email: tony@lathes.co.uk
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Cincinnati No. 2MI
and 203/205/307/410 MI & ML
Milling Machines
A Service & Parts Manual and an Operation Manual are available for the Cincinnati No. 2 MI and 205 M1 milling machines.
Dial Type Millers  Early Dial Types  Late Dial Types  Operating the Dial Type 
Accessories   Factory   Cincinnati Cinedo   Cincinnati Toolmaster
2MI, 2ML 203, 205, 307 & 410    8" x 18" Tool & Die Miller   
Cincinnati Contourmaster




Introduced in the U.S.A and Great Britain during 1946 (at £1045 in the latter, then around twice the price of a good semi-detached house), and manufactured until the 1970s (as the 203, 205, 307 and 410 and variants), the No. 2 M1 was the Company's entry-level, general-purpose knee-type model. Fitting in below the established, much larger and more expensive "Dial Type" machines, it was built in one size only (as the No. 2) and had smooth, rounded and contemporary lines that reflected the era's fascination with "streamlined" styling. It was available in three forms: as a Plain Horizontal, a Universal (with a table able to be swung 45°either side of central and fitted with a powered dividing head), and, from the late 1940s, as a Vertical. In addition, each of the two horizontal types could be converted into very useful ram-type vertical machines by the addition of a self-contained overarm with a motorised gearbox and swivelling end section. The later machines, as made from the the early 1960s were given new Model types, MI and ML, and suffix numbers: 203, 205, 307 and 410m -designations from which the basic specification of a machine could be deduced.  The first digit "2", "3" or "4" indicated a table travel that was, respectively, 28, 34 and 42 inches. The next two digits "03", "05" etc. was the motor horsepower (3 h.p. 5 h.p. ) with the final two digits giving the table width in inches. e.g. the 205-12 MI had a 28-inch travel table, a 5 h.p. motor and a table 12 inches wide.
Table & Feeds
Reflecting the latest thinking and careful design, the miller's neat appearance was partially the result of ensuring that the saddle, knee and coolant pump drive shafts were fully enclosed (with the cross-feed screw protected by sliding covers against the ingress of swarf and dirt) and the knee sealed, with non of its mechanisms exposed. Early examples of the M1 had a table with a working area of 49" x 10" (with an over-all size of 52.75" x 10") with three 11/16" T-slots spaced 2.3125" apart. The longitudinal travel was 28", in traverse 10" and vertically 19" - although on the Universal, with the increase in saddle thickness to accommodate the swivel mechanism, the last figure was reduced to 18". From the spindle centre line to the table surface was a maximum of 19" on the plain horizontal model and 18" on the Universal - with a minimum of 0". Driven from the main motor, table feeds on both horizontal travels had a usefully wide range of settings with rates from ¼" to 30" per minute and from 1/8" to 15" vertically (a set that spanned a ratio of 120 : 1). As a no-cost option the miller could, when ordered, be fitted with quicker feeds from ½" to 60" per minute. Able to be operated with or without the spindle running (and so ideal for assisting with the set-up of long jobs), rapids were fitted to all feeds - both horizontal being at 150" per minute and vertically half as fast (with the rate remaining the same when the faster feed set had been specified). Changes of rate were by a crank, positioned conveniently on the front of the knee (an arrangement introduced on later Dial Type models) where a half-turn of the pull-out handle selected the next higher or lower rate - a large, clearly-marked dial showing the chosen setting. Conveniently positioned short levers - that for longitudinal being set centrally on top of the saddle, for traverse on top of the knee and for vertical to the front of the knee's left-hand face - controlled the feed engagement. Each control had a positive neutral, forward and reverse position - not always the case on competitors' machines. When the power feeds or rapids were engaged the heavy, flywheel-effect handwheels - which include an open segment, opposite the handle (to allow the operator's fingers to grip the rim for a better feel on fine feeds) - were, for safety, automatically disengaged. Relatively small but beautifully engraved, the micrometer dials used a pull-and-turn mechanism (against light spring pressure), to zero them - an arrangement that eliminated possible setting errors as a locking knob or ring was loosened or tightened. In addition to the expected adjustable table stops on each axis, the 2MI was fitted with positive limit stops for each travel, thus ensuring that a machinist could not overrun the limits of the table or knee travels and wreck the mechanism. While the knee and saddle locking clamps were lever operated (the levers turning screws) that for the table required the services of a loose spanner; should an operator have forgotten to slacken the locks upon engaging a feed, damage was prevented by a safety clutch.
A fitting supplied as part of the standard equipment with the swing-table Universal model (and as an option on the plain and vertical) was a 10.5-inch centre height power-driven universal diving head with a threaded spindle nose, a No. 10 Brown & Sharp taper, a lift-lower-swivel tailstock and an intermediate steadyrest The unit was intended to help with the production of square and hexagon (etc.) sections, spur, spline, worm, spiral bevel and helical gears as well as cutters, reamers, face-mill cutters and cutter bodies, etc. Drive to the head was by enclosed gears driven from the right-hand end of the table's feedscrew.
Continued below:

