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South Bend 9-inch "Workshop" Lathe
Handbooks, Parts Lists, Catalog Sets & flat belts are available for these lathes
 
Original 1934 9-inch Model 5   South Bend Home Page   Accessories
South Bend 9-inch Clones   In the Factory   An Unused 9-inch

For many model and experimental engineers in the United States the definitive South Bend lathe is the 9-inch "Workshop" Precision backgeared and screwcutting model.  The success of the model, and its suitability as a general-purpose workshop lathe can gauged from the number of copies produced: English ones by Smart & Brown, Boxford and Ace; the Australian Hercus, Sheraton, Purcell and Parkanson (the latter the brand name of Theo. Park & Son, Engineers ,Melbourne); the Swedish Storebro and Blomqvist; the Brazillian-made Sanches Blanes, Joinville and Boffelli & Finazzi, the French UFP and from Argentine the S.R.L. San Francisco (CBA), Industria Argentina. Another copies were the mysterious NSTC (probably American, but about which nothing is known) and the Brtish "Unitol", a name more often found on the Heavy-10 South Bend but perhaps (like the Heavy-10), this was a real South Bend just rebranded with the Unitol name cast into the iron cover that guarded the belt running from motor to countershaft.
Designed and first manufactured in 1933, the lathe was not announced until January 1934 as the "Model 5" with a single, basic specification of screwcutting by (20DP) changewheels and hand-cross feed. This first model had virtually nothing in common with either of the earlier, cheaper South Bend lathes, the 8" and 9" Junior models, and was most commonly listed using the catalog number "405" - the "4" referring to a lathe intended to be driven by bench-mounted countershaft. The earliest mention of the lathe so far discovered comes in a January 1934 works pamphlet that provided examples of advertisements available for dealers to use in to their local press  - should you have an earlier mention the writer would be very interested to hear from you. More details of these very early 9-inch lathes, and their supporting literature, can be found here. Although a perfectly functional lathe the first model did have some shortcomings that were fully addressed by the manufacturer through an interim model (listed as the 415) manufactured from around September 1935 until the 1938/9 and the introduction of a new range consisting of "A", "B" and "C" versions - the latter with changewheels and hand cross feed and very similar to the 415. However, even as the lathe developed, by as early as 1935 the makers were boasting of  "Ten New Features" - though it has to be said that polishing the rims of the carriage and tailstock handwheels was allowed to account for two of them. The catalogue for November 1936 lists the 415 as the "New 1936 Workshop" - though even at this date it still retained a changewheel cover complete with the first type of (405) threading chart - but transposed from front to end face. The Model 5 (Type 405) and its development is covered in detail on these pages.
Taking account of the hard economic times of the 1930s the Model 5 was engineered to sell at a price that would appeal to the amateur and, in view of the fact that it would probably not be used for very heavy-duty work, constructed from rather light castings in comparison with other models in the range; however South Bend, it seems, were prepared to sacrifice nothing in the way of quality of fit and finish and the Model 5 and subsequent versions were very well built. The makers boasted in early advertising literature that the lathe was: "
built entirely of steel, cast iron and malleable iron .. No die cast metal is used." - the latter reference being a dig at Atlas with their mass-produced 9-inch lathe.
With its excellent materials, sound construction and decent specification the lathe found a ready market. Large enough to tackle most work the amateur owner or small repair workshop was likely to come across, the hole through the headstock spindle was 3/4" - although a few (much later) lathes have been found (in England) fitted with a modified headstock from the 10-inch lathe, complete with the huge 1
3/8" bore spindle. The headstock bearings were lubricated at first directly through top-mounted, spring-cap Gits-brand oilers with a feed passed onto filter felts, held within a groove, from where it dribbled downwards, hopefully less any dirt. After 1936 oil cups with dip wicks, were used; these allowed the operator to fill them at the beginning of a job and check when more was required. In 1938 the lathe was given even better protection from forgetful owners with oil fed through spring-loaded wicks from reservoirs built into the lower part of each bearing column (as on larger South Bend lathes) with Mobil Velocite 10 oil as a suitable and recommended modern equivalent to the original lubricant. The felt wicks were designed to deliver oil upwards - minus any dirt which may have worked its way in - by capillary action. Should you remove the spindle a problem arises: the felts pop up into the space created and prevented it from being replaced. The solution? If each "elbow" oiler is turned through 90 degrees a small hole is revealed, bored horizontally through the casting, designed to accept a length of stiff wire to hold the felt down while the spindle is replaced. A word on wicks: the felt used needs to be dense - it has to transmit the oil by capillary action, regulate the flow while also acting to filter out any dirt. Industrial-grade felts in various sections and thicknesses are still available from engineering supply companies and it pays to look out the correct type, not a household grade.
