Manufactured by Broadway Engineering of Wellington Hill West, Bristol 19, England (and Knapps Lane, St. George, Bristol 9) the Portmac miller was designed by Les Redman, a member of the Bristol Society of Model & Experimental Engineers. The machines were advertised for a time during the late 1940s and early 1950s (at ?5 : 18s : 6d) - but never made any great impression on the market, although the makers did claim that examples were in use by Government departments for experimental and research purposes.
At least two models were offered: a very rare horizontal, the "Redman Mini-Miller Type A", and the vertical "Type BC", the latter being the more common of the two found today - and shown below. Resembling a miniature jig borer, the BC had its table fixed to the base of the machine with a head that could be slid up and down ways machined on the inner surface of main column - in this respect it resembled, for example, the American Linley and Vernon types. All sliding surfaces were ground and then hand scraped to fit. With dimensions of 14" x 4", the table had 8" of longitudinal travel, a generous 5" across (aided by a well-spaced-out feed-screw end plate formed as a complete casting. The head could be slid up and down the face of the column through a range of 7" .
Fitted with a screw-on nose cap, the spindle accepted standard dead-length Crawford collets (1.5" long with capacities ranging from 1/8" to 1/2") and had a travel of just 1.5 inches with the feed handwheel, threaded internally, sitting just above and surrounding spindle housing so that it acted directly upon the quill - a most economical design, and possibly unique. The maximum clearance between spindle nose and table was a useful 8.5 inches. 4 spindle speeds, from 500 to 4000 rpm, were provided - the motor being mounted, drill-like, on a plate at the back of the column. Rather cleverly, the cast-aluminium motor plate and belt guard were connected to provide a means of both giving tension to, and allowing the quick release of the drive belt for speed changes. The guard was arranged to pivot vertically, with its right-hand arm projecting back and riding against the motor mounting plate. When positioned "down" (i.e. in the running position) the guard arm pressed against the motor-mounting plate (which was horizontally hinged on its left-hand side) and thus tensioned the drive. To ensure that the guard stayed locked down, the end of its arm was arranged to ride over a small raised 'button' cast in the plate. A 6-inch rotary table was, apparently, supplied as standard and featured a quickly-detachable worm to speed resetting and scales graduated to 5 minutes of arc.
Constructed in as simple a way as possible, the Mini-mill used round steel bars for its main column and both table ways. 9.25" long and 2 7/8" wide, the table had 5.15" of longitudinal travel, 1.625" across and the head could be moved through 2.125" vertically. No micrometer dials were fitted to any of the feed screws and the handles, instead of being an easy-to-use round type, were of the old fashioned crank pattern - a wonderful design when opening a canal lock gate, but not so suited to the slow, fine feeds required on a milling machine.
If any reader owns a Portmac miller, or knows more of their history, the writer would be delighted to hear from you..