GB2111886A

GB2111886A - Screwdriver

Info

Publication number: GB2111886A
Application number: GB08234131A
Authority: GB
Inventors: Hermann Reinhardt
Original assignee: SCHMALKALDEN WERKZEUG
Current assignee: SCHMALKALDEN WERKZEUG
Priority date: 1981-12-18
Filing date: 1982-11-30
Publication date: 1983-07-13
Also published as: SE8207220L; SE8207220D0

Abstract

A functional portion is formed, complementarily with a screw head recess, with longitudinal grooves 4 of trapezoidal cross-section having functional lateral surfaces 5 extending radially of the longitudinal axis 6 of the screwdriver stem. <IMAGE>

Description

SPECIFICATION Screwing tool The invention relates to a screwing tool, in particular not not exclusively a screw driver, having a functional portion which is formed at the front, preferably conical end of the screwing tool stem and is shaped complementarily with a screwhead recess.

Many varying constructions of screwing tools are known, e.g., after the fashion of screw drivers or screw spanners, whose functional portion differs from the known longitudinally and cross-slotted constructions, by having, for example, a three-wing or polygonal cross-section. (German Democratic Republic Patent Specifications 53 927 and 57 020; Federal German Patent Specifications O/S 2538 139 and O/S 29 46 781; Federal German Patent Specification A/S 17 28 574; Federal German Patent Specifications O/S 2451 373 and O/S 27 08 892.) The functional portions of the screwing tools intended for a slotted head or a cross-slotted head on set or lock screws are only moderately suitable for the transmission of relatively high torques and are susceptible of wearing out quickly and can get damaged.The functional portions of screwing tools constructed with wing-like or polygonal crosssectional shape have the disadvantage that the operative drive angle is unfavourable - i.e. relatively large - so that the screwing tool easily slips out, so that considerable torque losses occur, and moreover the screwhead recess is damaged.

The operative drive angle is understood to mean that angle which is formed by a straight line which extends radially from the centre of the screwing tool functional portion through a force-engaging point on its surface to a tangential line on such forceengaging point on the surface of the screwing tool functional portion.

Moreover, such functional portions, with substantially polygonal cross-sectional shape, which can sometimes also have rounded - i.e. cylindrical force-transmitting surfaces - require high manufacturing accuracy, so as to ensure a substantially correctly fit and registration of the force-transmitting surfaces in the coupling of the functional portions of the screwing tool and ofthe screwhead recess, and also so as to exclude excessive surface pressure or shear loading in the direction of the tightening forces transmitted from the screwing tool.

In addition, experience shows that tools of this kind, with a large "number of teeth" and resulting arrangement of the force-transmitting surfaces finished with rounded sections, can be brought into engagement with the engaged article only with difficulty; this makes it harder to handle such a screwing tool, in comparison with one with having fewer teeth.

This circumstance is particularly important in cases in which a set or lock screw to be actuated is difficu It to reach because of its orientation or lack of surrounding space, or in which the longitudinal axes of the screwing tool and screwhead recess are not in alignment.

It is an object of the invention to reduce these disadvantages and to attempt to provide firm, slip-proof engagement of the functional portions of the screwing tool and the screwhead construction, even if the screw axes are not exactly in alignment.

The screwing tool according to the invention has a functional portion formed with longitudinal grooves of trapezoidal cross-section which are formed, preferably machined, into the front, preferably conical, end of the screwing tool stem.

In an advantageous embodiment of the invention, the periphery of the screwing tool functional portion has three grooves which are offset symmetrically in relation to one another, thus preventing any geometrical overdefinition of the cross-section of the screwing tool functional portion in relation to the complementary functional portion of the screwhead recess, and ensuring a high supporting component in the functional surfaces engaging with one another.

This advantageous embodiment may be further improved by the feature of constructing the inclined lateral surfaces of the longitudinal grooves to extend substantially radially in relation to the longitudinal axis of the screwing tool stem.

This produces on the functional surfaces of the screwing tool functional portion a radial drive angle of 0 , which is favorable to the screwing tool and, as experience shows, ensures optimum operating behaviourfor handling technique.

Preferably, the groove bottom surfaces are constructed outwardly arcuate in the region of the functional portion of the screwing tool; this is advantageous as regards manufacturing technique and function.

According to another aspect of the invention there is provided a screw having a screwhead recess formed complementarily to the functional portion of the screwing tool of the invention.

The invention is particularly suitable for set or lock screws.

The parts of the functional portion of the screwhead recess which are subjected to shear stresses can be of larger dimensions that those of the screwing tool. This has the advantage that if any overloading occurs, the screwing tool is the first to shear off, at its functional portion, the tightening screw and its functional portion remain undamaged.

This may be an advantage, inasmuch as it may be easier and cheaper to replace a screwing tool than a set or locking screw which has been damaged and can no longer be operated by a screwing tool. One needs only to think of the trouble which it causes to remove a high-strength set or lock screw in a difficult to reach place by, for example, drilling it out.

To help understanding of the invention an embodiment thereof will now be described in greater detail with reference to the accompanying drawing, in which: Figure 1 is a diagrammatic cross-sectional view of a functional portion of a screwing tool, engaged in a complementary screwhead recess of a set or lock screw, and Figure 2 is a view of the front, conical end of the screwing tool stem.

The drawing shows how longitudinal grooves 4 of trapezoidal cross-section are machined into the front, conical end 1 of a screwing tool stem 2, in order to produce the functional portion 3 ofthe screwing tool. Their lateral surfaces 5 extend radially in relation to the longitudinal axis 6 of the screwing tool stem 2, at the same time forming a functional portion shape 7, as shown in cross-section in Figure 1, of a three-groove, symmetrical construction.

Advantageously the groove bottom surfaces are constructed outwardly arcuate; this contributes towards further improving the engagement conditions of the functional surfaces participating in the transmission of force. Formed into a screwhead 8, for example, of a set or lock screw, is a functional portion shape, corresponding complementarily to the functional portion shape 4,5 of the screwing tool, in the form of a screwhead recess 9, as shown in Figure 1.

The above described screw driver, according to the invention, has the advantages of having a functional portion which: - can be manufactured in a simple manner with relatively high accuracy; - and allows smooth coupling with the complementary operating profile on a screwhead recess, while - permitting easy handling, but nevertheless - ensuring the effective transmission of torque.

Claims

1. A screwing tool with a functional portion shaped complementarily with a screwhead recess, wherein the functional portion is formed with longitudinal grooves of trapezoidal cross-section which are formed, preferably machined, into the front, preferably conical, end of the screwing tool stem.

2. A screwing tool as claimed in Claim 1, wherein the inclined lateral surfaces of the said longitudinal grooves are constructed to extend substantially radially in relation to the longitudinal axis of the screwing tool stem.

3. A screwing tool as claimed in Claim 1 or Claim 2, wherein the said longitudinal grooves are formed on the periphery of the screwing tool offset symmetrically in relation to one another, three such grooves being preferably provided.

4. A screwing tool as claimed in Claim 1, Claim 2 or Claim 3 wherein the bottom surfaces of the said longitudinal grooves are outwardly arcuate.

5. A screw having a screwhead recess formed complementarily to the functional portion of the screwing tool of any one of Claims 1 to 4.

6. A screwing tool substantially as hereinbefore described with reference to the accompanying drawing.

7. A screw having a screwhead recess substantially as hereinbefore described with reference to the accompanying drawing.