Design for Manufacturing: Turned Part Style Selection

This article provides background and general best practices in selecting turned parts manufacturing systems.

Turned parts are those created from rotating a work-piece in order to subtract material from it using cutters. The work-piece is rotated about its center axis via a spindle. Turned work-pieces may be subjected to facing, straight turning, taper turning, grooving, cutoffs, threading, and many others.

In order to properly design an economical part, engineers must consider the method of subtractive manufacturing to be used on the part. Engine lathes are the least expensive and lowest quality option. The tool acts parallel and transverse to the axis of rotation of the work-piece with cutting tools mounted to turrets.

Turret lathes, sometimes referred to as “hard-screw machines,” utilize a cutting method where cutters are mounted on a hexagonal turret on a lathe bed. This turret is mounted to a saddle which is power driven down the lathe. This system is more expensive than the engine lathe but tends to produce parts faster.

CNC machines utilize numerical control recipes to drive a cutter through a pre-programmed sequence of actions as a work-piece is rotated on a lathe. CNC machines may act just through recipes or utilize a computer feedback system to ensure a higher quality part. CNC-style machines are much more expansive than turret lathes but have extremely high repeatability and speed.

Spindle chuckers operate by inserting the work-piece to a special chuck system. The cross-slide and end-turret tools automatically work the part once manufacturing has begun. These systems may use one or more chuckers to improve speed. Chuckers are both the most expensive tooling system and the fastest when it comes to turned parts and products.

While designing a turned part…

(a) Use engine and bench lathes for very low to low quantity production runs.
(b) Use turret lathes and tracer lathes for low to medium quantity production runs.
(c) Use numerically controlled and computer controlled lathes for low to medium quantity production runs.
(d) Use single-spindle chuckers for medium to high quantity production runs.
(e) Use multiple-spindle chuckers for high to very high quantity production runs.

By using this rule, economic selection of turning-machines for use in production is improved. This rule economizes manufacturing flow time and tooling costs to achieve the best overall solution.

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