Mechanical Feed & Rapid Clutches

There are 3 distinct types and 3 different sizes of mechanical clutches used for Feed and Rapid Traverse clutches on machine models 41B and 42B. The same clutch arrangement is used on certain other models as well and the same operational explanations apply to them.

The design of the clutch adjustment ring was changed over time and 2 different types of adjustment rings were used. The original adjustment ring was a nut with a flat spring wrapped around the outside. The flat spring was the adjustment-locking device. One end of the spring was folded over and pushed through a hole in the nut into a series of holes on the threaded part inside the nut. The clutch was adjusted by raising the end of the spring, then rotating the nut, then letting the end of the spring into the next available hole in the internal piece to lock the ring against rotation. The newer clutch adjustment ring is a simple split nut with a pinch-bolt across the split. Occasionally, modifications may need to be made when replacing the older style 'flat-spring' design with the newer split-ring design. The newer adjustment ring is larger in diameter than the old ring. Depending on the 'casting draft' on a specific feed gear bracket, it may be impossible to load the new clutch into position. There are modifications available that permit the installation of the new clutch. It is impossible to determine beforehand exactly which specific machine will and which will not require a modification, since they are primarily caused by slight variations in position and size of the casting walls.

The three sizes that were used are typically referred to as size 22 (the most common), size 23 and size 24. The same explanation of operation applies to all three size clutches. It should be noted that size 22 is the smallest (size 24 is the largest) and that there are conversion packages available for most serial numbers to allow installation of a larger clutch, however, more than just the clutch must usually be changed for the conversion to be installed.

The three Types are:

Type 1 - Hand-Lever-Operated (non-locking one side)

Size 22 = Stock Number 145384
Size 23 = No Stock Number - Custom Ordered
Size 24 = No Stock Number - Custom Ordered

Type 2 - Direct-Pull Electrical Solenoid Operated (non-locking both sides)

Size 22 = No Stock Number - Custom Ordered
Size 23 = No Stock Number - Custom Ordered
Size 24 = No Stock Number - Custom Ordered

Type 3 - Air Cylinder Operated (locking both sides)

Size 22 = Stock Number 905922
Size 23 = Stock Number 905923
Size 24 = Stock Number 905808

Type 1:

The Type 1 clutch is non-locking on the Rapid side and locking on the Feed side. In this manner, the non-locking rapid provides a measure of operator safety by releasing if the operator simply lets go of the handle. The feed side is locking so that the operator does not need to stand at the machine and hold the feed engaged. This is not only convenient for the operator; it promotes longer clutch life since the linkage shoes are not constantly pressing and wearing on the clutch engaging ring. This clutch must be installed in the proper orientation in the Feed Gear Bracket so that the locking side is connected to the feed gearing and the non-locking rapid side is connected to the rapid gearing. The clutches have an off-center setscrew between the clutch body and the drive shaft. In the 'old days' there was no specific instruction given to the assemblers as to which specific side of the clutch (relative to the setscrew) should be the locking side and which the non-locking side. Each assembler altered his clutch to suit and installed it. Lucas Precision produces clutches of this type by altering a standard 'double-locking' clutch and we always place the non-locking side in the same position relative to the setscrew (the non-locking side is opposite to the setscrew location). If the original setscrew hole in the shaft is on the 'wrong' side for a replacement clutch, we recommend that the shaft be re-drilled, using the clutch as a pilot, rather than attempting to reverse the clutch operation. Please be aware that the setscrew uses an extremely 'special' (archaic) thread form. The setscrew is a 'Dardelet self-locking' setscrew. If you use a common setscrew, you will permanently damage the clutch body and taps for this form are generally not available. We do NOT recommend that a common setscrew be used as a replacement. The Dardelet form is used to lock the screw so that it cannot be 'pitched out' and go through the gearing in the lower Speed Gear Box.

Type 2:

The Type 2 clutch is NON-locking on both the Feed and Rapid Traverse sides. The clutch is held into feed or rapid by electrical current operating the appropriate solenoid. The same degree of 'dead man' safety is afforded by the electrical switches of the machine, which mechanically latch for feed and do not latch for rapid.

