Britannia No. 8 Planing Machine with a 12 foot long by 25-inches wide bed. Built to special order only, this was one of the company's largest planers, the tool able to travel 8 feet horizontally and 39 inches laterally.

Britannia No. 6 Planing machine.
This was a heavily-built machine, able to plane a piece of metal 4 feet long, 2 feet wide and 2 feet high. The table, which ran on V ways, was carefully designed to allow the clamping of unusually-shaped workpieces, being made unusually thick, and carrying T slots both longitudinally and cross-ways.
The table feed was automatically reversed at high speed, but by an enclosed gear mechanism, rather than by an arrangement of belts and crown-wheel and pinions as in the company's smaller machines.
The No. 7 planer was very similar, but had a planing capacity of 6 feet, by 2 feet 6 inches by 2 feet 6 inches.

At one time the planer was considered an indispensable part of any machine shop; using very inexpensive tooling they were able to machine large components with relative ease. Some examples were gigantic, with beds fifty or sixty feet long and able to accommodate work sixteen feet high, whilst other were fitted with either fixed or pivoting grinding or milling heads in place of the ordinary "clapper-box" tool holder and so became known as "planer-millers" or "planer-grinders" - or, in some regions, "plano-millers"and "plano-grinders". On larger examples it was common to find more than one tool box fitted; the cross-rail (or cross-head) would often carry two, side by side, with several extra ones sometimes mounted at the bottom and sides of the cross-rail support columns. In addition, even smaller examples were sometime fitted with two cross heads, often adjustable in position along the bed and each fitted with multiple toolboxes.
Some planers were made "open-sided" to accommodate even larger jobs that could hang over one edge of the table, and as the species developed it became increasingly difficult to differentiate between planers and true millers - examples made by the huge American Niles-Bement-Pond Company included: Multiple Spindle Horizontal Milling Machines, Horizontal Slab Milling Machines, Horizontal Slab milling machine, Rod Milling and Fluting Machine, Duplex Milling Machines, Forge Milling Machines, Plate Planers, Rotary Planers and End Milling Machines. Although the name changed according to the specific use, the principal of operation remained essentially the same, a long sliding table passing beneath (or between) single or multiple cuttings heads.
Variations on the theme include Pit and Breast planers where the workpiece rested in a pit (or on a massive table) and the columns carrying the cross-rail and toolheads were made to travel over it; these huge machines were generally reserved for heavier kinds of armour-plate work.
Planers have been made in almost every size increment imaginable, the smallest being tiny hand-operated units designed for bench mounting.  Although rare, examples of planers suitable for the smaller workshop do occasionally turn up and are very sought after, not only for their novelty and historical value, but because they are still capable of their original task - the economical machining of large components in a limited space.