When to Utilize Chucker Mode

A handy reference guide

In a typical Swiss (sliding headstock) lathe, the bar stock is supported by the guide bushing with cutting tools located as near to the bushing as possible. The bar is fed through the tool(s) with all cutting operations performed at the most rigid point. Cutting forces are absorbed by the guide bushing, preventing distortion in the work piece. This is especially important for long-thin work pieces with a length to diameter ratio of at least 3:1.

Cross-section diagram of guide bush and headstock

The OD of the work piece rotates inside the guide bushing, exposing the ID of the guide bushing. The length between the turning tool and the opposite ID of the guide bushing remains constant. If the bar stock is even slightly elliptical (we recommend centerless ground stock) the final product will be elliptical as well.

Guide Bushless Type

Eliminating the guide bushing and bringing the face of the collet chuck into the toolzone effectively converts the machine to a chucker.

Cross-section diagram of chucker and headstock

Ideal for shorter parts: Guide bushless can be ideal for parts with length to diameter ratios less than 3:1.

Cross-section diagram illustrating diameter to length ratio

Centerless Ground Stock Not Required: The bar stock is gripped by a spindle collet chuck, and is not supported with a guide bushing. Bar stock roundness does not affect the machined accuracy and cold drawn bar stock can be used.

Characteristics

Characteristic Guide Bush-less Type Gude Bush Type
Work piece length Short work piece (Length should be less than 3 times OD) Both short and long
Bar stock
  1. Accuracy does not affect.
  2. The tolerance of OD is better than h9.
  3. Cold drawn bar can be used.
  4. Uses less stock.
  1. Accuracy affects machined accuracy.
  2. The tolerance of the OD is better than h8.
  3. Ground bar stock.
Machined roundness Excellent Better
Machined concentricity Excellent – provided high quality collet chucks are used. Excellent – Dependent on the geometrical accuracy of bar stock and the run out of the guide bushing.
Bar remnant Small Equal to headstock stroke
Spindle speed Equivalent Equivalent
Machining Method Rough turning and finish turning can be performed similar to conventional lathe. The OD must be turned in one pass. Each OD is turned gradually.