Drive Train

Lanston [i.e., American] Monotype-Thompson Type-Caster

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1. Scope

This Notebook covers the power or drive train of the Lanston Monotype Machine Company (that is, American) Monotype-Thompson Type-Caster. The treatment here is largely schematic.

Things Not Covered Here: (1) English Thompsons had a completely different drive train which employed a variable-speed motor. (2) Thompson Type-Machine Company era machines differed in some respects from later machines. In particular, they employed a different motor mounting method which was changed by Lanston Monotype starting with machine s/n 10,300. (3) At least one very early US machine had a completely different drive arrangement involving a multi-speed gearbox. (4) Early machines could also be "belt-driven from a counter-shaft" { The Quality Type Caster }. According to the { Instructions for Operating... (1925) }, this was done with a pulley, to be driven at 245 RPM, "mounted on the extending end of the main shaft." This is ambiguous because the Thompson does not have a part called a "main shaft"; I would think it likely that they meant the Friction Plate Shaft (Thompson F-833, later Lanston Monotype 17TC3) which extends out of the back of the machine. The discussion here covers none of these variations.

More Things Not Covered Here: This Notebook will have little to say about the motor itself, its mounting ("Motor Base"), and its wiring/control. For a discussion of the Motor Base, see the ../../ Illustrated Parts List -> Group 58TC Motor Base. For a discussion of the Motor Pinion, see the ../../ Illustrated Parts List -> Group 59TC Motor Pinion [writeup NOT DONE, but specifications re-derived thanks to Sky Shipley].

2. Plan

The drive train may be considered in two largely independent sections.

The first of these sections is the section which provides the continously variable speed capability. This section goes from the Motor through the variable speed mechanism and may be thought of as terminating at a particular gear (a18TC12) through which all power is transmitted to the rest of the machine. The operator interacts with this subsystem by means of the Friction Wheel Shifter Knob, by which he or she may vary the speed of the machine continuously within each of the two speed ranges.

The second of these sections is a two-speed gearbox which provides a low and a high speed range, as well as a neutral or idle position. This subsystem may be thought of as terminating at the Cam Shaft Gear, 2TC5, through which the Cam Shaft is driven. The operator interacts with this subsystem by means of the Clutch Shifter Rod Knob (a10TC22) by which he or she may throw the machine in or out of gear in either of the two speed ranges. When the Stop Motion is in use, it also controls the machine by manipulating this Clutch Shifter Rod interface.

While power is involved in the operation of the Cam Shaft and other parts of the machine, these are, I think, better considered as machine control rather than as purely power/drive components. Also, these later components from the Cam Shaft on are compatible between the English and American Thompsons, while their drive systems are entirely different.

3. Variable-Speed Drive Subsystem

The Motor is mounted in the machine with its shaft pointing toward the rear of the machine. In Thompson Type Machine Company machines, the Motor was mounted on two Motor Brackets (1925 manual, plates 5 and 24) which were fitted by the factory for each individual style of motor used. In Lanston Monotype machines from s/n 10,051 (the earliest serial number referenced in the existing parts lists) through s/n 10,299 (inclusive) what would appear to be an equivalent syle of mounting was supplied (now called a Motor Stand, 58TC1). From machine s/n 10,300 on, a completely different style of motor mounting, now called a Motor Base, was supplied (a58TC1). This style of Motor Base mounted the motor to the side of the machine's pedestal. (But note that even through the last known manual, in 1956, the earlier "Motor Stand" style of mounting is shown in Plate 5.) See ../../ Illustrated Parts List -> Group 58TC Motor Base. For the present, we'll just assume that the Motor is indeed, somehow, mounted.

Plate 4 of the 1956 manual shows the general arrangement of the variable-speed drive subsystem as seen from above. This Plate is just Plate 4 from the 1925 manual. Its reproduction quality is better in the 1925 manual, but the 1956 manual has the more useful Lanston-Monotype part numbers called out.

Beware when interpreting this Plate, however, because in one important respect it is very misleading.

Here it is, with the major components of the variable-speed drive highlighted:

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The Motor Pinion (a59TC2) is geared to and drives the periphery of the Friction Plate (17TC1T). The surface of the Friction Plate drives the periphery of the Friction Wheel (a18TC1T). Pressure from a spring behind the Friction Plate keeps it in contact with the Friction Wheel. The periphery of the Friction Wheel is an inset "Ring (Fiber)" 18TC2. This Ring is actually about an inch deep, and is set into the Friction Wheel. The material, called out as "fiber," is probably a phenolic material.

