1. Field of the Invention
This invention relates to a collar for mounting a radially separable circular cutting tool such as a split saw blade on a rotatable arbor and more specifically to a collar that will mount and hold the split saw blade in precise installed concentricity with the arbor.
2. Background of the Invention
In industries such as woodworking it is a normal practice to mount a plurality of individual circular cutting tools such as saw blades on a single driven arbor in axially spaced relation to each other. Such arrangements are commonly referred to as gang saws and a gang saw may include as many as twenty or thirty circular saw blades on a single arbor eight to ten feet in length. The purpose of a gang saw is to simultaneously cut a single wide piece of work stock into a plurality of narrower strips with only a single pass of the work stock through the gang saw. The saw blades comprising the gang saw must be removable from the arbor for replacement when damaged or for servicing such as sharpening. Because there is a plurality of bearing supports for the arbor and a drive connection to the arbor, it is not practical to slide all of the individual saw blades off the arbor when servicing is required, and even if done, it is a difficult and slow process when twenty or thirty blades are involved. The practice most often followed is to have a second replacement arbor completely assembled with bearings and sharpened saw blades. When the existing blades in the gang saw require service, the arbor is removed with all the blades thereon and the replacement arbor put in its place.
The disadvantages of removing the entire arbor are many. The user must, of course, incur the expense of purchasing two arbors, two sets of bearings and two sets of saw blades. The arbor may be up to 10 feet in length and with saw blades and bearings thereon, weigh 300 to 500 lbs. This weight requires a winch and two service people for removal. Obviously such service is slow, difficult and results in substantial downtime with subsequent lost production. There are also numerous occasions when only one circular saw in the center of the gang saw is damaged. Removal of the entire arbor to service only one blade is very unsatisfactory from a cost of service standpoint.
To minimize the need to remove the arbor or a plurality of the saw blades to get at one damaged blade, it is known to split each circular saw blade diametrically into two radially separable semicircular sectors. Such a blade is called a split saw blade. The arbor in turn is provided with a plurality of special collars, one for mounting the halves of each split saw blade on the arbor. The blades can be bolted to a flange of the collar or the collar may have axially extending driving pins therein that are radially spaced from a center arbor bore defined by the split saw blade sectors. In this latter case the split saw blades have sets of pin receiving apertures enabling them to be slid axially onto the driving pins of an open collar, and then clamped into the collar by a suitable clamping means such as a nut. The use of split saw blades and collars solves the problem of how to remove an individual saw blade without removing the entire arbor or disturbing any other saw blades thereon. However, split saw blades also introduce new problems such as concentricity and ease of removal and installation of the split saw blades.
At this point it will be helpful to define the various meanings of the word "concentricity" because the word "concentricity", when used alone relative to a saw blade, can imply several different meanings. Every tooth of a newly manufactured circular saw blade is at precisely the same distance from the center of the arbor bore in the blade. This will be referred to as "manufactured concentricity". The split saw blade sectors while being installed can move radially relative to each other and to the arbor shaft or collar and when installed normally have a concentricity which is less accurate than the manufactured concentricity of the new split saw blade. This will be termed "installed concentricity" or "installed nonconcentricity". When split saw blades are removed for sharpening, they are clamped in a jig and sharpened concentric to the jig. This is termed "resharpened concentricity". The goal, of course, of all split saw installations is to provide an installed concentricity which is as close as possible to the manufactured concentricity or the resharpened concentricity.
