Feed apparatus for automatic lathe

Abstract

A bar stock feeding apparatus for an automatic lathe, comprising a tube for guiding the bar stock. A piston is situated in the tube behind the bar stock for pushing it towards the headstock of the lathe, the piston itself being urged towards the headstock by means of oil pressure while part of the oil overtakes the piston by flowing through a clearance left between the piston and the inner wall of the tube and through an inner channel through the piston having an adjustable cross-section. Regulating means and non-return valve means are provided in the inner channel for rendering the piston retractable responsive to oil underpressure applied instead of the oil pressure.

What is claimed is: 
     
       1. A feed apparatus for an automatic lathe having a headstock equipped with a collet opening at the end of each working cycle of said lathe, comprising: at least one tube arranged for being disposed in alignment with said headstock for guiding a piece of bar stock engaged in said headstock, the front end of said tube being near said headstock and the rear end of said tube being remote from said headstock,   means for exerting pressure upon said bar stock for preventing it from remaining axially integral with said collet when said collet opens,   wherein said means for exerting pressure comprise: a piston engaged with clearance in said tube, said clearance forming a passage bypassing said piston,   means provided on said piston for pushing said bar stock towards said headstock responsive to a movement of said piston towards said headstock, and   a hydraulic arrangement adapted for supplying oil under pressure at said rear end of said tube and thereby urging said piston with said bar stock towards said headstock, said piston including:   an inner channel having an adjustable cross-section and being operatively parallel to said passage formed by said clearance, and   regulating means in said inner channel for adjusting said cross-section of said inner channel, wherein said oil supplied under pressure by said hydraulic arrangement passes by said piston with loss of pressure through said passage and through said inner channel in an amount determined by said regulating means.   
     
     
       2. A feed apparatus in accordance with claim 1, wherein said regulating means comprise a needle-valve arrangement adapted to close and open said inner channel to a greater or lesser extent. 
     
     
       3. A feed apparatus in accordance with claim 1, wherein said means provided on said piston for pushing said bar stock comprise an extension piece forming a continuation of said piston towards said front end of said tube and being axially connected to said piston in both directions, said extension piece having a sufficiently small diameter to penetrate into said headstock almost up to said collet, thereby allowing said bar stock, when reaching the end of its use, to be pushed until its rearward end is situated just behind said collet, and wherein said hydraulic arrangement is further adapted to draw said oil out of said tube by means of underpressure, whereby said piston and said extension piece are sufficiently retracted to disengage said extension piece completely from said headstock. 
     
     
       4. A feed apparatus in accordance with claim 3, wherein said piston further comprises non-return valve means disposed in said inner channel for allowing said oil to flow from behind said piston to in front of it to the full extent determined by said regulating means and for at least substantially preventing a return of said oil from in front of said piston to behind it through said inner channel. 
     
     
       5. A feed apparatus in accordance with claim 4, wherein said non-return valve means are ball-valve means. 
     
     
       6. A feed apparatus in accordance with claim 3, wherein there is a plurality of tubes disposed in the form of a drum, each tube being adapted to come in turn into alignment with the axis of said headstock, and wherein said means for exerting pressure comprise one piston in each tube and one said hydraulic arrangement common to all tubes provided with means for connecting a reversible-action oil-pump to whichever of said tubes is brought into alignment with said headstock, said plurality of tubes disposed in a drum form being further provided with an extractor and arranged to enable said extractor, each time another tube has to replace a preceding tube in alignment with the axis of said headstock, to enter said headstock for withdrawing therefrom the scrap end of a used bar stock. 
     
     
       7. A feed apparatus in accordance with claim 3, wherein said extension piece includes a stock pusher comprising a rod, the rearward end of which is axially attached to said piston, and a pushing head integral with said rod at the front end thereof. 
     
     
       8. A feed apparatus in accordance with claim 7, wherein said pushing head is designed to leave between it and said tube an oil passage having a cross-section at least equal to the greatest bypassing cross-section around and through said piston. 
     
     
       9. A feed apparatus in accordance with claim 8, wherein sensor means are disposed in the vicinity of said front end of said tube at a predetermined distance therefrom for detecting the arrival of said piston in an advanced position corresponding to the farthest permissible advance position of said pushing head into said headstock, said sensor means being responsive to oil pressure in said tube with such an adjustment that said sensor means are actuated by the operative oil pressure existing behind said piston but not actuated by the reduced pressure existing in front of said piston. 
     