The Friction Wheel slides left-to-right on its Friction Wheel Shaft, a18TC5T. The position of the Friction Wheel on its Shaft, and consequently its position relative to the Friction Plate, determines the speed of the machine (within the overall speed range later provided by the gearbox). Moving it leftward moves it toward the outside of the Friction Plate and results in a faster speed. Moving it rightward moves it toward the inside of the Friction Plate and results in a slower speed.

It is best practice that the Friction Wheel not be moved left/right unless the machine is powered on and it is turning. Sliding it leftward or rightward while stationary will in time wear flats on the Ring (fiber) 18TC2 on the Wheel. This is nontrivial to remedy. Moving it a few times will not generally be a problem (so don't panic if you forget), but as a rule the machine should be powered on when changing speed.

The Friction Wheel is moved leftward and rightward by the Friction Wheel Shifter a18TC18, which in turn moves on a threaded rod, the Friction Wheel Operating Screw a18TC22. The operator controls this with the Friction Wheel Operating Screw Knob, a18TC23. This is the lowest knob on the right-hand side of the machine.

This Operating Screw is a normal right-handed screw. So if you turn the Knob clockwise (top away from you as you stand in front of the machine), you are "tightening" it. So the Shifter moves toward the Knob (rightward), which pulls the Friction Wheel toward the inside of the Friction Plate and the machine slows. Turn it counterclockwise (top toward you) and you are "loosening" it. The Shifter then moves away from the Knob (leftward) which pushes the Friction Wheel toward the outside of the Friction Plate and the machine speeds up. Here it is, shown on machine s/n 12,492.

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Now comes the part where Plate 4 is very misleading. In Plate 4, it appears as if the Friction Wheel Shaft continues to the right from the Friction Wheel, becomes the main shaft for the gearbox, and terminates in the Handwheel. In fact it does not. The Friction Wheel Shaft does continue the full width of the machine, but as can be seen from the photograph above, it does so below the gearbox.

(The main shaft of the gearbox (which is called the Clutch Shaft) does indeed terminate on the right with the Handwheel, but it is a short shaft only about half as long as the machine is wide.)

The Friction Wheel Shaft, although it does not become the main shaft of the gearbox, does have three gears on it (as well as the Friction Wheel). This is not shown in any of the Plates in the manuals, and the gears do not have names which indicate their function. Here, then, is another view of the Friction Wheel Shaft with these gears identified (you'll have to click on the larger version to read the annotations):

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The first two gears on it (from left to right) are the "Shaft Gear 3 1/2 inch" a18TC15 and the "Shaft Gear 7 inch" a18TC14T. These gears are pinned together to form a single unit (with the "Large and Small Shaft Gear Pin" 18TC17; see Plate 10 of the 1956 manual). This pair of gears rotates freely on the Friction Wheel Shaft and plays no part in any of the motion of the variable-speed mechanism or, indeed, the Friction Wheel Shaft. It happens that the Friction Wheel Shaft was a convenient place for the designer to put them, but they could have been put on a separate shaft of their own.

The other gear on the Friction Wheel Shaft is the "Shaft Gear 4 inch," a18TC12. This gear is keyed to the Friction Wheel Shaft and rotates with it. It may be considered the endpoint of the variable-speed mechanism. All power goes through it into the gearbox and to the rest of the machine.

4. Two-Speed Gearbox

The second major subsystem of the drive is a simple (but clever, and not entirely obvious) two-speed gearbox. It takes the variable-speed input power from the 4" Shaft Gear a18TC12 and scales this speed to one of two possible speed ranges, low and high.

4.1. What To Call It?

The 1925 Thompson Type Machine Company manual, in Plate 3, refers to this mechanism as the Gear Yoke Assembly. It also calls out the frame which encloses it and provides the support for the left-hand side of the Clutch Shaft the "Clutch Gear Yoke" (S-803). The Lanston Monotype 1942 Parts Price List designates this mechanism as Group 10TC and calls it the "Clutch" (the former p/n S-803 is now a10TC24, the "Clutch Yoke.") This mechanism isn't really a clutch, though. It is a gearbox which has, within it, two clutches. I suppose that Lanston Monotype called it the "Clutch" as a whole because it does contain the mechanism (and clutches) by which the operator engages and disengages the machine, but if it were just a clutch it wouldn't need all those gears. So while I'll use the Lanston Monotype names exactly for the individual parts, I'll tend to call it a "gearbox."