It is extremely important that the split saw blade sectors be installed and held in installed concentricity with the arbor. Poor installed concentricity generates a host of long-standing, well known problems, all of which have expensive consequences. A nonconcentric blade has some teeth closer and some teeth farther from the arbor center, creating an imbalance. High speed rotation of an unbalanced blade causes it to "jump" as it rotates around the arbor center resulting in: arbor vibration; accelerated arbor bearing wear; more arbor fatigue breakage; uneven wear of the saw teeth because teeth closest to the arbor take light or no cuts while those teeth farthest from the center take heavy cuts and do most of the cutting; generation of heat in the saw blade making it likely that the blade will distort; and more noise. Distortion requires saw smithing--the hammering of a blade back into a flat condition--and this is extremely difficult with split saw blades. Vibration due to installed nonconcentricity causes the split saw blades to deviate from a true cutting path resulting in more chattering of the work piece and a rougher finish to the cut edges. The vibrating saw blade also cuts a wider kerf which creates more waste material and increases the power requirements of the gang saw.
An unsplit conventional circular saw blade with a center bore includes teeth thereon that have manufactured concentricity with the arbor on which it is mounted. An unsplit circular saw blade does not experience the problems discussed above because it cannot be radially separated to present installed nonconcentricity. Further, it is easy to manufacture an arbor bore in the circular blade that has a close installation tolerance, the clearance between the arbor and the blade bore, which will permit an easy sliding installation of the blade onto the arbor because the blade need only index itself to a single reference location provided by the arbor. This will be called "installation tolerance" and every blade must have this tolerance.
A split saw blade, on the other hand, is inherently different in that the arbor bore is radially separable. Because the split saw blade comprises two independent sectors, it has always been thought necessary that each sector must have a plurality of reference locations to enable it to be accurately installed on the arbor. Therefore it has been the practice to provide each sector with two or more reference locations to facilitate its installation in the collar. Specifically, prior art collars position each of the blade sectors relative to the center of the arbor axis by indexing each blade sector on a plurality of reference locations comprising the arbor and usually two driving pins or mounting bolts. Thus, normally there are three reference locations in a collar which must be accommodated by each blade sector. In theory it would seem simple to so precisely locate the sets of driving pin apertures and arbor bore in the split saw blade halves that installed concentricity will be the same as manufactured concentricity when the split saw sectors are slid onto the collar pins. In practice, with a multiplicity of reference locations it has proved to be impossible to achieve an installed concentricity which is the same as manufactured concentricity. As discussed above, the split saw blade sectors must be able to be easily slid axially onto and off of the driving pins and fit around the arbor or a center shaft of the collar, and this necessitates an installation tolerance between a plurality of reference locations such as the pins, saw blade pin holes and arbor. This installation tolerance always results in some looseness or play between components. When two saw blade sectors each have a plurality of reference locations that must be accommodated, a greater amount of play is required and the problem of achieving installed concentricity is greatly complicated. This play permits the saw blade sectors to inadvertently slip radially outward or inward while being clamped into the collar. Experience shows that it is not possible for the installers to know exactly where the blade should be located for best concentricity and further even if they did know they cannot force and hold the split saw blades in installed concentricity during installation. The split saw blades are large, weigh up to six pounds and normally require two service people for installation and removal. The installers are under pressure to get the job done quickly. One sector or the other invariably slips. Clamping jigs to hold the sectors are unwieldly, tend not to be used because they slow down the service people and, even when used, tightening the collar clamping means frequently causes the sectors to shift a minute unnoticed amount within the jig. The incredibly close tolerances that would be required to eliminate this play, while still allowing a free and easy sliding installation of the split saw blades on a plurality of reference locations, would increase the manufacturing costs to prohibitive levels. Further, with such close tolerances, minute nicks and burrs on the pins and saw blade apertures would prevent the blade sectors from slipping easily onto the pins.
