Manufactured by Broadway Engineering of Wellington Hill West, Bristol 19, England (and Knapps Lane, St. George, Bristol 9) Portmac millers were 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 £55 : 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, through a travel of 7 inches, on ways machined into the inner surface of the main column. In this respect, the design of the Portmac resembled, for example, the American Linley and Vernon machines. All sliding surfaces were ground and then hand scraped to fit. With dimensions of 14" x 4", the table had 8" of longitudinal travel and a generous 5" across, this aided by a well-spaced-out feed-screw endplate formed as a complete casting. As the handwheel for the table travel were of a large diameter, advantage was taken of this (on some examples only) to engrave their flat, outer rims with micrometer graduations.
Fitted with a screw-on nose cap, the spindle accepted standard dead-length Crawford collets - these being of the type used on, amongst others, the smallest models of Ward and Herbert capstan lathes. Pictures of these collets, with dimensions, can be found at the bottom of the page. The spindle 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 - but hardly easy or convenient to use compared to the more usual horizontal handwheel working through worm-and-wheel gearings. The maximum clearance between spindle nose and table was a useful 8.5 inches. Four 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 (as on some makes of drilling machine) 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 so 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 in 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 you own a Portmac miller, or know more of the Company's history, the writer would be delighted to hear from you..