When using handheld drilling machines it is very difficult to see and control the drilling direction. Thus the result often becomes more or less slanting holes that make mounting difficult and the result ugly. In other cases too, as erecting posts, fences and door frames, brick laying and other similiar works one is having problems making the construction straight. The problems are often of the art that one, as when drilling, must be able to adjust the direction during ongoing operation.

The implements for direction control in use still to-day are mainly the same as in older times and founded upon set squares, plumb-lines, levels and similiar utensils. The problems and detriments that accompany those primitive methods are well known. They are useless for continous control. They often demand helpers and do not give opportunity of control in more than one direction.

The present invention is aimed at solving the problem and concerns a new principle to observe and with security continously control direction in more than one plane, without eye movement, by using an optical system of mutually parallel reference lines and two slanting, reflecting, plane surfaces.

The system does not require special lighting above the normal one and may be designed either free-standing and independent of machines used or as an easily mount- and demount-able accessory part to the machine used. It may be used not only for horlsontal and vertical erections, but also for erections with arbitrary angles against the horlsontal and vertical plane. The optic is simple and does not contain any optically active curved surfaces, i. e. no sferical lenses, sf rical mirrors or like things. It is i principle parallax-free and has modest demands on eye position, which otherwise can be a problem at the use of optical systems.

The process according to the invention implays that one brings forth one or more with the intended direction parallell

reference lines and lets the reference lines and the object the direction of which is to be controlled be imaged in one or more plane reflecting surfaces.

Usually one wishes to control direction in more than one plane. For this is needed at least two plane reflecting surfaces. To make it possible to see simultanously the images in more than one reflecting surface the surfaces have to form angles with each other. Further if one wishes be able to see the images from an eye position close behind for instance a drilling machine the reflecting surfaces have to be slanting. The greatest precision is obtained if the angle between the base lines of the reflecting surfaces is straight or nearly straight, but other shapes may be used whenever they from design or product technical reasons bring advantages that surpass the relativly small loss of precision.

Fig. 1 and 2 show L e principles of an arrangement according to the invention.

Fig. 3 is a sketch of the essential features of a preferred way of carrying out the invention.

Fig. 4 is a specially preferred design where the implement has been designed with a corner piece (16) and provided with a back band to eliminate visual disturbances from the environment.

Fig. 5 is an alternative design, which may be better from the manufacturing point of wiew, but less preferred if the main aim is highest possible precision.

Fig. 6 Shows a preferred design that makes control at oblique direction possible.

Fig. 7 shows a design of the implement according to fig. 6 intended for mounting at a hand held drilling machine.

The way of carrying out the invention according to fig.3 can be described ae two units (1) and (2) coupled or able to be coupl d to each other at straight angle. The arrangement is

placed on or attached to the actual surface with the working point approximately symmetric between (1) and (2).

The essential elements of the units (1) and (2) consist of two transparent screens (fi) and (6) equipped with mutually parallell reference lines (7 and β) at straight angle against the long sides of the screens. The screens are arranged perpendicularly against the base plane of the implement. Further two against the base plane slanting (30 - 60°, preferably 45 - 50° angle) reflecting surfaces (3) and (4 ⁾ are included.

To make explanation easier one has in fig 1 and 2 placed an orthogonal coordinate system with origo at the working point and the axises x, y and z, where the x- and y axises lay in and define the base plane and the z-axiβ represents the intended direction. In fig. 2 one has for purposes of visuality put in a drill (11). When the straightening up is finished the drill direction coincides with the z-axis. By comparision with fig. 1 it is clear that in this situation the drill direction is correct when an eye placed behind or in front of the transparent screen (5) and observing the reference lines (7) and the drill (11) sees the direction of the drill as parallell to the reference lines. The angle between the x-axis and the drill is then correkt. At the same time information about the angle between the y-axis and the drill is missing. This information is obtained by the same procedure with respect to the screen (6) and the reference lines (β). To enable an operator to get simultanous information that the angle between vinkeln between x-axeln and the drill respectively the y-axis and the drill is correct a system is needed that makes images of the drill and the reference lines and makes it possible to look at those images simultanously. Fig. 2 shows such images made by a system of slanting, plane mirrors, which bring forth virtual images (9,10) of the reference lines (7, β) in the base plane and virtual images (12,13) of the drill in a plane that is situated below the base plane.

