We Make America Productive
Turnstiles - also known as Quick Motion Brackets - and sometimes referred to as 'the bull horns on the head' - are part of the Spindle Feed driving gear train on the Heads of model 41B & 42B machines.
They contain a 'de-clutching' mechanism that is intended to de-couple the turnstile from the Slow Motion Hand Wheel (the round hand wheel) so that the Spindle may be hand cranked in and out of the Head without having to 'back drive' the other feed gearing.
Most machines have a knurled-head screw in the middle of the Turnstile shaft that can be screwed 'in' to decouple the clutch completely, or un-screwed ('out') to allow the clutch to close and power to be transmitted from the Slow Motion Hand Wheel.
In the 'out' position, the cam explained in the next paragraph may still disengage the clutch. Note that not all early machines have the knurled-head disengagement screw. If the Turnstile clutch is decoupled, you cannot use either the Slow Motion Hand Wheel, nor power feed the Spindle.
A Bi-Directional cam arrangement inside the Turnstile mechanism will cause the clutch to decouple if the 'bull horns' are 'held back' against a Spindle power feed or if they are struck a sharp blow with the hand. This is useful in retracting a cutter from the work rapidly. You don't need to stop the power feed - just strike the 'bull horns' in the reverse direction and the cutter will be removed from the work. Since the cam is Bi-Directional, it may be used to disengage power feed in either direction.
Two things are needed for re-engagement of the clutch to re-enable power feed. You must first place the 'bull horns' in the center of the rotational backlash so that you are on the 'low part' of the cam, then rotate the Round Handwheel (the Slow Motion Handwheel) until the clutch teeth 'line up' and the teeth 'snap' back into engagement. Early machines used an external 'gear' sliding into an internal ring 'gear' for a clutching mechanism. Later machines used a face-type mechanical 'dog' clutch. The internal 'gear' type does not use an actual gear; the teeth are relatively coarse and might be thought of more like 'driving lobes' than actual gear teeth.
All of the clutching mechanisms must be arranged for proper travel and position of the sliding part of the clutch in relation to the non-sliding part of the clutch. The travel distance of the sliding part cannot be changed. It is determined by the length of the cross slot in the main shaft. Several fitting spacers on the shaft adjust the travel positions of the sliding part of the clutch by spacing the shaft position in the Head. Changing shaft bearings or other parts may require you to re-fit these spacers.
A somewhat common problem with Turnstiles is breakage of the bolts in the face clutch types of assembly.
Frequently, the face clutch mounting bolt heads drop into the internal gearing of the dial assembly and cause expensive damage to the dial gears. This is usually a result of either 'punching' a part with Spindle Feed at Rapid Traverse; or by taking an extremely heavy cut with the Spindle Feed - resulting in too much thrust being applied and the bolts being sheared.
A good 'tip' for 41B & 42B Turnstiles of this design is to use a small amount of Silicon RTV rubbehttp://www.lucasprecision.com/admin/edit.phpr on the bolt heads that secure the clutch assembly to the brass worm wheel inside the assembly. If the bolt heads are 'glued' in place with a small amount of RTV, the chances of dial gear damage will be lessened, since it will be much more difficult for the broken bolt heads to drop into the dial gearing.
The Dials on the Turnstile need to be 'timed' during assembly since they control the Spindle Feed Extreme Travel Limit Switches on most machines. Failure to 'time' the dials usually results in broken gears.
On the outer periphery of each dial will be found three ribs. Two of the ribs are relatively long and are used for operating the end-of-travel limits. The single 'pointy' rib is used by the operator to set up a 'trip out at depth of cut', semi-automatic operation of the Spindle Feed.
Just to the 'left' of the Turnstile dials is a limit switch that is operated by the ribs. The Spindle should be hand cranked to its full mechanical travel limits and the dial gears jumped in 'time' until an approximately equal amount of rib length is 'used' at each end of travel. By doing this, you will get a power-feed trip-out at approximately the same distance from each mechanical end-of-travel.