4.2. Schematic (in Neutral)

Here is a schematic diagram of this gearbox, from its power input with the Friction Wheel Shaft and 4-inch Shaft Gear to its power output to the Cam Shaft Gear 2TC5. It is shown in its neutral/disengaged/idle position. If the machine is powered on, then the Friction Wheel is turning but, as shown by the red line tracing power flow, no motion/power is transmitted through the gearbox.

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In the schematic diagram above, gears or wheels which are keyed to their shafts (or pinned to each other) are shown with a solid black box indicating the key or pin. All other gears rotate freely on their shafts.

The Clutch Shaft, a10TC10, is a short shaft which terminates on the left in a bearing on the Clutch Yoke (not shown in the schematic) and on the right with the Handwheel. It has four gears on it.

The Clutch Gear - Double," b10TC7T, is the source of the power. It is permanently engaged with the 4-inch Shaft Gear a18TC12 on the Friction Wheel Shaft, and always receives power from it. When the motor is turning, so is it. It is NOT, however, keyed to the Clutch Shaft; it rotates freely on it. It may also slide left and right on the Clutch Shaft.

The leftmost gear, "Shaft Gear, 7-inch," 10TC11, is keyed to the shaft and turns with it.

The rightmost gear, "Clutch Gear, 7-inch (Right)," b10TC1T, is also keyed to the shaft and turns with it. Moreover, this gear engages the Cam Shaft Gear 2TC5. Things are getting interesting.

The final gear is the second-from-the-left, "Clutch Gear, 3 1/2-inch (Left)," 10TC3T. It is NOT keyed to the shaft, and revolves freely on it.

The "Clutch Gear - Double" is moved left or right by a sort of fork or yoke, the Clutch Gear Shifter 10TC20. This Shifter is in turn moved by a rod, the Clutch Shifter Rod a10TC21. The operator controls this Rod using the Clutch Shifter Rod Knob a10TC22. (If the Stop Motion is in use, it also controls this Rod.) As shown above, the Clutch Shifter Rod is in its central position and the gearbox is in neutral; no power is transmitted through it. If the Clutch Shifter Rod is pushed leftward (in) then the "Clutch Gear - Double" is also pushed leftward. It then engages (via a clutch) with the "Clutch Gear 3 1/2 inch (Left)" 10TC3T. This engages one of the two speed ranges (the low range, as it happens). If instead the Clutch Shifter Rod is pulled rightward (out) then the "Clutch Gear - Double" is also pulled rightward. It then engages (via a different clutch) with the "Clutch Gear 7 inch (Right)" b10TC1T. This engages the other of the two speed ranges (the high range).

4.3. Clutches

By "clutch" one should not envision anything as sophisticated as, say, sets of friction disks. Rather, each of two gears which are to engage with each other has a raised ring on it which is cut away in two places in a sort of butterfly pattern (each cut being slightly more than 1/4 of its circumference). The clutch engages when the two gears are pushed together and the raised portions of this ring on each gear fall into the cut-away portions of it on the other. Here are the clutches as shown in the 1925 manual on the "Clutch Gear - Double" (left) and "Clutch Gear - 7 inch" (right):

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4.4. High-Speed Range

Even though the high speed range is not often used by modern Thompson operators, its mechanics are much easier to understand than the low speed range. I'll consider it first, then.

4.4.1. High-Speed Range Power Path

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When engaged in the high-speed range, power is transmitted from the Shaft Gear 4" a18TC12 (that is, the end of the variable-speed subsystem) through the "Clutch Gear - Double" b10TC7T and directly to the "Clutch Gear, 7 inch (Right)" b10TC1T. This transmits power in turn to the Cam Shaft Gear 2TC5 and thence the rest of the machine.

4.4.2. Gears Idling while in the High-Speed Range

When the machine is engaged in the high-speed range, the four gears 10TC3T, 10TC11, a18TC15, and a18TC14T will be turning, but play no part in the power transmission. They will be turning because 10TC11 (Shaft Gear 7 inch) is keyed to the Clutch Shaft and must turn with it. It meshes with a18TC15, which is pinned to a18TC14T. The last of these meshes with 10TC3T (Clutch Gear 3 1/2 inch (Left)), which simply spins on the Clutch Shaft and does nothing.

4.4.3. High-Speed Range Operation

The high-speed range is engaged by moving the "Clutch Gear - Double" to the right, causing its (half) clutch to engage the (half) clutch of the "Clutch Gear 7 inch (Right)" b10TC1T.

From the operator's point of view, this is accomplished by pulling the Clutch Shifter Rod Knob all of the way out.

