The Thompson Type-Caster

A Semi-Technical Overview

Casting and Delivery

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1. Introduction and Caveats

[THIS IS UNFINISHED. So far I've only written the section on Matrix Equipment. The next section is on the overall structure and components of the Mold. But I need to take a new series of photographs of a Mold as removed from the machine to do this.]

This Notebook describes, in semi-technical terms intended for the layperson generally interested in the machine, the mold, casting cycle, and type delivery of the Monotype-Thompson Type-Caster.

It describes an American Monotype-Thompson (that is, a machine made by the Lanston Monotype Machine Company). The mold and matrix equipment of the English machine are said to be identical, but I've never operated an English Thompson.

It describes the machine as equipped with the "Micrometer Set Width Adjusting Device." Although the name of this device makes it sound like a minor feature, it was actually a complete re-engineering of the set width and matrix equipment of the Thompson. While all Thompsons from the outset have had a generally similar mold, earlier machines equipped with the original "Set Block" method of set adjustment had completely different mold set adjusting equipment and incompatible matrix equipment. However, only half a dozen or so of these earlier machines survive, and none of them are presently operational. So the machine described here may be thought of as a "normal" Thompson for most 20th century and contemporary purposes.

The nomenclature I'll use is that of the 1942 Parts Price List for the Lanston Monotype Thompson. Please note that although there are a few generic terms in this nomenclature which apply to other type casters, in general the names of the parts of every different kind of type casting machine are unique to that machine. So for example in the Thompson there is a part called a "Top Block" which forms (part of) the top of the mold cavity. It is stationary during operation. But on a Barth Type Caster the type is delivered vertically upward, so it cannot have such a "top block." On other Monotype type casters, the matrix defines the top of the mold cavity. Every type casting machine is different.

DISCLAIMER: In this writeup, I'm cheating but not lying. That is, everything I say about the operation of the Thompson is true. But the photographs I'm using to illustrate it were not taken with the machine in operation. They're of a machine that is down for servicing. I've just changed the mold, but not done all of the proper adjustments. I'm also doing things like fitting a previously cast type back in the mold for purposes of illustration. If you look closely, there are gaps between various parts of the mold and of the type shown in it. If I were just to fire up this machine and cast, I'd get a serious "squirt" almost immediately.

2. Matrix Equipment

In this Notebook I'll illustrate the machine as set up for casting from Lanston Monotype Machine Company "display" matrices intended by them originally for their Type-&-Rule caster. These are probably the most common kind of mats used with the Thompson today. (Although the Thompson could cast from a wide variety of mats - Linotype-compatible, Ludlow, English Monotype display, Giant Caster, etc. - and was designed originally with Linotype mats in mind.)

The matrix carrier is a rectangular block of metal with a wooden handle on the operator's end. The version here is the "Adjustable Side-Wall Matrix Carrier" which was used on later Thompsons for holding American and English Monotype display matrices (and also old Thompson and Compositype matrices). However, the matrix carrier does not hold the matrix directly. Instead, it carries a matrix holder on the end opposite the handle. This matrix holder, in turn, holds the matrix. The matrix is clamped in the matrix holder, but it banks against the side wall of the matrix carrier.

The matrix is clamped in the matrix holder by the tall knob in the photograph below. As you can see from the photographs, in order to clamp the matrix the matrix holder projects a little bit beyond the surface of the matrix itself. It is important to ensure that this projecting bits do not contact the mold (if they do, then the matrix doesn't contact the mold and the mold cavity is not sealed - the resulting squirt is enough to remind you never to let this happen again).

There are three adjustments in the alignment of type: horizontal alignment, vertical alignment, and set width. Two of these are accomplished in the Matrix Carrier and Matrix Holder.

Horizontal alignment is accomplished by shifting the matrix left or right in its holder. When the adjustable side-wall matrix carrier is used, horizontal alignment is accomplished by loosening the matrix in the holder, adjusting the thickness of the side wall, ensuring that the matrix still banks agains the side wall, and then tightening the matrix holder. Calibration is by turns and fractional turns of the uncalibrated screw driving the wedge of the adjustable side wall.

(Other kinds of matrices, such as Linotype and Ludlow matrices, were held in very different kinds of matrix holders which in turn were fitted into different (non-adjustable-side-wall) matrix carriers. The discussion here applies only to American and English "flat mats" (display mats and old Thompson Type-Machine Company and Compositype mats.))

Vertical alignment is accomplished by moving the entire matrix holder up and down relative to the matrix carrier. This is done using a pin wrench to rotate the short knob on top of the matrix carrier.

(Set width adjustment is accomplished elsewhere in the machine.)

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As noted in the image below, the Thompson casts Anglo-American type which has its nick at the bottom of the type. But in most cases this type is cast "upside-down" on the Thompson, with the nick up. (The only exceptions to this are when Lanston Monotype "cellular" matrices and Giant Caster matrices are cast; these are cast nick-down. This requires special mold and type delivery equipment.) So the matrix goes into the matrix holder top-down.

The corner bevels on Lanston "display" matrices are used when the matrix is cast in the Lanston Monotype Type-&-Rule Caster. They have no function when the matrix is cast on the Thompson.

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An aside here to explain a term: The basic structure which holds the mold and type delivery parts of the Thompson (and also has the pivots for the front levers) is called the mold stand. Here's a photograph of a mold stand (still attached to the main stand and base) of a different Thompson that is in the process of being stripped down.

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The slides in which the matrix carrier runs are listed by the parts list as components of the mold stand. They're called, therefore, the mold stand slide (left) and mold stand slide (right). Below is a photograph of the matrix carrier, held in my left hand, approaching its home betwee the mold stand slides.

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(If it seems as if there's something missing in the photo above, it may be because I've got the melting pot swung away.)

The matrix carrier is held in place by a fork (formally the " Matrix-carrier-cam lever extension fork (for matrix carrier)" This fork is mounted in one of the several levers which control the action of the machine: the Matrix-carrier-cam lever.

This lever moves the matrix carrier (and thus the matrix) in toward the mold face for casting and draws it back away from the mold face after casting.

The matrix-carrier-cam lever is actually a two-part lever, pivoted in its middle. Between these two parts there is a strong compression spring. The lever pushes the matrix carrier and matrix up to the mold face, and a tiny bit beyond. This compresses the spring, holding the matrix firm against the mold face regardless of any slight variation in the lever postion. (In operation, you can actually see the nut holding this spring in place rise up slightly (about 1/64 inch) on every casting stroke as the spring compresses.)

(Aside: This spring also determines the ultimate pump pressure of the Thompson. It is possible, with certain pump pressure settings combined with sufficiently large matrices (both body size and set width) for the pump to overcome the pressure of this spring and blow the matrix off the mold face. This results in a very impressive four-way squirt.)

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Here's a view from the inside. The "mold cavity" in which the type will be formed is clearly visible.

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3. The Parts of the Mold


4. Appendix: Center Jet vs. Side Jet Molds