As a 21st century typefounder, the Thompson Type-Caster is a machine of special interest to me, in all of its aspects.
The Thompson Type Machine Company was acquired by the Lanston Monotype Machine Company in 1929, and at some point relatively soon after its part symboling system was converted to a form compatible with the Bancroft / Monotype system. Before that, however, the Thompson had at least two part numbering/symboling systems. The first was a very simplistic numbering of parts. The second was an interesting semi-systematic scheme that used symbols of the same form as the Mergenthaler system but with a degree of systemicity more in line with Monotype's.
Very little is known about the part numbering system used originally for the Thompson. No parts books or lists survive. The only surviving information is a 1916 manual, Instructions to Operators of the Thompson Typecaster (Chicago: The Thompson Type Machine Company, 1916; reprinted by David C. Churchman and presently available from Skyline Type Foundry). This book does call out parts by number in the text and identifies them in the illustrations.
Each part number is a simple three digit number. As far as I can tell, the numbering is essentially arbitrary. If there once was any system to it, that system has been lost and has not been rediscovered.
The next known (and indeed the only other known) pre-Monotype Thompson part symboling system was adopted at some point before their 1925 manual. We know that it must be the last pre-Monotype system, because the Monotype-Thompson manuals cross-reference their new part numbers to it.
It adopts an alphanumeric system which looks much like the Mergenthaler system (e.g., "M-520", which is the Mold Body Lever). But unlike the Mergenthaler system, the letters in this code are considered "Symbols" which refer to "Groups" within the machine. These are identified on p. 68 of the 1925 Thompson manual. Within limits, they are largely mnemonic (up to 'K' for Cam and 'L' for aLigning). The one two-letter symbol, SK, is for a component which would have been a later addition to the machine (the electric pot). The Micrometer Set Adjusting Device, for which there is no Symbol, was also a late addition.
The 1925 Thompson Type Caster manual is in the public domain. The scans from it reprinted here remain in the public domain.
All portions of this document not noted otherwise are Copyright © 2014 by David M. MacMillan and Rollande Krandall.
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