Shaft Lock Arrangment for a Power Tool

The invention is related to power tools having a rotating shaft and, in particular, to a shaft lock and lock-out switch arrangement for a router.

In power tools, such as a circular saw or router, an internal electric motor has a rotating shaft coupled to a cutting tool at an exposed end. These cutting tools are selectively mounted to or removed from the shaft depending upon the work to be performed by the cutting tool. It is a convenience to the operator, if the rotation of the shaft can be inhibited during the mounting or removal of the cutting tool since the mounting or removal of the cutting tool requires a rotary motion about an axis concentric with the shaft. Preferably, the mechanism for locking the shaft should also inhibit electrical power from being applied to the electric motor when the rotation of the shaft is inhibited to prevent damage to the motor or causing it to overheat.

Shaft locking mechanisms which include electrical cut-out switches to prevent electrical power from being applied to the motor when the shaft is locked are known in the art. Godfrey et al, in U.S. Pat. No. 2,897,302, discloses a control mechanism for the ON/OFF switch of a router which automatically locks the shaft when the electrical switch is placed in the OFF position and release the shaft when the electrical switch is placed in the ON position. In an alternate arrangement disclosed by McCurry in U.S. patent application Ser. No. 07/764,239, filed Sep. 23, 1991, discloses a shaft lock mechanism having a first position in which the shaft is locked and a cut-out switch is placed in an open position and is manually displaceable to a second position in which the shaft is free to rotate and the cut-out switch is placed in a closed position.

The invention is an improved shaft lock mechanism for a power tool.

The invention is a shaft lock arrangement for a power tool. The power tool being of the type having a housing, an electric motor mounted in the housing, an output shaft rotated by the electric motor and an ON/OFF switch selectively supplying electrical power to the electric motor from an external source of electrical power. The shaft lock arrangement consists of a non-circular portion provided at one end of the shaft and a shaft lock disposed in the housing engageable with the non-circular end of the output shaft. The shaft lock is displaceable from a RUN position in which the shaft lock is disengaged from the output shaft to a LOCKED position in which the shaft lock engages the non-circular end of the output shaft and prevents it from rotating. The shaft lock has a through aperture receiving the end of the output shaft. The through aperture having at least one portion lockingly engaging the non-circular portion of the output shaft preventing it from rotating when the shaft lock is in the LOCKED position. The shaft lock further has a run and a locked detent. A lock-out switch mounted in the housing and connected in series with the ON/OFF switch has a toggle to switch the lock-out switch from an open state to a closed state. The toggle is resiliently biased to engage the run detent when the shaft lock is in the RUN position and to engage the locked detent when the shaft lock is in the LOCKED position. The toggle is biased to produce a force sufficient to hold the shaft lock, alternatively in either the RUN or LOCKED positions. The lock-out switch is placed in a closed state when the toggle is in the RUN detent and in an open state when the toggle is in the LOCKED detent.

In the preferred embodiment, the non-circular portion of the output shaft has a pair of flat surfaces disposed on opposite sides and the through aperture has a keyhole shape having a circular portion circumscribing the shaft when the shaft lock is in the RUN position and a rectangular portion straddling the pair of flat surfaces when the shaft lock is in the LOCKED position.

One advantage of the shaft lock mechanism is that the electrical power to the motor is cut-off when the shaft lock is in the LOCKED position.

Another advantage of the shaft lock mechanism is that the force of the biased toggle of the cut-off switch holds the shaft lock in either the RUN or LOCKED positions eliminating the need for separate detent mechanisms.

These and other advantages of the shaft lock and lock-out mechanisms will become more apparent from a reading of the specification in conjunction with the drawings.

FIG. 1 is a partial cross-sectional front view of a router;

FIG. 2 is a partial cross-sectional top view of the router with the shaft lock in the RUN position;

FIG. 3 is a partial cross-sectional top view of the router with the shaft lock in the LOCKED position;

FIG. 4 is a top view of the shaft lock;

FIG. 5 is a cross-sectional side view of the shaft lock; and

FIG. 6 is a circuit diagram of the router.

FIG. 1 illustrates a router, designated generally by reference numeral 10, embodying the shaft lock and cut-out switch mechanism according to the invention. The router 10 includes a main housing 12 in which is mounted an electric motor 14 in a conventional manner. Electric power is supplied to the electric motor through a pair of brushes 16 and 18 which engage a commutator 20. The electric motor 14 has a rotary output shaft 22 which extends at its lower end external to the housing 12. A collet 24 to which an operator may attach a suitable cutting tool, such as a router bit 26, is attached to the lower end of output shaft 22. The router 10 also has a main power switch 28 (FIG. 6) by means of which an operator may supply electrical power to the motor 14 to rotate the motor's output shaft 22 to effect a cutting operation.

