GB2301797A - Improvements relating to jigs - Google Patents

Abstract

A band saw table (1) has grooves (6,7) in its upper surface to receive flat bars (9) which can slide along them and be clamped in desired positions. One bar (9) carries a member (13) which can be angularly adjusted about an axis normal to the table (1) and to which a fence can be fitted. This is adjustable in its longitudinal direction, and it has means for holding a workpiece to it. The workpiece can thus be presented to the saw blade at any angle and at selected points. Use of the jig for moulding curved cuts is described.

Description

"ImDrovements relating to Jigs" This invention relates to jigs. It is primarily concerned with jigs for holding and guiding workpieces to be cut on a band saw, but it can be used with other machine tools. It was primarily developed for working with small pieces of wood when making dolls' houses and other miniatures. However, there is no reason why it should not be scaled up in size.

When working with small pieces, it is obviously unsatisfactory to hold them by hand. The fingers get far too near the saw blade for safety, and also it is difficult to guide them with real precision.

It is the aim of this invention to provide a jig which will enable securely held pieces to be cut in various ways, in straight lines or curves, with greater accuracy and safety.

According to the present invention there is provided a jig for a band saw comprising a table through which the saw blade runs and provided with tracks for the guidance of a workpiece holder, the holder comprising a track follower which remains flush with or below the table top and a fence assembly pivoted to the follower about an axis perpendicular to the table top to enable the fence to be set at a selected angle to the saw blade plane, the fence further being adjustable in its longitudinal direction.

Conveniently, the tracks are grooves parallel to the edges of a square or rectangular table. The followers can simply be flat bars that are a close sliding fit in them.

Provision may be made for clamping them at selected positions.

The fence may also be basically a flat bar, with its face perpendicular to the table top. Clamping means can be fitted to it to hold the workpiece, these being in the form of stops adjustable along the bar and fixable at any selected positions along it.

The above arrangements are for straight cuts. For curved cuts, another groove will lead from the edge of the table towards the blade, perpendicular to the plane of the blade. A slide bar can fit in this and'be clamped at any selected position. A spike will stand proud of the table top and serve as a centering device for a workpiece. Rotated about this spike, the workpiece can be cut into a disc.

This bar may be augmented by a swinging arm pivoted about the spike. The arm carries a longitudinally adjustable member and the free end of this can be adapted to be fitted with the fence referred to above. This forms an adjustable assembly of T form that can be swung about the spike on the slide bar. A workpiece clamped to the fence can be cut in a curve, the radius of curvature being determined by the distance of the spike from the saw blade and the depth of cut of the workpiece being determined by the adjustment of the T assembly in relation to the swinging arm.

For a better understanding of the invention, one embodiment will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a plan view of a band saw table, Figure 2 is a plan view to a larger scale of a protractor or mitre jig, Figure 3 is a side view showing a detail of Figure 2, Figure 4 is a partial front elevation of a fence with stops used in conjunction with the protractor jig of Figure 2, Figure 5 is a vertical section to a larger scale again on the line V-V of Figure 4, Figure 6 is a plan view of a jig for holding workpieces to be cut in circular fashion, Figure 7 is a plan view of another jig for holding workpieces to be cut in circular fashion, Figure 8 is a plan view of a measuring device that can be used with the jig, Figure 9 is a plan view of part of the table with an extension and adjusting device.

Figure 10 is a perspective view of part of a modified fence, Figure 11 is a perspective view of a modified protractor jig, Figure 12 is a perspective view of part of a modified Figure 7 jig, Figure 13 is a side view of a jig for use in cutting polygonal section members, Figure 14 is a plan view of the jig of Figure 13, and Figure 15 is an end view of the jig of Figure 13.

Referring to Figure 1, a band saw table 1 is square with a narrow slot 2 leading from the middle of one edge to the centre where it opens into an aperture 3. This is largely closed by a plastic insert 4 with a slot to receive a band saw blade 5. This conventional arrangement enables the saw blade to be fitted and removed.

Inset from and parallel with each edge of the table 1 there are grooves 6 cut out from the flat table top. In this example they are square U section, but they could be dovetailed or otherwise undercut to give downward retention of slides to be described later. The grooves are open at their ends to the edges of the table 1. A further groove 7 extends from the middle of the edge parallel to the slot 2 and remote from the main spine of the band saw, indicated in outline at 8, to terminate near the aperture 3. It will be referred to as the radial groove.

