GB2177971A

GB2177971A - Straight edge for guiding power tools

Info

Publication number: GB2177971A
Application number: GB08517733A
Authority: GB
Inventors: Barry Graham Martin
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-07-13
Filing date: 1985-07-13
Publication date: 1987-02-04

Abstract

A straight edge 11 provided with means 12 to clamp the straight edge to a working surface is characterised by the provision of at least two scales 13 each of which, in use, can be caused to project from the working edge of the straight edge to reach the already-marked intended line of cut 25 in a sheet of wood or other workpiece, and thereby enable the straight edge to be aligned accurately in spaced parallelism with the line of cut before being clamped to the workpiece and/or to a surface supporting the workpiece; and each of the scales 13 can then be removed from or stowed on the straight edge to allow unimpeded travel of the base plate of a saw or other power tool along the working edge of the straight edge to cut the workpiece. <IMAGE>

Description

SPECIFICATION Straight edge for guiding power tools Field of the invention The invention relatestoastraightedgeforguiding power tools, for example power-driven portable cir cularsaws of the kind in widespread use amongst "do it yourself" enthusiasts and typified by the saws currently marketed in the United Kingdom by Black & BR< Decker Limited and driven by fractional horse power electric motor.

Background to the invention The problem which the invention is intended to solve arises when cutting sheets of wood with a portable powersawoftheBlack & eckerkind.These saws, run on a base plate which moves along the sheet to follow the line of cut. Conventionally, the "stand-off" distance from the blade to the edge ofthe base plate is marked on the sheet; a straight edged beam of wood is clamped to the sheet so that its straight edge runs at this distance from the intended line of cut and parallel to that line; and the cut is made by running the edge of the saw base plate along the straight edge of the beam and hence guiding the saw through the sheet along the intended line of cut.

The drawbacks ofthis method are that a spare beam with a straight edge always has to be kept handy; the beam needs to be taken care of, and its edge preserved, and this is not always likely to happen; the beam can warp with time and in poorstorage conditions; separate clamps haveto be kept handyto clamp the beam to the sheet; packing has to be used if the surface ofthe sheet is not to be damaged; and the intended line of cut has to befirstmeasuredoffand then drawn between the measured-off markings.

The only relevant art known to the applicant is a straight edge which incorporatesmeanstoclampthe straight edge to the bench orotherworking surface supporting the sheet during sawing. This edge is marketed in the United Kingdom by mail order bythe companyToolmail (1982) Limited of 7 London Road, Sevenoaks, KentTN13 1AH underthe model designation Hirsh TCE-96 Cutters Edge and is described and illustrated at page 22 of the 1985 Toolmail mail order catalogue. The meanstoclampthestraightedgeto the bench are secured to the underside of the straight edge, and the straight edge is not a wooden beam.In these respects, the straight edge incorporates means to prevent it from moving inadvertently on the bench under pressure from the travelling saw; and it also will notwarp or be as easilydamaged asthesimple wooden beams referred to above.

This Hirsh straight edge still, however, incorporates no means to align it in accurately spaced parallelism with the intended line of cut.

Summary ofthe invention The invention in its broadest aspect is embodied in a straight edge, with means to clamp the straight edge to a working surface, and characterised by the provision of at leasttwo scales each of which, in use, can be caused to project from the working edge ofthe straight edge to reach the already-marked intended line of cut in a sheet of wood orotherworkpiece, and thereby enablethe straightedgeto be aligned accurately in spaced parallelism with the line of cut before being clamped to the workpiece and/orto a surface supporting the workpiece; and each of which scales can then be removed from or stowed on the straight edge to allow unimpeded travel of the base plate of thesaworotherpowertool along the working edge of the straight edge to cut the workpiece.

The scales incorporate means which positively cooperate with the straight edge when the scales are initially caused to project from the working edge of the straightedge in orderto align and space that working edge from the intended line of cut, even though the scales maybewhollyremovedfromthe straight edge and stowed elsewhere before cutting subsequently commences.

In otherwords,the invention is not to be construed so broadly as to embody a combination of the known Hirsh Cutters Edge with two conventional rulers.

The scales may for example each have one end which is hooked so as to engage a projection and/or a recess formed adjacent the working edge of the straight edge, with the intention that once the scales have been used they can simply be unhooked and stowed elsewhere until they are next needed. This has the merit of simplicity and there are noworking parts to go wrong.

Alternatively the scales may fold into the straight edge, by pivoting and/orsliding and/ortelescoping.

