The D Type was one of the largest machines made by Denbigh and available in four models: D1, D2, D3 and D4.
D1 34" x 10" non-swivel table - 22.5" of travel
D2 34" x 10" swivel table - 25.25" of travel
D3 46" x 10" non-swivel table - 34.5" of travel
D4 46" x 10" swivel table - 37.25" of travel
The table drive used a 4-speed gearbox, chain-driven from the main spindle, which gave feed rates of: 0.027,  0.021,  0.013 and 0.01" per revolution of the cutter; an extra sprocket was supplied with the machine which offer four alternative, rather slower rates of : 0.013,  0.010, 0,007 and 0.005". The non-swivel table models had power feed in one direction only - whilst those with a swivel table enjoyed power in both directions as standard.
The ordinary drive system (a variable-speed drive was optional) employed two endless chrome-leather-faced plastic flat belts; one, 2" wide, ran from the motor to a ball-bearing countershaft and could not be adjusted - it was pre-tensioned at the factory and presumably had to be replaced if it ever started to slip. The second belt, 2.25" wide, ran from the countershaft up to a 3-step cone pulley which drove the 3% nickel-chrome steel, taper-roller bearing, No. 4 Morse taper horizontal spindle.
The whole of the countershaft system was balanced against two large springs and could be slackened and lifted to aid belt-position changes by the action of two levers at the rear of the machine. As an aid to heavy-duty metal removal, the miller was fitted with a two-stage, lathe-like backgear assembly. In "open gear" (without the backgear engaged) speeds of 180, 360 and 720 rpm were available; with the first stage of the backgear in speeds were reduced to 60, 120 and 240 rpm and with the gear in its lowest-ratio drive 19, 38 and 76 rpm. The variable-speed drive version was fitted with an expanding-and-contracting pulley assembly exactly like that employed on the Type C and M machines; it retained the double-backgear assembly as well and in open drive spanned 250 to 720 rpm; in backgear first stage 90 to 260 rpm and in backgear second stage 30 to 90 rpm.
A special model was manufactured, based on the D3, with an air-hydraulic table drive to aid automatic production processes; an air supply of 30 cubic feet a minute at a pressure of 100 psi was required to run the unit.
The machines weighed between 25.75 cwt and 32.75 cwt and required a floor space of 70" x 60".