 |  | Operations on Wood Turning Lathes - Course: Mechanical woodworking techniques. Trainees' handbook of lessons (Institut für Berufliche Entwicklung, 19 p.) | ||
 |  | 2. Assembly of a Lathe | ||
|  | (introduction...) | ||
| | 2.1. Chucking Facilities for Workpieces | ||
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Figure 1 - Wood turning lathe
1 cheeks, 2 stand, 3 spindle stock, 4 spindle, 5 chucking device, 6 gears, 7 motor, 8 tailstock, 9 tailstock centre, 10 support strip
The basic machine frame consists of two cheeks to which all the other elements have been attached. The cheeks hinge on two stands, the most important machine part is the headstock. It has been arranged on the left end of the cheeks and contains the spindle to which various chucking aids can be attached. The spindle is driven via gears from the motor. The gears make possible a rotational speed alignment to the respective workpiece diameter. A tailstock with tailstock centre serves as end support to the chucking device when processing longer workpieces. The turning tools held by hand are placed onto the support strip which can be adjusted in three directions and set in line with the respective tasks in hand.
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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