GB2185436A - Mitre cutting cramp - Google Patents

Abstract

The cramp is for cutting a mitred corner in a pair of workpieces 23,24 (such as timber strips). The workpieces are supported by a pair of angled arms 21,22 arranged to engage corresponding faces to the workpieces. The arms are either fixed or, preferably, pivotal, and are set, spaced apart, at a predetermined angle corresponding to the included angle to be created at the mitred corner between the workpieces; at least one of the arms is provided with a workpiece clamp 27, 29. The cramp further has a guide 30,31 for guiding a workpiece cutting member (such as a saw blade); the cutting member acts along a line traversing the end of the first workpiece, a gap between the two workpiece, and the end of the second workpiece (that is, the two workpieces are separated in such a way that the ends overlap and errors in the alignment in cutting one are compensated by corresponding errors in the reverse sense on the other workpiece). <IMAGE>

Description

SPECIFICATION Mitre cutting cramp The present invention is concerned with cramps for positioning elongate workpieces so that they can be cut to form mitred ends, for purposes such as assisting in the construction of picture frames.

A number of such cramps are available which enable two lengths of workpiece to be cut to form the mitred ends which will be joined together. Although there is usually a guide for guiding the cutting tool (for example, a saw), it is possible for the cutting tool to be slightly out of alignment so that, for example, it does not cut absolutely vertically. Because each workpiece is generally cut independently, the two mitred ends may not fit together perfectly.

I have now devised a cramp which permits two workpieces to be cut simultaneously in such a way that any error in the alignment in cutting one workpiece is compenssted by a corresponding error in the reverse sense in cutting the other workpiece.

According to the invention, there is provided a mitre cutting cramp for cutting a mitred corner in a pair of elongate workpieces, which comprises: a pair of workpiece-supporting surfaces; a corresponding pair of workpiece-engaging surfaces, each of which is upstanding relative to a respective one of said workpiece-supporting surfaces, said workpiece-engaging surfaces being arranged to be set, spaced apart, at a predetermined relative angle corresponding to the included angle of said corner; at least one clamping member arranged to clamp a respective workpiece against a corresponding workpiece-engaging surface; a cutting guide for guiding a cutting member along an elongate cut line traversing the space between the ends of said workpiece-engaging surfaces, said ends being spaced at the points where they intersect said line.

Since the cramp according to the invention allows the two workpieces to overlap in the region of the space between the workpieceengaging surfaces, the required mitred ends can be cut on both workpieces at one and the same time. Hence if the cutting member is held at a slight angle, this angle will be common to both workpieces so that they will fit together exactly.

The pair of workpiece-supporting surfaces may either lie on a common support member, or on separate support members (such as a pair of arms). In the latter case, the clamping members may be provided on one, or both, of the support members.

In accordance with one embodiment of the present invention, there is provided a mitre cutting cramp providing two arms which define the included angle to be created at a mitred corner, a cutting guide for guiding a cutting member across the junction of the two arms, and a clamp for each arm to clamp respective workpieces to be cut, such that the workpiece on one arm will be positioned towards the outer edge of that arm and the other workpiece will be positioned towards the inner edge of the other arm, thus enabling the two workpieces to overlap at the junction of the two arms.

In this latter embodiment, at least one of the clamps may operate so as to push a workpiece towards a bearing strip positioned towards an edge of an arm, alternatively at least one of the clamps may operate to pull a workpiece towards a bearing strip positioned towards an edge of an arm. In a preferred arrangement of this embodiment one of the clamps will push whilst the other will pull so that the projecting parts of the clamps which are held for rotation will both project either from the outer edges or from the inner edges of the two arms. Advantageously the bearing strip will be adjustable in position across the arm to allow for workpieces of differing widths so that the two workpieces can be positioned to overlap as closely as possible.

In some embodiments of the present invention, the cutting guide is so mounted that it can be swung to modify the direction which it subtends with respect to the directions of projection of the two arms, and a locking member is provided for securing the cutting guide at a required position. This enables a corner to be constructed from two workpieces of different widths, by ensuring that the lengths of the mitred ends of the two workpieces are nevertheless equal, because of the modification of the angle of cut across the two workpieces. In this embodiment, it is preferred that the two arms are interconnected in such a way that they can be rotated with respect to one another to alter the included angle and locking means is provided to secure the arms at a required angle.For many corner pieces a 90" angle is required, but by modifying the included angle achieved by cutting the ends of two workpieces it is possible, for example, to construct a hexagonal frame. For this purpose the two arms may advantageously be pivotally interconnected at the inner meeting point thereof.

