This invention relates generally to a chuck assembly for use in a veneer lathe system. More particularly, it relates to a chuck assembly having retractable inner and outer chucks for allowing the peeling process to peel large plyblocks down to a minimum core diameter.
One step in the manufacture of plywood is the production of the thin veneer sheets. Traditionally in the manufacture of commodity type plywood, usually from typical softwood species such as Douglas fir and the Southern pines, a rotary type veneer lathe is used. Briefly, a plyblock (usually an 8'6" long, fairly large log segment) is charged into the veneer lathe and chucked for spinning and peeling. The chucks support the plyblock and apply torque to turn it as it is peeled down by the knife moving inwardly toward the turning axis.
Over the years, the average block diameter being charged into the veneer lathe has descreased as the supply of large logs has decreased. Consequently, in today's veneer manufacturing facilities, the lathes must be capable of accommodating smaller plyblocks while maintaining an economic rate of production. As the cost of the incoming raw material (the plyblock) continues to escalate, it also becomes imperative to generate the maximum amount of veneer out of any particular plyblock that is charged into the lathe. In the past, for example, when large plyblocks were consistently available at a reasonable cost, there was not a great incentive to reduce the core diameter to lower levels. As previously pointed out, however, with the increasing cost in raw material, there is now an incentive to peel a plyblock down to the smallest feasible diameter.
Of course, as it will be recognized by those skilled in the art, one problem in peeling small logs or in peeling large logs down to a smaller core diameter, is that any chuck assembly within a veneer lathe must be able to function properly and not interfere with the action of the knife. It is known in the industry to utilize inner and outer chucks mounted on laterally movable spindles so as to be retractable, thereby accommodating the larger incoming logs while allowing the lathe and knife to peel the block down to a relatively small core diameter by having the large outer chucks retract, leaving the smaller inner chucks to continue turning the block. The inner and outer chucks will normally have a plurality of chisel-like teeth mounted on their outer faces for gripping and turning purposes.
During the typical plyblock charging step, an individual block will be appropriately positioned within the lathe between the chuck pairs which are then substantially simultaneously moved toward the log and grip it. The spindles are then caused to rotate in a controlled manner, thereby spinning the block. As the knife moves radially inwardly and begins generating a ribbon of veneer, both chucks will be driving the block. As the knife begins to approach the outer periphery of the large chucks, suitable sensing means will detect the presence of the large chucks and generate a signal to cause the large chucks to retract. The small chucks will continue turning the block and as the knife approaches the periphery of the small chucks, a signal will be generated to cause the knife to return and the small chucks to retract, thereby dropping the resulting core.
It is very advantageous to peel a plyblock down to a core diameter on the order of 3". Typically, the best available chucking systems for veneer lathes will result in a core diameter which is approximately 4" in diameter, thereby leaving a considerable amount of what could otherwise be converted to veneer on the core. It does present a problem when peeling plyblocks down to such a small diameter in that oftentimes the chucks will split the ends of the block and in some instances "spinout" will occur, which is a situation where the chucks have so much torque applied to them they spin within the block as the knife exerts its cutting force. Neither of these conditions is desirable and both result in a loss in usable veneer from the plyblock. Thus, in designing a chucking system for small logs and for peeling down to small core diameters, any resulting chuck structure should reduce the occurrence of both core spinouts and split ends.
In addition, any chucking system must be designed with ease of maintenance in mind, particularly when a dual chucking system is utilized where the small chuck slides within a bore of a large chuck. Oftentimes, teeth are broken and either the small chuck or the large chuck must be removed from the overall chucking system for maintenance or replacement. It thus becomes necessary to design the chucking assembly for quick removal and replacement.
Thus, from the foregoing, one object of the present invention is to allow the production of usable veneer from plyblocks down to a core diameter on the order of 3" or less.
Yet a further object of this invention is to provide a small log chucking system that has reduced spinouts and core splitting at the ends.
Yet a further object of this invention is to provide ease of maintenance when either the small or large chuck must be repaired or replaced.
These and many other objects of the present invention will be better understood and fully appreciated when reading the specification to follow in conjunction with the attached drawings.