There would then be less chance of them being lost in a typical workshop.

The scales may, in mannersimilartothatofa conventional ruler, be marked with measures; but they could alternatively or additionally have a scale surface so constituted that any individual user of the invention could mark the "stand-off" distances of his own various powertools on the scale surfaces, with orwithoutthe aid of premarked measurements.

These surfaces ofthe scales mayforexample beso constituted as to accept readily a pencil or pen marking, and may with particular advantage be so consti tutedthatanysuch marking, whilstvirtually permanent in normal intended use, could be removed to take into account the changing nature ofthe stock of tools held by individual users.

The clamping meansmaywithadvantagehavea "wedge-locking" clamping action. Clamping means with this action are known in themselves, and have the advantage of being quickly and easily clamped and unclamped by an essentially straightforward lever-action operation as opposed to having to be screwed into and out of their clamped position. It is particularly advantageous, and it is thought to be new and to involve an inventive step, to apply this known species of clamp to a straight edge embodying the invention.

Where the clamping means operate with a wedging clamping action, as just envisaged, and in orderto reduce the danger of damage to either surface ofthe sheet and/orthe surface supporting the sheet, it is preferredthatthe mechanism imparting the clamping movement incorporates a spring which, as the clamp is applied, cushions the force with which the clamping jaw grips the clamped surface. Any such spring-cushioned mechanism will of course be so arranged that the clamp still fulfills adequately its primary clamping function.

In one embodiment of the invention, to be described and illustrated in this specification, the work- ing edge of the straight edge is notformed integrally with the rest ofthe main body of the straight edge; but instead is initially formed separately and is linked to the main body ofthe straight edge by means which allowtheworking edgeto be extendedfrom and retracted backto the main body. This has the advan tagethat,when cutting a grooveforexample in a workpiece, the straight edge can be used to guide the baseplateofthesaworothertoolwithoutitbeing necessary to unclamp the main body ofthe straight edge from the workpiece in between one cut and the second cut.

Preferably, in embodiments having the feature just outlined, the working edge extends and retracts without altering its attitude in relation to the longitudinal axis ofthe main body of the straight edge. This is preferred for the reason that the use ofthe extensible and retractable straight edge will overwhelmingly be to cut successive lines in parallelism with one another.

An extensible and retractable straight edge, where embodied in the invention, is again preferably held in its extended positions by clamping means having a wedging clamping action.

The underside of the straight edge, and the surfaces ofthe clamping means which is use will grip the undersideofthesheetand/orofasurfacesupporting the sheet, may with advantage be coated with slipresistant material. This does away with the need for packing strips to protectthe sheet surfaces. It mini misesthedangerofdamageto either surface of the sheet, even without such packing strips.

The clamping means may also advantageously haveacushionedclamping action,forthesame reason asthatjustoutlined; and in this case itis particularly advantageous to use a slip-resistantsur face for the underside ofthe straight edge and forthe jaws of the clamping means.

Preferably there are two individual clamping means, one to clamp each opposite end region ofthe straight edge, just as there are at least two scales; and it is also preferredthatthescalesandtheclamping means are all freely adjustable along substantiallythe entire length of the straight edge.

In one current embodiment of the invention, to be described and illustrated in this specification,there are two scales and two individual clamps, and all are respectively separate entities. A scale may however be combined with a clamp in certain embodiments.

Brief description of the drawings The accompanying drawings show byway of example one embodiment of the invention. This is not necessarily the best way of putting the invention into practice, but it is the best ofthose currently known to the applicant and now reduced to practice. It will now be described with reference to the drawings, in which: Figure 1 shows the straight edge diagramatically and in perspective, and, and drawn to a scale reduced in comparison with the otherfigures of the drawings; Figure2 shows the main body of the straight edge in transverse section, whilst Figures 3 and 4 show respectively a clamp and a scale forming part ofthe straightedge; and Figure 5 shows the essential features of an alternative edge.

Description of the preferred embodiment The main body of a straight edge shown in Figure 1 is referenced generally 11 and is linear, elongate and free from any warping along its length. As shown, the body is rectangular in plan, and it is of constant cross section. It may be made in metal or in tough hard plastic, or in wood or any other material suited to its intended use. It carries two clamps 12 and two scales 13, all of which can slide along thewholeofthe length ofthe body 11, and can be wholly removed from the body 11, independently of one another.

Although the body 11 is illustrated as a single length of material, it could comprise two telescoped lengths and so increase its versatility. The details of how to construct a suitablytelescoping body such as the body 11 can readily be supplied without further inventive thought by the intended skilled addressee of this specification.

