GB2365817A

GB2365817A - Hand controlled electric tool

Info

Publication number: GB2365817A
Application number: GB0116728A
Authority: GB
Inventors: Guenther Berger; Albrecht Hofmann; Harald Krondorfer; Rudolf Fuchs; Thomas Schomisch
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2000-07-21
Filing date: 2001-07-09
Publication date: 2002-02-27
Anticipated expiration: 2021-07-09
Also published as: GB2365817B; JP2002036204A; GB0116728D0; JP5108185B2; DE10035560A1

Abstract

In a hand-controlled electric tool (1), in particular a face milling tool or electric plane, comprising a basic body (10), which comprises a reference face (14), and a rotatably driven cutting head (7) having at least one blade (2), the plane of engagement (24) of which in relation to the reference face (14) defines the cuffing depth (A), even in the event of unintended or uncontrolled setting-down of the electric tool damage to the workpiece surface is avoided and at the same time engagement into a surface is facilitated in that the electric tool (1) comprises an engagement control (16), by means of which the cutting depth (A) is variable between a minimum value (A0), which is equal to zero, and a maximum value (A1) counter to a force (F), in particular counter to the action of a spring (4).

Description

2365817 Hand-controlled electric tool

Background art

The invention proceeds from a hand-controlled electric tool having the genredefining features of claim 1.

For machining flat wooden surfaces, in particular for mechanically removing paint and similar coatings, eccentric, orbital and belt sanders are used. Such appliances operate with geometrically non-defined cutting edges, e.g. bonded abrasive bodies. Machining with such appliances is very time-consuming and requires a large quantity of abrasive. Furthermore, a defined adjustment of the removed material thickness is not possible. Only a belt sander with an additional sanding frame offers such a facility. The abrasive dust arising during sanding is so fine that it is inhaled by the operator of the appliance and deposits in the lungs, which is detrimental to health. It is therefore necessary to wear a breathing mask or equip the appliance with a dust extraction device, which entails a high cost.

For removing surface coatings, appliances with geometrically defined cutting edges are also used. Such an appliance is known from DE 195 43 992 Cl. Here, it is a case of a motor-driven hand tool in the form of a face milling tool, in which blades are disposed as cutting means on the face of a rotating cutter head. By said means the machining time and the wear of the cutting means is markedly reduced compared with the appliances described above. Furthen- nore, far less fine dust is produced because it is predominantly chips which are removed. When a surface is machined with such a face milling tool, the cutting tool acts directly upon the surface as soon as the appliance is placed onto the latter. The drawback of said appliance is that inadvertent machining of the surface, which as a rule may be equated with damage, may frequently occur. Say, for example, when setting down the machine while it is running. A rapid, unintentional application of the tool may also lead to damage of the cutting blades as a result of an impact load. With said appliances, moreover, it is only possible to approach a laterally opened face. In said case, the face milling tool first has to be positioned with its guide face on the edge and then guided onto the surface to be machined. Only then does the cutting tool engage at the surface to be machined. When the appliance is applied from above onto the surface, the rapidly rotating inserted tool at the instant of application mostly causes damage to the surface.

The same problems also arise with a hand-held electric plane operating with an adjustable blade infeed. Said appliance also has geometrically defined cutting edges. When the hand-held electric plane is placed onto the surface and additionally moved in feed direction, the usual set-down aids fold inwards and accidental damage of the surface to be machined may occur.

Advantages of the invention In contrast, the hand-controlled electric tool according to the invention having the characterizing features of claim I has the advantage of preventing the workpiece surface from being damaged as a result of unintended or uncontrolled setting-down of the electric tool. Furthermore, engagement of the tool into a surface is facilitated.

By virtue of the fact that the tool does not project beyond the reference face when there is no force acting upon the engagement control, the cutting depth equals zero. Even when the cutting head is rotating, the blade does not come into contact with the surface to be machined. It is only when the operator deliberately exerts a force upon the engagement control that the tool moves beyond the reference face until the cutting depth reaches a maximum value. The slow extending of the blade leads to a slow engagement into the surface to be machined. As soon as the operator is no longer exerting a force upon the engagement control, the blade readopts its original position and the cutting depth returns to the value zero. In said state, the blade no longer engages into the surface of the workpiece to be machined.

