Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND OF T~E IN~ENTION
Collets employed for use with Bridgeport-type
; milling machines have conventionally been made by drilling ;
: a uniform longitudinal bore through the rear and central
portions of the collet, following which a bushing is in-
serted into the rear portion of the bore. The bushing has
a threaded bore of reduced cross-sectional area for attach-
ment to the milling machine. In the manufacture of this
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type of collet, production cost is increased since the ass-
embly of the two parts of the collet is time consumingO `
Additionally, it has been found that the two part assembly `~
causes problems when used including, inter alia, the loosen-
ing of the bushing with use, diff~iculty in controlling opti-
mum assembly procedures and, inability to maintain the con-
centricity of the bushing thread.
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-; SUMM~RY OF THE INVENTION `:-~
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The present invention is directed to the provision
of a one~piece collet which may be used for Bridgeport-type
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~ milling machines, as well as other machines, and in which the ~
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~ 20 rear portion of the collet is cold worked to reduce the dia-
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meter of the bore extending through the rear and central por-
tions of the collet. ~-
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Ey cold working the rear portion of the collet, the
transitional area between the central and rear portions is
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characterized by a finer metallic grain structure and a smooth,
uniform grain flow of the metal with unbroken flow lines.
This results in a collet of increased tensile strength of en-
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tire draw bar end of the collet and increases fatigue life of ~
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- the collet.
The threads in the rear portion bore are of a
smoother finish and allow an easier and precisely centered
pull by the draw bar on the collet, resulting in a tighter
- grip and less run out of the tools held by the front portion
~ of the collet.
- The present invention further contemplates a process
for manufacturing collets in accordance with the present in-
vention wherein the rear portion of the collet is cold worked
by swaging, drawing or other suitable process to reduce the
diameter of the bore of the rear portion, and wherein the pro
cess may also be employed for cold working the front portion
of the collet to provide a reduced longitudinal bore of re-
duced diameter. -
; DESCRIPTIO~ OF FIGURES OF THE DRAWINGS
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Figure 1 is a side elevational view of a convention- ~
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~ al collet, a portion thereof being broken away to disclose de-
- tails of construction; '
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Figure 2 is a longitudinal sectional view of a part- -
ially constructed collet made in accordance with the present $3 `
invention; ~i
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E'igure 3 is a sectional view taken along the line
-~ 3 3 of Figure 2, looking in the direction of the arrows; `~
Figure 4 is a lonyitudinal sectional view similar ~ ;
; ,; . :' to Figure 2, wherein the rear portion of the collet has been
r,', cold worked in accordance with the present invention; `'`
, Figure 5 is a sectional view taken along the line ~ ;
5-5 of Figure 4, looking in the direction of the arrows; 1,
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Figure 6 is a longitudinal sectional view of a com-
pleted collet made in accordance with the present invention;
Figure 7 is a sectional view taken along the line
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7-7 of Figure 6, looking in the direction of the arrows;
Figure 8 is a longitudinal sectional view of a tu- '
bular blank of material for manufacturing a collet in accord-
;~ ance with a modified form of the present invention;
Figure 9 is a view similar to Figure 8 showing the
blank after machining in accordance with the present inven-
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: 10 tion;
Figure 10 is a view similar to Figures 8 and 9,
wherein the front and rear portions of the blank have been -
cold worked in accordance with the present invention;
Figure 11 is a longitudinal sectional vlew of a
completed collet constructed in accordance with the modified
form of this invention; and
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Figure 12 is a macrograph of a portion of the col- ~
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let made in accordance with the present invention illustrating -
the metallic flow lines thereof after swaging and after heat
treatment. .~.~! ' " ,
In Figure 1, there is illustrated a standard collet
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designated 20 which is particularly adapted for use with a
Bridgeport-type milling machine. Collet 20 includes a gener- ;
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ally cylindrical body including a front work gripping portion ~
22, the outer surface of which is frusto-conical as indicated , ;
at 24 to provide a camming surface. Collet 20 further includes ~ '
a central spring leaf portion 26 and a rear portion 28. Collet
20 is further provided with a longitudinal bore 30 of uniform
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cross~sectional area which extends through rear portion 28 -
and central spring leaf portion 26. A longitudinal bore 32 ::.
of reduced cross-sectional area extends axially through front
portion 22.
- A plurality of longitudinal slots 34 extend radially
; outwardly from bores 30 and 32 to the outer periphery of the ~-
collet, which slots extend through front portion 24 and a sub-
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~: stantial part of central portion 26~ thereby forming a plura-
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:: lity of resilient fingers. ~; :
In order to adapt the collet of Figure 1 for attach- `;.~ ~ -
ment to a Bridgeport-type milling machine, a bushing 36 is fit- ~ .
ted in the bore of rear portion 28, which bushing is provided ~:~
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with a threaded bore 38 for engagement with the draw bar of the
milling machine.
