2.1. Chucking Facilities for Workpieces

Turning out differently shaped workpieces and the utilisation of various kinds of materials presupposes the employment of various chucking facilities for clamping the workpieces to the machine spindle.

A number of frequently used chucking facilities feature among the basic accessories of a wood turning lathe. Further chucking devices can be provided for special processing technologies.

Chucking devices for long trunk turning

Trifurcatel

The trifurcate consists of a centre point and two driving spikes. The workpiece is clamped between the trifurcate and the tailstock centre. Thereby, the workpiece is fixed to the trifurcate with a light hammer blow.

Avoid splitting the workpiece at all costs. Otherwise the workpiece breaks during processing - danger of accidents -.

Turning whilst employing this chucking method is termed “turning between the centres” and is mainly utilised for processing longer workpieces.

Figure 2 - Trifurcate

Tongue or hollow chuck

This serves to chuck short trunk pieces without using the tailstock centre. By means of the previously twisted tenons the workpiece is driven into the conical bore of the chuck. The workpiece fits more snugly is the tenons are moistened somewhat beforehand.

Tongue and hollow chucks can also be used for certain hard wood turning operations. Turning without a tail-stock is known as “free-hand turning” or “overhead turning”.

Figure 3 - Hollow chuck with fastening screw thread

Figure 4 - Hollow chuck for clamping into a three-jaw chuck

Jaw chuck

Three- and four-jaw chucks can be used for chucking both long trunks and cross pieces. Jaw chucks comprise two sets of chucking jaws:

- a set of chucking jaws to chuck thin or hollow workpieces
- a set of chucking jaws to chuck thick workpieces.

When chucking heed the differing compressive strengths of the woods in various grain directions. During turning operations the workpiece must not be chucked again otherwise it no longer runs exactly true.

Figure 5 - Three-jaw chuck

Figure 6 - Internal jaws

Figure 7 - External jaws

Chucking facilities for cross piece turning

Screw chuck

The screw chuck augments the jaw chuck and is subsequently supplied for the driving or face plate. It comprises multi-layer wooden disks. This wooden disk is attached to the envisaged chuck and then level-turned. An inserted wooden screw for chucking the workpiece is in the centre. During turning the chuck cannot absorb too great chucking forces.

Figure 8 - Screw chuck

Driving and face plate

Bigger, flat workpieces can be attached to these chucking facilities by means of wooden screws. Beforehand the holding points are marked on the workpiece. Thereby, ensure that the screw holes do not impair future utilisation. If the workpiece diameter is less than that of the plate a 5 mm or so thick dummy disk is positioned between the workpiece and the chucking device. Thereby the workpiece narrow surface can be processed without damaging the disk.

Figure 9 - Chucking plate, faceplate

Why are different chucking facilities used for turning?
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When is a trifurcate used as a chucking means?
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Why must the workpiece not split when hitting the plugging chisel grippers?
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Why should be jaw chuck not be rechucked during turning operations?
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What is the task of the face plate?
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