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The Basingstoke Factory, November 1930

By 1930, John I Thornycroft and Co Ltd’s Basingstoke factory had been in business for over three decades, and the firm was a seasoned manufacturing organisation respected both inside and outside the engineering industry. A study of Thornycroft’s factory in 1930 is a reminder of how the UK was once a leading engineering design and manufacturing nation. It is not as if Thornycroft was unique, a manufacturing anomaly in a service-based economy, because Thornycroft’s engineering prowess was replicated by numerous other British engineering firms designing and producing technology goods. These goods were not only import-stoppers, but they also made a significant contribution to our export trade.

In 1930, Thornycroft had four important manufacturing centres. The Basingstoke factory built IC-engined commercial and municipal vehicles as well as fire engines. Thornycroft’s shipbuilding yard was at Woolston, near Southampton. At the other end of the marine scale, the works at Hampton-on-Thames covered small motor boats, cabin cruisers and other small craft, the engines for which were produced in Reading.

These pages take a general look at the Basingstoke works, and cover some important machine shop activities used in power-train production.

Site layout

The Basingstoke site occupied 15 acres (6.08 hectares), with buildings comprising around 12 acres (4.86 hectares). A paved yard ran the whole length of the site, allowing storage space for vehicles awaiting shipment and facilitating access between departments, all of which were at ground level apart from the stores. A railway siding on the edge of the site facilitated deliveries of materials and bought out items to the engine, fitting and chassis assembly shops. These shops included wood-working facilities for vehicle body production, from which suction pipes transferred the sawdust to a boiler room for firing two horizontal boilers. Steam from the latter was used for pickling castings and, during cold weather, for heating some of the shops.

Main machine and chassis assembly shops, for instance, were large open plan areas, and a 15 ton (15,240kg) electric crane served the principal bay of the main machine shop. Also, an extensive system of Morris overhead runways facilitated work handling in all departments.

Machine tools were generally grouped by type (e.g. lathes) for all but main components, comprising such items as cylinder blocks, gear boxes and rear axle casings. For these, a number of machine lines were installed, and the same machine lines handled a variety of different designs of component. The grinding section was separated from other sections by glass partitions for cleanliness.

A re-enforced concrete structure comprising vertical pillars and horizontal members ran along one side of the main machine shop. The horizontal member served as a mounting for electric motors. These were coupled by belt to line shafts running transversely across the shop, and the machine tools were driven by belts dropping down from the line shafting.

Production arrangements

Thornycroft offered a range of vehicles for meeting differing customer requirements. This complicated production, because no one vehicle type was in sufficient demand to provide continuous work for a machine line dedicated to one model. This difficulty was resolved by designing vehicles so that one unit or component could be made to serve on more than one vehicle types (e.g. engines). Also, the same machine lines were used for producing all varieties of a given component e.g. all varieties of cylinder block, using means of rapidly changing from one component design to another with minimum alteration in machine shop equipment.

A six-cylinder engine on testbed

In some cases, particularly for drilling operations, adjustable multi-spindle drill heads were used, with facilities such as means of varying their centres. Therefore, changing from one design of component to another was reduced to the simple process of adjusting drill spindles and clamping a different jig to the machine table. Several operations were performed on machines developed by Thornycroft for specific purposes, but most machines were standard types adapted for single purpose requirements.

To compensate for delays arising from frequent design changes, the machine shop always produced ahead of the needs of assembly departments - usually by about two weeks. Thus, a week’s work from the machine shop accumulated in store ready for issue to assembly departments the following week. No build took place until all components were at assembly stations.

Connecting rods and big-end bearings

Duralumin connecting rod forgings and gunmetal big-end bearing liners were received from stores. The big-end bearing and rod were processed side-by-side down the same machine line, so that at the final operation the rod was complete with the bearing ready for assembly into the engine.

Operations on connecting rods and big-end bearings

The connecting rod arrived at the machine shop with the big-end bearing cap as an integral part. The shank was of I-section except for a portion near the big-end in order to provide metal which could be cut away for balancing. Big and little-end bosses were machined to the same width on a vertical milling machine, with the rod mounted in a purpose-designed fixture - the little-end boss was reduced to the correct width later on. Rods were then passed on for rough drilling and boring. In the meantime, both ends of the big-end bearing liner were faced in capstan lathes supplied by H W Ward.

Die-casting big-end bearing

White metal was die cast into the big-end bearing liner in a Dorman die casting machine, the bearing being held in place by a fixture designed to ensure the white metal bore was square with end faces of the liner. After bearing removal from the die-casting machine, bearing ends were trimmed and the bearing outside diameter was then turned to size on a Ward capstan lathe, leaving flanges at each end.

