PARTS OF A CENTRE

LATHE

1)BED The bed of the lathe provides the foundation for the

whole machine and holds the headstock, tailstock and carriage in alignment. The surfaces of the bed that are finely machined - and upon which the carriage and tailstock slide - are known as "ways".Some beds have a gap near the headstock to allow extra-large diameters to be turned. Sometimes the gap is formed by the machined ways stopping short of the headstock, sometimes by a piece of bed that can be unbolted, removed--and lost.Some very large lathes have a "sliding bed" where the upper part, on which the carriage and tailstock sit, can be slid along a separate lower part - and so make the gap correspondingly larger or smaller.

CONDITIONS TO BE SATISFIED BY A LATHE BED

It should be sufficiently rigid to prevent deflection.

It must be massive with sufficient depth and width.

It must resist the twisting pressure due to the resultant of two forces.

The be should be seasoned naturally to avoid distortion and warp.

LATHE BED

2)SADDLE

The casting that fits onto the top of the bed and slides along it is known, almost universally, as the "Saddle" - a self-explanatory and very suitable term. 

3)APRON The vertical, often flat and rectangular "plate"

fastened to the front of the "Saddle" is known as the "Apron" and carries a selection of gears and controls that allow the carriage to be driven (by hand or power) up and down the bed. The mechanism inside can also engage the screwcutting feed and various powered tool feeds, should they be fitted. The leadscrew, and sometimes a power shaft as well, are often arranged to pass through the apron and provide it with a drive for the various functions. The sophistication of the apron-mounted controls, and their ease of use, is a reliable indicator of the quality of a lathe. Virtually all screw-cutting lathes have what is commonly-called a "half-nut" lever that closes down one and sometimes two halves of a split nut to grasp the leadscrew and provide a drive for screwcutting.

APRON

4)COMPOUND SLIDE REST Sitting on top of the "Saddle" is the "Cross Slide" -

that, as its name implies, moves across the bed - and on top of that there is often a "Top Slide" or "Tool Slide" that is invariably arranged so that it can be swivelled and locked into a new position.

When two slides are provided (or sometimes, on watchmaker's lathes, three) the complete assembly is known as the "Compound" or "Compound Slide" or even "Compound Slide-rest". Some makers have been known to label the "Top Slide" as the "Compound Rest" or even the "Compound Slide" - but as "to compound" means the 'joining of two or more' - not 'one' - this use of the term in incorrect. The top and cross slide together should be referred to as "the compound".

COMPOUND SLIDE REST

5)CARRIAGE

The whole assembly of  Saddle, Apron, Top and Cross Slide is known as the "Carriage". Some American publications (even makers' handbooks) have been known to casually refer to this as the "Saddle" - but this incorrect.

6)HEADSTOCK The lathe Headstock used, at one time, to be

called the "Fixed Headstock" or "Fixed Head", and the rotating shaft within it the "Mandrel". Today the mandrel is usually called the "Spindle", but this can cause confusion with the tailstock, where the sliding bar is known variously as the "ram", "barrel" - and "spindle".The headstock is normally mounted rigidly to the bed (exceptions exist in some production, CNC, automatic and "Swiss-auto" types) and holds all the mechanisms, including various kinds and combinations of pulleys or gears, so that the spindle can be made to turn at different speeds.

HEADSTOCK

7)HEADSTOCK SPINDLE The end of the headstock spindle is

usually machined so that it can carry a faceplate, chuck, drive-plate, internal or external collets - or even special attachments designed for particular jobs. In turn, these attachments hold the workpiece that is going to be machined.

HEADSTOCK SPINDLE

8)BACKGEAR As its name implies, "backgear" is a

gear mounted at the back of the headstock (although in practice it is often located in other positions) that allows the chuck to rotate slowly with greatly-increased torque (turning power). Backgeared lathes are sometimes referred to a "BG" or "BGSC" - the latter meaning "backgeared and screwcutting".

BACKGEAR

9)LEADSCREW Originally termed a "master thread", or

described as the "leading screw", but now always referred to as the "leadscrew", this is a long threaded rod normally found running along the front of the bed or, on some early examples running between the bed ways down the bed's centre line. By using a train of gears to connect the lathe spindle to the leadscrew  - and the leadscrew to the lathe carriage - the latter, together with its cutting tool, could be forced to move a set distance for every revolution of the spindle.

LEADSCREW

10)TAILSTOCK The Tailstock was once known in England as the

"loose stock",  " Proppet head" or "loose head" - the latter old-fashioned term being used by Harrison and other English firms in some of their advertising literature until the early 1970s. The unit is arranged to slide along the bed and can be locked to it at any convenient point; the upper portion of the unit is fitted with what is variously called a "barrel", "spindle" "ram" or "shoot" that can be moved in and out of the main casting by hand, lever or screw feed and carries a "Dead Centre" that supports the other end of work held (by various means) in the headstock. 

TAILSTOCK

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