To minimize manufacturing costs and the amount of installed nonconcentricity, while providing safety, it is known to manufacture a conventional circular saw blade with an arbor bore; mount an axially projecting circular hub on at least one side of the blade around the arbor bore usually by riveting; precisely machine this hub; and then cut the blade diametrically into two halves to produce a hubbed split saw blade. The collar for mounting hubbed split saw blades on the arbor is provided with precisely machined internal annular trepanned recesses into which the hubs fit. The outer periphery of the hub will abut the inner periphery of the trepanned recess to limit the amount of installed nonconcentricity that can occur during installation. Such a collar is termed a trepanned collar. Installing the hub on the blade and machining it increases the cost of the blade by as much as 50%. While the operating safety of such an assembly is excellent, installed concentricity remains poor because suitable installation tolerances must still be provided to allow the hub of each split saw blade sector to be easily slid into the trepanned recess in the collar. Two service people are still required, one to try to hold the blade halves and the other to tighten the collar. When removing the blades, one service person releases the collar while the other holds the saw blades to keep them from falling out of the collar onto the bed of the machine with probable resultant chipping or breaking of the carbide teeth on the sectors. The hubbed split saw presents installed concentricity problems because each half of the hubbed saw blade will only compressively seat against the inner peripheral surface of the trepanned recess in the collar when substantial centrifugal force is applied and this force is not created during normal static installation nor during placement of the sectors in a sharpening jib. Invariably during installation, gravity causes one of the sectors to move inward toward the arbor while the other sector moves radially outward against the inner periphery of the trepanned recess of the collar resulting in installed nonconcentricity.
Mounting a new split circular saw blade so that it will have installed concentricity has in the past proven to be virtually impossible. The use of the plurality of pins or bolts and resultant play required by installation tolerances makes it impossible to accurately position split saw blade sectors by indexing them with reference to the pins or bolts. Therefore, prior collars have not permitted the translation of the manufactured concentricity into installed concentricity. Further, when the split saw halves are to be resharpened they must then be clamped into a sharpening jig which holds the split saw blade halves concentric with a center. However, the jig also must have the same plurality of reference locations but they are never quite the same dimensionally as those of the collars on which the blade halves are mounted and the installed concentricity of resharpened blades is not as good as the resharpened concentricity. The only technique heretofore known to maximize installed concentricity is to sharpen or resharpen the split saw halves while they are clamped in the same collar that is used to mount them when they are in actual use. This is unsatisfactory because when resharpening is required the end user must remove both the collar and the blades from the arbor and send them to the resharpener for sharpening. This is very time-consuming and adds to the expense of service, but this technique is still actually being used in some instances in an attempt to solve the installed concentricity problem when a collar must be used. After sharpening, the end user must reinstall the collar without loosening or removing the split saw blades from the collar as such removal will destroy the installed concentricity of the split saw blades.
The prior art discloses various arrangements for adjusting the position of an unsplit circular cutting tool or the cutting teeth thereon relative to the arbor on which the blade is mounted. U.S. Pat. No. 3,656,393 to Willy J. Goellner discloses a carbide blade locking device wherein two driving and locking pins each have an eccentric head portion engaging apertures in an unsplit circular saw blade to adjust the entire unsplit saw blade circumferentially into firm engagement with the pins to prevent any backlash of the blade. U.S. Pat. No. 139,544 to S. W. Clemmens discloses a circular saw blade mounting collar having adjusting screws in spaced parallel relation to the arbor for tilting an unsplit circular saw blade into a perfect right angle relationship to the axis of the arbor. U.S. Pat. No. 4,706,531 to Wilfried Blauhut et al discloses a device for cutting strand shaped material wherein the cutting angle of the cutter blades can be individually adjusted.
This prior art does not deal with the problem of mounting the radially separable sectors of a cutting tool on an arbor so that the installed concentricity of the sectors will be virtually the same as the manufactured or resharpened concentricity of the sectors.
Split saw blade installations and their associated problems as discussed above have existed for more than 35 years without a satisfactory solution. As a matter of historical fact, the prior art relating to mounting unsplit saw blades did not render the present invention obvious to those skilled in the art because the problems persisted unsolved and troublesome for at least 35 years. Therefore in the present state of the art relating to the mounting of split saw blades prior to the present invention, the problem of providing an installed concentricity for split saw blades still exists inspite of long-standing efforts to eliminate it. Because of a lack of a solution, the manufacture and servicing of split saw blades remains very expensive and the known disadvantages are endured by end users of gang saws.