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The 121/2" x 20" Rivett 1020 was a limited-production model, introduced in 1941 but then withdrawn from sale. In post-war year the Model 1030 was manufactured in its place and this version is found in greater numbers as the Steelway Precision Toolroom Lathe. Both models resembled a Monarch Model EE toolroom lathe, were superbly made and boasted a comprehensive specification with a 12.75" wide bed, fitted with hardened steel ways, and enormously long saddle wings that gave a contact area of 55.5 square inches. Weighing 3900 lbs (1.6 tons) the lathe sat on a substantial cabinet stand of cast iron and held a cushion-mounted drive system that formed a complete unit and which could be maintained through large openings in the end and the back of the stand - or withdrawn completely through an end door.
Drive was by a 5 h.p. 3-phase 1750 r.p.m electric motor carried an expanding and contracting pulley, the opening and closing of which was activated by a small motor controlled by push buttons, marked Fast and Slow, positioned to the right of the screwcutting gearbox, and gave two variable-speed ranges. The drive from the motor passed to a shaft carrying a dog-clutch arrangement which allowed the motion to continue either to its end - and so drive a triple V belt connected to the backgear assembly in the headstock - or to be passed across to a parallel countershaft which directed the drive, via a 3-step V belt, straight to the end of the headstock spindle. The lower backgear ratio was 12.5 : 1 and gave speeds from 22 to 200 rpm whilst the higher ratio was 6.25 : 1 with speeds from 44 to 400 rpm. This arrangement ensured that the V belts did not loose their efficiency, their running speed never falling below 300 feet per minute.
Massively built and enormously strong the rounded headstock casting had, to ensure minimum weakening of the structure, the smallest possible inspection hatch in the top. It contained gears that were all machined from heat-treated alloy steel and either shaved or ground finished. The 1.25" bore main spindle carried an American Long Taper Key-drive nose, size L0 (a D-1 4" Camlock was optional) had no sliding gears and was supported by a centre bearing designed to reduce flex under heavy loads; it ran in super-precision ball races, a double-row preloaded set at the front, a single row at the rear and a single-row bearing in the centre. The layshaft sliding gears moved on six-tooth involute splined shafts and were supported in either ball or roller races. Rivett were justly proud of their finely engineered headstoc and prepared a special display model to more clearly explain how it worked. Collets could be fitted either directly into the headstock spindle - in which case the maximum capacity was 11/8" - or in either a "draw-in" collet chuck by Sjorgen or a Jacobs "Rubber-flex" unit with, in both cases, a maximum pass-through capacity was 1 3/8.A rev. counter was built into the head - an indispensable aid when using a variable-speed lathe.
Like that used on the Monarch 10EE Toolroom lathe the screwcutting gearbox used selector knobs each side of a central turn-push-pull selector. The box, built as a complete, independent unit, could be slid out of its housing in the bottom section of the headstock for servicing or repair. The unit contained an oil sump, fitted with a sight-glass level indicator, from which the gears and bearing were lubricated by splash whilst the idler gears, on the external drive, ran on grease sealed bearings. All the gears associated with the box were manufactured from heat-treated alloy steel - and either ground or shaved according to their particular function - whilst the shafts carrying the sliding gears were of the six-tooth involute splined type. A total of 72 rates of feed and 84 threads were available including, so the makers claimed, " …every world standard from 2 to 240 t.p.i." The actual range was: 2, 21/4, 23/8, 21/2, 23/4, 27/8, 3, 31/8, 31/4, 33/8, 31/2, 33/4, 4, 41/2, 43/4, 5, 51/2, 53/4, 6, 61/4, 61/2, 63/4, 7, 71/2, 8, 9, 91/2, 10, 11, 111/2, 12, 121/2, 13, 131/2, 14, 15, 16, 18, 19, 20, 22, 23, 24, 25, 26, 27, 28, 30, 32, 36, 38, 40, 44, 46, 48, 50, 52, 54, 56, 60, 64, 72, 76, 80, 88, 92, 96, 100, 104, 108, 112 and 1 20. In addition, by setting the lever under the rev. counter to "Feed" (which doubled the pitch of the previous twelve threads) the following pitches could be obtained: 128, 144, 152, 160, 176, 184, 192, 200, 208, 216, 224 and 240 t.p.i. A range of metric and other pitches could be obtained by employing different external pick-off gears on the drive from headstock to gearbox.
Bearing more than a passing resemblance in both appearance and function to that on the equally well-made Monarch 10EE toolroom lathe the carriage assembly of the Rivett 1020S was enormously heavy yet moved with silken smoothness along the bed. The leadscrew was reserved only for screwcutting with a powershaft providing a drive for the power sliding and surfacing feeds. Two separate, snap-up-and-down horizontal levers were used to select and engage the feeds with each working through safety overload-protected clutches. A precision carriage stop was fitted and arranged in two parts: a dial-test indicator, mounted on the left-hand edge of the saddle, engaged the rod of a micrometer held in a clamp on the lower face of the headstock - the combination of a positive stop, and a continuous, precision-reading of saddle travel being a most useful feature. The base of the double-walled apron contained an oil sump, with a sight-glass level indicator, from which lubricant was distributed to the bedways and all the apron gears, shafts and bearings by a plunger pump activated by the engagement of either feed. An interesting point (and one overlooked by many designers) was the attempt to minimise deflection by locating the carriage clamping bolt in the middle of the apron.
As might be expected the compound slide-rest feed screws were of hardened steel, precision ground and ran through nuts which could be adjusted to eliminate backlash. The zeroing micrometer dials were not as large as they might have been on a machine of this class but were fitted with neat locking screws. The cross feed screw was fitted with a useful ball stop which permitted the retraction and resetting of a threading tool without losing the initial micrometer setting. The penalty for having a neat, flush-fitting dial-thread indicator on top of the saddle was the permanent engagement of its gear with the leadscrew and the need to employ bevel gears to take its drive through a right-angle.
Advertising for the machine summed its capabilities in this neat sentence:
"It combines the feather-touch sensitivity of an instrument lathe with that heavy-biting ruggedness which carbide cutting tools require."
During the 1940s and 1950s Rivett also produced two plain turning lathes: the 918S had a 9" swing and admitted 18" between centres (with an infinitely-variable speed drive between 100 and 3750 rpm) whilst a smaller lathe, the 715, had a 7" swing lathe, 15" capacity between centres and used the same drive system but with a speed range from 200 to 3500 rpm..
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