Figure 2 shows the constant cross section of the body 11. A recess 14 is created between the main flat top portion 15 and the peripheral flat top portion 16 Of the body. The working edge 17 ofthe straight edge (i.e. the edge along which the base plate of the saw or other powertool travels in use) adjoins the recess 14.

Another recess 18 is created along the underside of the body 11 ofthe straight edge, beneath the flattop portion 15 and inboard of the recess 14.

Figure 2 shows one half of the cross section of the body 11. The other half is a mirror image of it and has similarly formed and positioned recesses corresponding to the recesses 14 and 18 shown in Figure 2.

All these recesses extend along the whole of the length of the body 11, and each of the recesses is open at each of its opposite ends.

The clamps 12 engage simultaneously in the opposed recesses 18 of the body 11, whilst the scales 13 engage the recess 14 adjoining the working edge 17 of the straight edge. Because the recesses are open-ended, the clamps and the scales can be freely inserted into and removed from the body 11. Once the clamps 12 are inserted into their recesses 18, they are held in the body 11 (although they can be adjusted, when not in clamping mode, up and down that body's length).

The body 11 in use rests with its undersidefirmlyon the sheet of wood or otherworkpiece to be cut by the power tool. A slip-resistant coating 19 of a rubberised solution is therefore provided. This coating, as well as resisting any tendency of the body 11 to slide on the workpiece once it has been clamped into place, also helps to prevent the workpiece from being marked.

Proprietary coatings or preformed strips of material which would be suitable will occurto the skilled reader.

Each scale 13 as shown in Figure 4 is of relatively simple construction and is, in this particular embodiment, bent up from metal strip. One of its surfaces is marked with graduations 21 in a mannersimilarto that of a conventional ruler. Its end is hooked, and is so proportioned thatthe flank 22 of the hook abuts the working edge 17 of the body 11 in use whilstthe base 23 ofthe hook sits on the surface 16 ofthe body; and the tail 24 of the hook engages the recess 14, all as shown in broken line in Figure 2.

Each scale 13 can thus befirmlyengaged adjacent the working edge 17 of the straight edge, at any point along the length of that working edge, and the two scales can be used to space the body 11 in accurate parallelism with the intended line of cut referenced 25 in Figure 1 - already marked on the sheetworkpiece.

Figure 3 now illustrates one specificform of clamp 12for use with the body 11 and the scales 13. Other forms of clamp could be used. The one illustrated is only by way of example, although in general it is preferred that any clamping has a wedging clamping action as does the clamp of Figure 3.

The head 26 of the clamp is circular. Diametrically opposite regions of its periphery engage respectively in each of the recesses 18 in the body 11,so thatthe clamp can slide up and down the length ofthe body whilst being retained on the body when not in clamping mode. A stem 27 is essentially an elongate rectan gularbarofconstantcrosssection and is joined to the head 26 by a pin 28 which allows the stem 27, and the parts carried by the stem, to pivot into substantially the same plane as the plane oftheflatcircularhead 26 from the position, shown in Figure 3, where the stem 27 and the parts carried by the stem depend from the head 26 and occupy a plane substantially at right angles to the plane of the head.

A jaw29 in the form of a rectangular block slides up and down the stem 27. Theclamping face ofthe jaw 29 is coated with a slip-resistant coating 31 identical to the coating 19 on the underside of the body 11 The through-aperture 32 which enables the clamping jaw 29to slide up and down the stem 27 also allowsthe jaw 29 a limited amount of sideways float, as Figure 3 shows.

Another block 33 is freely slidable up and down the stem 27 and again has allowanceforfloat. Aleaf spring 34 acts between the block 33 and one straight edge ofthe stem 27.A link35 is pivoted atone end 36 to the jaw 29 and at its other end incorporates a lost motion connection 37 securing it to the block 33.

A coiled compression spring 38 is housed in a cut out in the link35 and acts between one end ofthe cutout and the underside of the pin 36. A handle 39 is pivoted at41 to the block33 and is so shaped that, when the handle is turned clockwise when viewed as in Figure 3, a base region 42 ofthe handle acts as a cam on the rounded surface of the adjacent end of the link35 and pushes the link35 upwards (i.e. againstthe action of spring 38) to take up the lost motion connec tion in the link between block 33 and jaw 29.