Originally described as both the Model 9-inch "Workshop Lathe and the 9-inch "Workshop" Precision Lathe, by the end of World War Two (in 1945) the marketing department must have considered the term Workshop to be down-market and it was dropped from the catalogues - the single description Precision being used instead. The words "Precision" and "Toolroom" were freely used by South Bend throughout their catalogs for many years to indicate specifications and equipment levels - rather than any intrinsic merit, or mechanical superiority over other lathes in their range.  In general terms (and depending upon the particular size of machine) a "Toolroom" lathe would have had a taper turning attachment, a collet storage board, a collet draw bar for the spindle (and just a single collet) supplied as part of its standard equipment.
On its introduction the 405 -"Workshop" was available in eight "models" and four different bed lengths of  3 feet (model 15-YB), 3.5 feet (model 15-ZB), 4 feet (model 15-AB) and (very rarely) 4.5 feet (model 15-RB). These gave, respectively, between centres' capacities of 17", 23", 29" and 35"; the mechanical specification of the lathes' main components was identical, the only differences being in their ancillary equipment - the term "Model" being stretched to include numerous combinations of drive systems and stands.
Supplied without a countershaft unit, or motor, the basic lathe was priced, on its introduction, from $75 for the shortest-bed, 18"-between-centres version to $116 for the longest, 30-inch capacity model.  Other, more expensive options were available, including ones where the lathe was supplied complete on an underdrive stand with either a plain "Simplex" or "adjustable" countershaft fitted with an electric motor and reversing switch - and ready to run. The "plain" countershaft suffered from the disadvantage of having no provision to adjust the belt tension to ease the change from one speed to another - although both the motor and the base of the countershaft were slotted to allow initial belt tensions to be set; with these countershafts changing speeds meant having to "roll" the belt from one pulley to another - a method common at the time but still inconvenient.
Heavily built, the adjustable countershaft had a cast-iron upright hinged to a stout baseplate with an over-centre lever to set and lock the angle between them. The lever allowed the belt tension to be released instantly and the belt moved from pulley to pulley with ease; this countershaft could also be supplied with a 4-step V-belt drive for which, of course, a much greater release of tension was needed to allow the V belt to be moved out of its deep groove. Another advantage of the adjustable countershaft was that it allowed slight variations in belt tension between different grooves on the pulleys (which is often present no matter how carefully made are the pulley sets - and increases with wear) to be removed by making a small adjustment to the left-hand/right-hand threaded turnbuckle between the two halves of the tensioning rod. The plain-countershaft lathe, in short-bed form and ready to run, was priced at a total of $98.25 while the much more desirable model with an adjustable-countershaft was only an additional $5 - which probably explains why most 9-inch "Workshop" lathes are found today with that fitting.
During 1934 and 1935 the most expensive "ordinary" 9-inch Workshop lathe was the 4-speed V-belt drive long-bed model at $154; however, during the following year (1936) a "Toolroom" version was introduced, complete with a hand-wheel activated draw-in collet chuck (plus one collet of any size from the range), a taper-turning unit, micrometer-carriage stop, thread-cutting stop for the cross slide and a collet tray held on a supporting bracket which was clamped down over the back V of the lathe bed. This model (which differed in accuracy only in the fitting of what was claimed to be a more accurately cut leadscrew) was supplied with a 4-speed V-belt countershaft drive, a hardened headstock spindle and retailed for $205.25 in the shortest bed length - and $246.25 in the longest.
Continued below:

Not the first  9-inch "Workshop" lathe but the one advertised in 1935 with all the early changes complete. Although not called the "Model C" until 1939, that is the expression usually used when referring to this version. This example has the electrical reversing switch mounted on a special bed clamp and a horizontal-drive countershaft unit of the non-adjustable type. The headstock bearings have top-mounted flip-up Gits-brand oilers, the outside face of the spindle bull wheel is exposed and the changewheel guard not only open on its inside face but also without any method to lock it closed.

