Well, I managed to fool WordPress into accepting an animated GIF so here’s the one I made of the ribbon feed mechanism being operated manually. It’s a little rough because the original pictures were taken with the tower lying on the table, free to move around a bit. Nevertheless the basic steps can be seen:

1. The drive pawl engages the ratchet wheel.
2. The locking pawl clears the ratchet wheel.
3. The pawl ring rotates counterclockwise, turning the ratchet wheel with it.
4. The locking pawl engages the ratchet wheel.
5. The drive pawl clears the ratchet wheel.
6. The pawl ring rotates clockwise, with the ratchet wheel stationary.

Once the operating rod for the paper tower is adjusted, there are four adjustments left, all affecting the Air Bar 2G, Pressure Bar 3G, and air feed. Two of the adjustments are on the Connecting Bar 4G that links the Paper Tower Lever to the Clamping Lever, one is the screw 3G3 that actuates the air valve stem 2G8, and one is the stop nuts 2G6 that limit how far the Air Bar Springs 2G3 can expand. The two adjustments on the Connecting Bar are the overall length of the bar and a stop that limits is upwards travel. On older casters before serial number 503 the latter adjustment did not exist; instead there was a simple spacer tube and wear was compensated for by adding a washer to the end of the spacer tube.

The adjustments in Casting Machine Adjustments consists of setting the valve screw 3G3 to a specific amount of projection below the arm it is set in. Then a sheet of caster ribbon is used as a feeler gauge between the 3G3 screw and the valve stem, allowing the Air Bar Spring length to be adjusted. Third, the connecting bar length is adjusted to set the clearance between the air bar and the cross girt to three ribbon thicknesses just as the clockwise rotation of the pawl ring stops (and thus the ribbon stops). Fourth, the stop collar on the connecting bar is adjusted so the connecting bar has about 2 points of total motion. The book mentions that these adjustments interact with each other and that it might be necessary to repeat some of the earlier adjustments.

I have an alternative adjustment procedure which generally avoids the need for repeating adjustments, and also does not rely as much on rote distances.

Read more ›

The book Casting Machine Adjustments provides procedures for adjusting the Paper Tower, but I find that these adjustments are given in the wrong order (later adjustments can affect earlier ones) and some of the adjustments are rote settings which may not be appropriate on an older caster exhibiting wear in some of its linkages.

Read more ›

While refurbishing the paper tower for my Monotype caster I found that one of the pivot pins (part 16G, on which the locking pawl pivots) was slightly bent, and was nearly impossible to straighten properly. The bend was hard to see except when the pin was installed, and the pin was too short to tell exactly where it was bent.

Rather than trying to fix the existing pin I made a replacement one.

The geometry was fairly simple, but the dimensions had to be accurate to ensure that the pawl did not have too much play, which would have led to increased wear of the ratchet wheel and misalignment of the ribbon holes over the air ports. It fits well, although I cut the threads a bit deep, possibly weakening the threaded portion of the pin, but I don’t think there is enough pullout force to break it.

The paper tower is now reassembled, except for the two lower covers, and has been reinstalled on my caster. To discourage future air leakage around the base of the tower I applied a thin coat of spray adhesive to the mating surfaces. I actually sprayed it onto a piece of release paper, then applied that to the area around the ports, so that over spray would not enter the actual air lines. The adhesive should be strong enough to resist the air pressure but still weak enough not to prevent future removal of the tower. I would have used brush-on gasket sealant if I had had any.

The next job is to adjust all the linkages.

The other part of my caster’s paper tower that received a good cleaning is the ribbon feed mechanism. The ribbon itself is moved by two sprockets whose teeth engage in holes along either side of the ribbon. These sprockets are fixed to a shaft which has a gear-like ratchet wheel on the front end to drive it. The mechanism converts the reciprocating motion of the cam arm into a precise stepping motion of the ribbon.

First, a couple of notes about some of the screws that hold the casing of the paper tower together. On the front end of the paper tower, the two screw near the top which attach the end casing to the cross girt are not immediately accessible.

The lower of these (one of three 1G12) is visible but sufficiently covered by the quadding counting wheel that it cannot be removed or installed without removing the counting wheel first. This in turn requires removing the small taper pin that connects the quadding ratchet wheel to its shaft inside the tower casing. The counting wheel and its shaft can then be pulled out providing access to this screw.