Simultaneous operations on connecting rod and big-end bearing

The next operations on the connecting rod and big-end bearing took place concurrently. The big end boss was rough bored, the small end boss was drilled and a radius was formed at one end of the big-end bearing. These operations were carried out on a standard Jones & Shipman pillar drilling machine, fitted with a Thornycroft-designed adjustable drill holding three tools. After removal from the machine, the bearing was landed in a chute and transferred to a spindle drilling machine for machining bolt clearances in each side.

Indexing drill jig

The connecting rod passed to another Jones & Shipman pillar drilling machine for drilling, reaming and counter boring the holes for bearing cap bolts. This machine had a six spindle drill head arranged so that spindles were grouped in pairs and both spindles of each pair could be adjusted for centre distance one from the other and locked in place. Three connecting rods were clamped in vertically in a revolving jig, with big-ends uppermost, allowing a sequence of operations comprising starting the hole, counter boring, drilling and then reaming. After this, small oil holes were drilled in the connecting rod using a three-spindle drilling machine.

Finish boring operation

The connecting rod was finish bored along the same lines as the roughing operation (described previously), and a chamfering tool was used to radius the edge of the hole in the big-end boss. The rod was now ready to receive its big-end bearing, for which the bearing cap was sawn from the rod simultaneously with splitting the bearing. These operations were carried out on a Cincinnati milling machine, which had a fixture for holding two connecting rods and two big-end bearings, and was suitable for a range of rod sizes. After sawing, enough metal was left on the joint faces of connecting rod, bearing cap and big-end bearing to allow a truing cut to be taken, using a milling machine supplied by H W Ward.

Inserting snugs

Snugs were used to prevent bearing cap bolt rotation, and were inserted with a special-purpose hand tool. After assembling the big-end bearing on to the connecting rod, the hole was sized using a single point boring tool on a pillar drill, which removed 0.03ins (0.76mm) from the white metal. The gudgeon pin hole was finally sized at one pass of a combined broaching and burnishing tool.


Thornycroft pistons were made of aluminium die-castings or cast iron. Both types of piston were similar in design and were machined by the same methods on a line of machines converging on the connecting rod machine line.

Operations on pistons

All piston turning and boring operations took place on No 4 Capstan lathes supplied by Alfred Herbert. After receipt from stores, the piston skirt was rough and finish bored and radiussed on the outside edge by a series of three turret tools, and faced to length by a front cross-slide tool. Following the above, the piston’s outside diameter was rough turned by a knee turning tool on the turret, at the same time the piston head (the portion between upper piston ring and crown) was rough turned by a tool in the front cross slide turret. Then three piston ring grooves were rough formed by a corresponding number of tools mounted in a special holder on the rear cross-slide tool post.

The gudgeon pin hole was bored next. First, the hole was rough bored using a reamer mounted in the lathe turret, followed by another pass with a boring bar. Final hole sizing was carried out with an expanding reamer mounted in the turret, and the inside faces of both piston bosses were machined by two tools mounted on a bar held in the turret. A similar tool was used to cut grooves towards each end of the hole for housing the gudgeon pin retaining rings. After the above operations, the open end of the piston was lightly ground on the piston ring grinding machine supplied by Harry F Atkins. Piston ring grooves were finished by a similar arrangement of tools to those used for roughing (see above), mounted on the front cross slide turret.

A second cut was taken on the outside diameter of the piston with a knee turning tool mounted on the turret, 0.008ins (0.203mm) surplus being left for final sizing, which was carried out by four diamond tools mounted in knee type holders in the turret. One of these four tools sized the piston body diameter while the other three tools sized the lands between the ring grooves and the piston head. These diameters reduced in increments of a few thousandths of inch from the body diameter towards the head. Diamond tools gave a high finish and very exact sizing for long periods between resetting. Operations on the piston called for a limit of 0.001ins (0.025mm) on the main diameter and a very fine limit of 0.0003ins (0.0076mm) on the gudgeon pin hole, along with a variation of 0.25oz (7.09gm) in finished weight.

Rear axles

All Thornycroft vehicles had worm drive rear axles and drive shafts housed in a steel casing weighing approximately 200lb (91kg). The worm, wheel and differential were mounted in a cast steel support, and the resulting assembly was housed in a central differential casing which was, itself, part of the complete rear axle casing. Components were machined in two side-by-side machine lines so that parts moved along in unison, and work handling was facilitated by overhead runways above the machines.