The Clutch Shifter Rod has three annular grooves cut into it, one or more of which may be outside of the main pedestal of the machine. There is also a Clutch Shifter Rod Latch a11TC1 (not shown in the schematic) which can be raised or lowered by the operator into these grooves to keep the Shifter Rod in a particular position. (This Latch may be held out of the way by a spring catch as necessary.)

Finally, there may also be a larger "Main Spring" 84TC16T pressing in on the Clutch Shifter Rod Knob. This spring is technically part of the Stop Motion. It is not shown on the schematic above. (See Plate 17 of the 1956 manual.)

To shift the machine from neutral and engage it in high-speed operation, the operator would:

1. Turn on the motor (the clutch may not engage unless the gears are turning).

2. Swing the Stop Motion Main Spring, 84TC16T, away so that it does not press on the Clutch Shifter Rod Knob.

3. Raise the Clutch Shifter Rod Latch a11TC1 and hold it up, and the same time...

4. Pull the Clutch Shifter Rod (Knob) out fully. All three annular grooves cut into it should be visible.

5. Drop the Latch into the innermost ring to keep the Clutch Shifter Rod in this position.

4.4.4. Modified Operating Mechanisms

Some machines (in particular the ex-Perfection Type machines currently operational at Skyline Type Foundry) have been modified with a collar which restricts the motion of the Clutch Shifter Rod such that the high-speed range cannot be engaged.

Some machines have various styles of shop-made or aftermarket operating levers attached to simplify operator use of the Clutch Shifter Rod Knob. However, I do not yet know of any such arrangement which handles high-speed operation. The nicest such levers I have seen are those on the ex-Perfection Type machines at Skyline; as noted, these machines have their high-speed range disabled. The rather crude pushrod-and-wedge system on the ex-Barco machines in my own shop do not handle high-speed operation (although it is not disabled).

4.5. Low-Speed Range

The low-speed range involves a much more complex power transmission path with two sets of reduction gears. It is also more difficult to understand for several reasons:

I'll consider it in four stages:

4.5.1. Low-Speed Range Power Path

When engaged in the low-speed range, the "Clutch Gear - Double" is pushed all the way to the left and it locks (clutches) to the "Clutch Gear 3 1/2 inch (Left)". The power transmission path is shown by the red line in the schematic below:

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image link-to-geartrain-03-with-shifter-in-low-1024x-whitebackground-sf0.jpg

In greater detail:

1. The Friction Wheel turns, and turns the Friction Wheel Shaft to which it is keyed.

2. The Friction Wheel Shaft turns the "Shaft Gear 4-inch" a18TC12 which is keyed to it. (Remember, the two other Shaft Gears rotate freely on it.)

3. The Shaft Gear 4-inch turns the "Clutch Gear - Double." So far, this is just the ordinary power input as is the case in all situations - low, neutral, or high. Note the the "Clutch Gear - Double" rotates freely on the Clutch Shaft; it is not keyed to it, and transmits no motion to the Shaft.

4. The "Clutch Gear - Double" is, however, locked/clutched to the "Clutch Gear 3 1/2 inch (Left)" 10TC3T. Both gears therefore rotate at the same speed. Neither is keyed to the Clutch Shaft or transmits any motion to it.

5. The "Clutch Gear 3 1/2 inch (Left)" 10TC3T. meshes with the "Shaft Gear 7 inch" a18TC14T. This Shaft Gear happens to be on the Friction Wheel Shaft, but that's just a handy place to put it. It is not keyed to that shaft, and transmits no motion to it. This meshing of a 3 1/2 inch to a 7 inch gear gives a 2:1 speed reduction.

6. The "Shaft Gear 7 inch" a18TC14T. is, however, pinned to the "Shaft Gear 3 1/2 inch" a18TC15 (which is also on the Friction Wheel Shaft and also not keyed to it). They rotate as a pair.

7. The "Shaft Gear 3 1/2 inch" a18TC15 meshes with the "Shaft Gear 7 inch" 10TC11 (not to be confused with a18TC14T of the same name). This meshing of a 3 1/2 inch to a 7 inch gear gives a second 2:1 speed reduction.

8. The "Shaft Gear 7 inch" 10TC11 is keyed to the Clutch Shaft and drives it. The Clutch Shaft in turn transmits this motion to the "Clutch Gear 7 inch (Right)" (passing through 10TC3T and b10TC7T which are not keyed to it).

9. "Clutch Gear 7 inch (Right)" is keyed to the Clutch Shaft and meshes with the Cam Shaft Gear, 2TC5. This drives the Cam Shaft and completes the Thompson drive/power mechanism.

