email: tony@lathes.co.uk
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Potter Lathes - USA
If you have a Potter, the writer would be interested to hear from you
A comprehensive Potter catalog is available

Based at 77E 130th Street in New York City, the firm of S.A. Potter were manufacturers of taps and dies, cutters, reamers, small tools and "special-purpose engineering machinery made to order". Their precision bench lathes were produced as a natural adjunct to this business and their design - although perhaps not of such fine quality, but certainly cheaper in price - mirrored to a great extent that of their better-known US competitors such as B.C.Ames, Hjorth, Potter  Pratt & Whitney, Rivett, Stark, Wade, Waltham Machine Works, Wade, Rivett, Cataract, Hardinge, Elgin,, Remington, and Sloan & Chace - with others here.
Until the late 1940s,  the term "bench lathe" was used in America to describe a small lathe built to a very high standard of fit and finish - it did not just refer to the physical size of the machine.


Above: the Potter's No. 5 bench lathe displayed in its basic specification and with standard equipment: a hand -rest, a "combination drive plate with centre" mounted on a draw-in collet - and a tailstock centre.
The swing was 7
3/8", the capacity between centres 16", the spindle bore a useful 15/16" and the maximum collet capacity 3/4".
The bed was of traditional bench-lathe design with a round form, flattened on the top with bevelled edges with a single T slot running down the centre in which were located the headstock, tailstock and accessories.
For a precision lathe, the design of the headstock contained no surprises - the bearings, as Potter admitted, being of the "
standard double-cone type, hardened, ground and stoned to a perfect fit" - in other words, beautifully constructed from high-quality materials. The spindle was threaded on its nose (some Precision Bench Lathes could accept only collet fittings) and was thus able to mount conventional chucks, faceplates and other fittings. The nose thread on the hardened spindle was ground to a 'gage fit' and the internal taper, so important for the precise location of collets, was finish ground only after the spindle was assembled into its bearings. A single lock nut on the end of the spindle retained it in place - removing it allowed the spindle to be withdrawn completely from the bearings.
Like many other precision lathes the Potter's 3-step cone pulley had its smallest diameter by the spindle nose, so allowing the all-important front bearing to be increased in size and surrounded by a greater mass of supporting metal; two rings of indexing holes, engaged by pins passing through the end face of the headstock, were spaced around the inner flange of the largest diameter pulley.
The tailstock was fitted with a hardened and ground barrel - and like that most fitted to precision lathes it was fully supported even when fully extended. It was moved by a 10 t.p.i square-section tool-steel thread running through a bronze nut. Both headstock and tailstock carried a No. 4 Jarno taper.

Potter lathe set up for production work with a lever-action collet closer, lever-action double-toolpost cut-off and forming slide - and a 6-station indexing capstan unit.

Screw-feed compound slide rest with, for the era, deently large 13/8" diameter zeroing-micrometer dials - and a very clearly engraved circular scale with which to set the top-slide at up to 60 degrees each side of centre. The cross-slide end plate (which carried the boss to support the micrometer dial)  was held on by 4 screws - a minor point, but one which demonstrates the care which Potter put into the design of their lathes.

Part of the production equipment available for the Potter was this lever-action, double-toolpost, cut-off or "forming" slide. Robust front and back stops with fine-screw adjusters were fitted, the toolposts could be located at any position along their mounting slot and the operating handle adjusted to any convenient height.

A popular accessory on quality lathes of all types, the lever action tailstock provided a sensitivity of feel - especially when using very small drills - far superior to that given by an ordinary screw feed. A screw adjuster provided a means of limiting the movement of the hollow spindel.

Once a very popular accessory, the indexing tailstock capstan unit still finds a place today in the workshop of the model and experimental engineer who needs to make quantities of identical small parts.
For the manufacture of more complex or larger parts a bed-mounted capstan unit was available.

"Large Turret" attachment. This was 7 inches long and mounted a 9-inch long slide with 3 inches of travel and a 4-inch diameter turret with six 5/8" holes. It was designed for light production work and all its working parts were of hardened steel. The head was self -indexing, the rotation taking place at the end of the stroke and using up 1.125" inches of travel - leaving just 17/8" of sliding tool movement for machining operations.