     
       10. A feed apparatus in accordance with claim 3, wherein a single reversible-action oil-pump is provided for supplying said oil pressure and said oil underpressure, said oil pressure being approximately 1-3 kg/sq.cm. above atmospheric pressure and said underpressure being approximately 0.6-0.8 kg/sq.cm. below atmospheric pressure. 
     
     
       11. A feed apparatus in accordance with claim 4, wherein said piston comprises: a body of generally cylindrical form and comprising symmetrically a middle part adapted to be guided in said tube with said clearance, and two end parts of equal diameter, said diameter being less than that of said middle part,   an axial bore passing through said body and having a throttling over a length axially corresponding to said middle part, and two non-throttled portions over the lengths axially corresponding to said end parts, tapered transition portions being disposed at both ends of said length presenting a throttling for rejoining said non-throttled portions,   radial bores constituting at both end parts at least one flowpath between the peripheral surface of said end part and the corresponding non-throttled portion of said axial bore, a needle screwed from the rearward end into the rear non-throttled portion of said axial bore for providing said regulating means in cooperation with one of said tapered transition portions,   a ball with a diameter larger than that of said radial bores, disposed in the front non-throttled portion of said axial bore for providing said non-return valve means in cooperation with the other of said tapered transition portions, and   a coupler adapted to axially secure said extension piece to said piston and screwed from in front into said front non-throttled portion of said axial bore for providing a stop closing off said front non-throttled portion and preventing said ball from escaping therefrom. .Iadd. 12. A feed apparatus for an automatic lathe having a headstock equipped with holding device opening at the end of each working cycle of said lathe, comprising:   at least one tube arrranged for being disposed in alignment with said headstock for guiding a piece of bar stock engaged in said headstock, the front end of said tube being near said headstock, and the rear end of said tube being remote from said headstock,   means for exerting pressure upon said bar stock for preventing it from remaining axially integral with said holding means when it opens,   wherein said means for exerting pressure comprise a piston in said tube,   means responsive to movement of said piston towards said headstock for moving said bar stock towards said headstock and a hydraulic arrangement for supplying oil under pressure at said rear end of said tube to urge said piston towards said headstock,   passage means extending between the rear end of said tube to a position in said tube on the other side of said piston, said passageway means being independent of the surface of maximum diameter of said piston,   regulating means to vary the cross section of said passage means so that oil under pressure biasing said piston toward said headstock passes beyond said piston with loss of pressure across the piston but total flow through said passage means is in an amount determined by said regulating means. .Iaddend. .Iadd. 13. A feed apparatus for an automatic lathe having a headstock equipped with a holding device opening at the end of each working cycle of said lathe, comprising:   at least one tube arranged for being disposed in alignment with said headstock for guiding a piece of bar stock engaged in said headstock, the front end of said tube being near said headstock, and the rear end of said tube being remote from said headstock,   means for exerting pressure upon said bar stock for preventing it from remaining axially integral with said holding means when it opens,   wherein said means for exerting pressure comprise a piston in said tube,   means responsive to movement of said piston towards said headstock for moving said bar stock towards said headstock and a hydraulic arrangement for supplying oil under pressure at said rear end of said tube to urge said piston toward said headstock,   said piston defining at least in part passage means extending between its opposite faces,   regulating means to vary the cross section of said passage means so that oil under pressure biasing said piston toward said headstock passes beyond said piston with loss of pressure across the piston but total flow through said passage means is in an amount determined by said regulating means. .Iaddend. .Iadd. 14. A feed apparatus for an automatic lathe having a headstock equipped with a holding device opening at the end of each working cycle of said lathe, comprising:   at least one tube arranged for being disposed in alignment with said headstock for guiding a piece of bar stock engaged in said headstock, the front end of said tube being near said headstock, and the rear end of said tube being remote from said headstock,   means for exerting pressure upon said bar stock for preventing it from remaining axially integral with said holding device when it opens,   wherein said means for exerting pressure comprise a piston in said tube,   means responsive to movement of said piston towards said headstock for moving said bar stock toward said headstock and a hydraulic arrangement for supplying oil under pressure at said rear end of said tube to urge said piston toward said headstock,   said piston defining at least in part two passages extending between its opposite faces,   regulating means to vary the cross section of one of said passages, the dimensions of the other of said passages being such that oil supplied under pressure by said hydraulic arrangement passes beyond said piston with loss of pressure across said one passage, the flow through said other passage being controlled by said regulating means. .Iaddend.