GB2194906A

GB2194906A - Lathe structure

Info

Publication number: GB2194906A
Application number: GB08621641A
Authority: GB
Inventors: Eric Jeffrey Wightman
Original assignee: Individual
Current assignee: Individual
Priority date: 1986-09-09
Filing date: 1986-09-09
Publication date: 1988-03-23
Anticipated expiration: 2006-09-09
Also published as: GB2194906B; GB8621641D0

Abstract

The bed, the headstock pillar (1) and the tailstock pillar (2) of a lathe are formed as an integral structure, and the product of the moment of the section and the Young's modulus of the material is equal for the headstock and tailstock pillars so that there are similar deflections of the headstock and tailstock under bending loads which tends to maintain the workpiece parallel to the bed. The bed is preferably of uniform section between the headstock and tailstock pillars, and, together with at least the sides of the headstock pillar and the tailstock pillar, may be fabricated from steel plate of constant thickness. Preferably also the headstock spindle (3) and the tailstock quill (4) are of substantially equal diameter, and they are adjustable to suit the length of the workpiece. <IMAGE>

Description

SPECIFICATION Improvements in machine tools This invention relates to machine tools, and in particular to lathes.

Conventional turning lathes comprise a lathe bed, normally made of cast iron, a headstock with means for holding a component in a chuck, and a tailstock with an adjustable quill.

This latter allows components of different lengths to be supported at the end opposite to the chuck against the cutting forces exerted by the turning tools.

In the accompanying drawings Figures la and 1b illustrate prior art lathes, and Figure 2 shows a lathe according to the invention.

The known lathe of Fig. la comprises a lathe bed 1 with a headstock 2 at one end.

The tailstock 3 is a separate structure which slides along a slideway formed on the bed, as does a toolholder 4. In an alternative arrangement, shown in Fig. 1 b, the tailstock is mounted on an arm supported on a carriage sliding on a secondary slideway system, and is arranged to swing into position when required.

In order to achieve accurate turning, that is, constant roundness and parallelism along the entire length of the component for a given setting of cutting tool position, the structure of the lathe must be as stiff as possible, so as to minimise deflections of the parts of the lathe which would introduce errors of shape into the turned component.

In the customary construction of lathe the bed is usually a box section which may be of cast iron, or fabricated from steel, or may be a steel shell filled wth concrete, the slideways being cast integrally or made separately and fastened on. The headstock, similarly, is of substantial proportions, these being dictated by the size of the spindle bearings, the spacing of the bearings necessary to support the main drive spindle for the chuck, and the loads imposed on the spindle by the drive system. The tailstock, on the other hand, is a secondary structure which may be brought into position when required, as described above with reference to Figs. 1a and 1b.

The problems of designing a structure of this kind of sufficient rigidity are very great, and are compounded by interfacing problems between the headstock and the bed, and between the tailstock and the bed. Lathes tend, therefore, to be designed with very large factors of safety, and are of as substantial proportions as space will allow. They also require a great deal of costly precision machining to ensure compatibility between the interfaces of the parts.

The present invention, which is defined in the claims appended hereto, is directed towards overcoming these difficulties. It makes use of a structure in which the lathe body, headstock pillar and tailstock pillar are integral and iso-elastic, so that the deflections which take place are symmetrical and the workpiece remains generally parallel to its initial position.

A lathe according to the invention is shown schematically in Fig. 2. In this lathe the integral structure formed by the headstock 1, lathe bed, and tailstock 2 is symmetrical about a vertical axis, and the drive spindle 3 and the tailstock quill 4 are of similar cross-section.

The classical mathematical relationship between deflection and stiffness of a structure is d =WL3/2EI where d = deflection W= load L= length E=Young's modulus and I-moment of inertia By making the quantity E/l equal for the headstock and tailstock pillars, which is preferably achieved by making them of the same material and dimensions, the deflections caused by end thrusts will be similar at both ends. The axis of the turned component always moves parallel to the lathe bed, so eliminating a major cause of taper.

Preferably the lathe body is of uniform section between the headstock and tailstock pillars. In a convenient construction the lathe body and at least the sides of the headstock pillar and the tailstock pillar are fabricated from steel plate of constant thickness. The transverse end bulkheads need not necessarily be of the same thickness, but are chosen so that the resulting rectangular box sections of the headstock and tailstock pillars satisfy the condition set out above.

Preferably the headstock spindle and the tailstock quill are of substantially equal diameter, in which case either or both should be adjustable to suit the length of the workpiece.

The optimum arrangement is for both to be adjustable over a wide range, so that the tailstock quill extension may be made equal to the overhang of the headstock drive spindle and chuck to further ensure that the deflections are symmetrical. The tailstock quill should be adjusted initially so as to exert a compressive force in excess of the maximum expected reaction from the cutting force. This ensures that the deflection due to the cutting force is significantly less than the quill force, and may be ignored.