Initial boring and facing

The first operation on the axle casing comprised boring and facing the differential casing (No 4 Capstan lathe supplied by Alfred Herbert). Tools were mounted on an extension to the machine spindle, comprising a boring head and, behind it, a facing head.

Multi-spindle drilling

The next operation on the rear axle entailed drilling 0.5ins (12.7mm) holes for tapping in the differential casing for taking studs, using a standard Jones & Shipman pillar drilling machine fitted with a drill head carrying 12 spindles, the latter being driven from the standard machine spindle through spur gearing.

Axle shaft holes were then bored and, at the same time stud holes for the rear brake drums were drilled in flanges at each end of the rear axle casing. Also, two oil holes were drilled at an angle close behind the flanges into the axle shaft holes. The machine used was adapted from a lathe bed, in the middle of which was a fixture for locating the axle casing. A group of six drill spindles and a central boring spindle in each of two heads were used (one head for each end of the axle casing). Both heads moved towards each other simultaneously. After boring and drilling, relevant holes were tapped. Flange ends were turned to diameter and faced with the casing mounted in a Blaisdell centre lathe.

Duplex milling operations

For carrying brake lever brackets, seatings on each side of the axle casing were milled by a Kempsmith horizontal spindle milling machine, with a two spindle milling head. The axle casing was clamped such that both sides of the casing were milled concurrently. The final operation on the rear axle casing entailed tapping holes in the differential casing, and further drilling and tapping of holes towards each end of casing, carried out on two radial drilling machines supplied by Kitchen and Wade. The axle casing was placed in a jig which could be adjusted for use on six different types of axle casing.

Worm gear housing operations

The first operation on the worm gear housing entailed turning spigot faces and seats for worm wheel shaft bearing caps, carried out on a boring mill with two work tables, upon each of which a gear housing was mounted. After this, the spigot face was drilled with the same type of multi-spindle drill head used for drilling the corresponding face on the axle casing. Holes were of 33/64ins (13.1mm) diameter.

Self-contained multi-spindle drill heads

The only other operation on the worm gear housing was drilling, tapping and studding all holes other than those in the spigot or joint face, using a single spindle Cincinnati-Bickford pillar drill. The work was located on a trunnion type fixture to allow drilling from four different angles. Holes were drilled using a multispindle head, developed by Thornycroft, driven through gearing from the machine’s single spindle.

Cylinder blocks and liners

Thornycroft engines had separate cylinder blocks and crankcases, the former were of cast iron while the latter were of aluminium castings in two halves. Most types of engine had renewable cylinder bore liners and, in many cases, valve seats. Dry and wet liners were used. Dry liner wall thickness varied with bore diameter.

Machining liners

Liners were straight cylindrical sleeves with small locating flanges at each end. Liners were machined by facing and turning flanges, and boring to size, less 1/32ins (0.794mm) allowance for finish boring after liners had been pressed into place in the cylinder block. Additionally, the liner’s exterior was turned. Liners were brought to a finished state by grinding, and after boring, reaming and honing the cylinder block holes, liners were pressed into the block under hydraulic pressure. Thereafter liners were an integral part of the block, and cylinder bores were finished by boring to within 0.003ins (0.076mm) and then honing, finished bore limits being -0.000 to + 0.001ins (0.025mm) on all bore sizes.

Machining cylinder blocks

Machining operations were common to all sizes of cylinder block, and work started with milling top, bottom, end and side faces. The latter were finished direct by milling, while top and bottom faces were left with excess allowance of 0.005ins (0.127mm) for grinding to final size to give a good finish and gas tightness. Top and bottom faces were milled on a Cincinnati duplex milling machine. Work was held in a fixture common to all types of cylinder block.

Several rotary and traversing table surface grinding machines by the Lumsden Machine Tool Co were used. The work table of each machine was equipped with fixtures, which enabled more than one cylinder block for a particular type of engine to be machined at each setting. Alternatively, fixtures could be arranged so that several different faces on the same cylinder block were machined in order to produce a finished component each time the fixtures were unloaded.

Duplex spindle boring machine

After the cylinder block had been milled and ground, 18 stud holes were drilled in the bottom face, two being reamed for locating purposes for subsequent operations. Cylinders were rough and finish bored on a Thornycroft-developed boring machine, and spacing between this machine’s boring heads was adjustable to suit the engine type. The cylinder block was mounted under one set of spindles for rough boring and then transferred under a second set of spindles for finish boring, leaving an excess allowance of 0.003ins (0.076mm) for honing to size on a single spindle Hutto honing machine.