It is hoped that band saws will eventually be provided with this type of table at manufacture. However, at the outset it may have to be produced as a replacement table, to fit onto existing mountings, perhaps through an adaptor.

Obviously, the dimension between the aperture 3 and the side adjacent the spine 8 is limited, but there could be variations elsewhere, with the table being expanded to rectangular form, for example. Alternatively, provision may be made to have extensions or leaves that can be fitted to any of the three free edges, and an example is shown in Figure 9 to be described later.

Referring to Figures 2 and 3, the protractor or mitre jig has a slide 9 which fits closely in any of the grooves 6 and 7 and which when so fitted will be flush with the table top, In use, it can be slid along the groove in which it is engaged, or it may need to be held secure. For this, it has a cam 10 recessed into its underside and operable by a counter-sunk screw 11 accessible on the upper side. A quarter turn of this screw shifts the cam from being within the span of the sides of the slide 9 to projecting slightly from one side or the other. When in that position, it jams against the side of the groove and thus holds the jig. It can be locked in the free position so that there is no inadvertent jamming by a further small screw 12 counter-sunk into one side.

The slide 9 carries a half disc 13 with a diametral flange 14 upstanding from its straight edge. This member is pivoted about the centre of curvature of the half disc and can thus be rotated as indicated by the double arrows. An angular scale 15 is marked around the curved edge and cooperates with a pointer 16. The member 13 can be swung to any desired angle in relation to the slide 9, guided by this pointer, and then clamped by a screw knob 17 through an arcuate slot 18 in the half disc. There may be detents to help locate the member 13 at significant angles such as 300, 450, 600 and 900. On the side of the flange 14 remote from the half disc there is a horizontal T-section rail 19 whose purpose will be explained in relation to Figures 4 and 5.

Referring to those figures, a fence can be fitted to the protractor jig just described. Its main body is a flat bar 20, and extending along its rear face it has parallel hooked ribs 21 which form an undercut channel in which the rail 19 is a close sliding fit. When so engaged, the lower edge of the bar 20 sits on the top of the table 1, and the front face of the bar is at right angles to that table top.

At various positions along this lower edge there are cutouts 22 of different sizes. This is for when the fence is used in conjunction with a router table, which will not be described in detail. They give clearance over the router bits.

It will be appreciated that the fence can be slid longitudinally with respect to the flange 14, and there will be means (not shown) for clamping it in the desired setting.

The fence carries stops 23 to hold a workpiece. They are of opposite hand, and only one will be described in detail. It consists of a plate 24 with a hooked formation 25 which fits closely over the upper edge of the bar 20, thereby holding the plate 24 against the front face of the bar. From one vertical edge there projects at right angles away from the bar 20 a flange 26, and at its lower corner adjacent the plate 24 there is a square cut-out 27. This stop 23 can be slid along the fence 19 and clamped in any desired position by a screw 28. The two stops 23 are arranged so that the flanges 26 are adjacent each other.

In one mode of use, the fence bar 20 is brought towards the saw blade for a cut through a workpiece held between the stops 23. If that workpiece was hard up against the front face of the bar 20, the blade, on cutting through, would hit the bar with disastrous results. The cut-outs 27 are provided to enable a wooden spacer to be fitted between the workpiece and the bar 20, to "cushion" the saw blade as it breaks through. This spacer can simply be a square section rod that fits the cut-outs closely.

It will be appreciated that a workpiece can be clamped between the stops 23, but sometimes it is necessary to have very fine adjustment of this clamping. To achieve this, there is associated with each stop a micrometer device 29.

Each one comprises a saddle 30 which fits closely over the upper edge of the bar 20 and which can be clamped there by a screw 31. A horizontal screw 32, parallel with the upper edge of the bar 20 threads through the upper part of the saddle 30 and engages a socket 33 on the end of the formation 25 opposite the flange 26.

In a typical clamping operation, one stop 23 is set where required, the workpiece is offered up to the bar 20 and abutted against that stop, and the other stop is slid along to abut the other end of the workpiece, but is not secured. Then the micrometer device 29 associated with that second stop is brought up and clamped, followed by the screw 32 being operated to push the second stop 23 hard up against the workpiece. The socket 33 prevents any tilting. When the workpiece is secured, the second stop 23 is locked in place by its screw 28.

