Elongated-member-driving apparatus – Explosive-type driving means
Patent
1991-08-23
1992-08-04
Yost, Frank T.
Elongated-member-driving apparatus
Explosive-type driving means
42 6901, B25C 108
Patent
active
051351510
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to power actuated fastener tools.
Power actuated tools for driving a fastener such as a nail, into a substrate, such as a concrete beam, conventionally comprise a barrel from which the fastener is expelled by means of a piston driven by detonation of an explosive charge. The charge is fired by release of a firing pin after cocking of the tool. In conventional firing mechanisms the firing pin has a slot of sufficient depth to allow a pawl to be contained within the slot. A spring inside the slot biases the pawl to project out of the slot to engage with, and be retained by, a cocking piece. To cock the tool, the forward end of the barrel is pressed hard against the work surface and this results in the rear face of the barrel pushing against the cocking piece which retracts the firing pin against the bias of a firing pin spring. When the firing pin is in the cocked position, a sear which is connected to the trigger is aligned with the pawl. When the trigger is actuated, the sear retracts the pawl into the firing pin, thus releasing the firing pin from the cocking piece whereby the firing pin is driven by the firing pin spring towards the explosive charge to fire the power actuated tool.
The firing pin is of relatively small diameter and the space available for mounting the pawl within the firing pin is limited. For the tool to perform consistantly the fit between the pawl and the slot in the firing pin must be maintained. It has been found that repeated firing results in the pawl wearing against both the cocking piece and the slot wall. This results in the pawl becoming loose within the cocking piece and firing pin. Consequently when the sear applies the upward force upon actuation of the trigger, instead of driving the pawl upward into the slot of the firing pin, the pawl may twist and jam. Thus a greater release force is required which makes actuation of the trigger increasingly difficult. It has also been known for a pawl to jam and then to suddenly, and unexpectedly, release, thus firing the tool, which can be very dangerous.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a power actuated tool for driving a fastener into a substrate, comprising a firing mechanism including a firing pin for firing an explosive charge to drive the fastener from a barrel of the tool, spring means for driving the firing pin, and a rotary sear pivotal between a position in which the sear engages an abutment surface of the pin whereby to entrain the pin and a released position in which the sear is released from the abutment surface whereby to permit driving of the firing pin towards the charge under the bias of the spring means.
DESCRIPTION OF THE PREFERRED EMBODIMENT
An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:
FIG. 1 is a sectional view of a power actuated tool fitted with a firing mechanism in accordance with the present invention, the tool being shown in its cocked condition.
FIG. 2 is a fragmentary schematic view of a firing pin, rotary sear and trigger sear plate in the cocked condition.
FIG. 3 is a view similar to FIG. 2, but after firing;
FIG. 4 is a fragmentary schematic view on line 4--4 of FIG. 1 and showing the firing pin, rotary sear, and sear plate in the cocked position; and
FIG. 5 is a view similar to FIG. 4, but after firing.
The power actuated tool 1 comprises a barrel 3 mounted in a receiver assembly 5, and a firing mechanism 7 having a firing pin 9 mounted in the receiver assembly rearwardly of the barrel 3. The barrel 3 houses a piston (not shown) which is actuated by an explosive charge mounted in a charge chamber 11 at the rear of the barrel 3, to drive a fastener within the forward end of the barrel 3 into a substrate such as a beam. The barrel 3 is mounted for axial movement within the receiver assembly 5 and after firing can be moved forwardly of the receiver assembly 5 in order to reset the piston into the rear end of t
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patent: 3048850 (1962-08-01), Schilling
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patent: 3447525 (1969-06-01), Cermak et al.
patent: 3548590 (1970-12-01), Mulno
patent: 3816951 (1974-06-01), Larsson
patent: 4598851 (1986-07-01), Kopf
patent: 4686786 (1987-08-01), Termet
Rada Rinaldi
Ramset Fasteners (Aust.) Pty. Limited
Yost Frank T.
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