Above:: South Bend 9" Model A "Precision" 1952-version with an "English-threads" gearbox and rear-drive countershaft. Note that, while much appears to be unaltered in comparison with earlier versions, this lathe has longer, heavier and more robust bed feet. Oddly, during 1947 (at a time that seems to have coincided with a new number system in march of that year) , a batch of lathes was produced that might be described as an "interim" model with longer, convex-ended feet and a bed that must have been from a new mould. This bed, which was used for a short production run only, lacked the pronounced rib along the lower edges, had a "square" profile in cross section (in comparison to the original round style) and (most distinctive of all) the word South Bed cast into the top face of two bed cross-ribs. After this the later style feet were adopted and the bed revered to the older style.
The 1952 lathe makes an interesting comparison with the much more modern-looking model that was fitted to a sheet-metal underdrive stand. The Model A was fitted with a screwcutting gearbox and power cross feed apron. The machine illustrated above has the optional 12-speed countershaft unit with a 4-step V-belt pulley on the headstock and an adjustable belt tensioner and over-centre locking handle arrangement. The guards for backgear and changewheels are a little fuller - and include protection along their previously  open edges - but the latter could still not be locked closed. The headstock spindle -  hardened as standard on all V-belt drive models - was lubricated by spring-loaded felts dipping into reservoirs formed below the spindle line and filled from angled flip-top oil caps positioned just below the bearing caps. The bed feet were, by this time, very much more substantial and gave the lathe a heavier and more purposeful look.
The 9" South Bend "Workshop" lathe was eventually available in main three forms - and from 1939 (and the introduction of the "Super-finished" spindle and screwcutting gearbox) was know as:
Model A with screwcutting gearbox and power cross feed
Model B with screwcutting by changewheels and power cross feed
Model C with changewheel screwcutting and hand-operated cross feed - this lathe was built from 1935 but its designation as the "Model C" did not happen until 1939, though the term "Model C" is widely applied to all the ordinary pre-1939 9-inch Workshop lathes.
Gap Bed Model in A, B and C form - introduced during 1962.
Initially the model C was available with either a six-speed flat belt drive or an eight-speed V-belt drive; screwcutting was by changewheels and an interesting option, for heavy-duty manufacturing use, was a headstock spindle driven by triple V belts from a single-size pulley.
What colour was a South Bend 9-inch lathe ? If experiences with other machine tools are a guide the original shade of a "greenish grey" would have varied in tint over the years, it being notoriously difficult to obtain consistencies in paint colours from one batch to another. A good starting point for a rebuild would be a Benjamin Moore Urethane Alkyd Industrial Enamel to the formula: M22-3B, OY-15, BK-27, MA-1 1/2 per quart.
After WW2 a 10-inch version of the lathe was developed, the "South Bend Light Ten"; this featured an increased centre height, a larger hole through the spindle, a more securely guarded headstock  - and was available as either a standard bench version or mounted on a neat, under-drive cabinet stand. This lathe did not replace the 9", but ran along side it until the mid 1970s. While the older design of heavy 10" underdrive lathe is quite common outside the USA, the "Light Ten" is much rarer. More South Bend History.
It is interesting to compare the original South Bend 9-inch lathe with the English copies by Smart & Brown, Boxford and Ace; the Australian Hercus, Sheraton, Purcell and Parkanson (the latter the brand name of Theo. Park & Son, Engineers ,Melbourne); the Swedish Storebro and Blomqvist; the Brazillian-made Sanches Blanes, Joinville and Boffelli & Finazzi and from Argentine the S.R.L. San Francisco (CBA), Industria Argentina. Another copy might have been the "Unitol" - a name more often found on the Heavy-10 South Bend - but perhaps (like the Heavy-10) this was a real South Bend just rebranded with the Unitol name cast into the iron cover guarding the motor to countershaft belt.
For an interesting, highly practical and well-illustrated article about rebuilding a South Bend power-feed apron (Hercus version) click here
An active and intelligently moderated South Bend Users' Group can be found on Yahoo here and parts for the lathe here.