Five-way drilling machine

Valve seats and valve guide holes in the cylinder block were machined on a 12 spindle machine similar in design to the cylinder boring machine previously mentioned. For drilling remaining holes in the block, a special five-way machine developed by Thornycroft was used, with drill heads disposed in front of the four sides and over the top of the block. All heads worked together to drill 40 holes concurrently.

Gear box casing

Thornycroft vehicles were fitted with cast aluminium gearbox casings incorporating a clutch bell housing.

Gear box casing operations

The first operation comprised facing and boring the main shaft hole at the rear of the gearbox casing. After this, 16 holes of 15/32ins (11.91mm) diameter were drilled round the circular bell-housing flange, using a machine with an adjustable multi-spindle drill head developed by Thornycroft. Cutting speed was 120 feet/min (36.6m/min), and feed was by hand. The drilling machine could take different bell housing flange diameters. Open faces on the gearbox portion of the casing and clutch inspection cover face were machined on a vertical spindle milling machine supplied by Kendall & Gent. Finally, various holes were drilled, bored and reamed within the gearbox.


Gears were made from drop forgings of high grade alloy steels, varying in tensile strength according to the gear’s duty.

Gear operations

Machining operations started by drilling and facing on a box column drilling machine supplied by Jones & Shipman. The shank end of the drill was slotted to hold a facing cutter, which came into action as the drill passed through the work. After drilling, hole-sizing was carried out by broaching, following which the gear was rough and finish turned, using Lodge and Shipley Duomatic lathes which each handled a pair of gears.

Gear teeth were generated by the hobbing process on machines of various makes, and gears were hardened by heat treatment. After grinding internal and external diameters, teeth were finish ground on machines supplied by Lees Bradner.


Thornycroft engine crankcases comprised two aluminium castings and these were machined in such a manner as both parts may be regarded as one component.

Initial crankcase operations

The first operation for both crankcase castings entailed milling the joint faces using a milling machine supplied by Alfred Herbert. After this, top and bottom faces of the crankcase were machined, then holes by which both halves were held together were drilled, using a Thornycroft-built multi spindle drilling machine, with a fixed head mounting a cluster of 30 adjustable drill spindles. Holes were either 3/8ins (9.53mm) for tapping, or clearance, according to the crankcase member.

Indexing drill jig

Small holes were drilled in the top and side faces of the crankcase on a Cincinnati Bickford radial drilling machine. A Thornycroft-built four spindle boring machine bored holes for the main bearings, the latter being contained in the top half of the crankcase. Holes were also bored for the camshaft, starter motor support, etc. Various boring bars supported by fixtures at each end were driven by quick change couplings attached to the boring spindles.

Two way drilling

The clutch and timing gear housings at their respective ends of the crankcase were faced. Following this, the two faces were drilled simultaneously, using adjustable multi-spindle drilling heads, holes being drilled by traversing tables first towards one head and then the other.

The top half of the crankcase was fitted with main bearings and these were line reamed on a machine similar to that used for the boring operation (see above). Bearings were not subsequently bedded but were used as machined. Before fitting into the crankcase, main bearings were measured and graded into one of three classes varying between limits of 0.00025ins (0.0064mm). The crankshafts, which were bought in ready to use, and connecting rods were similarly treated. The crankcase was tested for timing gear centres. For this purpose shafts were inserted in the respective bores and on these accurately ground cast iron discs were mounted. Correct centres ensured that both discs just cleared each other and were designed to pass a 0.006ins (0.15mm) feeler gauge.

Engine testing

Dynamometers were used for testing all engines off the production line, the nature and duration of tests depending upon the conditions of a particular contract. Engine test equipment included eight electric dynamometers built by the Highfield Electrical Co, and installed by Heenan and Froude. Four of these dynamometers could test engines up to 100hp. Electrical output generated by the dynamometers from engines under test was added to the works supply. Dynamometers were also designed to act as electric motors for running engines in, under automatically fixed torque conditions. Power absorbed was measures on wattmeters.

A large proportion of Thornycroft vehicle production was supplied to the WO and other government departments at home and abroad, and one dynamometer was equipped for taking torque reaction measurements, using spring balances. This was done to meet WO test requirements, which specified that hp be measured by torque reaction reading.

Regardless of customer test requirements, engines that had passed through their tests were randomly selected from stock and, without any special preparation were subjected to a 24 hour non-stop run at full throttle at 2,000rpm. At the end of this test it was usually found that the difference in output did not vary by more that one per cent from normal. In all cases, after engines had been tested they were stripped down and finally adjusted before being mounted in a chassis. The latter were sent out for a road test carrying a full load and equipment for accurately measuring petrol consumption.

The Work Yards