In a preferred arrangement the arms are slidingly mounted towards the ends thereof remote from the junction of the arms on an arcuate support. Where the movable cutting guide is provided this can have an extending limb which is slidingly interconnected with the support. Ideally the support will carry markings defining angles subtended by the arms from the junction thereof. This enables the user readily to achieve any desired included angle or cutting angle for a particular shape of corner.

The cutting guide may comprise upstanding pillars defining guide slots and positioned respectively at the inner and outer meeting points of the two arms. Preferably the guide slots are each defined between pairs of rollers whose rotational axes lie parallel to the guide slot.

As a further modification, the parts of the cramp can be so interconnected that they can be rotated about the junction of the two arms into a modified position in which the two arms do not lie in a common plane. This would result in a non-vertical cut at the mitred ends of the two workpieces thus enabling the workpieces to be fitted, for example, as a plinth around the base of the pillar.

The ends of the arms remote from the junction thereof may carry adjustable stops for the ends of the workpieces to be cut, thus enabling a workpiece to be cut to a required length. If required, the stops could be so provided that they can be moved to a position wherein they do not obstruct the ends of the workpieces to be cut.

Preferred embodiments of the present invention will now be described by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a first exemplary embodiment of mitre cutting cramp according to the invention (with fixed workpiece-supporting and workpiece-engaging surfaces); Figure 2 is a perspective view of a second exemplary embodiment of mitre cutting cramp according to the invention, with pivotal arms constituting the workpiece-supporting and workpiece-engaging surfaces; Figure 3 is a perspective view of a third exemplary embodiment of mitre cutting cramp according to the invention with pivotal arms broadly similar to those in the embodiment of Figure 2; Figures 4a and 4b show two workpieces cut at a mitred corner angle greater than 90';; and Figures 4c and 4d show two workpieces of different widths cut at a mitred corner angle of 90".

Referring to Figure 1, the mitre cutting cramp comprises a body 1 having an upper support surface 2 for supporting two workpieces 3,4.

Secured to the upper surface 2 are a pair of workpiece-engaging strips 5,6 which subtend an angle of 90'. The ends of strips 5,6 are bevelled, and the bevelled ends 7,8 are substantially parallel to a narrow gap 9 therebetween. Parallel to and beneath the gap 9 is an elongate saw groove 10; saw guiding projections 11 and 12 are secured to the upper surface 2 adjacent to the saw groove 10.

Strip 5 engages the workpiece 3 on its outer edge 14; a clamp 15 serves to urge the workpiece 3 towards the outer edge. Strip 6 engages the workpiece 4 on its inner edge 17. Workpieces 3 and 4 are located so as to overlap the saw groove 10; in operation, the ends of the workpieces are sawn off along saw lines 18, 19, respectively. After cutting, the workpiece 4 may be located on the outer edge of strip 6 to facilitate nailing and/or gluing of the cut ends of the two workpieces.

The mitre cutting cramp illustrated in Figure 2 incorporates two arms 21,22 providing support surfaces on which can be mounted two elongate workpieces 23,24 which are to be cut to create mitred ends, 23a,24a, separated by a short gap 25 along the cut line. As can be seen from the drawing the workpiece 23 is pressed against a bearing strip 26 at the inner edge of the arm 21 by means of a clamping screw 27 having a mushroom shape bearing head 27a. The workpiece 24 is held against a bearing strip 28 at the outer edge of the arm 22 by means of a clamping screw 29. The end portions of the workpieces (prior to cutting) will then overlap, enabling mitred ends to be cut on the two workpieces at the same time.A cutting tool (for example a handsaw or a motor driven circular saw) is positioned within slots in guide pillars 30 and 31 so that cutting of the mitred ends on the workpieces progresses along a constant angle. Advantageously, the pillars 30 and 31 will incorporate rollers which between them define the slots through which the cutting tool will pass.

It will be noted that the projecting ends of the arms 21 and 22 are mounted on an arcuate support 32. The two arms 21 and 22 are connected together by means of a pivot (not shown) so that each arm can be moved along the arcuate support 32 and held at new positions so as to define a desired included angle.

A limb 33 carrying the guide pillars 30 and 31 also extends to the arcuate support 32 and is fixed thereto by means of a removable screw 34. The limb 33 is also pivotally mounted at the junction of the two arms 21 and 22 so that when the screw 34 is removed, the limb can be rotsted to a new position on the support 32 and held there by the screw 34. This provides a different angle of cut across the ends of the two workpieces which would be required if they are of differing widths. By choosing a suitable angle, when the mitred ends have been cut on the two workpieces, they may be joined together to create a properly formed corner as illustrated in Figures 4c and 4d.

The result of cutting of two workpieces at an obtuse angle is illustrated in Figures 4a and 4b; when the two workpieces are interconnected to form a corner, the angle defined at that corner can be seen clearly from Figure 4b.

