Bar puller with adjustable jaw-opening

A bar puller is provided having adjustable jaws comprising fingers made of a resilient material. The fingers extend forward from a housing adapted to be mounted at a tool station of a computer numerically controlled lathe having a turret. Front and side guiding surfaces are provided on the ends of the fingers to cause the jaws to deflect outwardly and grip a bar when forcibly engaged therewith. The lathe chuck releases the bar allowing the bar puller to withdraw the end of the bar a desired distance out of the chuck. The chuck is closed while the turret continues moving away from the chuck causing the bar to be withdrawn from between the jaws of the bar puller, readying the machine for its next cycle.

FIELD OF THE INVENTION 
The present invention relates generally to field of computer numerically 
controlled (CNC) machine tools and in particular to a bar puller for a CNC 
lathe having a turret. 
BACKGROUND OF THE INVENTION 
CNC machines are becoming ever more widely used for producing machined 
parts. As a result, numerous tools have been designed for use with CNC 
machines. Bar pullers are one such type of tool. 
Prior art CNC machine bar pullers, such as the bar puller disclosed in 
United States Pat. No. 4,522,091 to Toffolon have not been easily or fully 
adjustable. The bar puller in Toffolon uses a pair of toothed jaws for 
gripping, biased by a pair of coil springs. The jaws are affixed to a 
rectangular head by screws. The head contains a series of threaded 
openings to which the jaws may be secured. The opening of the jaws is 
adjusted in steps by securing the jaws to different threaded openings in 
the rectangular head. As a result of the incremental size adjustment of 
the opening only bar stock of compatible sizes may be used. 
There exists a need for a bar puller providing easier adjustment of the jaw 
opening than prior art bar pullers. Such a bar puller should be adjustable 
without requiring removal from the CNC machine; be continuously variable 
within the size range of the bar puller, provide a desired gripping force 
at each size adjustment; offer cross-slide and axial engagement; and have 
a self centering jaw opening. 
SUMMARY OF THE INVENTION 
The present invention provides a bar puller comprising a housing having a 
hollow head and shank portion. The shank portion has a opening at one end 
and is threaded along a portion of its inner surface. At least two jaws 
are mounted on the head portion of the puller defining a jaw opening. The 
jaws each comprise a resilient finger and an adjusting arm. The jaws are 
pivotally mounted with the fingers projecting forward from the housing. 
The ends of the fingers turn inward towards the long axis of the housing 
to provide clearance when gripping the end portion of a bar. The fingers 
have front and side guiding surfaces at their ends to direct the end of 
the bar into the jaw opening of the puller. These surfaces provide guiding 
and spring forces upon abutting engagement with the bar. The guiding 
forces tend to center the bar between the fingers. The spring forces bias 
the fingers outward enlarging the opening between the fingers sufficiently 
to permit the bar to move therebetween. The front guiding surfaces are 
angled with respect to the motion of the bar along the long axis of the 
puller. The side guiding surfaces are located at the ends of the front 
guiding surfaces and are angled with respect to the motion of the bar 
along the transverse axis of the puller. The adjusting arm of each jaw 
extends beyond the pivot point of the jaw, at an angle of about 90.degree. 
to the finger, into the head portion of the housing. A rod is located in 
the housing which engages the adjusting arm and is used to change the 
position of the fingers. One end of the rod extends through the open end 
of the shank portion of the housing. The other end of the rod is located 
in the head portion of the housing. A groove extends around the 
circumference of the rod near this end. The groove engages the adjusting 
arms of the fingers. The rod additionally has a threaded portion which 
engages the threaded portion of the inside of the housing. When the rod is 
rotated, the engagement of the housing and rod threads cause axial 
movement of the rod relative to the housing. This movement is translated 
to the adjusting arms by the groove in the rod, causing the fingers to 
rotate on their pivots. Adjustment of the fingers to a desired position 
may thereby be accomplished. The rod preferably has a slot on its end 
extending through the housing permitting the rod to be rotated by use of a 
screwdriver. A locking nut is threaded on the end of the rod extending 
outside the housing, and is tightened against the end of the housing to 
prevent the rod from turning during use of the bar puller. 
The foregoing and other advantageous and distinguishing features of the 
invention are described in detail below and are recited in the appended 
claims.

