the length 20 to resist turning thereof so that the tool Will tend
to A shave a slightly excessive amount of metal
of the threads in a plane parallel to the axis of
from each side of the gear teeth thereby provid- '
ing clearance when the gear is used with a Worm
the cylindrical body and` lying substantially tan
'gent at one side
to the surface thereof. ‘ Ifde'
sired, in order to increase the number of cutting ' of the same size as the tool.
edges additional slots I1 similarly formed may be -26 For cutting helical spur gear teeth an addi
tional motion is introduced as illustrated in Fig
cut in_ the teeth between the slots I6. `yThe slots
ure 3 in a direction substantially parallel to the
I6 and I1 are substantially identical except that
teeth on'the blank or
‘
the slots I6 extend throughout' the full tooth
30
threads, the
being to increase the strength
teeth.
'
.
It will be noted particularly from Figure 2
that the cutting edges formedwby the slots I6 35
and I1 on one side of the teeth I5 lie in a sub
stantially straight line as shown at I8, this line
gear shafts to the proper center distance.
corresponding to the helicoidal line of action of
When this additional
the teeth. On the opposite side of the teeth,
movement is introduced,>
since the slots, are not truly tangent to the cylin 40 the teeth on the gear blank will be formed uni
drical body at this point due to the helix angle »
ghout their length at an angle to
of the teeth, the cutting edges formed by the
shaft 23 determined by the helical
pitch ofthe teeth I5 on the cutting tool and by
slots are curved as shown at I9. This curvature
' will exist in any cutting edge not lying along the
the angle between the cylindrical body i4 and
the shaft.
»
.
helicoidal` line of action of the worm tooth, as
for example if the slots are cut tangent to acyl
For cutting straight spur gear teeth, the gear
inder other than the base cylinder of the tool,
blank, as shown at 24 in Figures 5 and 6, may be
but I‘have found that the tool operates enîiciently
whether or not the cutting edges are straight or
curved as shown. -
Á
l
-
Figures 3 and 4 illustrate method of using this
tool `to cut or shave teeth 22 on a blank 2|, which
can be either a “concave face worm gear” or a
helical spur gear. According to this method the
cylindrical body I4 may be power driven by any 55
suitable machine and the blank 2i may be mount
ed on a shaft 23 which is rotatable and which is
arranged at right angles to the axis of the body
I4. 'I'he tool mayy then be moved into :the body
or conversely, the tool turning the body through 00
the gear teeth 22 at a rate depending on the
relative ratios therebetween. As soon as any
‘ tightness occurs shaving or cutting of the teeth
22 will take place, the axis of the body I4 and 65
the shaft 23 being moved gradually together dur
ing the cutting operation until the desired center
distance. has been reached.
-
During the cutting operation either the body
I4 or the shaft 23 is moved in a direction parallel
'to the axis of the body between the two relative
extremes of movement indicated by dotted lines
in Figure 3.
'I'his operation produces an even `
rate of wear on the tool throughout its length
and compensates for any minor inaccuracies in 76
2,410,544
i
5
'
of precision worm gears by power driven ma
chinery and the present invention provides such
a process by which extremely "accurate gears can
6
‘
`
5. The method of forming gear teeth `which
-
comprises forming on a blank a series of gear
teeth substantially to the iinal tooth depth but >of
a section slightly larger than the final tooth form,
be produced rapidly and economically.
forming on a base cylinder a helical tooth of a
While two specific forms oi invention have been
shown and described in detail, it will be under
stood that, numerous variations might be made
therein and that the particular forms shown and
size and shape to’ mesh with teeth of the ñnal
tooth> form, forming in the faces of said helical
tooth a plurality of cutting edges~ lying substan
tially tangent to the base cylinder, engaging the
described are illustrative only and are not to be
on the blank with
10 helical tooth with the teeth
taken as a‘ definition of the scope ofthe inven
' the axes of the blank and the base cylinder
tion, reference being had for this purpose to the>
spaced a greater distance than the normal center
appended claims.
`
What is claimed is:
.
Y
`
`
l'
' distance. rotating the base cylinder, moving the ‘
-
'
base cylinder and blank _together to their normal
g
. l. The method of forming gear teeth which
center distance, and simultaneously moving', the
comprises forming ona blank a series of gear 15 blank and base cylinder relative to each other in a
teeth substantially to the final tooth depth'butv
yof slightly larger section than" the ñnal tooth
direction generally.~ parallel to the length of the
form, meshing with the teeth'on the blank the
teeth of a master worm, forming in the flanks
v6. The method of forming gear teeth which
teeth on the blank.