Rare, circa 1960 gap-bed 9-inch Model A South Bend

South Bend 9-inch "Workshop" Lathe
First modern-pattern Underdrive Model
First made available during 1942 the Underdrive Model on its sheet-metal stand (a design previously adopted by many other makers) had a much more up-to-date appearance than the company's earlier products. The lathe was available in the usual South Bend combinations of Model A, B and C together with versions equipped for "toolroom" use and one with production equipment mounted: a 6-position self-indexing capstan head, a screw-or lever-feed cut-off slide, a lever-operated collet closer and coolant.
12 spindle speeds were provided in two ranges of high and low - the difference being achieved by a double-step pulley on the motor and countershaft: in backgear the low range gave 41, 72, 127 rpm and 212, 370 and 658 rpm in direct dive; in high-range backgear the speeds were became 79, 138, and 246 rpm and in high range direct drive 408, 716 and 1270 rpm. The final drive was by flat belt, the one provided being leather and laced together
Initially only one between-centres capacity of 22 inches between centres was available but with a year alternative specifications of 16 inches and 28 inches were being offered. Built into the tailstock-end bed foot was a new feature, and adjuster by which means the lathe could be levelled correctly. There were two screws, one at the front and one at the back; by tightening one and loosening the other (both should be tight when the adjustment is complete) the bed could be "twisted" into the correct alignment.

Model A Underdrive fitted out for "toolroom" use with the usual South Bend specification of a screwcutting gearbox, power sliding and surfacing and a collet tray bolted to the tailstock end of the bed.

The Model 900 and 1000 Production lathes could be supplied to the same specification as the  engine (centre) lathes in A, B or C Models and fitted with either screw or lever feed to the cross slide.

South Bend 9-inch "Workshop" Lathe
Stands and Drive Systems
During the first two years of production the "Workshop" lathe was sold as either a bench unit with a separate but self-contained countershaft drive - or fitted to cast iron legs, in which case the drive system had to be remotely mounted on the wall or ceiling.
During 1937 South bend introduced the first of the Workshop "Underdrive" models; these were fitted to well-built wooden stands and incorporated a version of the drive system already in use on larger models in the range. In order to accommodate the drive from underneath the headstock casting was completely new with wide, cast-in tunnels to allow the belt to pass directly downwards. The bed and its headstock-end supporting foot were cast as one and a deep, hinged guard provided to cover the belt. In the same year the cast-iron "leg" stands were improved by the addition of a tall, floor-mounted countershaft unit which allowed the machine independence from the tyranny of wall and ceiling-mounted countershafts.
By 1947 the first of the more modern-looking underdrive 9-inch models had been introduced; fitted to neat, self-contained sheet-metal cabinet stands the design then evolved, with very few alterations, into the Light 10 Model that remained in production as South Bend's standard small lathe until 2002 - though batches of these late-models examples were made by Hercus in Australia, rather than in the USA.

Typical South Bend countershaft assembly. The electric-motor shaft carried a V pulley with the V belt driving onto a large-diameter, narrow, flat pulley. This rather unusual arrangement (of a V belt driving on a flat pulley)  worked very well even if, to modern eyes at least, it appears illogical. The final drive to the headstock was either by a 3-step flat belt or, less commonly, a 4-step V-belt with hardened headstock spindle.
The countershaft was arranged to hinge about its base and an over-centre tensioning device was fitted - the long slotted adjuster for which can be seen above the motor between the upper and lower belt run.
An optional 2-step pulley set was available that, with a powerful-enough motor, doubled the number of spindle speeds to 12.