Referring now to Figure 6, this shows a simple jig which co-operates with the radial groove 7. It comprises a bar 34 with a rounded forward end which fits the groove 7 to be flush with the table top. It can be locked in a set position by a device 35 similar to that shown in Figure 3.

At the forward end, a short pin 36 projects proud of the table top from the centre of a socket 37 in the bar 34. A workpiece pressed down on this pin can be rotated about it and cut into a disc with a radius equal to the distance of the pin 36 from the blade 5. A further socket 38 in the upper face is provided towards the other end of the bar 34, and a bore 39 is drilled and threaded horizontally into that other end.

Referring to Figure 7, the bar 34 is also used with this jig. But here, a stud (not shown) is fitted in one of the sockets 37 and 38 to serve as the pivot for a flat arm 40 which will slide over the top of the table 1. This arm 40 is provided with a guide 41 for the stem 42 of a T-shaped member 43 which can be slid longitudinally of the arm 40 and clamped at a desired position by a screw 44. The arm 40 also carries a micrometer device 46 which can operate on the end of the stem 41 in the manner of the device 29. It can be adjusted longitudinally of the arm 40 and clamped by a screw 47. The cross member 48 of the T is provided on the side remote from the stem 42 with a rail (not shown) to cooperate with the ribs 21 of the fence bar 20. The fence can therefore be fitted, carrying its stops, to hold the workpiece for a curved cut as indicated by the chain dotted line.The radius and depth of this cut is set by the position of the bar 34 and the relation of the T-member 43 to the arm 40.

The table top along one side of the groove 7 and the bar 34 could be marked to indicate the distance of the pin 36 from the saw blade. However the position of the latter can vary within limits and the markings can then be unreliable. It is thought that it would be simpler to use the device of Figure 8. This has a short slide 49 which can fit the grooves 6 and a ruler 50 held parallel to that slide on an arm 51. With the slide 49 in a groove 6 perpendicular to the slot 2, one end of the ruler 50 can be brought up to bear on the side of the saw blade 5 so that one edge of the ruler lies over the radial groove 7. The bar 34 is then adjusted until the pin 36 is opposite the desired mark.

Figure 9 illustrates an extension 52 for the table 1, effectively lengthening it in the direction of the radial groove 7. It is essentially an E-shaped frame whose three fingers 53 align with the groove 7 and with the grooves 6 parallel to it. The fingers are also grooved to provide continuations of the grooves 6 and 7 so that they will support and guide slides moving beyond the table 1. The spine 54 of the E is shown carrying at its centre a removable mounting block 55 for another micrometer screw device.

This has a shaft 56 aligned with the groove 7, slidable through the mounting block 55, and cut at regular intervals with annular grooves 57. At its end remote from the table 1 it has a knob 58, while at its other end 59 it is screwthreaded to engage the threaded bore 39 in the end of the bar 34. A latch 60 pivoted at 61 can be dropped into any selected groove 57 for coarse adjustment of the shaft 56.

Rotation of the knob 58 will then, by the action of the screw-threaded end 59, cause the bar 34 to be finely adjusted. When set, the shaft 56 can be locked by a screw 62, adding to the security afforded by the locking device 35.

The block 55 and associated micrometer screw device can be shifted to align with either of the other fingers 53.

The arrangement of Figure 5 with hooked ribs 21 makes it a bit slow and cumbersome to change over from the protractor jig to the jig of Figure 7. It is not really necessary for the fence and either jig to have a sliding relationship. An alternative fixing arrangement is shown in Figures 10, 11 and 12.

Here, the fence 20 has on its rear face a block 63.

From this project two parallel, horizontal studs 64, and beside them there are screw threaded holes 65 drilled into the block.

The flange 14 of the protractor has two apertures 66 which will register with and receive the studs 64. At the same time, screws 67 carried by the flange 14 will register with the holes 65. These have knurled ends so that they can be done up by fingers alone. The fitting of the protractor jig is therefore a quick plug-in operation followed by the tightening of two screws, and it is equally quickly removed.

Referring to Figure 12, the jig has a block 68 in place of the cross-member 48, and this has two blind holes 69 to register with and receive the studs 64. The jig is secured by finger-operated screws 70, similar to the screws 67, threaded through the sides of the block 68 to clamp against the studs 64.

