Despite such machines being available from a number of competing manufacturers it is surprising that Atlas never offered a stand-alone vertical miller - nor even a vertical head to convert their popular horizontal model. However, during the late 1940s and early 1950s, at least two  third-party suppliers - one the Marvin Machine Products Company of Detroit and the other unknown - offered neat (non-quill feed) vertical heads with Marvin also producing a slotting attachment. Carried on the end of the overarm the Marvin vertical head was driven by a V-belt from a  pulley attached to the end of the horizontal spindle with the belt passing round a pair of adjustable jockey pulleys - almost certainly held within an eccentric mount to provide some means of adjusting belt tension. The slotting head's horizontal shaft was driven directly, pulley-to-pulley, with a single jockey pulley used to adjust the belt tension.
Devoid of any maker's marking the "unknown" vertical attachment was fitted with step-up gearing that approximately doubled the speed to give a range suitable to run small-diameter milling cutters successfully. Drive came from a horizontal shaft that fitted into the No. 2 Morse taper end of the miller's horizontal spindle. A pair of bevel gears turned the drive through 90-degrees to rotate a spindle fitted with a simple draw-bar retained collet holder - the holder and its collets looking remarkably like those used decades later on the East German Hobbymat BF Series vertical miller. The unit was given sufficient forward reach to enable reasonably-sized jobs to be machines, although its horizontal stem was perhaps unnecessarily light in construction. If any reader has one of these attachments the writer would be interested to hear from them.