`
`
comprises forming on a blank a series of gear
of the worm teeth cutting edges lying in planes 20 teeth substantially to the final tooth depth but
substantially tangential to the base circle of the
of a section slightly larger than the final tooth
worm, and driving this worm in tight-mesh with
form, forming on a base cylinder a helical tooth
' the teeth of the gear blank so that as the worm ‘
of a. size and shape to mesh with teeth of the
is rotated said cutting edges will lie in the heli
-final
tooth form, forming in the faces of said
coidal line of action of the master worm to shave 25 helical tooth a plurality of cutting edges lying
the gear teeth to a corresponding mating~ sur
substantially tangent-to the base cylinder, en~
face.
'
gaging the» helical tooth with the teeth on the
2. The method of forming( gear teeth which
blank with the axes of the blank and the base '
comprises forming on a blank a series of. gear
cylinder spaced a greater‘distance than the nor
teeth substantially to the ñnal tOOth depth but - mal center distance, and simultaneously moving
of slightly'larger section than the final tooth
the blank and the base cylinder relative to each
form, meshing with the teeth on the blank the
other in directions parallel to the axis oi’ the
teeth of a master worm, forming in the ~flanks
base cylinder and to the length of the teeth on
of the worm teeth cutting edges lying in planes
substantially tangential to the base circle of the
Worm, driving the worm and simultaneously
causing relative movement between the blank
the blank.
‘ '
l
'
' '1. A tool for forming gear teeth comprising a
master worm having a helical tooth of a size and
` to that of the teeth to be
Y section complementary
and the master worm in a direction parallel to
formed, the helical tooth having formed in its
the axis of the worm.
flanks cutting edges lying in planes tangent to
40
3. The method of forming gear teeth which
the base cylinder of the worm and substantially
a blank a series of gear
' comprises yforming on
teeth substantially to the iinal tooth depth but
of a section slightly larger than the ilnal toothv .
coinciding with the helicoidal line of action4 of
the tooth.
v
~
Y 8. A tool for forming gear teeth comprising a
form, forming on a base cylinder a helical tooth
master worm having a helical tooth of a size and
of a size and shape to mesh with teeth of the 45 `section complementary to that of the teeth to be
final tooth form, forming in the >faces of said
formed, the helical tooth having cut away por
tions in its iianks to provide cutting edges in the
substantially tangent to the base. cylinder, en- '
flank surfaces in planes tangent to the base cy'l.-~
gaging the helical tooth with the teeth on the
luder of the worm and substantially coinciding
blank with the axes of the blank and the base 50 with the helicoidal line of action of the tooth. - '
cylinder spaced a greater distance than vthe nor
9. A tool for forming gear teeth comprising a
mal center distance. rotating the' base cylinder,
master- worm having a helical tooth of a size and
and moving the axes of the blank and the base
'
to that of the teeth to
- cylinder together to -their normal vcenter distance.
tooth Yhaving a slot cut
4. The method of forming gear teeth which -55 therein in a plane tangent tothe base cylinder
comprises forming on a blank'a series of gear
oi' the worm _and extending through the tooth to
teeth substantially to the ilnal tooth depth but
form cutting edges on both -ñanks thereof.
of a section slightly larger than the final
_ tooth
10. A tool for _forming gear teeth comprising'a
helical tooth a plurality of cutting edges lying -
form, forming on a base cylinder a helical tooth
master worm having a helical tooth of a. size
of a size and shape to mesh with teeth o! the 60 and section complementary to thatvof the teeth to
final tooth form, forming in the faces of said
be formed, the helical tooth having a plurality of
helical tooth a plurality of cutting edges lying
substantially tangent to the base cylinder, engag
ing the helical tooth with the teeth on the blank
with the axes of the blank and the base cylinder
spaced a greater distance than the normal center
distance, rotating the base cylinder, -movingthe
axes of the blank and the base‘cylinder together
to their normal center distance, and simul
taneously moving the blank and base -cylinder
relative to each-other in. a- direction parallel to
the axis of the base cylinder. _
slots extending through the several turns thereof
and lying in planes tangent to the base cylinder
of the worm, certain of the slots extending com
pletely through the depth of the tooth into the
worm body and the other slots terminating short
of the root of the worm thread.
ARTHUR. MACKMANN.
‘
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