Lever Chuck Closer (at the time what are now called collets were known as "chucks") was supplied as an aid to production work and fastened to the end of the bed by one bolt. As a aid to efficiency the unit could be set so that the collet opened as soon as the operator released the closing pressure on the hand lever.

Milling and "Live Spindle" Attachment. This required the use of the compound slide rest for its mounting - the unit was bolted into the T slot of the top slide and carried an indexing unit which accepted the same collets as used in the lathe headstock.
The unit could be used to hold, move and index any circular material against a cutter held in the lathe headstock - or, alternatively, a pulley could be substituted for the division plate and the unit used as a live spindle for high-speed drilling and grinding.

3-speed "Grinding Countershaft" for wall or ceiling mounting.
Typical of the drive units made for precision bench lathes and other small machine tools - i.e. heavy and expensive - the 32" long Potter unit has the merit of simplicity being based on two steel bars held in clamps. The final 3-step drive pulley to the lathe was on the left-hand side of the unit while the centre section contained three sets of fast-and-loose pulleys, each fitted with a belt-shifter crank which would have been foot operated by individual pedals..
Mounted above the main countershaft - and driven from as flat pulley on the right-hand side - was a large round-rope pulley to power grinding and drilling heads mounted in the lathe's toolpost.
A two-speed version, without the grinding pulley attachment, was also manufactured.

Internal and Traverse Grinding Attachment.
The quickest way to wear out any lathe is to use it for unprotected grinding - perhaps that's why so many makers were keen to encourage its use for this damaging activity  - and Potter offered the usual range of slide-rest mounted units to convert their lathes into useful little grinding machines.
The unit shown above was intended for light, internal grinding and featured completely enclosed, dust-cap protected bearings which were separate from the hand-held sliding shaft that moved the grinding wheel to and fro.

Universal Grinding Attachment.
This accessory (which accepted wheels up to 3" in diameter) was fitted to a base which could be moved up and down through a rocker mechanism which was claimed by Potter to be a design unique to them. The spindle was fitted with dust-sealed double-row ball bearings capable of letting the (unguarded) wheel attain speeds as high as 25,000 rpm.

The Chase Screwcutting Attachment being used to cut the thread on a collet

The Potter, like most other genuine "Precision Bench Lathes" manufacturers, employed the "Chase" method of thread generation on their machines. The method involved a Master Thread (also variously known as a hob or leader) mounted behind the headstock and driven through a set of changewheels. A "half-nut" pressed onto the Master Thread and conveyed its pitch, via a sliding bar connected to an adjustable toolholder, to the cutting tool which was in contact with the workpiece. The system was devised by Joseph Nason of New York who obtained US Patent No. 10,383 on January 3rd, 1854 for an "arrangement for cutting screws in lathes."
The interconnection of the cutter holder and the half nut allowed the nut to be lifted out of engagement (by a handle attached to the toolpost upright) and the cutting tool returned by hand to the start without stopping or reversing the lathe. A little additional depth of cut could then be applied by the tool slide, the half-nut rested back on the Master Thread - and the cut restarted.
While the chase system produced absolutely accurate threads (and was especially suited to delicate operations on thin-wall tubes used to construct such items as microscopes) the length and pitch of thread that could be cut depended upon the availability of the appropriate Master - although in the case of the Potter the thread length of five inches would have been sufficient for most jobs and the eight additional changewheels supplied as standard multiplied by eight the number of threads each Master could generate. Each hardened Master Thread - they were available in both inch and metric forms - was provided with a fluted section at one end so that it could be used to "hob out" its own replacement half-nut.
To use the attachment the lathe was run in reverse for right-hand threads - with the toolholder moving from left to right. For left-hand threads the master thread and its nut were reversed, and the toolholder moved from right to left.
Unusually, unlike many of its competitors, the Potter needed neither another slot in the back of the bed, nor a special headstock casting to use the attachment, instead the whole unit was mounted on brackets which clamped to the top of the bed. A neat touch was the provision of a pad which fitted on the bed and protected it from accidental blows by the heavy hand lever.
Similar chase-screwcutting arrangements can be seen on the pages devoted to the American makers Goodell-PrattPratt & WhitneyAmesWaltham Machine Works and Wade.

Then ...

...and in 2010...

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

Potter Lathes - USA
If you have a Potter, the writer would be interested to hear from you
A comprehensive Potter catalog is available