Power tool

An apparatus for applying a rotational force to a coil spring connected to a collar, said collar having holes and being mounted on a shaft of a door counterbalancing structure comprising:

• a casing having a slot with an open end to accommodate the shaft, a rotatable drive member rotatably mounted on the casing, said drive member having a slot with an open end to accommodate the shaft, power transmitting means mounted on the casing for rotating the drive member, said power transmitting means adapted to be connected to a motor whereby on operation of the motor the power transmitting means rotates the drive member, and means connecting the drive member to the collar whereby the collar is rotated on said shaft to apply a rotational force to the coil spring, said means connecting the drive member to the collar comprising a disc having a slot with an open end to accommodate the shaft, fastening means securing the disc to the drive member and locating the slot in the disc in side-by-side alignment with the slot in the drive member, and means mounted on the disc engageable with the collar whereby the collar is rotated with the disc.

An apparatus for applying a rotational force to a coil spring having a first end connected to a rotatable collar and a second end connected to a fixed anchor, said collar having a central hole and a side wall with a plurality of keyhole slots, a shaft extended through said spring and the hole in the collar, comprising:

• a casing having a slot with an open end to accommodate the shaft, a rotatable drive member rotatably mounted on the casing, said drive member having a slot with an open end locatable in transverse alignment with the slot in the casing to accommodate the shaft, power transmission means mounted on the casing for rotating the drive member, said power transmission means adapted to be connected to a motor whereby on operation of the motor the power transmission means rotates the drive member, a plurality of transversely projected bolts secured to the drive member, each of said bolts having a head adapted to be located in a keyhole slot in the side wall of the collar whereby the collar is rotated on said shaft to apply a rotational force to the coil spring on rotation of the drive member by operation of the motor.

In combination, a power tool and a door counterbalancing structure comprising:

• a shaft, a fixed anchor located adjacent the shaft, a collar rotatably mounted on the shaft, means to secure the collar to the shaft, a coil spring having a first end connected to the collar and a second end fixed to the anchor, said power tool comprising a casing having a slot with an open end accommodating the shaft, a rotatable drive member rotatably mounted on the casing, said drive member having a slot with an open end locatable in transverse alignment with the slot in the casing to accommodate the shaft, power transmitting means mounted on the casing for rotating the drive member, said power transmitting means adapted to be connected to a motor whereby on operation of the motor the power transmitting means rotates the drive member, and means connecting the drive member to the collar whereby the collar is rotated relative to said shaft in response to rotation of the drive member by the motor to apply a rotational force to the coil spring to load the spring, said means to secure the collar to the shaft operable to fix the collar to the shaft after the spring is loaded whereby the rotational force of the spring is applied to the shaft.