Made for a short time during the early 1950s in both 45/8" and 51/8" centre heights, and sharing its "Dreadnaught" name with a number of other both heavier and lighter Portass models, this was not only the largest-ever Portass made but also the rarest. Only six of the smaller version are known to have been manufactured and it was also the only Portass ever to be offered with the option of power cross feed and a screwcutting and feeds gearbox. However, it seems that only the larger model had this superior specification, the smaller version being confined to changewheel screwcutting and a hand-driven cross feed. Fitted with No. 3 Morse taper barrel the tailstock could be set-over for the turning of slight tapers and was locked to the bed by a permanently-fitted handle set at an angle to the rear of the casting. Both models were sold exclusively on a very heavy, cast-iron underdrive stand, there being no option for a bench-mounted model (though unfortunately the well-preserved model below has lost its original stand).
Surely a unique feature - the writer has never seen another like it - the Perspex window on the hinge-open face of the headstock enabled the fascinated owner to watch in jaw-dropping amazement as the "works went round" - though why it was included is a mystery as it seems to have no functional value at all.
Power cross feed was arranged in a very Victorian way with a keyway-equipped power-shaft, driven from the screwcutting changewheels, running along the back of the bed and driving through worm-and-wheel gearing connected to the end of the cross feed screw - similar examples of this mechanism (that frees the apron from having to carry a complex arrangement of gears) can be seen on pages featuring the larger Spencer lathe, the Pools Major, the Mellor and Jones & Burton
When in his teens the writer (who lived only a few miles from the Portass works) owned the shattered remains of the larger type, but, missing many parts and completely worn out it was, he is ashamed to say, relegated to the scrap bin. It was, upon reflection, a typical Portass product: a strong, no-nonsense design though with no effort made to impart a decent cosmetic finish on some pretty rough castings.
If you have a lathe like this - let's call it the "Portass Window" -  the writer would be very interested to hear from you.