The upper screw (1G13) is behind the paper feed pawl ring b14GG and so the entire feed mechanism must be removed before this screw can be reached. It also differs from the three 1G12 screws insofar as having a specially thin head, so it does not protrude and interfere with the pawl ring’s movement.

The pawl ring is held in place by two sets of washers, springs, and shoulder screws (14G2, 3, and 4) which allow the ring to rotate but provide some friction which is essential to keeping the pawls seated in the ratchet wheel.

The pawls themselves are mounted on a set of arms which (when adjusted) accurately advances the shaft by one notch with no back motion.

The locking pawl (b13G) is mounted to the end casing on pivot 16G and has a tooth which can engage the ratchet wheel at a fixed location near the top of the wheel. This defines the position of the ribbon when it is stopped for reading. I find it interesting that there is no adjustment in this to get the punch holes in the ribbon lined up with the air ports on the cross girt.

The feed pawl 13G6 pivots on pin 15G which is mounted on the pawl ring and so this pawl can move around the center of the shaft.

Both pawls have stops that limit how far they can move away from the ratchet wheel. A spring pulls the two pawls together so that their idle state is to be both lightly engaged in notches in the ratchet wheel.

The set of levers formed by b13G3 and 13G7 is designed such that upward pull on the end of b13G3 releases the feed pawl, presses the locking pawl into its ratchet wheel notch, and also tries to turn the pawl ring clockwise. Downward pull presses the feed pawl into its ratchet wheel notch, releases the locking pawl, and tries to turn the pawl ring and ratchet wheel counterclockwise. In either case the friction provided by the mounting of the pawl ring is transmitted as pressure on the pawl that remains engaged in the ratchet wheel.

The stop screws 1G20 are adjusted such that, with the locking pawl engaged and the pawl ring at either end of its motion (with its lug against one of the stop screws), the feed pawl is perfectly lined up to engage a notch in the ratchet wheel. As a result there is no stutter or back motion when one pawl locks and the other releases.

I was going to post the motion of this mechanism as one or more animated GIFs but WordPress seems to choke when I try including one in my post. When I get some time I’ll post it as a video on YouTube.

In the meantime I have to make a replacement 16G (the fixed pivot for the locking pawl) because the one on my caster is bent. Such things are very difficult to straighten out so it will probably be easier to make a replacement than to fix the bent one.

This post provides a detailed view of one of the mechanisms in the Monotype paper tower. When the Quadding mechanism is engaged a notched wheel on the front side of the paper tower turns one position per cycle, and the (absence of) a notch on this wheel prevents the ribbon from advancing, causing the character coded by the current ribbon position to repeat until the counting wheel advances to the next notch. In this manner a character can be cast 5 or 10 times (depending on how the notched wheel is set) from a single row on the ribbon.

This would save some keyboarding time and make ribbons shorter for material with a lot of wide spacing or leaders in the lines, but otherwise would not speed up the caster. When using a computer interface, this feature is essentially pointless.

It is also a bit of a nuisance because if the counting wheel is not at a notch position but the ribbon is not on a row signalling for quadding, the ribbon will never advance because the counter wheel will not turn. This can happen if the ribbon is manually repositioned during a quadding countdown or if the counting wheel is accidentally moved manually.

Because this is only marginally useful and somewhat of a nuisance, many casters I have seen (including my own) have this feature disabled by removing the arm that senses for a notch in the counting wheel. The ribbon advance then essentially always senses a notch and thus always advances the ribbon.

Despite the limited utility of this mechanism, I had my paper tower disassembled and cleaned so I am posting some photos of how the counting wheel is advanced.

First, the mechanism, with parts identified by symbol:

This view is of the inside of the front end plate of the paper tower; in the assembled paper tower this view direction would be obscured by the air pipes and the entire area enclosed by the side covers of the tower. My mechanism is missing 29G17, a spring (wavy) washer behind the plain washer 29G18, but it seems to operate fine without it. The parts are illustrated on Plate 49 of Spare Parts List for Monotype Composition and Type and Rule Casters (Monotype Corporation), and also on pages 62/63 of Plate Book, Monotype Typesetting Machine, the Composition Type-Caster (Lanston Monotype Machine Corp, 1955)

This mechanism is driven by a pin on the air tower lever c19G which passes through the tower side panel and engages link a29G14 about where the arrowhead for a29G9 is. The pin is eccentrically mounted on the air tower lever to provide some adjustment to the quadding counting wheel mechanism.