It is advantageous when the engagement control displaces the cutting head, which rotates about a vertical axis, along said axis. The engagement control may therefore be constructed on a face milling tool.

It is further advantageous when the cutting head is connected to a handle, which projects beyond the basic body, is fixed relative to the cutting head and displaceable relative to the machine basic body and lies on the vertical axis. The engagement control may therefore be of a very simple design and is very easy for the operator to operate.

It is particularly preferred when the cutting depth is definable by means of a stop between handle and basic body. By displacing and then fixing the stop the maximum cutting depth, to which the engagement control may be pressed through by the operator, is defined. Such a refinement is very easy and inexpensive to manufacture and yet offers a very high degree of mechanical stability and safety.

Another advantageous development of the invention provides that the cutting head rotates about a horizontal axis, the reference face is displaceable relative to the basic body and the basic body comprises a guide face. By said means it is possible to construct the engagement control on a hand-guided electric plane. Simultaneously moving.the electric plane and pressing on the engagement control has the effect of moving the reference face relative to the cutting edge circle of the cutting head so that the cutting depth changes from its minimum value, i.e. zero, in the no-load state to its maximum value. As soon as the pressure on the engagement control is removed, the reference face returns to its original position and comes to lie outside of the cutting edge circle of the cutting head. It is thereby guaranteed that machining of the surface occl exclusively as a result of deliberately pressing on the engagement control.

It is particularly preferred when the reference face is formed on a sliding pad, which is movable along an oblique plane on the basic body. It is thereby possible for the force exerted upon the engagement control to be utilized simultaneously to move the electric plane. The operator may therefore move the electric plane much more easily and with less expenditure of force. Handling of the appliance is improved as a result.

It is particularly preferred when the cutting depth is definable by means of a movable and lockable stop on the basic body. Such a stop may be constructed very easily and inexpensively on the appliance and yet offers a high degree of mechanical safety.

It is particularly advantageous when the basic body comprises a protective casing, which is disposed around the cutting head. Good lateral protection is thereby guaranteed, so that the risk of injury to the operator of the appliance is reduced virtually to zero.

Further advantages of the invention are the subject matter of the subclaims.

Drawings There now follows a detailed description of two embodiments of the invention with reference to the accompanying drawings. The drawings show:

Figure I a diagrammatic section through a face milling tool according to the invention, wherein the engagement control is in the inoperative state, Figure 2 a section as in Fig. 1, wherein the engagement control is in operating position, Figure 3 a diagrammatic section through an electric plane according to the invention, wherein the engagement control is in its inoperative position, and Figure 4 a section as in Fig. 3, wherein the engagement control is in its operating position.

Figure I shows a hand-guided electric tool 1, in the form of a face milling tool, having a rotating cutting head 7. The cutting head 7 is firmly connected to a drive shaft 5. The drive shaft 5 is driven by means which are known as such.

For example, by means of the diagrammatically indicated drive motor I I and the belt drive 12 plus belt pulley 6. However, as the latter are not essential to the invention, they are not described in greater detail. The drive shaft 5 rotates about a vertical axis 9. The face milling tool comprises a basic body 10, which in the form of a protective casing 13 radially encloses the cutting head 7.

Blades 2 are disposed axially remote from the basic body 10 on the cutting head 7. The blades 2 project both axially and radially beyond the cutting head 7. When the cutting head 7 rotates, the blades 2 define the cutting edge circle.

The drive shaft 5 is supported via a needle bearing 8 in the machine housing 10. At its free end the drive shaft 5 is supported via a ball bearing 17 in a pot 18. The pot 18 is firmly connected to one end of a handle 3. The head 19 of the handle 3 projects from the machine housing 10. Between the machine housing 10 and the head 19 of the handle 3 a stop 15 is firrnly connected to the machine housing 10. A spring 4, which encloses the bottom part of the handle 3, is disposed between the machine housing 10 and the head 19 of the handle 3. The spring 4 presses the handle 3 away from the machine housing 10. The spring 4 is so strong that, when no force is being exerted upon the handle 3, the blades 2 are entirely taken up in axial direction in the protective casing 13. In said case, the handle 3, the spring 4 and the pot 18 fonn the very simply designed engagement control 16.