Wherever possible, such finger operated screws will replace the screws described previously, which are shown as requiring screwdriver operation.

Another improvement indicated in Figure 10 is a groove 71 in the rear side of the fence 20 extending along it just below the upper edge. This can provide more positive retention for the stops 23 and the devices 29.

Referring now to Figures 13, 14 and 15, these show a jig for use in cutting polygonal section members. The jig has two vertical, parallel end plates 71 and 72 which can be adjusted towards and away from each other on guide rods 73, to which they can be clamped by screws 74. The plate 71 carries a head stock 75 and a plate 72 carries a tail stock 76 aligned therewith. The head stock 75 has a gripper plate 77 on the inside of the plate 71 and is journalled by a shaft that carries a pinion 78 outside the plate. The pinion can be held in a desired angular position by a projection 79 engaging between a pair of its teeth, the projection being part of a lever 80 biased by a spring 81 into engagement with the pinion 78.The number of teeth will be selected to be divisible by most numbers up to 12, say, so that the pinion can be indexed round in regular steps to create different sided regular polygons up to twelve sided ones.

Further divisions could be provided, but are unlikely to be required. The pinion 78 can be marked on its exposed face to facilitate setting it correctly.

The tail stock 76 simply comprises a screw threaded shaft presenting a coned point 82 towards the head stock 75, and which can be locked in place by a nut 83.

This jig can be clamped to the fence using the stops 23 on the plates 71 and 72. A workpiece is fitted between the head and tail stocks and the pinion 78 is locked in one position. A pass through the saw is made, slicing off a slab of the workpiece. The cut may be straight and parallel to the bar 73, it may be slightly skew to those bars, giving a taper, or the cut could be curved with the fence moving through an arc.

The lever 80 is then pulled bac: to free the projection 79 and the pinion 78 is indexed round by an angle equal to that subtended at the centre by one side of the intended polygon. It is then fixed again by the lever 80 being released. A second cut is made, taking off another slab and producing a second side. This is continued until the workpiece is shaped completely into a member with a polygonal cross section.

Claims (13)

1. A jig for a band saw comprising a table through which the saw blade runs and provided with tracks for the guidance of a workpiece holder, the holder comprising a track follower which remains flush with or below the table top and a fence assembly pivoted to the follower about an axis perpendicular to the table top to enable the fence to be set at a selected angle to the saw blade plane.

2. A jig for a band saw as claimed in Claim 1, wherein the fence is adjustable in its longitudinal direction.

3. A jig for a band saw as claimed in Claim 1 or 2, wherein the tracks are grooves parallel to the edges of a square or rectangular table.

4. A jig for a band saw as claimed in Claim 3, wherein the follower is a flat bar which is a close sliding fit in the grooves.

5. A jig for a band saw as claimed in Claim 3 or 4, wherein there are means for clamping the follower at selected positions in the grooves.

6. A jig for a band saw as claimed in any preceding Claim, wherein the fence has a flat face perpendicular to the table top.

7. A jig for a band saw as claimed in any preceding Claim, wherein clamping means are fittable to the fence to hold a workpiece thereto at any selected position along the fence.

8. A jig for a band saw as claimed in any preceding Claim, wherein the tracks include a groove leading from the edge of the table towards the blade, perpendicular to the plane of the blade, there being a further follower adapted to co-operate with this groove and having means for centering a workpiece, allowing it to be rotated and thereby cut into a disc.

9. A jig for a band saw as claimed in Claim 8 as appendant to Claim 7, and further comprising a member that can co-operate with the centering means and which is adapted to have the fence fitted thereto, a workpiece clamped to the fence thus being cuttable in a curve as said member is rotated about the centering means.

10. A jig for a band saw as claimed in Claim 9, wherein the radius of said member is adjustable.

11. A jig for a band saw as claimed in any preceding Claim, and further comprising an extension fittable to an edge of the table and thereby providing lengthened tracks.

12. A jig for a band saw as claimed in any preceding Claim, and further comprising a device securable to the fence and adapted to hold a workpiece in a plurality of angular positions about an axis thereof, enabling the workpiece to be cut with a polygonal section.

13. A jig for a band saw substantially as hereinbefore described with reference to the accompanying drawings.