Precision Head for a Machine Tool

This invention relates to precision machine tools, for example, those used in electrical discharge machining or in electrochemical machining, and more specifically, to an improved construction which provides accurate vertical movement: and axial stability of a ram relative to a ram support so that there is little or no deflection of the ram about its vertical axis.

Conventional machine tools for electrical discharge machining, electrochemical machining or like operations, such as disclosed in my earlier U.S. Pat. No. 3,859,003, provide improved axial stability of a ram with respect to an outer ram support over earlier precision heads. However the costs associated with manufacturing such heads is substantial because of the raceway construction for receiving ball bearings which support the ram for axial movement within the outer ram support.

Also, in my two raceway embodiment, the ram when fully extended has been detected to deflect in a transverse direction to the plane extending through the two raceways. My four raceway embodiment is costly to manufacture and it is difficult to maintain alignment along the axial length of ram travel because of the four corner support.

An object of the present invention is to provide a precision head for a machine tool that utilizes three-point support for supporting a ram within a ram support to ensure axial stability of the ram with respect to the ram support.

Another object of the invention is to provide a precision head for a machine tool that is simpler in construction and provides economy of manufacture.

It is another object of the present invention to provide a precision head for a machine tool that utilizes two sets of three-point supports spaced from each other at a distance of at least 11/2 times the travel distance of the ram to eliminate deflection about the vertical movement.

In carrying out the above objects and other objects of the invention, a precision head for a machine tool includes a ram axially movable along an axis. An outer stationary ram support supports the ram for axial movement. The ram support: has a pair of fixed bearing portions spaced from each other on one side of the support and a central bearing portion on the other side of the ram support and located between the fixed bearing portions supports. A pair of adjustable bearing portions bias the ram against the pair of fixed bearing portions.

One of the adjustable bearing portions is positioned on the central bearing portion of the stationary ram support and the other of the adjustable bearing portions is positioned in the outer stationary ram support in opposed relation to one of the pair of fixed bearing portions. The adjustable bearing portion on the central portion is adjustable to position the ram with respect to the pair of fixed bearing portions. The other of the adjustable bearing portions is adjustable to position the ram with respect to one of the pair of fixed bearing portions whereby the ram is positionable totally with respect to the outer stationary ram support by adjustment of only two adjustable bearing portions.

Preferably, the bearing portions are roller bearings mounted in bearing holders and the precision head includes two sets of the fixed and adjustable bearing portions in spaced relation along the axis of the ram. Preferably, the spacing of the two sets of fixed and adjustable bearing portions is at a distance greater than the length of movement of the ram.

The precision head includes a locking means including an adjusting screw and lock screw commonly referred to as a hollow lock screw for locking the adjustable bearing portions against the ram to urge the ram into a prealigned relationship.

The above objects and other objects, features, and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.

FIG. 1 is a general perspective view of a precision head constructed in accordance with the present invention;

FIG. 2 is a sectional plan view of the precision head illustrating a ram and outer stationary ram support having fixed and adjustable bearing portions;

FIG. 3 is an elevational view of the ram and outer stationary ram support illustrating the spacing between two sets of fixed and adjustable bearing portions; and

FIG. 4 is an exploded sectional view of an adjustable lock mechanism for biasing the adjustable bearing portions against the ram.

Referring to FIG. 1 of the drawings, an improved precision head for a machine tool constructed in accordance with the present invention is generally indicated by reference numeral 10 and is used in conjunction with machining operations, such as electrical discharge machining from stamping, extrusion and forging dies and plastic molds, to jewelry and coining. A general discussion of such a head is given in my earlier U.S. Pat. No. 3,859,003 which is hereby incorporated by reference. As is more fully hereinafter described, the improved precision head 10 utilizes three-point support for supporting a ram 12 within an outer stationary ram support 14 to assure axial stability of the ram with respect to the ram support, provide economy of manufacture and eliminate deflection about the vertical movement. It will be understood that the present invention is not limited in its application to machine tools for electrical discharge machining or electrochemical machining, but indeed may be applied to any machine tool in which there is required accurate and precise movement of a tool or workpiece carrying ram in a vertical direction. It is likewise adaptable to machine tools in which the ram is movable along an axis other than the vertical one.

As shown in FIGS. 2 and 3, the precision head 10 includes ram 12 illustrated as having a rectangular cross section and being movable along an axis designated A. The outer stationary ram support 14 is of a polygonal shape and has a pair of fixed bearing portions or bearings 16,17 spaced from each other on one side 18 of the stationary ram support and a central bearing portion 20 on the other side 22 of the ram support between the fixed bearing portions. A pair of adjustable bearing portions or bearings 24, 25 bias the ram against the pair of fixed bearing portions 16, 17.

One of the adjustable bearings 24 is positioned on the central bearing portion 20 of the stationary ram support 14 and the other adjustable bearing portion 25 is positioned in the outer stationary ram support in opposed relation to one of the pair of fixed bearing portions 17. The adjustable bearing 24 on the central portion is adjustable to position the ram 12 with respect to the pair of fixed bearing portions 16, 17. The other adjustable bearing 25 is adjustable to position the ram 12 with respect to fixed bearing portion 16 whereby the ram is positionable totally with respect to the outer stationary ram support 14 by the adjustment of the two adjustable bearings.

In the preferred embodiment of the invention the bearing portions 16,17 and bearings 24,25 are roller bearings mounted in bearing holders 28 as best seen in FIG. 4. Fixed bearing portion 16 includes two bearings 30,31 having perpendicular axis of rotation mounted in one corner 34 of the outer stationary ram support 14. Fixed bearing portion 17 includes bearing 36 mounted in the adjacent corner 38 of the outer stationary ram support 14.

With reference to FIG. 3, the stationary ram support 14 is elongate and includes two sets of fixed and adjustable bearing portions 16,17 and bearings 24,25, respectively. Each set is spaced from each other along the axis A a distance greater than the length of movement of the ram 12. Preferably the spacing is at least one-and-one-half times greater than the length of movement of the ram 12.

With reference to FIGS. 2 and 4, the outer stationary ram support 14 includes a hollow lock screw assembly 40 for locking the adjustable bearings 24,25 against the ram 12 to urge the ram into a prealigned relationship. The ram support 14 includes a first threaded portion 42 and the adjustable bearing holders 28 include a second threaded portion 44. The threaded portions 42,44 are coaxial with each other. An adjustment screw 46 having an aperture 48 therethrough extends through the first threaded portion 42 for initially engaging and preloading one of the adjustable bearings 24,25 against the ram 12. A lock screw 50 axially extendable through the aperture 48 and threadably engaging the second threaded portion 44 and having its head in abutment with the head of adjusting screw 46 locks it by pulling outwardly on the preloaded adjusting screw.

The triangular positioning of the fixed and adjustable bearing portions 16,17 and 24,25, respectively, creates a simplified positioning arrangement whereby the ram 12 is kept in position along the corner 34 by preloading the adjustable bearings 24,25 against the fixed bearing portion 16.

While the best mode for carrying out the invention has been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claims.