Left and below: the first underdrive system for the 9-inch "Workshop" Lathe was designed to be incorporated within a wooden bench which could either be supplied by the factory - or built by the owner to a set of plans provided free with every lathe (if any reader has a set of these plans the author would very much like to hear from them).
Note the modified headstock and cover; the bed and its left-hand mounting foot were cast in one piece.
Where a 2-step pulley set was used on the motor and countershaft (to double the number of speeds) the idea of using a V belt running on a flat pulley made sense - there was no need to provide any method of slackening the belt before it could be moved - it simply had to be rolled off one countershaft pulley, slipped into the other V pulley on the motor and rolled back onto the other countershaft pulley.
The final, rather more modern-looking version of the underdrive arrangement can be seen here

Underdrive countershaft unit for the 9-Inch "Workshop" Lathe fitted with final drive by V-belt.

9-Inch Workshop Lathes on cast-iron stands had previously required a separate wall or ceiling-mounted countershaft unit. The floor-mounted unit, although a clumsy design,  allowed complete flexibility in deciding where in the workshop to place the lathe.

End view of the floor-mounted countershaft unit.

South Bend 9-inch "Workshop" Lathe
Headstock Details

Early "top-oiler" headstock picture cut away (with the backgear guards removed) to show the ball thrust bearing inboard of the left-hand headstock bearing. A fibre washer was placed between the adjustment "screw-ring" on the outside of the bearing and the headstock casting; this can, with advantage, be replaced by a standard radial needle-roller bearing thrust bearing that comes complete with hardened washers to mount each side. The use of this type of bearing allows the spindle end float to be reduced from 0.001" to almost zero--however, because these very thin needle-roller races have to use parallel rollers (instead of the usual tapered type) the outside of each roller is moving faster than the inside and some compensatory skidding has to take place. It is thus vital to leave a few "tenths of a thou" clearance to allow for heat expansion and give the rollers chance to "find their place".

Ball thrust bearing inboard of the left-hand headstock bearing.

Various and changing specification details of headstock spindles and bearings on the 9-inch lathe make it difficult to untangle their development. In early catalogs, rather than own up to the fact that the spindle was running directly in the cast iron of the headstock, South Bend either admitted it by omission - or referred to the subject only obliquely (they must have imported a political-speech writer, for they did this very successfully) - however, they need not have been so shy, the method, widely employed on other makes of lathe and machine tool had already been proved a success. What South Bend did was match the specification of the spindle to the type of use it was likely to encounter: thus, on its introduction in 1934 the 9-inch "Workshop" lathe was fitted with a ground steel spindle that could be ordered hardened for an extra $10, a charge later reduced to $6. In 1938 a completely revised and much improved capillary oiling system and hard spindles were introduced on the (now rare) "S" toolroom version of the 9-inch, with every model being fitted with the same system by 1940. The "alloy steel" spindle had its bearing surfaces carburized, hardened and ground - but with the 12-speed and "Toolroom" models being treated to a "Superfinished" process that gave a smoothness of 5 micro-inches ( .000005" ). The spindle ran directly in cast iron of the headstock and, if provided with clean oil (Mobil Velocite 10 is recommended), and not run beyond its deign limits, proved capable of lasting a very long time indeed. As a matter of interest, though never mentioned in any contemporary catalog, some 9-inch lathes left the factory with thin-walled bronze bearings - which have only been discovered on stripping machines down.
If the headstock assembly is dismantled it's important to replace, if fitted, the felt oiling pads. On some machines from the late 1930s, the left-hand bearing had two grooves were machined in the split between the bearing shells. The slots were about 5/32" wide, by about 1/16" deep with another groove cut across the end of the bearing shell. A cut piece of felt, intended to distribute oil to the diameter of the spindle bearing journal (and also to the thrust  race in the rear bearing) was pressed into the grooves. With the advent of the  new oiling system the felts were no longer needed..

