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Drummond B-Type Power Cross Feed
Admiralty Model (Type B.S.) Lathe

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Introduced for Admiralty use at the start of WW1 in 1914, the Mk. 1 "B.S. Type" included a range of modifications to improve its ease of use on board ships as they corkscrewed around in heavy seas - the most important being the provision of power cross feed and tumble-reverse mechanism. The lathe was based closely on the standard "B-Type", but fitted with the required power-feed apron (with both longitudinal and cross feeds) driven from a shaft fitted below the leadscrew and geared to its left-hand end.
In order to make the assembly work correctly the simple full nut that connected leadscrew to apron  was replaced by a proper double clasp nut. A saddle traverse by hand-operated rack and pinion was also fitted to the B.S. and a tumble reverse for the leadscrew drive attached to the slotted bracket on the headstock front - a bracket that normally carried a stud to mount the extra changewheel required for left-hand screwcutting. When the tumble-reverse unit became available on the navel B.S. it also entered the accessory lists for the standard machine - however, the full B.S. specification was only available for Drummond B and M-Types, and Myford M-Type, as was destined exclusively for naval use - it was never offered openly on the civilian market nor, so as far as is known, never featured in any publicity literature.
On the very rare Mk. 1 BS the power-feed selector arm worked across the front of the apron whilst on much more common Mk. 2 it was positioned to hang downwards and indent into slots machined into the underside face. A standard-fit tumble-reverse assemble was included on all but the earliest models - an essential fitment for shipboard use that gave power feeds up and down the bed as well an in and out. The unit later became available as an accessory on the Myford-manufactured M-Type ..

A very rare Mk. 1 BS Type with the power-feed quadrant selector arm working across the face of the Apron.

Mk. 2 BS Type
The bottom edge of the distinctly different apron of the B.S. Type carried a  spring-loaded quadrant selector with indent positions for hand or power cross feed. The ordinary B had a solid nut on the leadscrew but the fitting of power sliding and surfacing meant that a split nut, that could be disengaged, was required; this was operated by a tapered lever positioned at the top right of the apron. The spring-loaded operating knob that engaged the cross feed was of an identical design (and something of a Drummond trademark) to that used for the engagement and disengagement of  the leadscrew clasp nuts on later versions of the lathe.

Power was supplied to the apron by a separate shaft, gear-driven from the left-hand end of the leadscrew.

Power-shaft drive gears

Tailstock end of the power-feed shaft

In order to make the assembly work correctly the simple full nut used on the ordinary model to connected leadscrew to apron  was replaced by a proper double clasp nut.

The simple, clutchless, power-feed mechanism was contained within a two-part, cast-iron housing - the inner section of which was secured to the front of the saddle by just two slot-headed set screws.

The outer cover held "tumble gears" that selected either power sliding (along the bed) or surfacing (across)
In the picture to the right can be see, at 9 o'clock, the snail-cam mechanism by which means one feed was locked from engagement when the other was engaged

The inner plate was used to mount the feed-reduction and hand traverse gearing

Left and below: the final drive to the cross-feed screw was by a gear connected to the square rod that slid through the upper drive gear.

An essential part of the modifications carried out to the lathe to make it suitable for on-board use, was a tumble-reverse mechanism carried in the slotted arm on the headstock normally used to hold the extra changewheel necessary when cutting left-hand threads.

Another view of the tumble-reverse mechanism




E-MAIL   Tony@lathes.co.uk
Home   Machine Tool Archive   Machine-tools for Sale & Wanted
Machine Tool Manuals   Machine Tool Catalogues   Belts   
Books   Accessories


Drummond B-Type Power Cross Feed
Admiralty Model (Type B.S.) Lathe

A variety of Drummond literature is available

Drummond Home Page