Woodworking – Process – Mechanical cutting or shaping
Patent
1996-09-04
1998-03-03
Bray, W. Donald
Woodworking
Process
Mechanical cutting or shaping
144 4, 144 2413, 1442088, B27L 100, B27M 100
Patent
active
057224757
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates especially to machining logs with natural shape such as those used for poles and log houses. The method and device of the invention enable flexible adjustment of working parameters during the machining operation.
BACKGROUND AND PRIOR ART
Machines of hollow-rotor type are known and widely used for debarking of logs. Dressing of poles is done by rotating the log rotates. Due to difficulties in controlling the centrifucal forces, the performance is limited. When the length and bow of the log increases, the hollow-rotor principle becomes advantageous also in dressing the logs. As in such a case the rotor speed must be kept at a relatively low level, the best surface finish is achieved by using fast rotating cutting heads. Cutting heads are attached to supporting arms which are pivoted at the rotor disc and turn the cutting heads against the log substantially in a radial direction in relation to the log. Owing to requirements related to balancing and efficiency, the number of arms with corresponding cutting heads is normally two at the minimum. The arms let the cutting heads float against the log under a force, produced, for example, by springs, counter weights or such. The drive for rotating the cutting heads is obtained simply from a wheel attached a stationary body by means of a gear-chain-or belt transmission. When rotating, the rotor disc also provides drive for the attached power transmissions of the cutting heads, too. A typical basic solution is described in a patent publication DE 2027399.
Hollow-rotor lathes with rotating cutting heads have not proven popular due to limitations related to solutions of the prior art, especially due to poor controllability. Practically the only easily controllable feature has been the longitudinal feed rate. This isn't enough. In pole dressing the diameter of the very same pole may range within 15-35 cm. Butt flare, bow and other irregularities increase the variations further. Therefore a possibility to adjust the rotor speed 1s necessary. But this changes the speed of rotation of the cutting heads affecting the quality and efficiency of machining very adversely.
When initiating the machining the cutting tools climb on the log in a screw form of movement. The method is widely used in debarking machines and described e.g. in patent publication FI 28928. The shapes of cutter supporting arms which enable the climbing, have been described in numerous patent publications e.g. FI 35237. In debarking machines climbing along the guidance of the supporting arm is a straight forward and practical way. The parent publication FI 81993 describes a similar solution adapted to a lathe. In such case the mass of the cutter supporting arms should be kept low, however, they must be strong enough. Because in practise both requirements are difficult to fulfil simultaneously, is desirable to limit the impact force applied on the supporting arms.
During the machining, especially when dressing poles, it is frequently necessary to change the cutting depth even within the range 1-10 mm along same pole. With the hollow-rotor lathes of the prior the cutting depth can be changed by means of an adjustable follower which, however, cannot be adjusted during the machining operation. Furthermore a follower of the prior art forces the cutting head to jump up when encountering local surface irregularities, such as poorly sawn branches, which worsens the surface finish. Several patent documents e.g. DE P 2320450.4 ( FI 1184/74), FI 40044 describe various methods for adjusting the force applied on cutting heads to push them against the log. The adjustment can be executed even during machining operation. By this way, however, the cutting depth cannot be adjusted accurately enough.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a system in which the drawbacks above can be eliminated by employing non-sophisticated techniques.
The system according to the invention enables maintaining constant rotational speed at the cutting heads ev
REFERENCES:
patent: 2646092 (1953-07-01), Kolpe et al.
patent: 2767750 (1956-10-01), Skwart
patent: 2779363 (1957-01-01), Laughton
patent: 2799304 (1957-07-01), Stewart
patent: 3789893 (1974-02-01), Carson et al.
patent: 3913644 (1975-10-01), Braun
patent: 4303111 (1981-12-01), Neville
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