Fig. 2 shows the hand-guided electric tool 1 in its state, in which the blades 2 are exposed. As the construction of the electric tool I is identical to that in Fig. 1, it is not described in detail again. The state illustrated in Fig. 2 is achieved by exerting a force F axially upon the engagement control 16 via the handle 3. As a result, the handle 3 is moved downwards counter to the action of the spring 4. The pot 18 firmly connected to the one end of the handle 3 is consequently pressed downwards. At the same time, the drive shaft 5 supported via the ball bearing 17 in the pot 18 is consequently moved downwards. This is possible by virtue of the needle bearing 8 being movable along an opening 25 in the machine housing 10, in which it is supported. This finally leads to the cutting head 7, which is firmly connected to the drive shaft 5, being pressed axially downwards. As a result, as soon as the blades 2 situated on the rotating cutting head 7 move beyond the reference face 14, an engagement into the surface to be machined occurs. Said engagement, which represents the cutting depth A, is slowly increased until the cutting depth A has reached its maximum value Al. It reaches said value when the head 19 of the handle 3 strikes against the stop 15. Thus, the maximum value Al of the cutting depth A may be adjusted by providing various spacers between the stop and the head 19. Another possibility is for the stop 15 to be disposed rotatably on the machine housing 10 and be screwable in the form of a thread into or out of said machine housing.

It is thereby guaranteed that, so long as there is no force F acting upon the engagement control 16, then, even if the cutting head 7 is rotating, there is no machining of the surface, on which the reference face 14 of the machine housing 10 is supported. Even if the electric tool I is pushed back and forth on the surface, the blades 2 do not in any way engage with the surface. It is only when the operator deliberately exerts a force F upon the engagement control 16 that an engagement of the blades 2 into the surface occurs. This is effected continuously so that, as the cutting head 7 rotates, the blades 2 move slowly from the minimum cutting depth AO, which is zero, to the maximum cutting depth Al. The result is therefore a gradual engaging of the blades 2 into the surface, which leads to easier handling of the electric tool 1. As soon as the operator is no longer exerting pressure on the head 19, the cutting head 7 and hence the blades 2 fastened therein return to the original position, wherein the minimum cutting depth AO is restored. The blades 2 are therefore no longer in engagement with the surface. Accidental damage of the surface is therefore virtually ruled out.

Figures 3 and 4 show a second embodiment of a hand-controlled electric tool I according to the invention, this time in the form of an electric plane. Parts acting in an identical manner are denoted by the same reference numbers as in Figures 1 and 2. In Figure 3 the electric plane is shown in a state comparable to Figure 1, while the electric plane is shown in Figure 4 in a state comparable to Figure 2. In the case of electric plane, the cutting head 7 moves about a horizontal axle 20, which is supported in a stationary manner in the machine housing 10. The cutting head 7 here is set in rotation by known drive means which are not described in detail. Projecting radially beyond the cutting head 7 are blades 2, which therefore form a flight circle. An engagement plane 24 is defined by the lowest point of the flight circle. Formed at the underside of the machine housing 10 is a guide face 22, at which the electric tool slides over the surface to be machined. The flight circle of the blades 2 in said case does not project beyond the guide face 22. A sliding pad 30 is disposed likewise at the underside of the machine housing 10 and is displaceable along an oblique plane 23, which is formed on the machine housing 10, so as to be movable relative to the machine housing 10. Guidance of the sliding pad 30 along the oblique plane 23 is effected by means of known guide means, which are not shown. A stop 15 is formed on the oblique plane 23. Disposed between the stop 15 and the sliding pad 30 is a spring 4, which presses the sliding pad 30 away from the stop 15. At the top of the machine housing remote from the sliding pad 30 a handle 21 is provided. The engagement control 16, here, is formed by the sliding pad 30, the spring 4 and the oblique plane 23.

