GB2185199A

GB2185199A - Workpiece holding means

Info

Publication number: GB2185199A
Application number: GB08600627A
Authority: GB
Inventors: Howard Rowe
Original assignee: Individual
Current assignee: Individual
Priority date: 1986-01-11
Filing date: 1986-01-11
Publication date: 1987-07-15
Also published as: GB2185199B; GB8600627D0

Abstract

A clamp member for securing a workpiece to a machine bed provided with T-slots has a bar web, slideable along the narrower T-slot section and spaced lugs 2 or raised surface portions each side, slideable in the wider T-slot section. An integral threaded socket 3 is provided to receive a threaded clamping element. By means of the spaced bed engaging portions, the clamp member spreads the clamping load in the machine bed. <IMAGE>

Description

SPECIFICATION Improvements in or relating to workpiece holding means Description of the Invention This invention relates to workpiece holding means, particularly for securing a workpiece to the bed of a milling machine during a milling operation on the workpiece.

Background of the Invention The machine bed of milling machines is provided with T-slots, that is slots extending through the body of the machine bed having the cross-section of an inverted "T". The customary method of securing a workpiece to the machine bed is by means of a clamped bridge bar which extends from a marginal edge of the workpiece to a packing block of the same height. The bridge bar is firmly clamped onto the workpiece by a T-bolt which extends through a T-slot in the machine bed, the bolt head being housed in the wide portion of the inverted-T slot, and the threaded portion extending through a hole in the bridge bar. The bridge bar is thus clamped by tightening a nut above the bridge bar hole.

It is customary to use one or more such bridge bars on each side of the workpiece.

This customary holding arrangement has a serious disadvantage, in that the securing Tbolt head develops an upward reaction force, equal to the downward force of the bridge bar upon both the packing block and the workpiece. This reaction force is applied over the small area of contact of the bolt head and the T-slot underside flange and, with additional working load, results in excessively high local stress in the machine bed. Since machine beds are customarily made of cast iron, fracture of the T-slot flange may result, thus damaging the machine bed beyond repair.

The object of the invention is to provide improved holding means and holding method.

Accordingly, the present invention provides means for use in securing a workpiece to a machine bed provided with T-slots, comprising a bar dimensioned to slide in the narrower Tsection of said T-slots having at its base, on each side of said bar, a plurality of spacedapart lugs dimensioned to locate under the Tslot flanges formed by the wider T-section of said T-slots, the top of said bar having a threaded, upwardly-projecting member for receiving a threaded rod and clamping nut.

In use, the bar is slid into a T-slot to a required position, the threaded rod is screwed into the threaded member and, passing through an apertured bridge bar, a nut on the threaded rod above the bridge bar is tightened to clamp the bridge bar in its position.

The invention further provides a method of holding a workpiece comprising using securing means of the invention in the manner aforesaid.

Brief Description of the Drawings An embodiment of the invention, and a modification thereof, will now be described in detail, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a preferred embodiment; Figure 2 is a heavy-duty variant of the embodiment of Fig. 1; Figure 3, Figure 4 and Figure 5 are, respectively, plan view, end elevation view and side elevation view of the embodiment of Fig. 1; and Figure 6 is a side elevation view showing the manner of use.

Description of the Embodiment In the drawings, wherein corresponding members in the various views bear the same reference numerals in all the figures, a bar 1, of rectangular plan and rectangular longitudinal section, has a transverse rectangular section dimensioned to enable the bar 1 to slide in a T-slot of a machine bed. At the four corners of the base, the bar 1 is provided with four lugs 2. The overall width of the lugs 2 is greater than the width of the narrower part of the machine bed slot T-section, so that the lugs 2 extend into the wider part of the slot T-section, the upper faces 2' of the lugs abutting the underside of the flanges formed by the slot T-section.

Extending upwardly from the top face of the bar 1, there is provided a cylindrical boss 3, which is internally threaded at 4, see Fig. 1.

In this embodiment, the boss 3 is intermediate the ends of the bar 1, approximately one-third and two-thirds the overall length from the two ends. The parts of the device, as so far described, can be seen in plan view, end elevation and side elevation in the views of Figs. 3, 4 and 5.

Referring to Fig. 2, wherein there is shown a heavy-duty embodiment, it will be seen that the end lugs 2 are strengthened by a continuous shoulder 5, the top face 5' of which, however, is recessed below the top face surfaces 2' of the lugs 2.

