email: tony@lathes.co.uk
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George Adams of London
"Portass Mk. 5" Lathe Photo Essay

Mk. 5 Page 2   Mk. 5 Page 3

George Adams Home Page

GA Lathe Model 21/2  

G.A. Watchmakers' Lathes 

G.A. Round Bed Lathe

3.25" & 4.75" Screwcutting Lathes Models D, E, F, G & H

4" & 5.25" 4" & 5.25" Screwcutting Models A, B, L, KF1 and CL

3.25" & 4.75" Precision Lathes Models D, E, F, G & H

2.75" Screwcutting Lathe Model CS

Advertisements 1930

GA 21/2" Precision Plain Lathe

Watchmakers' Lathes

Portass-built Mk. 5 Lathe Photo Essay


Amongst the models listed by George Adams from the early 1930s onwards was an inexpensive, gap-bed, backgeared and screwcutting 3" x 16" lathe - a machine that must, judging by the number of survivors, have sold in very limited numbers  rarest, only a handful having come to light in recent years. An entirely conventional machine, the lathe was also badged by the makers, Portass of Sheffield, as their own under the description the "MK. 5. 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) and a spindle bored through 3/8" with a No. 1 Morse taper socket and a 3/4" 12 t.p.i BSF nose. Oddly, 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 threaded for 11 inches of its length 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 5 x 2" 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 - an unfortunate oversight when it was likely to be gripped by oily hands.
Although most owners were happy to save the pennies and risk their fingers, Portass did offer, on their own model, a swing-open, cast-iron changewheel guard, though few can have been sold..




Mk. 5 Page 2   Mk. 5 Page 3

George Adams Home Page

GA Lathe Model 21/2  

G.A. Watchmakers' Lathes 

G.A. Round Bed Lathe

3.25" & 4.75" Screwcutting Lathes Models D, E, F, G & H

4" & 5.25" 4" & 5.25" Screwcutting Models A, B, L, KF1 and CL

3.25" & 4.75" Precision Lathes Models D, E, F, G & H

2.75" Screwcutting Lathe Model CS

Advertisements 1930

GA 21/2" Precision Plain Lathe

Watchmakers' Lathes

Portass-built Mk. 5 Lathe Photo Essay

George Adams of London
"Portass Mk. 5" Lathe Photo Essay
email: tony@lathes.co.uk
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