email: tony@lathes.co.uk
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"Precise" Milling Machine - USA

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Founded in Racine, Wisconsin in 1941 with the title Precise Products Corporation, the Precise Company had its origins in Düsseldorf, Germany, when in 1882 an instrument maker, Adolph Schumann, founded Firma A. Schumann to manufacture scientific instruments and precision optical equipment. The skills necessary to succeed in such a field also allowed the Company, post-WW1, to move into the highly specialised area of accurate scale models of scientific and industrial projects used for exhibitions, research and sales. As any modern-day amateur model engineer or home-workshop owner knows, all small-scale jobs are greatly eased by possession of a lightweight, high-speed, hand-held drill-cum-grinder now universally known as a Dremel - as made by the Company of that name based in Racine and founded there in 1932. As no such devices were available to the Schumann Company, in the early 1930s Robert Schumann, son of the founder, developed his own, the first of a range of 30,000 r.p.m. units that was eventually to be sold through Europe using the trade name "Diros".
Just prior to WW2, in the late 1930s, Robert and his son, Helmut - both graduate electrical engineers - were in the United States to open a second plant, choosing Racine where, using superior American electrical equipment, they redesigned the original tool to give higher speeds - 45,000 r.p.m. - with greater power (1/7 h.p.) and improved accuracy. Housed in black plastic casings, this new design was avertised as the
Precise 35 with an even more powerful model, the Precise 40, following shortly afterwards. Post WW2 the introduction of carbide tooling meant that, to get the best from this new much harder material, even higher speeds were needed together with tools better able to stand up to the rigors of the greater pressures and harder work they demanded. Unfortunately the plastic bodies of the original Precise models proved inadequate and began to crack; bearings wore out prematurely and the collet chucks were insufficiently accurate at the higher speeds involved. Hence, a complete redesign was undertaken that resulted, during 1948, in a new range of top-class, professional-quality machines the first of which was the Super 40. Using an aluminium housing machined on the outside and precision bored on the inner surfaces, four costly super-precision sealed-for life bearings (of, apparently, a former military specification) were used, a quill of improved rigidity fitted together with a collet chuck claimed to be more accurate than those found on lathes of the finest quality. The new, more powerful motor ran up to 48,000 r.p.m. with its commutator diamond turned at 45,000 r.p.m. to close limits of accuracy and surface finish; as a final touch to ensure the smoothest possible running, all rotating parts were statically and dynamically balanced using electronic equipment. Reliability was assured by running each completed quill assembly for eight hours when temperature, horse power and r.p.m. were checked and recorded. As a result, so superior to the earlier design was this newer type that - aided by the robust aluminium casing -  it proved possible to employ it as an auxiliary grinding and cutter-holding spindle on conventional machine tools such as lathes, millers, surface grinders and drills. To aid this process and encourage sales, the younger Schumann designed and developed a range of precision mountings that greatly eased the problem of holding the spindles securely and in the correct position. Units were available that fastened to the overarms of horizontal millers, clamped in lathe toolposts and to the columns of a drill presses, etc. with all types offered in rigid, single and double-swivel versions.
By the early 1950s the Company's range had expanded to include other models amongst which were the tiny lightweight (35 oz)
Super 30 with 1/5th H.P. and 45,000 r.p.m.; the 1/4 h.p. Super 50 Power Quill with a robust, precision ground and honed alloy-steel housing (so making it even more suitable for general machine-shop use) and, by 1956, an even more powerful pair, the 1/2 h.p. Super 60 Power Quill and 1.5 h.p. Super 80 Power Quill - the latter with a speed range from 7000 to 25,000 r.p.m.
In 1948, recognising a need for a particularly high-speed (45,000 r.p.m.) miniature milling machine the Company had introduced the "Precise", a model described in straightforward terms by the makers as their "
High  r.p.m. Milling Machine".  Constructed in the form of a miniature jig borer, the aptly named "Precise" had a base 10.625" wide and 15" deep cast in a "semi-steel" with a non-elevating table and the cutter head arranged to be moved by a feedscrew up and down a slideway formed (very unusually) on the right-hand face of the 21-inch high (semi-steel), precision ground main column. In addition to forming a rigid structure, this layout allowed a cross slide of decent width to be incorporated - a decided advantage for any boring or milling machine - while also permitting economical mounting on a customer's existing bench.
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A "Precise" Model U  fitted with the bracket necessary to bring the high-speed spindle into position for vertical milling