In accordance with the present invention, cylindrical
stock of alloy steel or other suitable metal, is machined, as
shown in Figure 2 and 3 tociprovide a central body portion 40
having an enlarged longitudinal bore 42, the wall of which por- ::
tion is of relatively thin, uniform thickness. `~:
.: 20 The forward end of central body portion 40 issues .`
. into a front portion 44 having a frusto-conical camming surface ~
46. The aft end of central portion 40 issues into a rear por- :. :
. tion 48 having a bore which is an extension of bore 42 of cen- ~:
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tral portion 40. The wall of rear portion 48 is approximately .
. twice the thickness of the wall of central portion 40 and, as ;~.
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; shown in Figure 2, extends beyond the peripheral limits of the ~ :
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wall of central portion 40. .
In accordance with the process of the present inven~
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.. tion, rear portion 4~ i~ cold worked, i.e. plastically de~
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formed below the recrys-tallization temperature of the metal, -
`. by swaging, drawing, or other suitable process, until the ~ .
.-: outer diameter of the rear portion is substantially the same :
. as that of the central portion 40, as illustrated to advantage :
in Figure 4 and 5. Correspondingly, the internal diameter of
the wall of rear portion 48 is reduced, thereby forming a long-
.~- itudinal bore 50 wh;ch is of substantially smaller cross-sec- ~
tional area in diameter than bore 42. .
Referring now to Figures 6, and 7, manufacture of :
the collet is completed by threading bore 50 as indicated at .-~
52, drilling an axial bore 54 through front portion ~4 of re- ~.:
'- duced cross-sectional area as compared with bore 42, and form- . ..
ing a plurality of longitudinal slots 56 in the front and cen- i
.~ tral portions to provide a plurality of resilient fingers or ~.
:- furcations in accordance with conventional practice. ~'~ . :.
Rear portion 48 has now been work hardened below the
recrystallization temperature of metal by the swaging process ~.
. and the front and central portions of the collet are heak - :
treated, thereby completing the manufacturing process. ..
` Referring now to Figure 12 of the drawings, there is ..
, illustrated a macrograph of the rear portion of two collets, ;~
. the collet on the left illustrating a collet which has been
cold worked by swaging and the collet on the right illustra~
ting a collet which has been cold worked by swaging and then
heat treated.
It will be noted from a consideration of Figure 12
.. that the cold working of the rear portion of the collet effects
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` a transitional area indicated at A which is characterized by
close grain structure and a smooth, uniform grain flow with
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unbroken flow lines following the contour of the inner wall
of the collet. As a result, the tensile strength of the en-
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tire draw bar end of the collet is increased by cold working.
This further effects a smoother thread finish than has here- i~
tofore been possible and allows an easier and precisely cen-
tered pull by the draw bar on a collet with resultant tighter
grip and with less run out of the tools held in the front hole. '
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The cold working of the rear portion of the collet
further eliminates tool marks inside or outside of the collet,
and finish yrinding time is accordingly reduced. Tool mark ;~
stress risers are also eliminated which otherwise might result
in cracks during heat treatment.
In Figures 8 to 11, there is illustrated a modified
form of manufacturing a collet in accordance with the present
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invention. In accordance with this form of the invention, a ,
cylindrical blank 58 is milled to provide an axial bore 60
extending therethrough. The wall of stock 58 is relatively ;
thick in order to permit machining of the outer wall thereof `~
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to the shape shown in Figure 10. The machine blank includes a ,;
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rear portion q~, a central portion 64 and a front portion 66.
It will be noted from a consideration of Figure 10 that the
wall of central portion 64 is relatively thin as compared to
that of rear portion 62 and that the wall of front portion 66
is of substantially frusto-conical shape to provide a camming
surface 68.
In accordance with this form of the invention, both
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-. the rear and front portions 62 and 66 are cold worked by .
swaging, drawing or other process to reshape the blank to the
form shown in Figure 10. Cold working of the blank ~orms a
bore extending therethrough which is non-uniform and includes : :
a rear por~ion bore 70 of uniform cross~section throughout its
leng~h, which bore is in communication with a larger bore 72 ;:
~ which extends through central portion 64. Enlarged bore 72 :
. in turn communicates with an inwardl.y tapering bore 74 which
e~tends to the outer terminal of front portion 66. Manufac-
ture of the collet is completed by threading bore 70 as indi- ~
cated at 76, drilling a work holding front bore 78 in front .:.
portion 66, and cutting a plurality of longitudinal slots 80 .
in the front and central portions to provide a plurality of .~
resilient fingers or furcations. The collet is then heated . .
for hardness as set out above in connection with the form of . ~ :
:~ invention illustrated in Figures 1 through 7. .. :-
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The collet illustrated in Figures 8 to 11, and manu- ' ..
. factured in accordance with the present process, possesses the ~
same characteristics of both the front and rear transitional :~
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~ 20 areas as set out above in connection with the form of inven- '; .
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tion of Figures 1 to 7. Accordingly, the transitional areas `!,.
between central portion 64 and rear and front portions 62 and .
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66 which have been cold worked, results in a uniform flow of ~.
metal in these area!s which increases the tensile strength of
the collet, and increases the fatigue life of the collet.
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While there has been herein shown and described the
presently preferred form of this invention, it is to be under- .-
stood that such has been done for purposes of illustration only,
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and that various changes may be made therein within the
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~j scope of the appended claims. ~,
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