In order to change the cutting tools, it is a convenience for the operator to be able to mechanically lock the output shaft 22 against rotation. It is also desirable to prevent electrical power from being applied to the motor 14 when the output shaft is mechanically locked.

To accommodate the mechanical locking of the output shaft 22, its upper end is provided with a non-circular parallel flat portions 30 and 32 shown in FIG. 4. A cut-out switch 34, such as Arklers single pole single throw switch, model number S-2111SR10-0 is connected in series with the main power switch 28 and is switched to an open state whenever the shaft 22 is mechanically locked against rotation. This prevents electrical power from being applied to the motor 14 when the shaft 22 is locked.

The mechanism for locking the output shaft is a shaft lock 36 provided in the housing 12 adjacent to the upper end of the output shaft 22. The shaft lock 36 is received in rectangular openings on opposite sides of the housing 12 and is manually displaceable by the operator in a direction transverse to the output shaft 22 from an UNLOCKED or RUN position, shown in FIGS. 1 and 2 to a LOCKED position, shown in FIG. 3.

The shaft lock 36, shown more clearly in FIGS. 4 and 5 consists of a lock plate 38 and a pair of end members 40 and 42. The end members 40 and 42 may be molded directly into the lock plate 38 or may be pressed onto the ends of the lock plate 38 in a conventional manner. The end members 40 and 42 have external contours which mate with the adjacent external contour of the housing. The lock plate 38 has a keyhole-shaped aperture 44 having a circular portion 46 which circumscribes the output shaft 22 when the shaft lock 36 is in the UNLOCKED or RUN position, and a rectangular portion 48 which straddles the parallel flat portions 30 and 32 of the output shaft 22 when the shaft lock 36 is in the LOCKED position.

The distance between the parallel sides 50 and 52 of the rectangular portion 48 is selected to be slightly greater than the distance between the parallel flat portions 30 and 32 of the output shaft 22 so that when the flat portions 30 and 32 of the output shaft 22 are oriented parallel to the parallel sides 50 and 52 of the rectangular portion 48, the lock plate 38 may be displaced to the locked position as illustrated in FIGS. 3 and 4. In the locked position, the parallel sides 50 and 52 of the rectangular portion 48 prevent the rotation of the output shaft 22 permitting the collet 24 to be rotated relative to the shaft 22 enabling the mounting and/or removal of a cutting tool.

The end member 42 has a run detent 56 and a lock detect 58 which, in the alternative, are engaged by the toggle 60 of the lock-out switch 34. The run and lock detents 56 and 58 are spaced apart in a direction parallel to the direction of motion of the shaft lock 36 indicated by double-headed arrow 62 and are offset from each other in a direction normal to the direction of motion. When the shaft lock 36 is in the RUN position, the toggle 60 of the lock-out switch 34 is engaged in the run detent 56, which closes lock-out switch 34, permitting electrical power to be applied to the motor 14. In the alternative, when the shaft lock 36 is placed in the LOCKED position in which the shaft 22 is prohibited from rotating, the toggle 60 is engaged in lock detent 58. A ramp 64 is provided between run detent 56 and lock detent 58 to facilitate the displacement of the toggle 60 from lock detent 58 to RUN detent 56 when the shaft lock 36 is manually displaced from the LOCKED position to the RUN position.

The toggle 60 of the lock-out switch 34 is resiliently biased to the normally open position with a force sufficient to hold the shaft lock 36 in the RUN position when the toggle 60 is in run detent 56 and in the locked position when the toggle 60 is in lock detent 58. This eliminates the need for any other type of holding mechanism to secure the shaft lock 36 in either the RUN or LOCKED positions.

The housing 12 consists of two clam shell members 66 and 68 which are secured to each other by screw-type fasteners 70 at various locations. Each clam shell member 66 and 68 has a portion of a top 72 which secures the shaft lock 36 in the housing as shown in FIG. 1.

Referring to FIG. 6, electrical power is supplied to the electric motor 14 via a line cord 72 having a male connector plug 74 receivable in a standard household electrical outlet. As previously stated, the cut-out switch 34 is connected in series between the main power switch 28 and the electric motor 14.

While a best mode embodiment of the shaft lock and lock-out switch arrangement has been disclosed herein, it is understood that various modification and improvements will be apparent to those of ordinary skill in the art within the scope of the invention as set forth in the appended claims.