The edge of stem 27 parallel with the edge against which the leaf spring 34 operates is crenellated, as shown. A pin 43 in block 33 engages individual ones of the crenellations, but the float inherent in block33 (together with the pivoting action of link 35 allowed by pivot 36) enables block 33 to move to the right when viewed as in Figure 3, and againstthe action of spring 34, to bring pin 43 out of engagement with the crenellations.

Block 33 and hence jaw 29 can then be moved up stem 27 to trap a workpiece and/or a workpiecesupporting surface between the two coatings 19 and 31, assuming the clamp to be in position in thebody 11. Pin 43 is allowed to ride back into the nearest adjacentcrenellation underthe action of spring 34.

Handle 39 isthen turned clockwisewhen viewed as in Figure 3,to push link 35 and hence jaw 29 hard againstthe underside of the workpiece and/orworkpiece-supporting surface with what amounts to an essentially spring-cushioned action.

In Figure 5, the working edge 17 of the straight edge is extensible and retractable in relation to the main body of the straight edge. Rigid legs 44 extend from the initially separately formed working edge portion 17 to slide in respective grooves 45 cut into the top surface 15 ofthe main body ofthe straight edge in such a way that, as the legs slide along the grooves, the working edge 17 moves away from and back towards the main body. Wedge-action cam locks 46 canclampthelegs44againstthesidesoftheirre- spective grooves 45 to hold the legs, and hence the working edge 17, in anyone of a plurality of positions spaced from the main body of the straight edge.

Respective end blocks 47 fit into the recesses 18 in thqirnain body, in this particular embodiment, once the clamps 12 have been inserted.Theend blocks 47 can be a tight fit, and/or can be secured by screws, in a manner which forms no essential part of the present invention and which can beselected by the skilled reader.

Scale markings may be distributed along the length of each ofthe legs 44, in a manner similarto the markings on the surface 21 ofthe measuring gauges.

Claims

1. Astraight edge, with means to clampthe straight edge to a working surface, and characterised by the provision of at least two scales each of which, in use, can be caused to project from the working edge of the straight edge to reach the already-marked intended line of cut in a sheet of wood or otherworkpiece, and thereby enable the straight edge to be aligned accurately in spaced parallelism with the line of cut before being clamped to the workpiece and/or to a surface supporting the workpiece; and each of which scales can then be removed from or stowed on the straight edgeto allow unimpeded travel ofthe base plate of the saw or other power tool along the working edge of the straight edge to cut the workpiece.

2. A straight edge according to Claim 1 and in which the scales each have one end which is hooked so as to engage a projection and/or a recess formed adjacent the working edge of the straight edge such that, once the scales have been used, they can be unhooked and stowed elsewhere until they are next needed.

3. A straight edge according to Claim 1 and in whichthescalesfold into the straight edge.

4. Astraightedge according to any ofthe preced ing Claims and in which the scales have surfaces so constituted as to accept readily a pencil or pen marking.

5. Astraightedge according to Claim 4 and in which the scale surfaces are so constituted that any such marking can be readily removed.

6. Astraightedge according to any ofthe preceding Claims and in which the clamping means have a "wedge-locking" clamping action.

7. A straight edge according to Claim 6 and in which the mechanism imparting the clamping movement incorporates a spring which, as the clamp is applied, cushions theforcewith which the clamping jaw grips the clamped surface.

8. A straight edge according to any of the preceding Claims and in which the working edge of the straight edge is linked to the main body of the straight edge by means which allowtheworking edge to be extended from and retracted backto the main body.

9. Astraightedgeaccordingto Claim8and in which the working edge extends and retracts without altering its attitude in relation to the longitudinal axis of the main body of the straight edge.

10. A straight edge according to Claim 8 or Claim 9 and in which the working edge is held in its extended positions by clamping means having a wedging clamping action.

11. Astraightedge according to anyofthepreceding Claims and in which the jaw surfaces ofthe clamping means are coated with slip-resistant material.

12. Astraightedgeaccordingtoanyofthepre- ceding Claims and in which the scales and the clamping means are all freely adjustable along substantially the entire length of the straight edge.

13. A straight edge substantially as described herein with reference to and as illustrated in Figures 1,2 and 4 of th e accompanying drawings.

14. Astraightedge according to Claim 13 and comprising clamping meanssubstantiallyasde- scribed herein with reference to and as illustrated in Figure 3 of the accompanying drawings.

15. Astraight edge according to Claim 13 orClaim 14 and comprising an extensible and retractable working edge substantially as described herein with reference to and as illustrated in Figure 5 ofthe accompanying drawings.