The ratchet wheel 29G1 is held at one of 20 positions by the detent spring a29G2, and is pinned to the counting wheel shaft assembly 29G23G by the taper pin a29G22.

When Quadding is not selected by the ribbon, the mechanism moves but does not rotate the ratchet wheel:

When the air tower lever is at the top of its stroke, the pawl 29G4 is rotated clockwise by contact with the pawl lever a29G5.

As the air tower lever descends, the pawl moves clockwise around the ratchet wheel.

When the air tower lever has descended all the way the pawl has moved further around the ratchet wheel but remains disengaged from it.

The return stroke is the same sequence in reverse.

If the ribbon row selects quadding, at the bottom of the stroke air is admitted through the ribbon to the various air lines, and the quadding actuator piston a29G9 rises pushing the pawl lever a29G5 up, which in turn rotates the pawl until it engages the ratchet wheel.

The pawl has been engaged in the ratchet wheel by the actuator piston.

As the air tower lever rises the movement of the pawl rotates the ratchet wheel. The air is released from the ribbon air bar and the actuator piston drops again.

With enough rotation the detent spring a29G2 drops into the next ratchet tooth.

The pawl contacts the end of the pawl lever which starts to force the pawl back to its disengaged position.

Once the pawl is disengaged from the ratchet wheel the detent spring snaps the ratchet wheel back a bit and the mechanism is back at its idle position from the first photo.

There are three adjustments in this mechanism: The detent spring can be shifted up or down so that the pawl disengages just after the spring catch drops over a ratchet tooth. The eccentric pin on the drive arm can be rotated to move the entire range of motion of the arm a29G14 up or down so the pawl reliably engages a ratchet wheel tooth without excessive slop and also to a lesser extent to adjust the length of this stroke. Not shown here, but the arm on the ribbon advance mechanism that senses the presence of the notch on the counting wheel can also be adjusted to match the notch position. None of the copies of the book Casting Machine Adjustments I have seen describe these adjustments, probably because they predate the Quadding feature. I do however have an article entitled Automatic Quadding and Centering on the Monotype by Lanston which gives a somewhat rote adjustment method. It essentially amounts to setting the eccentric to a central position, adjusting the detent spring so the pawl engages with 0.020″ clearance from the ratchet tooth, then fiddling with both adjustments aimlessly if it does not advance properly.

Although there are openings in the two paper tower covers to allow oiling of this mechanism it is difficult to oil it properly without just shooting in a big squirt of oil and hoping it hits all the moving parts. Removing the left cover of the paper tower gives better access allowing the oil to be applied to all the moving parts properly.

After refurbishing both air pin blocks and replacing the paper tower air connector on my Monotype, I tried another dry run with the ribbon I had. I was finding that there still seemed to be substantial air leaks, which sounded like they were inside the paper tower. I removed the side covers from the tower and tried to trace the leaks from their sound. Eventually I applied soapy water to see where the bubbled originated. They seemed to be coming from two places at the base of the tower and I thought that somehow a couple of the air lines were leaking where they were inserted into the tower base.

In order to fix this, I started doing a job I was hoping to avoid for now, namely refurbishing the paper tower. I disassembled it to clean the parts, and it was only after disassembly, on examining the base plate, that I realized where the leaks were.

This plate just makes flat contact with the table of the caster, but to avoid air leaking at this joint from one air line to another nearby one, each port is surrounded with a shallow groove. These grooves all connect to each other, and also to two extra holes that allow the leaking air to vent out. Right where I had observed “leaks.” So the apparent leaks I had observed were in fact leakage where the face of the tower base meets the table top. This could be caused by a fleck of dirt, or slight warping of the parts as the casting age. I checked the base for flatness (the blue stuff showing in the photo is residue from the marking compound) and found a bit of a scratch with a raised burr so I cleaned that up with a hard sharpening stone.

By then, I had the tower in pieces, so I proceeded to clean everything. Here are all the cleaned parts, with some of the subunits already assembled, and some of the dirt removed in a pile top left.

It’s a good thing I like taking stuff apart and reassembling it!

Upcoming posts will show details of some of these subunits which are not well shown in the Monotype documentation.