Heavy Duty 4-inch Mk. 5 Portass Portass PD5 First Portass Lathes
Portass Model C Shaper Portass Junior Portass Model XL
Eclipse Portass Portass Round Bed
Amongst the plethora of models listed by Portass from the 1930s to the 1950s the 3" x 16" Mk. 5 (not to be confused with the later PD5) must be amongst the rarest - only three having come to light in recent years. An entirely conventional machine the lathe was also, surprisingly, badged as a "George Adams" - a brand more normally associated with high-class machine tools and prices to match. Weighing around 50 lbs, the Mk. 5 was entirely conventional with a simple split-bronze bearing backgeared headstock (at a ratio of 1 : 6.75) with a spindle bored through 3/8" and with a No. 1 Morse taper and a 3/4" 12 t.p.i BSF nose. The headstock has been found both as a bolt-on unit and cast as-one with the flat-topped , V-edged, gap bed. Driven by changewheels 3/8" thick, with a 5/8" keyed bore and a sixth-of-an-inch circular pitch - about 18.812. DP - an odd figure presumably caused by the economical use of pre-war, non-standard gear cutters. The 24-inch long leadscrew was thread for 11 of its inches with a 9/16" 8 t.p.i. square thread and gripped by proper clasp nuts. Although a low-cost product the lathe still had a compound slide assembly with a T-slotted 5¼ x 2½" cross slide driven by a 5/16" 18 t.p.i. screw,
Of the simplest kind, the tailstock was unable to be set-over for taper turning and held a 2-inch travel barrel (lock with a crude, direct acting screw) with a 10 t.p.i. square thread that passed thorough the smooth-edged handwheel.
Although most owners were happy to save the pennies and risk their fingers, Portass did offer a swing-open, cast-iron changewheel guard, though few can have been sold.
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The headstock, cast (in this example) as one with the bed flat-topped, V-edged bed, carried simple split bronze headstock bearings. The backgear was a full-width, sliding type and, surprisingly for a cheap lathe of the period, a cast-iron cover was provided to guard the changewheels. |
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Although the leadscrew handwheel with its horn handle looks a little on the luxurious side for an early Portass the rest of the machine was typical of the maker with in-house manufactured handwheels and an inverted carriage rack that was prone to fill up with swarf and jam. The single-sided "thumb-action" compound slide rest handwheels were rather Drummond-like in appearance and, typical of an economy machine of the time, lacked any form of micrometer dial. The owner of this example has assembled the tailstock "back to front" on the bed, the clamp should be at the rear. |
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