Patent Publication Number: US-RE35258-E

Title: Counterbalanced reciprocating mechanism

Description:
This invention relates to reciprocating saws of the type using an eccentric drive. Saws of this type develop considerable vibration. This invention is directed to reducing such vibration. 
     CROSS REFERENCE TO COPENDING APPLICATION 
     My application Ser. No. 541,093 filed Jun. 20, 1990, .Iadd.now U.S. Pat. No. 5,025,562, .Iaddend.as a continuation-in-part of Ser. No. 487,219 filed Mar. 1, 1990, .Iadd.now abandoned, .Iaddend.shows an in-line saw using a counterbalanced wobble plate drive. 
     SUMMARY OF THE INVENTION 
     This invention provides a pinion gear driving a crown gear which has an eccentric drive to the shaft on which a saw blade is mounted. The crown gear also has an eccentric drive to a counterbalance, the saw blade and the counterbalance reciprocate 180 degrees out of phase, thus essentially eliminating all vibration. 
     More specifically, this invention provides an eccentric drive to a saw blade to reciprocate the saw blade while at the same time reciprocating a counterbalance. The eccentric drive of the saw blade is somewhat conventional. The spindle which supports the saw blade reciprocates inside a tube fixed in the housing. A counterbalance mass reciprocates on the tube and is prevented from rotating about the tube. The crown gear is provided with a cylindrical drive which is eccentric to the center of the crown gear. This cylindrical circular drive engages the counterbalance which, as noted, is constrained to reciprocating motion. The momentum of the counterbalance and the combined momentum of the spindle and a typical saw blade are essentially equal so the vibration is cancelled. Material is removed from the crown gear and cylindrical drive member to ensure that the crown gear, the eccentric drive and the cylindrical drive are balanced and do not set up lateral vibration. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevation view of a reciprocating saw provided with this invention. 
     FIG. 2 is a vertical section through a portion of the saw shown in FIG. 1. 
     FIG. 3 is a horizontal view taken on line 3--3 in FIG. 2. 
     FIG. 4 is an exploded perspective view of the main parts of the drive for the spindle and the counterbalance. 
    
    
     DETAILED DESCRIPTION OF THE DRAWING 
     The reciprocating saw shown in the drawings has a gear case 10 on the front of handle portion 12. Drive motor 14 has a drive shaft 16 with gear 18 driving crown gear 20 which is fixed on shaft 22 by key 24. Shaft 22 is rotatably mounted in bearings 26, 28 fixed in the gear case 10. Bearing 26 is retained in the case by annular plate 30 held in place by screws 32. 
     Spindle 34 on which saw blade 36 is mounted in the usual manner reciprocates in tube 38 which has its ends fixed in the gear case. The bottom portion of the tube is cut away as indicated by the dashed line 40 in FIG. 2 to allow the inverted channel 42, which is connected to the spindle 34 by fastener 44, to move between the ends of the cutout. A first or primary eccentric drive means, reciprocates the spindle. This drive means includes eccentric drive pin 46 which projects upwardly from the top of the crown gear and has a square drive block 48 mounted thereon on roller bearings 50. The opposed sides of the block slideably fit inside the depending legs of the inverted channel. The flat sides of the block minimize the loading between the drive pin and the channel to thereby reduce wear. As the crown gear rotates, the eccentric drive pin and block force the channel and spindle to reciprocate in the tube 38. 
     A secondary or second drive means reciprocates the counterweight and includes a cylindrical drive member 52 which projects upwardly from the top of the crown gear and is eccentric to the center of the crown gear in the direction opposite the eccentricity of the pin. This cylindrical member engages cylindrical hole 54 in the generally square transfer block 56. Block 56 engages the depending legs 58, 58 of counterweight 60 which slides on the outside of tube 38. Since there is a substantial surface contact between the block and the legs of the counterweight wear is minimized. If desired, a ring bearing can be provided between the circular drive member and hole 54 in the block. 
     It will be noted that the crown gear and cylindrical drive member have a crescent shaped cutout 62 to reduce material and counterbalance both the block 56 and the cylindrical eccentric drive member/gear about the gear axis. It is well to keep in mind that the crown gear and the associated eccentric drives (pin 46 and cylindrical member 52) and the transfer block 48 are effectively a unitary rotating mass and the removal of the material in the cutout can balance the mass. Thus, the counterbalance 60 counterbalances the spindle and saw blade while the eccentric drives for both the spindle and the counterbalance are counterbalanced to avoid inducing vibration either parallel to or transverse to the spindle motion.