Pratt & Whitney 7" and 10" Precision Lathe (3.5" and 5" centre height)
Prior to World War 2, this particular pattern of lathe was greatly favoured by professional tool, watch, clock and instrument makers for their critically-dimensioned work (see American patents: 1980336 and 210177)
Also advertised in a 10-inch version (a 5-inch centre height) the bed length was usually 32", giving 16" between centres. The spindle was made from tool steel, hardened and ground and running in a plain bearings of the same material with a double taper at the chuck end and a plain cylindrical bearing at the other. In order to achieve the necessary accuracy and long life associated with type of set-up in 1899 the American Machinist reported that P & W had built a set of specialised grinding machines that employed diamond laps to finish both the bearings and the spindles. As an interesting aside (although other companies had also developed successful models) P & W were also responsible for the design, again in 1899, of what was to become almost the standard machine for the manufacture of bicycle ball bearing cups and cones; it was capable of running up to 28,500 rpm and working to within limits of  0.00025".
When equipped with the maker's two-speed countershaft unit and a 3/4 H.P. motor, the lathe had 6 spindle speeds from 144 to 1208 rpm. The left-hand face of the headstock cone pulley was equipped with a ring of 48 indexing holes - with the option of a 60-hole ring to special order. Both headstock and tailstock tapers were listed as No. 4 Jarno, but examples have been found with both 2 Morse Taper and 3C (or 3AT) collet fittings in the headstock - and tailstocks with a No. 1 Morse Taper. Many special accessories were also offered including: screwcutting, grinding, milling,  power filing,  special tailstocks, a "Complete Workshop" Unit, a Double Lathe Mounting and a Geared Countershaft Drive Unit..

Last of the No. 3 Series lathes was the 1940s Type 3C - a machine improved in detail with variable-speed drive, longer travels on top and cross slide, larger micrometer dials and a number of other minor improvements.
If any reader has a good quality picture of a late-model Pratt & Whitney 3C lathe the writer would be interested to hear from you.

Listed as the Bench Machine Tool Set the unit above consisted of the No. 3 precision lathe, No. 0 Sigourney High-Speed Sensitive Drill and the No. 3 Horizontal Miller. The pine and cast-iron unit was factory built, with a complete "fast and loose" countershaft unit with foot treadle control - and could be ordered with any combination of accessories and extras from the maker's lists.

Above: master thread with, on the left-hand end, a hob of the same pitch  Right: the cutter holder

Three types of grinding attachment were available, all driven from an extra pulley on the overhead countershaft unit.
The "Grinding Rest with Traversing Spindle" mounted directly on the slide rest and could be moved in and out by hand. To assist in taking measurements the device was arranged to hinge out of the way and could be locked down when in operation by the U-shaped catch.
The "Slide-rest Grinder", for fitting to the cross slide, was a simpler device which used a similar spindle to that in the "Grinding Rest" unit.
The "Tool Post Grinder" was mounted in the regular toolpost and used the traversing movement of the compound slide to set the wheel position.
Two sizes of internal wheel arbor, 1/8" and 1/4" were available as well a range of external and internal grinding wheels.

Plain Lever-action Tailstock with rack-feed barrel and adjustable depth stop. This tailstock was also available mounted on a "cross slide" unit.

Half-Open Tailstock - designed for light manufacturing work where quick interchange of spindles and tools was required.

"Quill Rest"
This special fitting was designed  for extremely accurate work and placed just in front of the headstock and driven from it.
The top of the tailstock was arranged to hinge open to allow the rapid changing of quills which were available in two styles,  the "chuck" type, the front end of which was a duplicate of the headstock spindle, and the "faceplate" type which was available with either tapped holes (1/4"  -20 U.S.F. arranged in eight rows) or T slots.

Quill Driver - pulled into headstock by standard draw tube

Faceplate type Quill

Above: Index Pawl and Block
This accessory could be used either on the headstock or the Quill Rest. An index pawl unit was clamped to the bed and the Index Plate (shown below) mounted above it on either the rear of the headstock spindle - or on any of the Quill Rest quills.

Left: the index plate

Unusual in that, instead of being adapted to fit the standard slide rest, the Pratt & Whitney swivelling vertical milling attachment was complete with its own compound slide unit - and thus could be used on lathes fitted with were only equipped with the simpler types of hand-tool rest.
The slide carried an indexing unit, of the same collet fitting as the headstock, designed to hold small components whilst milling cutters, diamond laps or grinding wheels, held it the headstock spindle, were applied to them.
A separate high-speed cutter head, driven by an extra pulley on the countershaft and designed to allow work held in the headstock spindle to be machined, was provided as standard.

The powered Filing Attachment - a remarkable Pratt & Whitney accessory and probably unique to a small number of fine-quality American Precision Bench Lathe manufacturers.
Those who have used a "filing machines" will know that they are not what, to the layman, they might seem: a rough and ready method of removing metal, but precisely the opposite. A top-class filing machine was an expensive item - and an experienced operator could achieve almost miraculously accurate results with one. They were not designed to be employed in general workshops but found a valuable niche in better-equipped toolrooms.
The Pratt & Whitney unit slid onto the bed and was fastened in position by an eccentric clamp. A tilting rectangular table 4" x 6" was fitted as standard.

In common with other makers of precision lathes, Pratt & Whitney offered a toolroom-class milling machine which used either the complete headstock from the lathe, or an identical spindle assembly. More details of these machines can be seen here.

A Pratt & Whitney No. 3 with the maker's beautifully-constructed countershaft holding a built-in 2-speed gearbox - similar in some ways to the system used on the Swiss Simonet precision lathe.
If there is one thing that flat belts like, it's plenty of "wrap" onto the pulleys -  which was exactly what the wide, heavy-duty tensioning  system provided on the installation above. More pictures of the gearbox can be seen here.