DETAILED DESCRIPTION 
The bar puller of the current invention is used to extract lengths of bar 
stock from the chuck of a computer numerically controlled (CNC) lathe 
having a plurality of tool stations mounted on a turret. The tool stations 
are individually movable towards and away from the bar both by axial 
movement along the axis of the rotation of the bar and by cross-slide 
movement in a direction transverse to that axis. To utilize the present 
invention the bar puller is mounted on a tool station and is forcibly 
engaged with the residual end of a bar. The bar is extracted a short 
distance from the chuck then removed from the bar puller as described more 
fully below. 
The bar puller comprises a hollow housing 1 having a head portion 2 and a 
shank portion 3. A shoulder 4 located at the juncture of the head 2 and 
shank 3 portions provides a stop when the bar puller is mounted on a tool 
position as shown in FIG. 1. The head portion 2 contains two or more 
radial slots 5. In each slot a jaw 6 is pivotally mounted by a roll pin 7. 
As depicted in FIG. 2, the jaws 6 comprise a jaw opening 11 around the 
long axis 12 of the housing 1. Each roll pin 7 is tightly pressed through 
a pair of holes 8 located on either side of each slot 5 and is fitted 
through a hole 9 in each jaw 6. The hole 9 receives the pin 7 as a pivot. 
The jaws 6 comprise a portion or finger 13 on one side of the hole 9 and 
an adjusting arm portion 15 on the other side of the hole. The adjusting 
arm 15 extends outwardly from the portion 10 of the jaw which contains the 
pivot hole 9, at an angle of about 90.degree. with respect to the finger 
portion 13 of the jaw. As depicted in FIG. 1, the fingers 13 curve inward 
towards the long axis of the housing 1 to provide a clearance 17 between 
the ends and the remainder of the fingers, such that only the ends of the 
fingers contact a bar when in gripping engagement therewith. The fingers 
13 are comprised of a first pair of relatively wider and a second pair of 
relatively narrower opposing surfaces set perpendicular to each other. The 
relatively wider opposing surfaces face in the direction of the movement 
of the fingers 13 defined by the opening and closing of the jaws 6. The 
relatively narrower pair of opposing surfaces of a thickness which 
permitting the jaws 6 to be resilient. The jaws 6 are tapered towards 
their ends to provide additional resiliency in the end portions of the 
fingers 13 to reduce breakage during use. 
As shown in FIG. 1, the housing 1 has two flat surfaces 18 along the side 
portions of the shank 3 to permit the housing to be secured into a tool 
position of the lathe of holding screws. The housing 1 is mounted such 
that the long axis 12 of the housing is aligned with the axis of rotation 
of the bar. 
As may be seen in FIGS. 2 & 3, a hollow 19 extends through the housing 1, 
centered on the long axis 12. At least a portion of the hollow has threads 
20 in the shank 3 near the end opposite to the shoulder 4. The hollow is 
enlarged in the head portion 2 of the housing. An adjusting rod 21 is 
located in the hollow 19. The rod 21 has a relatively larger end portion 
22 disposed in the head portion of the hollow 19. The larger end portion 
22 contains a groove 23 extending circumferentially around it. 
The ends 16 of the adjusting arms 15 extend into the groove 23, as shown in 
FIG. 2. The remainder of the rod 21 extends through the shank 3 protruding 
from the opening at the end of the shank. The rod 21 has threads 24 near 
its smaller end. The threads 24 of the rod 21 engage the threads 20 of the 
shank 3 permitting the rod 21 to be translated along the axis 12 when 
rotated. The rod 21 has a transverse slot 25 formed in its smaller end to 
permit its rotation by a screwdriver. 
When the rod 21 is rotated, the circumferential groove 23 moves axially 
within the head 2. The ends 16 of the adjusting arms 15 move along with 
the groove 23 causing the jaws 6 to rotate about the roll pins 7. This 
rotation causes movement of the fingers permitting adjustment of the jaw 
opening 11. 
A locking nut 26 is threaded onto the threaded portion of the rod 21 
extending outside the shank 3. The nut 26 is secured against end of the 
shank 27 to fasten the rod 21 in place relative to the housing 1. 
The fingers 13 terminate with a gripping-tooth 14 as shown in FIG. 2. As 
additionally shown in FIG. 5, this tooth 14 is formed by several guiding 
surfaces 28, 29 on the end of the fingers 13. The surfaces 28, 29 are 
angled, relative to the motion of the bar puller, when transported by a 
tool station along the rotational axis of the bar. 
Upon abutting engagement of the jaws 6 with the bar, the surfaces 28, 29 
direct the end of the bar into the jaw opening 11 of the bar puller. The 
front guiding surfaces 28 cause the fingers 13 to deflect away from the 
axis 12 of the housing 1, guiding and centering the bar between the 
fingers 13, when the jaws 6 engage the bar by movement along the axis of 
rotation of the bar. The side guiding surfaces 29 causes the fingers 13 to 
deflect away from the axis 12 of the housing 1, guiding and centering the 
bar between the fingers 13, when the jaws 6 engage the bar by movement 
transverse to the axis of rotation of the bar. 
In normal operation, the jaw opening 11 is adjusted to a size slightly 
smaller than the size of the bar. Exemplary jaw openings from 0.002" to 
0.06" smaller than the diameter of the bar permit the guiding surfaces 28, 
29 to properly engage the bar. This difference between the size of the jaw 
opening and the diameter of the bar forces the fingers 13 to be deflected 
outward by the guiding surfaces 28, 29 upon engagement with the bar. The 
elasticity of the fingers results in a return force being applied by the 
fingers to the bar. The greater the differential between the size of the 
bar and the size of the jaw opening, the greater the gripping pressure of 
the fingers on the bar. After engagement of the bar with the bar puller, 
the lathe chuck is opened. Movement of the turret withdraws the end of the 
bar a desired distance out of the chuck exposing a new length of the bar 
for machining. The chuck is then closed holding the bar in place while the 
turret returns to its index position. This forcibly withdraws the end of 
the bar from between the fingers. The CNC machine is then ready for its 
next cycle. 
In view of the foregoing description of the invention, those skilled in the 
relevant arts will have no difficulties making changes and modifications 
in the different described elements of the invention in order to meet 
their specific requirements or conditions. For example, a bar puller 
having more than two jaws may be utilized as shown in FIG. 5. Such changes 
and modifications may be made with out departing from the scope and spirit 
of the invention as set forth in the following claims.