Abstract: An indirect speed sensor for an electric motor, such as an electric motor of the universal type, provides for a resistive element in series with the motor windings so that current pertubations that occur as a consequence of armature rotation are manifested as speed-dependent voltage signals across the resistive element. The voltage signals are amplified and filtered to remove frequency components above and below the expected signal spectrum and then provided to an analog-to-digital converter that converts the filtered analog signal to digital values that are stored in a memory. A stored-program controlled microprocessor analyzes the stored digital information by performing a fast Fourier transform to provide an equivalent amplitude spectrum. The maximum amplitude spectral component is then identified to determine the speed of the motor.

Abstract: A portable electric tool has a switching device for reversing the direction of the current through the motor to reverse the motor. The switching device comprises two pairs of contacts which extend in cantilever fashion from a circuit board, a rotatable shaft having axially spaced apart terminals thereon, and the terminals being electrically insulated from the contacts by insulating collars secured to the shaft. Each collar has a window therein for access to the respective terminal, the contacts being resiliently biased against the collars with one of each pair of contacts engaging a respective terminal through the respective window in one direction of rotation of the motor and the other of each pair of contacts engaging the opposite respective terminal through the respective window in the opposite direction of rotation of the motor. A shoulder on the shaft may have flats to prevent rotation of the shaft while the trigger of a trigger-switch is actuated.

Abstract: An elongated stamped sheet-metal slider member facilitates the alinement and support for the guiding pulley of a band saw. The slider member has several integrally-formed portions. A first portion depends within the housing, and the pulley is rotatably supported thereon about an axis substantially perpendicular thereto. A second portion of the slider member is bent away, forming an obtuse angle with the first portion, and extends through a slotted opening formed in the housing. This second portion has a pair of ears projecting laterally of the slotted opening for preventing the slider from passing completely into the housing. The ears have respective side edge portions engaging the outer surface of the housing and forming therebetween a fulcrum for pivotal movement of the slider member and hence the pulley about an axis which is above the pulley axis and transverse thereto. A jack screw is carried by the housing for engaging the first portion of the slider member below the pulley axis.

Abstract: A tool holder has a rotatable drive sleeve adapted to receive therein a tool and having a pair of diametrically opposed slots disposed axially along part of its length. A key extends inwardly into each slot and is movable through its sot for retaining and rotatably driving the tool. The slots have an axial length greater than that of the keys which are slidable axially there along. A locking collar, having an internal surface diverging progressively outwardly over at least a portion of its length in the axial direction, encircles the sleeve and is movable axially in one direction for locking the keys in engagement with the tool, and in the opposite direction to allow disengagement of the tool. The action of the divergent surface portion on the keys enables the keys to be locked in position over a range of inward penetrations to accommodate tools having driving recesses of different depths.