Machine tool power speed changer

A retrofit power accessory for a turret mill provides a motor drive for changing machine tool speed, replacing a handwheel. A frame is attached to the mill by a pair of adjustable brackets which accommodate various models of mills. The frame carries a spider coupling which attaches to the rotatable machine shaft formerly holding the hand wheel. The spider coupling is driven by a gear motor on the frame through a timing belt and timing gears to positively drive the machine shaft. A manual switch controls the motor in either direction to effect the desired machine tool speed change. A rotary knob is also coupled to the spider coupling to allow manual intervention.

FIELD OF THE INVENTION 
This invention relates to machine tool controls and particularly to a 
retrofit power control for a tool speed changer. 
BACKGROUND OF THE INVENTION 
It is standard practice to provide conventional machine tools with manually 
controlled hand wheels to make adjustments. In some cases the manipulation 
of the hand wheels consumes substantial time and over a long period of 
time can be stressful to the machine operator. Turret mills, for example, 
have such a hand wheel which must be rotated, often for many rotations to 
select the machine tool speed each time a speed change is needed. 
SUMMARY OF THE INVENTION 
It is therefore an object of the invention to eliminate manual cranking of 
hand wheels particularly to changing speed of machine tools. Another 
object is to provide a retrofit accessory for conversion of existing 
machine tools such as turret mills to power tool speed changing. 
Turret mills, which are sold under the trade name "Bridgeport" as well as 
other brands, have a variable speed drive comprising variable pitch 
pulleys which are adjusted by turning a rotatable shaft by a handwheel. By 
removing the handwheel and substituting a power drive controlled by an 
electric switch, the speed change is accomplished rapidly and with no 
operator stress. 
A retrofit power drive is attached to the turret mill by a pair of arms or 
bars which attach to the head of the machine tool and to the power drive. 
Adjustable connections such as slotted areas for receiving fasteners 
assist in adapting a given model of accessory to nearly all turret mills. 
A spider coupling allows attachment of the power output to the speed 
control shaft when the output and the shaft are approximately aligned, 
since the spider coupling permits rotary drive in spite of some 
misalignment. 
The power accessory itself has a support frame carrying a motor and a 
control housing on the outside, and the power output and a belt and pulley 
drive on the inside. A first power shaft extends through the housing to 
carry a first pulley and the input side of a drive coupling, and a 
manually operable knob or wheel on the outside of the frame. A second 
power shaft extends through the housing to couple the motor to a second 
pulley. A drive belt links the pulleys for synchronous rotation. The motor 
operates at a constant speed, when energized, and has a speed reducing 
gearbox at its output to drive the pulleys at a moderate speed. The motor 
torque is chosen to be low to avoid damage when the position limits of the 
speed change mechanism are reached. In the event other torque conditions 
cause the motor to stall, the manually operated knob is used to 
momentarily assist the power drive. 
The control housing contains an ON/OFF switch which admits power to the 
accessory. A pilot light is illuminated when the power is on. The same 
switch effects overload protection to turn off when the current exceeds a 
prescribed value. An operator controlled switch is normally in a neutral 
off position but can be moved in either direction and held there to cause 
motor operation in either direction for machine tool speed increase or 
decrease. When the switch is released it returns to neutral.

DESCRIPTION OF THE INVENTION 
The head 10 or drive portion of a typical prior art turret mill is shown in 
FIG. 1. A hand wheel 12 attached to a rotatable shaft 14 operates an 
internal speed change mechanism to select the machine tool speed, and a 
rotary indicator 16 on the front of the head shows the selected speed. 
Many turns of the handwheel are required to traverse the whole speed range 
of the machine. The time waste and operator stress of such wheel rotation 
is reduced or eliminated by removing the hand wheel 12 and, as shown in 
FIG. 2, substituting a power speed change apparatus 20. 
As further shown in FIGS. 3, 4 and 5, the power speed change device 20 
includes a frame 22 having a plate-like web 24 and a peripheral flange 26 
for added frame strength and for protection of moving parts. The flange 26 
also assists in mounting the device 20 to the turret mill 10. The turret 
mills generally have a reduced section below the speed change mechanism 
which provides a shoulder 28 or horizontal surface for attaching a pair of 
mounting brackets 30. The brackets 30 each comprise an elongated arm 
having a mounting hole 32 at one end for bolting to the shoulder 28. The 
brackets have a longitudinal slot 34 for adjustably receiving bolts 36 for 
attachment to the bottom flange 26 of the frame. Extra bolt holes 38 in 
the flange 26 allow a variety of mounting configurations, depending on the 
shape of the machine being converted. 
A first power shaft 40 extends through and is journaled in the frame 22 and 
has a manually operated knob 42 secured to the outer end. Inside the 
frame, the shaft 40 has a pulley 44 and a first coupling half 46 of a 
spider coupling 48. The pulley 44 and the coupling half 46 are secured for 
rotation with the shaft by a flat (not shown) on the shaft 40. The second 
coupling half 50 is secured to the rotatable shaft 14 by a set screw 52. 
Each coupling half has a pair of fingers 54 extending between the fingers 
of the other half, and are spaced by a rubber spider 56 which is 
sandwiched between the coupling halves. This type of coupling is well 
known and permits positive transmission of rotary movement but does not 
require precise alignment of the two coupling halves. Thus some lateral or 
angular misalignment of the power shaft 40 and the machine shaft 14 is 
permitted. 
A second power shaft 60 extends through the frame 22 and comprises the 
output of a gear reduction box 62 which is mounted outside the frame 22. 
The gear reduction box 62 is packaged as part of a motor 64 so that the 
shaft 60 is effectively the power output of the motor. A pulley 66 on the 
shaft 60 inside the frame is secured to rotate with the shaft, and is 
drivingly coupled to the pulley 44 by a belt 68. Preferably, the belt 68 
is a toothed timing belt and the pulleys 44 and 66 are timing gears to 
effect driving without slippage. 
The motor 64 is a permanent split capacitor motor which may be, for 
example, 1/25 hp, running at a constant speed, and the gearbox 62 output 
shaft 60 turns at 154 rpm. The capacitor 70 for the motor is housed in a 
box 72 which also receives 110 v input power on line 74. An ON/OFF switch 
76 has a manual toggle control 78 accessible at the bottom of the box 72. 
The switch 76 also has circuit protection feature which turns off the 
switch when current exceeds a threshold value. This same feature serves as 
a torque limiting cutout. A control switch 80 is accessible at the front 
of the box 72 and has an actuator 82 which is spring-biased to a neutral 
OFF position. The actuator 82 must be manually moved up and held to 
energize the motor for rotation in a direction to increase machine tool 
speed, and moved down and held to decrease machine tool speed. When the 
actuator is released, it returns to OFF position. A pilot lamp 86 is 
illuminated whenever the power is on. 
As will be apparent, the retrofit power accessory device is readily 
attached to the turret mill by removing the handwheel from the mill, 
attaching the coupling half 50 to the rotatable shaft 14, attaching the 
brackets 30 to the head 10 and to the power device, making adjustments to 
complete the spider coupling 48. 
In operation, the ON/OFF switch 76 is turned on, and the switch 80 is moved 
in the direction of the desired speed change and held until the target 
speed is attained, and then released. To slowly close in on the target 
speed the switch may be operated intermittently. In the event the motor 
torque is insufficient to drive the speed mechanism, a manual assist may 
be given by turning the knob 42. 
Thus it will be apparent that the retrofit power speed change device is a 
simple and efficient conversion which is easily applied and provides 
substantial benefits.