4.5.2. Low-Speed Range Operation (Simplified)

Assume, to begin with, that the Stop Motion Main Spring (which normally pushes on the Clutch Shifter Rod Knob) is not present.

To engage the machine in the low-speed range, the operator would:

1. Turn on the motor (the clutch may not engage unless the gears are turning).

2. Raise the Clutch Shifter Rod Latch a11TC1 and hold it up, and at the same time...

3. Push the Clutch Shifter Rod (Knob) in fully. Only one of the three annular grooves cut into it should be visible.

4. Drop the Latch into this visible ring (the outermost of the three) to keep the Clutch Shifter Rod in this position.

4.5.3. Low-Speed Range Operation (with Spring)

If the Stop Motion Main Spring is in fact present and is pressing on the Clutch Shifter Rod Knob, then only two operational changes are needed.

First, it is not necessary to push the Rod in as in step 3 above, as the spring will do this for you.

Second, it is not necessary to worry about dropping the Latch as in step 4 above, as the Spring will keep the Rod pushed in.

This is the normal way of accomplishing low-speed operation.

4.5.4. Low-Speed Range Operation (with Stop Motion)

The Stop Motion mechanism is best considered as a subject in its own right. I'll mention it here only because it interacts with the Shifter.

One way to consider the Stop Motion mechanism is as a kind of a robot which operates the Shifter and shifts the machine into and out of low-speed operation. (Stop Motion operation in the high-speed range is neither sensible nor accomodated by the machine design.)

As noted above, the Stop Motion has a Main Spring 84TC16T which is constantly trying to push the Clutch Shifter Rod in. That is to say, the Stop Motion Main Spring is always trying to engage machine in the low-speed range. In non-Stop-Motion operation, as discussed above, it is prevented from doing so by the Latch (until the operator releases the Latch and lets it do so).

The Stop Motion also has a Clutch Shifting Fork 84TC10. This Fork pushes against the inside of the Clutch Shifting Rod Knob, and has two positions:

1. It may be released by the Stop Motion, in which case it is free to move leftward and to let the Stop Motion Main Spring push the Clutch Shifting Rod Knob left (engaging low-speed operation).

2. It may be engaged, in which case it moves the Clutch Shifting Rod Knob rightward and puts the machine back in neutral.

(Philosophical aside: The Stop Motion is an interrupter, and so its states are the inverse of the machine's. When the Stop Motion releases, the machine may engage; when it engages, the machine must stop.)

From the operator's point of view, the only difference in engaging the Clutch in low-speed operation with or without Stop Motion is that when in Stop Motion it is necessary to retain the Latch in its up position via a spring clip. If this is not done, then the Latch will re-engaged the neutral ring of the Clutch Shifter Rod when the Stop Motion next puts the machine into neutral, and no more casting cycles will occur.

4.5.5. Modified Operating Mechanisms

The "stock" Thompson operating interface (the Clutch Shifter Rod Knob) is awkward (at least at first). Several shop-made or aftermarket operating mechanisms have been devised to supplement it. I am at present familiar with only two of these.

Skyline Type Foundry has several ex-Perfection Type machines to which a lovely operating lever has been fitted. This lever operats a sort of tab (effectively a wedge, but nicely shaped) which in its disengaged position pushes the Clutch Shifter Rod Knob out to neutral. In the engaged position, this tab is moved out of the way and the Main Spring of the Stop Motion mechanism pushes the Shifter Rod into the low-speed position. High-speed operation has been locked out on these machines with a collar restricting the motion of the Clutch Shifter Rod.

The two ex-Barco Type Foundry machines at CircuitousRoot have a mechanism which is kinematically similar but much less elegant in implementation. It is an L-shaped bar in a vertical orientation with a wedge on the bottom end of it. When pulled up, the wedge is removed from the path of the Clutch Shifter Rod Knob and the Main Spring of the Stop Motion pushes the Shifter Rod in, engaging the machine in low-speed operation. When pushed down, the wedge pushes the Knob back out to the neutral position. High-speed operation has not been disabled on these machines (though I'm not sure the high-speed clutch on s/n 12,492 actually works), but high-speed operation is not addressed by this bar-and-wedge.

The Thompson formerly owned by the late Jim Rimmer also has a lever for operation; I need to view the film Making Faces again to doublecheck its mode of operation.

5. Diagram Sources

Just in case they might be useful to you for future work, here are the SVG-format source files for the schematic diagrams.


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