Metal lathe

The design of lathes can vary greatly depending on the intended application; however, basic features are common to most types.

Better machines are solidly constructed with broad bearing surfaces (slide-ways) for stability, and manufactured with great precision.

The spindle runs in precision bearings and is fitted with some means of attaching workholding devices such as chucks or faceplates.

On older machines ('50s) the spindle was directly driven by a flat belt pulley with lower speeds available by manipulating the bull gear.

The bed is a robust base that connects to the headstock and permits the carriage and tailstock to be moved parallel with the axis of the spindle.

The leadscrew of accurate pitch, drives the carriage holding the cutting tool via a gearbox driven from the headstock.

[citation needed] When a lathe is installed, the first step is to level it, which refers to making sure the bed is not twisted or bowed.

The leadscrew will be manufactured to either imperial or metric standards and will require a conversion ratio to be introduced to create thread forms from a different family.

In its simplest form the carriage holds the tool bit and moves it longitudinally (turning) or perpendicularly (facing) under the control of the operator.

Usually, the compound rest has a protractor marked in its base (2b), enabling the operator to adjust its axis to precise angles.

The suite of gun boring mills at the Royal Arsenal, Woolwich, in the 1780s by the Verbruggan family also had slide rests.

A practical and versatile screw-cutting lathe incorporating the trio of leadscrew, change gears, and slide rest was Maudslay's most important achievement.

The image shows a reduction gear box (T2) between the handwheel and spindle, where large drills may necessitate the extra leverage.

It stands stationary from a rigid mounting on the bed, and it supports the workpiece at the rest's center, typically with three contact points 120° apart.

[3][4] Follower rests can provide support that directly counteracts the springing force of the tool bit, right at the region of the workpiece being cut at any moment.

The name bench lathe implies a version of this class small enough to be mounted on a workbench (but still full-featured, and larger than mini-lathes or micro-lathes).

The works would have one large steam engine which would provide power to all the machines via a line shaft system of belts.

Cone-head lathes usually had a countershaft (layshaft) on the back side of the cone which could be engaged to provide a lower set of speeds than was obtainable by direct belt drive.

At the same time the state of the art in gear and bearing practice was advancing to the point that manufacturers began to make fully geared headstocks, using gearboxes analogous to automobile transmissions to obtain various spindle speeds and feed rates while transmitting the higher amounts of power needed to take full advantage of high-speed steel tools.

It is essentially just a top-of-the-line center lathe, with all of the best optional features that may be omitted from less expensive models, such as a collet closer, taper attachment, and others.

There has also been an implication over the years of selective assembly and extra fitting, with every care taken in the building of a toolroom model to make it the smoothest-running, most-accurate version of the machine that can be built.

A gang-tool lathe is one that has a row of tools set up on its cross-slide, which is long and flat and is similar to a milling machine table.

The idea is essentially the same as with turret lathes: to set up multiple tools and then easily index between them for each part-cutting cycle.

Screw machines usually work from bar stock, while chuckers automatically chuck up individual blanks from a magazine.

Typical minimum profitable production lot size on a screw machine is in the thousands of parts due to the large setup time.

Once set up, a screw machine can rapidly and efficiently produce thousands of parts on a continuous basis with high accuracy, low cycle time, and very little human intervention.

These are exclusive to the hobbyist and MRO markets, as they inevitably involve compromises in size, features, rigidity, and precision in order to remain affordable.

[6] A lathe for large diameter, though short work, built over a recess in the floor to admit the lower part of the workpiece thus allowing the toolrest to stand at the turner's waist height.

For even larger diameter and heavier work, such as pressure vessels or marine engines, the lathe is rotated so it takes the form of a turntable on which parts are placed.

Oil country lathes are equipped with large-bore hollow spindles, a second chuck on the opposite side of the headstock, and frequently outboard steadies for supporting long workpieces.