The standard spindle for the 9-inch Workshop lathe was bored through 0.75". The front bearing was 113/16" in diameter and 21/4" long - and the rear 13/8" in both diameter and length. However, on its introduction the spindle nose was 13/8" in diameter with a 10 t.p.i thread but this was quickly changed to the familiar 11/2" diameter 8 t.p.i U.S.F thread. The Taper in the spindle of the original machine appeared to be a No. 3 Morse and was supplied with a sleeve to bring it down to a No. 2. The advent of the larger spindle allowed the fitting of what seemed to be, at first sight, a No. 5 Morse taper, again with a reduction sleeve. However, South Bend's specification for this part differs from the "standard" Morse of  0.6315" per foot and used instead 0.602" per foot. Hence, if the sleeve adaptor is missing the right one will have to be acquired (try Scott Logan at www.lathe.com). The same taper was also used on the Light 10, (Heavy 10, 13-inch, 14-1/2-inch and 16-inch lathes.
Owners also report examples of lathes with (8 t.p.i) spindle-thread diameters of 1
1/4", though this figure has yet to be found in a catalog specification.
The relatively large spindle bore meant that a hardened adaptor, to take a 3C collet, could be fitted inside the spindle and draw-in collets used with either a screw or lever-action closer (when the 10K version of the lathe was introduced in the late 1940s, the spindle was altered to allow the direct fitting (i.e. no sleeve was required) of 6K collets. Originally 3C collets were limited to a maximum through size of 1/2" (though subsequently some makers produced a (9/16" version) while the 6K collets allowed a useful increase to a maximum bore of 5/8". 
See: http://www.hardingetooling.com

Section through the V-belt drive headstock showing the handwheel collet assembly. This is an earlier model with top-mounted oilers

Section through the Flat-belt drive headstock showing the handwheel collet assembly

South Bend 9-inch "Workshop" Lathe
Carriage Assembly

Carriage Assembly - 1936. An art-worked picture - in reality the cross-slide casting was one piece from front to back, there being no detachable swarf plate at the rear.
The compound slide, typical of South Bend (and other lathes of the time) had micrometer dials that were far too small - although they did allow the cross slide to be drawn over them, so improving the length of its travel. As an option in later years a larger dial was offered but, as these would have limited the slide's travel, the stem that screwed into the face of the saddle was increased in length. Unfortunately the cross slide that was devoid of T slots - an omission that precluding the fitting of a rear toolpost or the mounting of third-party vertical milling slide - both useful accessories for the model and experimental engineer. For many years the English Boxford lathe (a South Bend clone) was available with a T-slotted cross slide and one of these can, with considerable advantages as to rigidity and versatility, be fitted as a direct replacement on all versions of the South Bend 9-inch. The larger Boxford micrometer dial and its inner datum collar can also be fitted but this does involve some light machining to get everything lined up.
On lathes with a taper attachment there is a bed bracket, held by two bolts, which connects it to the saddle. These bolts, if fully tightened when the taper unit is not in use, can cause the cross slide feed screw turn stiffly; loosening the bolts slightly will allow the slide to turn smoothly.

Plain (non-power cross feed) single-wall apron from a 1936 machine. Note the oil pipe (a cast-in lip was used on the very first lathes) that fed lubricant into a channel that ran along the top of the upper leadscrew clasp nut.
Whereas all the larger South Bend lathes had aprons with "double walls" - allowing the gear-carrying studs to be supported at both end - all types of  9-inch apron, even the power sliding and surfacing versions as fitted to the models A and B, were all constructed from single-thickness castings.

Power sliding and surfacing apron as fitted to the Model B and Model A. A little-appreciated benefit of the Model B (in addition to the power cross feed) was the ability to produce much slower rates of power sliding feed - the drive being taken from a worm and wheel arrangement driven from a key sliding in a slot on the leadscrew.  Although the screwcutting charts for the model B and C are the same (the drive coming from the claps nuts) the former (because of the added reduction in ratio through the apron worm gear) has a selection of finer feeds marked.
It is tempting to convert a non-power feed South Bend by using the apron from a scrapped Model A or B. However, although this can sometimes be successfully accomplished, it is not always the case - with gears being either to tightly or not sufficiently engaged. The problem has been traced to South Bend being less particular in their machining of the saddles fitted to non-power apron models. An article on rebuilding this type of apron can be found here