The Cincinnati No. 2 MI as advertised during 1946

Continued:
Spindle, Drive and Arbor Arrangements

Fitted with a No. 50 INT nose and carrying a large drive gear designed to add inertia, the spindle was manufactured from a nickel-steel forging, ground all over and ran in Timken taper roller bearings at the front and centre with a precision roller race at the rear. Driven by a 1450 r.p.m., cradle-mounted, 5 h.p. motor through four V-belts, a single-plate dry clutch and a gearbox, it had 16 speeds of: 25, 33, 43, 56, 76, 100, 130, 168, 225, 295, 385, 500, 680, 895, 1160 and 1500 r.p.m. Alternatively, low or high-speed ranges were available - the former spanning 20 to 1200 and the latter 33 to 2000 r.p.m. Like the table feeds, spindle rates were changed by a trade-mark Cincinnati speed dial with crank; positioned on the left-hand face of the column it was possible for the operator to lean over the table and reach the handle - one half-turn of which selected the next higher or lower setting - a separate quadrant lever immediately beneath being used to select forward, neutral or reverse. All gear shifting (spindle speeds and table feeds) were, even on this less-expensive model, by hydraulics. To start and stop the machine an adjustable lever was provided that could positioned where required - the operator simply having to lift it up to disengage the gear teeth on its end, swing it round and drop it back into place. As a safety precaution, when the spindle was running the speed selector was locked (more expensive Cincinnati millers could change speeds while running, their gearboxes being fitted with synchromesh cones). The arbor was supported by a rectangular-section overarm constructed so as to provide a degree of damping using what Cincinnati called their "Dynapoise" system. The arm was repositioned by a 2-spoke capstan handwheel, through the hub of which passed one of the two securing bolts - each passing right through the casting to give the best possible lock against its dovetail ways. Two arbor supports (drop brackets) were supplied with each machine: both were made of aluminium and complete with an oil reservoir large enough to last for several days' use. Type A was intended for arbors with a plain end while the other, Type B, was for those fitted with bearing collars. The Type B also had provision to clamp on an overarm-to-knee bracing bar that was reversible and hence able to be fitted to either the left or right hand side; at extra cost the type could be supplied without the mounting point.
As an aid to maintenance, the three main mechanical parts of the miller - the spindle gearbox, hydraulic speed-change unit and the table feed's gearbox (the latter bolted to the underside of the knee) - were built as cassettes, enabling them to be removed as a whole for maintenance or repair. In order to minimise down time, if a factory had a sufficient number of hard-used MIs in use, it would have been possible, and economical, for them to hold in stock reconditioned units for immediate replacement.
Continued below:

Typical of contemporary American design - the clean lines and neat detailing of the Cincinnati No. 2 MI