The non-locking style is necessary since the relatively weak kick-out spring of an electrical solenoid does not have enough force to un-seat the internal latches of a type 3 clutch. Although this arrangement results in clutch wear from the linkage shoes, it cannot be made to function otherwise. This type is of extremely limited distribution. It was, historically, a 'stepping stone' between the Type 1 clutches and the Type 3 clutches and it was abandoned after only a short production run.

Type 3:

The Type 3 clutch is locking for both Feed and Rapid Traverse and is the type that is most commonly seen.

This type of clutch is operated by air cylinders alternately pushing upwards on opposite ends of a pivoting lever. Air pressure to the left-hand air cylinder pushed upwards on the left end of the lever and engages the feed clutch. Air pressure to the right-hand air cylinder pushed upwards on the right end of the lever and engages the rapid clutch. When Air pressure is removed from both cylinders, heavy internal springs inside the air cylinders pull the lever back to the center and release the clutch.

The clutches may be identified by size as follows:
 

Clutch Operation:

The air cylinders and the operating linkages are the most common reason for premature failure of these clutches. While the air cylinder used to operate the lever visually appears to be a common truck part - it has been internally modified for use with these clutches. Using an un-modified air cylinder WILL DESTROY the clutch.

Here are the differences:

The cylinder is usually shipped with the full 3-inch rod for trimming at installation.

The air cylinders may be rapidly and simply tested by measuring the stroke with a tape measure and then pulling on the cylinder rod with hand pressure to determine if the heavier spring is installed.

If the cylinder stroke is too long, then the operating linkage continues to push on the clutch after it is already engaged. This will result in the linkage shoes and the clutch operating-slot wearing rapidly. In a short time, the parts are worn sufficiently that it is no longer possible to engage the clutch.

If the cylinder spring is too weak, the clutch will not release when the air pressure is removed from the cylinder. This is frequently mis-diagnosed as an incorrectly adjusted clutch. If the clutch is adjusted too loose, it will be able to 'kick out' with the overly weak spring, however, it will soon wear the clutch plates and stop driving. If the clutch is adjusted too tight, it will fail to internally latch. While this will also allow the clutch to release (since it is not latched), the clutch linkage will be holding the plates together rather than the internal clutch latch. In short order, the linkage shoes and the clutch operating-slot will become worn and the clutch will no longer engage.

Over the approximately 30 years that these clutches and air cylinders were used on 41B and 42B machines there were many different designs for the travel-limiting stops and the heavier kick-out springs that were used inside the air cylinders. Repair parts are available only for the most recent design. If you discover that you need parts for an older design, it will be necessary to completely upgrade the air cylinder to the current design.

The Current-Design air cylinder internal parts are:
 

Linkage Adjustment Check - Size 22 Clutches:

With both air cylinders fully 'down' (retracted), the pivoting lever is horizontal. The 'cross pins' are initially 'set' to just barely touch the tops of the slots in the rod-end blocks. They are then (normally) BOTH tightened an additional 1-1/2 turns. In this position, the clutch-operating ring is centered and there is no force on the operating linkage shoes where they engage into the clutch.

When either air cylinder is 'up' (extended), the 'cross pin' will be touching the bottom of the slot on the 'up' air cylinder rod-end block, the 'cross pin' on the 'down' cylinder will not be touching the bottom of the 'down' air cylinder rod-end block and there will be no force on the operating linkage shoes where they engage into the clutch operating ring. You should be able to easily rotate BOTH of the 'cross-pins' when the clutch is engaged in either Feed or Rapid. You should find that the pins rotate with difficulty when the clutch is in the neutral position due to the '1-1/2' turns of 'preloading' previously applied.

Linkage Adjustment Check - Size 23 and Size 24 Clutches:

With both air cylinders fully 'down' (retracted), the pivoting lever is horizontal. The 'cross pins' are set to be just barely touching the tops of the slots in the rod-end blocks. In this position, the clutch-operating ring is centered and there is no force on the operating linkage shoes where they engage into the clutch.

When either air cylinder is 'up' (extended), the 'cross pin' will be touching the bottom of the slot on the 'up' air cylinder rod-end block, the 'cross pin' on the 'down' cylinder will not be touching the bottom of the 'down' air cylinder rod-end block and there will be no force on the operating linkage shoes where they engage into the clutch operating ring. You should be able to easily rotate BOTH of the 'cross-pins' at all three positions of the linkage.