Top slide degree graduations - 1936 Model

South Bend 9-inch "Workshop" Lathe
Screwcutting
Both the Model C and Model B 9-inch lathes used changewheels for screwcutting while the Model A was always fitted with a screwcutting gearbox.
Although all but the very first lathes (the Model 504) were fitted with a tumble-reverse mechanism it was not until the late 1950s that South Bend include a spring-loaded tumble reverse selector lever in the specification. Until then, to reverse the direction of the carriage movement, or to disengage the drive, a square-headed spanner (wrench) had to be used to slacken the pivot arm before it could be moved. The English copy by Boxford employed a much more convenient and quicker acting spring-loaded mechanism from its first production model in April 1948.
Although the vast majority of 9-inch Workshop lathes for the American market were supplied with 8 t.p.i leadscrews numbers were manufactured for export with a 6 mm pitch metric leadscrews in both Model B and C form (with changewheels) and as Model As with proper, all-metric screwcutting gearboxes. The English and metric screwcutting gearboxes were different externally, and very easily recognised the former having the diagonal line of indent holes on the right hand half of the box's front face, the latter with them across the left-hand half.   
"English" threading Lathes with an 8-t.p.i leadscrew and changewheels for screwcutting (i.e. without a screwcutting Gearbox) were supplied with the following changewheels when they left the factory: *16, 24, 36, 40, 44, 46, 48, 52, 54, 56, 60, *80,  *72/18 compound,  *80 idler (with boss)
(* gears on machine as dispatched from factory for standard feeds)
To convert a Model B or C (non-gearbox) English-specification lathe to cut metric threads the following gears are needed: 20, 100, 127/100 combination
In addition, to cut the following five pitches extra gears are required as follows: 0.45 mm = 18t gear,   0.55 mm = 22 t gear,   0.65 mm = 26 t gear,  0.7 mm and 3.5 mm = 28 t gear. 
Metric Threading Lathes with a 3mm pitch leadscrew and changewheels for screwcutting (i.e. without a screwcutting gearbox): were supplied with the following gears as standard. *16, 24, 28, 30, 36, 40, 44, 48, 52, 56, 60,  *80,  *72/18 compound,  *54/18 compound,  *80 idler (with boss)
(* gears on machine as dispatched from factory for standard feeds)
To convert a non-gearbox Metric-leadscrew lathe to cut English threads the following gears are needed: 18, 22, 26, 38, 54, 64, 88, 135/127 compound, 48/24 compound.
"English" threading Model A lathes with an 8 threads-per-inch leadscrew and a screwcutting gearbox had a standard ex-factory drive train consisting of: 20t,  40t, 56t and an 80t idler. To convert this gearbox to cut Metric threads the following gears are needed: 24, 26, 28, 32, 36, 44, 48, 127/100 compound
Metric threading Model A lathes with a 3 mm pitch leadscrew and a screwcutting gearbox had a standard ex-factory drive train consisting of: 20t,  45t,  50t and an 80t idler. To convert this gearbox to cut English threads the following gears are needed: 38, 40, 44, 52, 56, and a 135/127 compound
As an alternative to the 127/100 gear for metric conversion with a standard changewheel lathe it is possible to use a 37/47 transposing gear and then use a formula to calculate the necessary gear trains, as follows:
Pitch of thread in mm = 2.5 x (stud gear teeth divided by leadscrew gear teeth) or, to find the gear necessary to fit on the leadscrew: leadscrew gear = (2.5 x Stud Gear) divided by Pitch in mm
All the gears necessary to generate metric and other pitches are now available at a good saving on the factory price.
The gear on the end of the spindle - and the two gear tumble-reverse gears beneath that mesh with it - are 20 DP. The tumble-reverse output gear, and the train of changewheels it drives are 18 DP and the gears inside the gearbox 16 DP.