As already mentioned the control implement according to the invention may be used for straightening up even at oblique angle to the working plane. This may be done by using a non- orthogonal coordinate system i. . slanting the reference lines in one or both planes. A more preferred way is to use an orthogonal coordinate system i.e. let the reference lines be perpendikular to the xy-plane and adjust the angle between it and and the working surface.

A preferred design for straightening up at oblique angle to the working plane is shown in fig. 6 where (16) is a corner piece that with the aid of a post (18) is joined to a foot (19). Between foot plate (19) and corner piece (16) there is a knee joint (17). The knee joint (17) can be adjusted to and locked into desired position. For reasons of visuality the figure shows a hinge plane parallell to the y, z-plane. Generally a positioning at a plane situated between the y, z- and x, z- planes, for instance a plane through the bisektrice, might be preferred. By approplate design of the post (18) and the corner piece (16), for instance an octagonal post and the corresponding passage, the hinge plane can easily be adapted to, for each application, approplate place. I some cases there may be need for increasing respectively decreasing the height of the post between the joint and the corner piece. An approplate way of doing this is to let the post pass the corner piece and equip the unit with suitable arrangements for fixing at desired levels.

In the design according to fig. 7 the post (18) has been elongated and equipped with a steering (20) that via a cuff (21) has been fastened to the neck of the drilling machine (23). The steering keeps the post parallell to the axis of the drilling machine. Inside the steering the post is easily movable in axial direction. The upper end of the post is loaded by a spring (22). Between the steering (20) and the corner piece (16) the post (18) is provided with an easily movable ball joint (24). The extent of the ball joint's movements is normally situated within a calotte area of about 30°. The ball

joint causes that the whole foot plate makes contact with the ground surface when the operator presses the machine against it. With the aid of of the mirrors the operator can easily adjust any misdirection of the machine. The arrangement may be designed in such a way that it is indicating drilling depth and thus replaces the depth indicators that are common at modern drilling machines. The holder that fix the steering may be designed with a handle that gives a two hand grip tn the drilling machine.

The number of reference lines may be limited to just one. For the straightening up of posts, brick laying etc this reference line may be constituted of a hanging plumb-line and be part of a preferred way of carrying out the invention.

At drilling etc. the use of just one reference line puts big demands upon the orientation of the implement. A relatively big number of reference lines distributed in two planes that form straight or nearly straight angle to each other iu preferred. The mutual distance and the length of the reference lines is adapted to the dimensions of the controlled object. The length of the planes is adapted to the need of free working space between the working point and the control implement.

The? reference lines may be constituted of etched or in other ways made lines on transparent plates, but also of for instance a system with sticks designed as a comb. For vertical straightening ups an interesting alternative may be a system of plumb-lines or freely suspended bars. A number of other possibilities besides the mentioned appear as self-evident to a professional man.

Specially preferred designs include beside reference line system and image producing means a back shield to eliminate disturbing visual impressions from the environment that often may be very unruly. A kind of such a shield is shown in fig. 4 where the back shield is constituted of an easily flexible band (14) of metal or plastic with anchoring points at the ends of

the units (1,2). A number of other possibilities appear useful to a professional man.

As the illumination conditions may be bad at places where the implement is used the design should be done in such a way that the reference lines and by means of this the reference line images get good contrast with the background. This may be done among other ways by the choice of colour. Concerning transparent plates with etched or in other ways made lines the same effect may be obtained by giving the material different translucent properties.

A preferred arrangement according to the invention meant for drilling consists of two to each other angled planes with reference lines together with two to the reference line planes joined oblique reflecting surfaces. A arrangement for sawing with for instance an electrically driven circle saw may be constituted of the mentioned components and beside that a reflecting surface applied at the saw blade.

The implement can be made in a number of different materials. Concerning smaller units meant for instance for drilling production by casting of plastic of optical quality is a interesting alternative. At doing this one can by approplate choice of angles, in order to get total reflexion, avoid the need of special preparation to make reflecting surfaces.

At plastic casting it may be preferable to increase the number of planes in such a way that one obtains a horse shoe shaped design with more than two reference line planes.

If a design according to fig. 3 is chosen the units (1,2) can be made foldable. This to reduce the need for space at storing between uses. The foldability may be brought forth in several different ways. A simple, preferred way is to make the units jointed to each other by appropiate design of the combining piece.