GB191229906A - Improvements in or relating to Dash-pot Mechanism for Hack Saw Machines. - Google Patents

Abstract

29,906. Herbert, E. G., and Fletcher, C. Dec. 30. Dash-pots.-Relates to dash-pot mechanism used in hack-saw machines in which the saw is set obliquely to the saw-frame guides for supporting the saw during the return stroke, and consists is providing means for regulating the movements of the dash-pot piston. Fig. 1 shows a dash-pot piston a formed with perforations b, c covered by a flexible metal plate d secured at the centre to the piston or held yieldingly by a spring e and nut f. The tapered end of an adjustable spindle i screwing into a perforated boss h on the piston projects into the hole b and into a small hole b<1> in the metal plate d so as to control the flow of the liquid from below to above the piston during the return stroke of the saw. The piston can move upwards freely during the forward stroke, the liquid passing freely through the holes c and past the yielding plate d. A pin g on the piston holds the plate d in such a position that the holes b, b<1> register. In modifications of the dash-pot, (1) the hole b is restricted so that the plate d need not extend below it; (2) the spindle i is replaced by a screwadjusted valve or a non-return valve controlled by an adjustable spring i; (3) the piston is provided with two or more adjacent holes b or a single elongated hole, and the plate d with two or more adjacent holes b<1>, a plate hinged below the plate d being swivelled to cover or uncover one or more of the additional holes b<1>; (4) a tube fitted with a spring-controlled non-return valve connects the parts of the dash-pot cylinder above and below the piston, the holes b, b<1> being dispensed with (5) a screw-adjusted wedge strip in a recess in the dash-pot cylinder fits into a recess in the piston, a variable-sized gap being left to permit the liquid to escape from below to above the piston; or an adjustable strip of wedge or other shape may lie wholly in the recess in the cylinder; and (6) a single large hole c is used, and the passage of the liquid through it is regulated by means of a screw-adjusted or spring-loaded valve spindle, the pressure of the saw on the work during the cutting stroke being controlled by this means. In a modified arrangement of machine, two dash-pots such as that shown in Fig. 1 are arranged one on each side of the saw-frame guides, one controlling the downward movement of the saw during the return stroke, and the other the pressure of the saw upon the work during the cutting stroke. Fig. 18 shows an arrangement of two dash-pots, one on each side of the saw-frame guides, having perforated pistons fitted with metal plates d and connected together by a pipe u, in which is fitted a valve casing v. The casing v is divided by a central partition fitted with spring valves v', v<2>, which are adjusted to control the movement of the dash-pot pistons. The upper parts of the dashpot are connected by a pipe z to allow excess of liquid in one cylinder to pass to the other In a further modified arrangement, the dashpot cylinders are connected by two pipes each fitted with a regulating and non-return valve. The dash-pots may be arranged on the same side of the saw-guide axis, the valve-plate being arranged in one case below the piston and the other above. The dash-pot mechanism described may be applied to vertical hack-saw machines as well as to horizontal hack-saw machines.