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Above: later Model 5 screwcutting chart as mounted on the end face of the changewheel cover
Even though relatively fine-pitch changewheels of 20 D.P. were used, the smallest gear in the original standard set was only a 24t and the largest a 69t; this specification, combined with the limitations imposed by the single-slot changewheel bracket, made it difficult to set up a compound-reduction gear train to give a carriage feed that was slow enough for very fine feeds. Reference to the range of changewheels supplied with early and late 9-inch lathes shows the improvement brought about by including both smaller and larger gears and the introduction of a forked bracket to carry them: gears supplied with the very first Model 405 were: 24t, 30t, 33t, 36t, 39t, 42t, 45t, 48t, 54t, 60t, 69t that limited the treading range from 4 to 40 t.p.i. Almost immediately an alteration was made and a compound gear pair with 110/20t added to the set that, combined with the other gears, gave a finest feed of 0.0028" per revolution of the spindle (120 t.p.i.), so enough to give a good surface finish. To help beginners identify the fine-feed gears the pair on the banjo arm were clearly marked: compound gear 1 to 5 (with 110/20t) and, on the leadscrew, a single gear marked turning gear 105t. The later, more fully-developed "proper" 9-inch models (with a forked banjo and the gear DP changed from 20 to 18) were equipped with: 16t, 24t, 36t, 40t, 44t, 46t, 48t, 52t, 54t, 56t, 60t, 80t, a 72/18t compound and an 80t idler with a boss that gave the same span of 4 to 120 t.p.i. Interestingly, reference to pictures in the October 1934 catalog shows that South Bend must have reacted quickly to improve the situation for, though a single-slot bracket is shown in Bulletin 5-D, a 72/18t compound and the distinctive boss-equipped 80t idler gear (as supplied with later lathes) are also illustrated; these were, presumably, included as an interim measure to slow the feed rate until the improved bracket could be put into production to give a threading range that extended to 60 t.p.i. A screwcutting chart for a single-slot banjo machine that includes these "between-model" gears has yet to be found - but, knowing the detailed attention South Bend paid to such matters, would almost certainly have been produced. The changewheel chart for the 405 was, naturally, unique to the model and in its original form riveted to the front face of the changewheel cover. Before production of the 405 ceased (and almost certainly coinciding with the change to a double-slot bracket) it had been replaced by a larger and more useful version, complete with diagrams, and moved to the larger surface on the end face of the changewheel cover. As all pre-WW2 South Bend screwcutting and other plates are smooth on the rear, it's likely that they were produced by a process called chemical milling (rolling through a die or stamping leaves an imprint on the back). While it's possible that during the 1950s a cheaper silk-screen process was used, before then enamel was used to colour them. A paint in power form was applied in the low areas and then heated to melting point; the paint ran to its own level producing a superb, durable finish. A final touch was to lightly polish the raised letters and numbers. South Bend would not have produced their own plates, this was a process best left to a specialist maker..
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