The Model B and C South Bend 9-inch lathe used changewheels for screwcutting. The tumble-reverse arm had to be released by a square-headed nut before it could be moved to reverse the direction of rotation of the leadscrew. The earliest lathes, made in 1934, had a single-arm bracket and a simple "reversing" stud by which means an addition gear could be incorporated in the train to cut left-hand threads.
Because there is no shear pin in the changewheel drive it is a good idea to just "nip" the bolt that secures the changewheel bracket to the boss on the headstock-end bearing hanger; this will allow the gears to push them selves out of mesh before mechanical mayhem sets in.

English pitch screwcutting chart for the changewheel-equipped Model C and Model B. A chart for the gearbox-equipped lathe can be seen here
It's likely that all Pre-WW2 South Bend screwcutting and other data plates were produced by a process called chemical milling - instead of rolling through a die or stamping, processes that leave an imprint on the back - all South Bend Plates are smooth on the rear. 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 powder 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

South Bend 9-inch "Workshop" Lathe
Screwcutting Gearbox
It was five years after the lathe's introduction, in 1939, before South Bend finally offered the option of a screwcutting gearbox on the 9-inch. Both Metric and English versions were produced, with kits available to convert one type into the other by the use of  translation gears mounted externally on the forked quadrant arm.
The English and metric screwcutting gearboxes were different - and are easily distinguished. The English box had the diagonal line of indent holes on the right hand half of the box's front face, the metric version had them across the left-hand half. The chart for the top of the English-threads gearbox is on this page and the metric Gearbox on this page.
"English" threading Model A lathes with an 8 threads-per-inch leadscrew and a screwcutting gearbox had a standard ex-factory drive train consisting of: 20t,  40t, 56t and an 80t idler. To convert this gearbox to cut Metric threads the following gears are needed: 24, 26, 28, 32, 36, 44, 48, 127/100 compound
Metric threading Model A lathes with a 6 mm pitch leadscrew and a screwcutting gearbox had a standard ex-factory drive train consisting of: 20t,  45t,  50t and an 80t idler. To convert this gearbox to cut English threads the following gears are needed: 18,  22,  26,  38,  54,  64,  88,  135/127 compound and a 48/24 compound.
Because these gearboxes have no supply of oil to dip into, it is essential to be liberal with the oil can, especially into the bearings. Keep the bracket arm that carries the changewheels just nipped tight; if the bearings seize, or the carriage runs into the chuck, this will allow the gears to force themselves out of mesh and avoid expensive damage.
It is very straightforward, in theory, to convert a changewheel-equipped model C or B to carry both the gearbox and power-feed apron from a Model A and, should you have one of the two lesser models and come across a poor-condition A with the necessary parts, it would be a good idea to acquire it and upgrade your own machine. As a minimum you would need not only the complete apron and gearbox but also a cross-feed screw with a drive gear, the correct changewheels (20t, 45t, 50t and an 80 idler with a boss) the slotted leadscrew and the "Y-shaped"  changewheel bracket (the bracket on the B and C is slightly different--the bulge where the clamping bolt passes through fouls the gearbox). On pre-gearbox year models it will be necessary to drill an extra hole through the bed at the headstock end to take the third mounting screw. When everything is in place check (by hand and with the changewheel bracket removed) that the assembly rotates easily; if it doesn't, slacken the screws holding both the gearbox and the leadscrew hanger bracket, then retighten them a little at a time rotating the leadscrew while you do so. Unfortunately there is a caveat to all this for, although the gearbox is a problem-free fit, experienced South Bend mechanics report that the company did not hold the tolerances of saddles fitted to the C to the same tightness as those intended for an A. The result is that the gear on the cross-feed screw may not mesh properly with its apron-mounted drive, being either too slack or too tight. 

All the gears necessary to generate metric and other pitches are now available at a good saving on the factory price.           

Metric Screwcutting Gearbox - in contrast to the English box, illustrated below, the position of the levers is reversed laterally with the diagonal line of indexing holes moved to the left-hand side.

English Screwcutting Gearbox - a picture of the gear-position chart is shown below .

E-Mail Tony@lathes.co.uk 
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South Bend 9-inch "Workshop" Lathe
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04/04/2014 20:14:10