1. A lathe comprising a lathe body, a headstock pillar and a tailstock pillar formed as an integral structure, and in which the product of the moment of the section about a vertical axis and the Young's modulus of the

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Improvements in machine tools This invention relates to machine tools, and in particular to lathes. Conventional turning lathes comprise a lathe bed, normally made of cast iron, a headstock with means for holding a component in a chuck, and a tailstock with an adjustable quill. This latter allows components of different lengths to be supported at the end opposite to the chuck against the cutting forces exerted by the turning tools. In the accompanying drawings Figures la and 1b illustrate prior art lathes, and Figure 2 shows a lathe according to the invention. The known lathe of Fig. la comprises a lathe bed 1 with a headstock 2 at one end. The tailstock 3 is a separate structure which slides along a slideway formed on the bed, as does a toolholder 4. In an alternative arrangement, shown in Fig. 1 b, the tailstock is mounted on an arm supported on a carriage sliding on a secondary slideway system, and is arranged to swing into position when required. In order to achieve accurate turning, that is, constant roundness and parallelism along the entire length of the component for a given setting of cutting tool position, the structure of the lathe must be as stiff as possible, so as to minimise deflections of the parts of the lathe which would introduce errors of shape into the turned component. In the customary construction of lathe the bed is usually a box section which may be of cast iron, or fabricated from steel, or may be a steel shell filled wth concrete, the slideways being cast integrally or made separately and fastened on. The headstock, similarly, is of substantial proportions, these being dictated by the size of the spindle bearings, the spacing of the bearings necessary to support the main drive spindle for the chuck, and the loads imposed on the spindle by the drive system. The tailstock, on the other hand, is a secondary structure which may be brought into position when required, as described above with reference to Figs. 1a and 1b. The problems of designing a structure of this kind of sufficient rigidity are very great, and are compounded by interfacing problems between the headstock and the bed, and between the tailstock and the bed. Lathes tend, therefore, to be designed with very large factors of safety, and are of as substantial proportions as space will allow. They also require a great deal of costly precision machining to ensure compatibility between the interfaces of the parts. The present invention, which is defined in the claims appended hereto, is directed towards overcoming these difficulties. It makes use of a structure in which the lathe body, headstock pillar and tailstock pillar are integral and iso-elastic, so that the deflections which take place are symmetrical and the workpiece remains generally parallel to its initial position. A lathe according to the invention is shown schematically in Fig. 2. In this lathe the integral structure formed by the headstock 1, lathe bed, and tailstock 2 is symmetrical about a vertical axis, and the drive spindle 3 and the tailstock quill 4 are of similar cross-section. The classical mathematical relationship between deflection and stiffness of a structure is d =WL3/2EI where d = deflection W= load L= length E=Young's modulus and I-moment of inertia By making the quantity E/l equal for the headstock and tailstock pillars, which is preferably achieved by making them of the same material and dimensions, the deflections caused by end thrusts will be similar at both ends. The axis of the turned component always moves parallel to the lathe bed, so eliminating a major cause of taper. Preferably the lathe body is of uniform section between the headstock and tailstock pillars. In a convenient construction the lathe body and at least the sides of the headstock pillar and the tailstock pillar are fabricated from steel plate of constant thickness. The transverse end bulkheads need not necessarily be of the same thickness, but are chosen so that the resulting rectangular box sections of the headstock and tailstock pillars satisfy the condition set out above. Preferably the headstock spindle and the tailstock quill are of substantially equal diameter, in which case either or both should be adjustable to suit the length of the workpiece. The optimum arrangement is for both to be adjustable over a wide range, so that the tailstock quill extension may be made equal to the overhang of the headstock drive spindle and chuck to further ensure that the deflections are symmetrical. The tailstock quill should be adjusted initially so as to exert a compressive force in excess of the maximum expected reaction from the cutting force. This ensures that the deflection due to the cutting force is significantly less than the quill force, and may be ignored. CLAIMS

1. A lathe comprising a lathe body, a headstock pillar and a tailstock pillar formed as an integral structure, and in which the product of the moment of the section about a vertical axis and the Young's modulus of the material is equal for the headstock and tailstock pillars.

2. A lathe according to claim 1 in which the lathe body is of uniform section between the headstock and tailstock pillars.

3. A lathe according to claim 1 or claim 2 in which the lathe body and at least the sides of the headstock pillar and the tailstock pillar are fabricated from steel plate of constant thickness.

4. A lathe according to any preceding claim in which the headstock spindle and the tailstock quill are of substantially equal diameter, and either or both of the headstock spindle and the tailstock quill are adjustable to suit the length of the workpiece.

5. A method of using a lathe according to claim 4 in which the tailstock quill extension is substantially equal to the overhang of the headstock drive spindle and chuck, and the tailstock quill is initially adjusted to exert a compressive force in excess of the maximum expected reaction from the cutting force.