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With its built-in motor and no belt drive to get in the way, the head could be rotated to either a horizontal or vertical position - though for the latter, to put the spindle into the correct frontal position, the makers provided a special adapter collar. As already mentioned, all the Company's spindles at this time were of the same arrangement and contained components of identical design and specification - a dynamically balanced shaft turning in pre-loaded, high-precision ball bearings and driven by an integral motor of particularly high quality. Motor speed, infinitely variable between 10,000 and 45,000 r.p.m., was controlled by a large circular dial mounted on the  machine's rear face, a ring of engraved numbers being provided to indicate the selected revolutions.
With 5" of longitudinal and 3" inches across, the 12" x 4" table had a single 1/2" T-slot down its centre line and another along the front to mount stops. It could be moved on its horizontal axes by a choice of hardened and ground feed-screws with zeroing micrometer dials, quick-action levers or air-hydraulic feeds. Head travel was restricted to hand-screw only with the feed moving at right-angles to the table - the one drawback to the machine being the lack of a quill-feed along the spindle axis.
Four versions of the "
Precise" were offered: the Model U had its head fitted to a bracket that allowed it to be swivelled 45° each side from vertical as well as being rotated through 360°; the Model H was offered with the head less the swivel bracket, so limiting it to horizontal wok only; the Model "Indicator" was the Type U equipped with dial indicators on all three axes of movement (with the dials fitted to detachable bracets and used in conjunction with stops mounted in T-slots machined into the table's front and head casting's left-hand faces); the final version was the"Commutator Undercutter", a model fitted with a lever-feed to the table's longitudinal travel and a special table-mounted assembly that allowed electric motor commutators up to 7" long to be mounted either on centres or in special brackets for centreless shafts. Although just four basic Models were offered a wide variety of specifications was available and the miller could be ordered with many different combinations of features. The maker's codes for the various options were:
"U" = basic model with swiveling head
"H" = basic model with non-swiveling head
"M" = feed-screw with micrometer dial
"L" = hand lever feed
"P1" = air-hydraulic power feed to table's longitudinal travel in one direction with rapid return
"P2" = air-hydraulic power feed to table's longitudinal travel in both directions
"DC" = adjustable dial-indicator stops on the column
"DT" = adjustable dial -indicator stops on the table
"DS" = adjustable dial indicator stops on the saddle
"50" =
Super 50 Power Quill (1/4 h.p.)
"60"=
Super 60 Power Quill (1/2 h.p.)
Hence, a machine label carrying the following inscription::
CAT. No. U P2 MDS 60 would have been a Basic Model "U" with air-hydraulic power feed to the table's longitudinal feed in both directions; a hand-driven micrometer dial equipped screw-feed to the table's cross motion with dial indicator and adjustable stops - and a 1/2 h.p. Super 60 Power Quill.
A number of useful and specially-made accessories were available including a 4" x 6.5" magnetic base; a swivel-base machine vice with 3.25" wide hardened jaws with an opening capacity of 1.75"; a quick-lock vice with jaws 3.5" wide and an opening capacity of 2"; an indexing unit consisting of a No. 7 B & S taper headstock and tailstock assembly able to swing work 6" in diameter and fitted as standard with a 48-division plate; a 4.5" diameter rotary table; a 2" raiser block to lift the main column; complete coolant equipment with electric pump and tank and a "
Vapor lub unit", as assembly that sprayed a coolant mixture onto the workpiece from a self-contained 2-gallon tank and pump unit.
What would a machine as unique as the Precise have been intended for? Even the makers admitted that several such small millers were already on the market (they may have had in mind the American Derbyshire Micromill, English BCA, Swiss Hauser M1 and the smallest of  the
Société Genevoise d'Instruments de Physique (SIP) models, the Pointing Machine) but reminded potential buyers that non ran at such very high revolutions as theirs. Turning at full speed a "Precise" could have handled extremely small-diameter carbide-tipped cutters and grinding wheels that would have been useful for the machining of difficult materials to very high standards of accuracy.
A number of other complete tools were also listed including a pair of drill presses and three very simple "speed lathes" with horizontally mounted spindles that overlapped a plain table devoid of any sort of tool rest.
A successful company and still with branches in the USA and Germany, the Precise Corporation is still well known today for its spindles, these being used in specialist milling, drilling, cutting and grinding operations with companies as diverse as mobile-home makers Winnebago, Boeing Aircraft and Mikron Bostomatic employing them.
Further details of the Precise Company can be found here..

Precise fitted with the "P2" equipment: air-hydraulic power feed to table's longitudinal feed in both directions

Precise Model "H" with horizontal spindle and lever-operated feed table

Precise Model "Indicator" Note the T-slot in the side face of the head

The"Commutator Undercutter", a model fitted with a lever-feed to the table's longitudinal travel and a special table-mounted assembly that allowed electric motor commutators up to 7" long to be mounted either on centres or in special brackets for centreless shafts.

Precise Model "Indicator" with detachable brackets mounted to carry dial indicators ion all three axes of travel. Note the T-slot machined into the head's left-hand face. Various jigs and adapters are mounted on the table

Precise Continued on Page 2 of 2


email: tony@lathes.co.uk
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"Precise" Milling Machine - USA