As also shown in Figure 2, sliding stop members 35,36 are provided at the outer ends of each of the arms 21 and 22. 8upport arms for the stop members 35,36 can be secured below the arms 21 and 22 by fixing means (not shown) to determine a required length for a workpiece which is to be cut. If desired the stop members may be remover swung out of position to enable the cut te made at the first end of a workpiece wher the overall length does not yet need to be defined.

The mitre cutting cramp illustrated in Figure 2 may be modified further so as to have a pivot running along the junction between the two arms 21 and 22 so that these arms can be swung downwardly. For this purpose a hinge at the centre of the arcuate support 32 would also be required. When the arms 21 and 22 are swung down to some extent the mitred ends cut on the workpieces will be other than at right angles to the flat base of each of the workpieces. Thus the workpieces can then be cut so as to fit, for example, around the base of a pillar.

The clamping screw 29 could be re-positioned so as to extend beyond the outer wall of the bearing strip 28 and project below the arm 22 to act on a clamping member projecting up through the base of the arm 22 so as to bear against the workpiece 24. The strip 22 can incorporate a slot in which such a bearing member can slide. By this means both of the clamping screws 27 and 29 would be situated on outer faces. If desired the clamping screw 27 could be replaced by a similar arrangement passing below the arm 21.

Referring to Figure 3, the mitre cutting cramp illustrated comprises a base member 40 with a pair of pivotally connected arms, 41,42. Each arm has a respective substantially horizontal face 43,44 and upstanding flange 45,46. Flange 45 is outwardly facing and engages a workpiece 47 between it and screw clamping member 48. Flange 46 is inwardly facing and engages workpiece 49 on its inner edge.

The arms 41,42 are pivotal in such a way that guide members 50,51, travel along guide grooves 52,53 respectively; the base member 40 may be provided with angle calibrations so as to enable the mitred corner to be cut at a desired angle.

The ends 54,55 of the arms nearest the pivot have a gap 56 therebetween; a pair of cutting guides 57,58 are provided in such a manner that an imaginary line drawn between the cutting guides intersects the- gap 56, enabling the ends 59,60 of workpieces 47,49 to be cut at the desired mitre angle.

The cramp according to the invention can of course be used for cutting any desired material such as wood, metal or plastics items.

The present invention has been described with reference to a cramp for cutting mitred corners. Mitred corners can be crested at any desired angle using a cramp according to the invention, even with the workpieces at an angle of 180". (The resulting joints between workpieces at an angle of 180" would generally be referred to as butt joints when the cut line is perpendicular to the workpieces, and scarf joints when the cut line is at an acute angle to the workpieces).

Claims (11)

1. A mitre cutting cramp for cutting a mitred corner in a pair of elongate workpieces, which comprises: a pair of workpiece-supporting surfaces; a corresponding pair of workpiece-engaging surfaces, each of which is upstanding relative to a respective one of said workpiece-supporting surfaces, said workpieceengaging surfaces being arranged to be set, spaced apart, at a predetermined relative angle corresponding to the included angle of said corner, at least one clamping member arranged to clamp a respective workpiece against a corresponding workpiece-engaging surface; a cutting guide for guiding a cutting member slong an elongate cut line traversing the space between the ends of said workpiece-engaging surfaces, said ends being spaced at the points where they intersect said line.

2. A cramp according to claim 1, in which the pair of workpiece-supporting surfaces lie on a common support member.

3. A cramp according to claim 1, in which the pair of workpiece-supporting surfaces lie on separate support members.

4. A cramp according to claim 3, in which the separate support members comprise a pair of arms.

5. A cramp according to claim 3 or 4, in which one of said clamping members is provided on each of said arms.

6. A cramp according to claim 5, in which one workpiece-engaging surface is towards the outer edge of one arm and the other workpiece-engaging surface is towards the inner edge of the other arm, so as to permit the workpieces to overlap at the junction of the two arms.

7. A cramp according to any of claims 1 to 6, in which one of said workpiece-supporting surfaces, and its corresponding workpieceengsging surface, is pivotal relative to the other one thereof.

8. A cramp according to claim 7, in which said pivotal workpiece-supporting surface is provided with means for setting the angle to be cut in the mitred corner.

9. A cramp according to any one of claims 1 to 8, in which at least one of said workpiece-supporting surfaces is provided with means for setting the length of the workpiece to be cut.

10. A cramp according to any one of claims 1 to 9, in which the cutting guide comprises pairs of upstanding pillars each defining guide slots.

11. A mitre cutting cramp substantially as described herein with reference to any of Figures 1 to 3 of the accompanying drawings.