Referring now to Fig. 6, there is shown the manner of use of the device of Figs. 1-5, and in like manner the device of Fig. 2. In Fig. 6, a threaded rod 6 is screwed at one end thereof into the boss 3 and extends vertically upwards therefrom. The rod 6 passes through a clearance hole 8 provided in a bridge bar 7, which bridges the gap between a packing block 9 and a workpiece 10. The bridge bar 7 is clamped by tightening a nut 11, threaded onto the top end of the threaded rod 6, against the top face of the bridge bar 7, by way of an intermediate washer 12.

It is particularly to be noted that the bar 1 is dimensioned in length, and the corner lugs 2 consequently located, so that the areas of upward pressure of the lug faces 2' on the underside of the T-slot opposite flanges coincide with areas of downward pressure, upon the machine bed 13 top face 13', of the packing block 9 and the workpiece 10.

In the embodiment described above, also, the vertical side face of the boss 3 provides an abutment stop for the workpiece 10 end face and the boss 3 diameter is accurately determined so that the side face of the boss 3 provides precise positioning for the workpiece 10 by registering the end face at the vertical line indicated by the arrow "V" in Fig.

6.

The two particular advantages achieved by the described manner of use of the device are that, firstly, the stress upon the maching bed T-slot flanges is a compressive stress, instead of a shearing stress as when using a conventional T-bolt and nut, and, secondly, longitudinal working load forces cannot result in a rocking of the bridge bar and its securing elements, as when using a conventional T-bolt and nut.

A further use of the device of the invention is as an accurate jigging element. For this purpose, again referring to Figs. 1-5, the bar 1 is provided with a vertical, threaded hole 20 near each end and centrally of the length of the lugs 2. Each hole 20 receives a grub screw 21. These bear against the bottom of the machine bed T-slots, as shown in Fig. 6, the two centre lines of the grub screws 21 thus providing precise locating points, as shown by the arrows ''A" and "B" in Fig. 6, relatively to the locating line "V" provided by the boss 3 face.

As an extension of this jigging use, a predrilled template may be used to position a number of devices according to the invention in a required pattern, thereby defining the relative location references "A" and "B", and "V" of all the devices. The grub-screws 21 provided may be tightened to retain the positions so that, when the template is removed, an accurate jig is ready for use in such manner as is required.

Claims

1. Clamp means, for use in securing a workpiece to a machine bed provided with Tslots, comprising a bar dimensioned to slide in the narrower T-section of said T-slots having at its base, on each side of said bar, a plurality of spaced-apart lugs dimensioned to locate under the T-slot flanges formed by the wider T-section of said T-slots, the top of said bar having a threaded, upwardly-projecting socket for receiving a threaded clamping post and clamping nut.

2. Clamp means as claimed in Claim 1, including a pair of lugs, each side of said bar, located at the ends of said bar.

3. Clamp means as claimed in Claim 1 or Claim 2, in which, on each side of said bar, said lugs are joined together by a flange extending along said bar.

4. Clamp means as claimed in any one of the preceding claims, including a clamping post threaded at both ends, one end threaded into said upwardly-projecting socket and the other end carrying a clamping nut.

5. Clamp means as claimed in Claim 4, in which the clamping post extends through a bridge bar, between said socket and said clamping nut.

6. Clamp means as claimed in any one of the preceding claims, for use as jigging means, in which said bar is provided with threaded holes near each end, on the face having said socket, each said threaded hole having a grub screw, for bearing against the bottom of the machine bed T-slots.

7. A method of securing a workpiece to a machine bed provided with T-slots, using clamp means as claimed in Claim 1, comprising sliding said bar into a T-slot to a position in which said upwardly-projecting socket is positioned between a workpiece and a packing block, the threaded clamping post is screwed into said socket and said clamping nut is tightened onto a bridge bar bridging said workpiece and said packing block.

8. Clamp means as claimed in Claim 1, substantially as described herein with reference to the accompanying drawings.

9. Clamp means and jigging means as claimed in Claim 6, substantially as described herein with reference to the accompanying drawings.

10. A method of securing a workpiece to a machine bed provided with T-slots as claimed in Claim 7, substantially as described herein with reference to the accompanying drawings.