Continued:
Lubrication
Like the Company's larger models, the MI the spindle and feeds' gearboxes were each positively lubricated by a separate mechanically driven plunger pump. On the main column oil was lifted by the pump to a "distribution" centre at the top from where it drained by gravity through a network of pipes. One interesting touch was the effort made to prolong the life of the heavily stressed, one-piece, nitrided-steel vertical feed-screw: this was supported on taper roller bearings, ran through an aluminium-bronze nut and was completely enclosed in a separate bath of EP oil - a reservoir positioned to one side (and level with the screw's top) feeding oil down a pipe to fill a surrounding housing. Table and saddle ways - and the table and saddle screws and nuts and the gears and bearings between the table screw and the horizontal drive shaft along the right-hand side of the knee - were lubricated by a hand-pump drawing oil from a sight-glass-equipped reservoir built into the front of the saddle.
Vertical Models
By the early 1950s, and using the same knee, saddle, table and complete drive system as the Plain Horizontal model, the Vertical version of the No. 2 MI had been introduced. At this stage in the model's evolution the table had been increased slightly in length - to 54.25" - and redesigned so that the whole of the top surface could be used as the working area. While the longitudinal travel, at 28", remained the same as the other types, on the Vertical the knee lift, at 14" was some 5" than the Plain Horizontal but the cross travel, at 12" some 2" greater. However, the number and rate of table feeds (16 from 1/4" to 30" per min horizontally and half that vertically), remained the same.  Equipped with a positive lubrication system and a 4-position rotating turret stop, the vertical head held a spindle with a No. 50 INT nose running in Timken taper roller bearings. The head was constructed so that a front element (that holding the spindle) was arranged to slide on a back section (the moving section always being fully supported within its ways), the drive being by a screw and nut flooded with oil from a pressure supply (a scavenge pump being provided to prevent leakage). Head locking used a particularly effective clamp - a lever acting to move a tapered gib strip that clamped the chosen setting tightly.
As well as a handwheel for manually controlled fine feed of the spindle, 16 rates of power feed were also provided from 1/8" to 15" per minute and with rapids at 75" per minute - enabling the machine to be used for boring and heavy-duty drilling - though the maximum head travel of just 2.5 inches did limit its usefulness.
Spindle speeds were identical to the horizontal models - sixteen in number between 25 and 1500 r.p.m. - with the head having a backgear so that two ranges were provided, high and low. Selection of individual speeds was still by the same crank handle and dial used on the horizontal models but with an additional lever control, on the head, to engage and disengage backgear.
Later Type 205-12 MI
Listed in catalogues from the early 1960s was what appeared to be a new machine that was to be listed in a number of versions including the 203-10 ML plain (28" table travel, 3 h.p. motor and 10-inch wide table), 203-10ML Universal, 205-12MI Plain, 205-12 MI Universal, 205-12 MI Vertical, 307-12 MI Plain, 307-12 MI Universal, 307-12 MI Vertical, 307-14 MI Plain, 307-14MI Universal, 410-14 MI Plain and the 410-14 MI Universal, the 205-12 MI Model LL. However, all these models were, essentially, of the same mechanical construction as the No. 2 MI but with a number of improvements. Most obvious of the alterations was the use of a separate 1.5 h.p. feed-drive motor and the use of the previously optional faster range of 16 feed rates from 0.5" to 60" per minute as standard - though the slower rate of 0.25 to 30" remained as a no-cost specification. The new design eliminated the complex and costly train of gears that had previously been needed to transfer power from the main motor to the knee, so improving reliability and saving both production and maintenance costs. The table was made fractionally longer - by 7/16" - and a useful 2" wider with the same three 11/16" T-slots spaced 2.3125" apart. In line with other Cincinnati models of the early 1960s, the new Arbor-Loc spindle nose fitting was used. This design allowed a speedy change of tools to be made (while offering just as much rigidity as before) and also largely eliminated the need to use arbor draw bolts - a boon on vertical heads, where safety was thus greatly enhanced.
Fitted as standard to the new models was a rear control for the table's longitudinal feed (other controls could also be duplicated in this position at extra cost), and an automatic backlash eliminator on the same feed. With the separate feed motor came a redesign of the knee and column castings with rear hinged cover over the drive system simplified - a single smooth rear face replacing the previous bulge that followed the outline of the drive system.
Extras
A number of useful accessories was available that mirrored both those offered on other models made by the company and competing firms. The range including a variety of heads, all driven from the horizontal spindle, with the most useful being a high-speed universal (available with a parking mount on the right of the column and a built-in crane to manoeuvre it into place), a heavy-duty vertical, a double-swivel universal type, one specialist type for rack milling and others for slotting, circular milling and cam milling. If a factory was expecting to handle complex or awkwardly shaped jobs that required an operator to stand and observe from both front and rear, it could order a machine fitted with duplicated, rear-mounted table-feed controls.
If it was necessary to convert either a Plain or Universal to a proper vertical type, it was possible to replace the overarm with the self-contained
Motor Driven Universal Attachment. Fitted with a motor mounted at the rear, and a speed-change gearbox, this unit actually turned the miller into a form of ram-head machine - although (unlike a Bridgeport), the turret could not be rotated on top of the column. Early versions of the unit, as made until the late 1940s with an exposed 2 h.p. motor and two speed-change levers, were rather crude in appearance; later versions were much tidier, with a fully enclosed drive from a 3 h.p. motor and with three speed-change levers.
One useful attachment, that required building in on the production line, was an automatic backlash eliminator for the longitudinal feed screw. Used on many Cincinnati models from the mid 1940s onwards, the device was intended for use during climb milling. The latter is a process where, instead of the workpiece being pushed against the rotation of the cutter (and so any backlash between feedscrew and nut automatically eliminated) the work is fed into the cutter in the opposite direction - producing a tendency for the table to be violently "grabbed" forwards.  During automatic table-cycle processes, where a cut was required in both directions, climb milling was, of course, necessary and the Backlash Eliminator an essential fitting. The mechanism was contained in a single housing and comprised two separate feed nuts, each machined on its outside with teeth that meshed with a rack. The racks were arranged to sit at each side of a spur gear that, when rotated, moved one rack forwards and the other backwards - so forcing the nuts to rotate slightly in opposite directions. As the nuts turned, the effect was to remove backlash by seating each firmly against opposite sides of the feedscrew thread and so "load up" the assembly.  With the unit engaged climb milling became as easy as conventional - and, in a production process, could double the effective work rate of the machine..

