Lathe Workholding

Spindle Nose

Almost all workholding on the lathe starts by adapting to the lathe spindle nose. There are several standard spindle nose configurations in use in modern lathes. These include the threaded spindle, D-Series (Camlock), A series (short taper), L-Series (Long Taper) and DIN 55027 (ISO 702/III). See also ANSI/ASME B5.9 “Spindle Noses.”

Many spindles are fitted with Morse tapers on their interior bore to allow for additional workholding configurations.

ANSI/ASME B5.9

A D1-4 Spindle with a MT5 Tapered Bore

Morse Tapers

Many lathes are fitted with Morse tapers for mounting tooling and workholding devices.

Centers

Centers are an accurate way to hold a workpiece. They consist of a conical end that is precision ground to a point. The typical included angle of a center is 60°. A special drill bit called a center drill is used to drill the conical hole required for use with centers.

Live Center

Live centers are designed with ball bearings or other rolling elements to reduce the friction of spinning. Live centers are commonly used in lathe tailstocks to support long workpieces.

Live centers rotate with the work.

Dead Center

Dead centers do not rotate with the workpiece. Therefore, they must be well lubricated to prevent excessive heat buildup. Live centers tend to be more common for most applications.

Dead centers do not rotate with the workpiece.

Specialty Centers

Turning Between Centers

One of the most accurate and repeatable ways to hold a workpiece in a lathe is to position it between centers. However, the convenience of other methods means this is rarely done.

Turning Between Centers

Lathe Dogs and Drive Plates

In order to transmit torque from the spindle to the workpiece, a separate device, called a lathe dog or lathe carrier is used. The lathe dog is driven by a drive plate affixed to the spindle nose.

A lathe dog used in conjunction with a drive plate.
A typical lath dog/drive plate setup.

Chucks

One of the most popular ways to hold work on in a lathe is by using chucks or jaw chucks. Chucks can have 2, 3, 4, or 6 jaws, however 3 and 4 jaw chucks are the most popular. Chucks can either be self-centering or independent and may be operated manually or with hydraulic or pneumatic power.

Self Centering

Self-centering chucks allow fast loading and unloading of round workpieces when accuracy and repeatability are not critical. When tightening a self-centering chuck all of the jaws move together. The scroll chuck is the most common type of manually operated self-centering chucks.

Chucks that are not made for a particular spindle may be adapted using a back plate.

A typical 3-jaw, self-centering scroll chuck.

Chuck Jaws

See also: Chuck Jaws (main article)

Chuck jaws can be single-piece or can be two-piece, at top jaw mounted on master jaws. Chuck jaws can be reversed to clamp on the outside of a part, or can clamp outwardly to fixture ring-shaped parts.

Independent Jaw

Independent jaw movement is typical of 4 jaw manual chucks. Independent movement of the jaws allows an operator to adjust the concentricity of the workpiece to eliminate runout or to machine eccentric features. Independent chucks can also grip a variety of non-round workpieces.

A 4-jaw independent chuck holding a rectangular workpiece.

Soft Jaws

Soft jaws are available that can be machined to fit oddly-shaped workpieces that cannot be fixtured using standard jaws.

Collets

Most lathes can be adapted to hold collets in their spindle. Collets are precision workholding devices that consist of a segmented cylindrical body with a tapered end. Collets are tightened by pulling them into a tapered bore by means of threaded shaft or tube called a drawbar or drawtube.


Collets are designed to fit a narrow range of sizes, so individual collets are required for different size work. Collets can be purchased to fit a wide variety of workpieces, and so-called emergency collets can be custom machined to fit an even wider range of workpieces.

A 5C Collet

Because of the convenience of having a continuous hole through the spindle bore, lathe collets are usually tightened using collet closer fitted with a hollow drawtube.

When the drawtube pulls on the collet, it forces the tapered fingers against the workpiece.

Sometimes collets are fitted with stops that position the work axially.

A collet stop positions the work axially

Faceplates

Irregular workpieces can be clamped to faceplates.

Irregular workpieces can be mounted to faceplates.

Arbors & Mandrels

For turning hollow parts.

Expanding mandrels such as this one can hold thin-walled hollow cylindrical work.

Steady Rests

For long workpieces, steady rests may be used either with or without a center. Steady rests mount to the bedways and are stationary.

Follow Rests

Long workpieces, rides along carriage.

A follow rest is attached to the carriage and moves along with the cutting tool.