In Figure 3 there is no force acting along the oblique plane 23 upon the sliding pad 30. In said case, the spring 4 presses the sliding pad 30 down along the oblique plane 23 to such an extent that the reference face 14 formed at the underside of the sliding pad is situated lower than the engagement plane 24 of the blades 2. This means that, even if the electric plane is moved in direction of motion B over the surface of the workpiece to be machined, the blades do not engage into the surface.

In Figure 4 the electric plane is loaded with a force F, which acts parallel to the oblique plane 23 upon the handle 2 1. The electric plane is moreover additionally guided in direction of motion B over the surface. By virtue of the force F the sliding pad 30 is moved along the oblique plane 23 towards the stop 15 counter to the action of the spring 4. As soon as the reference face 14 is situated higher than the engagement plane 24 of the blades 2, with the cutting head 7 rotating the removal of material from the surface begins. This is effected continuously because the cutting depth A, which is defined by the difference between the reference face 14 and the engagement plane 24, steadily increases. As soon as the sliding pad 30 strikes against the stop 15, the maximum cutting depth Al has been attained. When the electric plane is guided with a uniform force F in direction of motion B over the surface, a uniform removal of material from the surface is guaranteed.

As soon as the operator reduces the force F upon the handle 2 1, the sliding pad 30 moves back down under the action of the spring 4. This continues until the force F is zero, i.e. the operator is no longer pressing at all upon the electric plane. The state illustrated in Figure 3 is then restored.

In said embodiment too, accidental damage of the surface is ruled out by that fact that the blades 2 may come into engagement with the surface only as a result of deliberate pressure upon the handle 2 1.

List of reference characters I hand-guided electric tool 2 blade 3 handle 4 spring 5 drive shaft 6 belt pulley 7 cutting head 8 needle bearing 9 vertical axis 10 machine housing I I drive motor 12 belt drive 13 protective casing 14 reference face 15 stop 16 engagement control 17 ball bearing 18 pot 19 head 20 horizontal axis/axle 21 handle 22 guide face 23 oblique plane 24 engagement plane 25 opening 30 sliding pad A cutting depth I I AO minimum cutting depth Al maximum cutting depth B direction of motion F force

Claims

1. Hand-controlled electric tool (1), in particular a face milling tool or electric plane, comprising a basic body (10), which comprises a reference face (14), and a rotatably driven cutting head (7) having at least one blade (2), the plane of engagement (24) of which in relation to the reference face (14) defines the cutting depth (A), characterized in that it comprises an engagement control (16), by means of which the cutting depth (A) is variable between a minimum value (AO), which is equal to zero, and a maximum value (Al) counter to a force (F), in particular counter to the action of a spring (4).

2. Electric tool (1) according to claim 1, characterized in that the engagement control (16) displaces the cutting head (7), which is rotatable about a vertical axis (9), along said vertical axis (9).

3. Electric tool (1) according to claim 2, characterized in that the cutting head (7) is connected to a handle (3), which projects beyond the basic body (10), is fixed relative to the cutting head (7) and displaceable relative to the basic body (10) and lies on the vertical axis (9).

4. Electric tool (1) according to one of claims 2 or 3, characterized in that the cutting depth (A) is definable by means of a stop (15) between handle (3) and basic body (10).

5. Electric tool (1) according to claim 1, characterized in that the cutting head (7) rotates about a horizontal axis (20), the reference face (14) is displaceable relative to the basic body (10) and the basic body (10) comprises a guide face (22).

6. Electric tool (1) according to claim 5, characterized in that the reference face (14) is formed on a sliding pad (30), which is movable along an oblique plane (23) on the basic body (10).

7. Electric tool (1) according to one of claims 5 or 6, characterized in that the cutting depth (A) is definable by means of a movable and lockable stop (15) on the basic body (10).

8. Electric tool (1) according to one of the preceding claims, characterized in that the basic body (10) comprises a protective casing (13), which is disposed around the cutting head (7).

9. A hand-controlled electric tool substantially as herein described with reference to Figures I and 2 or Figures 3 and 4 of the accompanying drawings.