Early 1950s version of the Cincinnati MI vertical milling machine

As well as a handwheel for manually controlled fine feed of the spindle, 16 rates of power feed were also provided from 1/8" to 15" per minute and with rapids at 75" per minute - enabling the machine to be used for boring and heavy-duty drilling - though the maximum head travel of just 2.5 inches did limit its usefulness. The 4-position rotating stop on the downfeed was fitted as part of the regular equipment. The machine illustrated is fitted with hydraulically driven auto-cycle control - the operating joystick for which can be seen protruding horizontally from the front of the saddle.

Late-model No. 2 MI vertical with the feeds powered from a separate knee-mounted motor. The arrangement was identical on the Plain and Universal models.

The head was constructed so that a front element (that holding the spindle) was arranged to slide on a back section (the moving section always being fully supported within its ways), the drive being by a screw and nut flooded with oil from a pressure supply (a scavenge pump being provided to prevent leakage). Head locking used a particularly effective clamp - a lever acting to move a tapered gib strip that clamped the chosen setting tightly.

Fitted with a No. 50 INT nose and carrying a large drive gear designed to add inertia, the spindle was manufactured from a nickel-steel forging, ground all over and ran in Timken taper roller bearings at the front and centre with a precision roller race at the rear.

Section through the horizontal  spindle

Automatic backlash eliminator - at first an option and later a standard fitment. The mechanism was contained in a single housing and comprised two separate feed nuts, each machined on its outside with teeth that meshed with a rack. The racks were arranged to sit at each side of a spur gear that, when rotated, moved one rack forwards and the other backwards - so forcing the nuts to rotate slightly in opposite directions and so take out any play between nuts and screw.

Motor mount and drive system

Early model - fully enclosed drive to the table feed gearbox and rapids unit

Fully enclosed knee

The back of the knee was raised to give additional support and rigidity

Reversible bracing bar between knee and overarm

Two arbor supports (drop brackets) were supplied with each machine: both were made of aluminium and complete with an oil reservoir large enough to last for several days' use. Type A was intended for arbors with a plain end and the other, Type B, for those fitted with bearing collars - the latter also having provision to clamp on the overarm-to-knee bracing bar .

Relatively small but beautifully engraved, the micrometer dials used a pull-and-turn mechanism (against light spring pressure), to zero them - an arrangement that eliminated possible setting errors as a locking knob or ring was loosened or tightened.

Spindle speed selector mechanism--built as one easily-removed unit

The complete spindle gearbox could be removed as one unit

. Table and saddle ways - and the table feed-screw end bearings - were lubricated by a hand-pump drawing oil from a sight-glass-equipped reservoir built into the front of the saddle.

email: tony@lathes.co.uk
Home   Machine Tool Archive   Machine-tools for Sale & Wanted
Machine Tool Manuals   Machine Tool Catalogues   Belts   
Books   Accessories

Cincinnati No. 2MI
and 203/205/307/410 MI & ML
Milling Machines
A Service & Parts Manual and an Operation Manual are available for the Cincinnati No. 2 MI and 205 M1 milling machines.
Dial Type Millers  Early Dial Types  Late Dial Types  Operating the Dial Type 
Accessories   Factory   Cincinnati Cinedo   Cincinnati Toolmaster
2MI, 2ML 203, 205, 307 & 410    8" x 18" Tool & Die Miller   
Cincinnati Contourmaster