JANSSON, Torgny (Kungsgatan 13, Lindesberg, S-711 30, SE)
| CLAIMS 1. An attachment arrangement for attaching a grindstone (1) on a shaft (3) therefore, an inner washer (4), against which the grindstone is supported, being in supporting engagement against a shaft shoulder, characterized in that a washer nut (7) in direct contact with the outer surface of the grindstone (1) is in thread engagement with the end of the shaft (3), that the thread of the washer nut and of the shaft has a pitch angle of 4 - 8°, more preferred 5 - 7°, most preferred 6°, and that the rotation direction of the grindstone (1) is such that the washer nut (7) will be tightened against the grindstone at rotation of the grindstone. 2. An arrangement according to claim 1, wherein the thread of the washer nut and of the shaft end has a pitch of 3-5 mm, preferably 4 mm, at a shaft diameter of 12 mm. 3. An arrangement according to claim 1, wherein the thread has two entrances. 4. An arrangement according to claim 1, wherein the washer nut (7) has a chamfered surface at its side facing the grindstone (1). 5. An arrangement according to claim 1, wherein the washer nut (7) has a knurled periphery. |
Technical Field
The present invention relates to an attachment arrangement for attaching a grindstone on a shaft therefore, an inner washer, against which the grindstone is supported, being in supporting engagement against a shaft shoulder.
Background of the Invention
In a conventional attachment arrangement of the above kind, an outer washer and a conventional nut are mounted at the shaft end extending out through the grindstone. The nut, which for a shaft with a diameter of 12 mm may have a
standardized pitch of 1.5 mm, or in other words a pitch angle of some 2.3°, is tightened by means of a tool such as a spanner or a wrench. In order to obtain the necessary tightening torque it may even be necessary to hit the spanner or wrench with a hammer or the like. Depending on the rotational direction of the grindstone in relation to the thread winding direction, the tightening may either be positively or negatively affected. When the grindstone is to be replaced or removed for other reasons, the joint to the shaft may be extremely difficult to loosen, even with the aid of tools.
The Invention
A far better attachment arrangement is according to the invention attained in that a washer nut in direct contact with the outer surface of the grindstone is in thread engagement with the end of the shaft,
that the thread of the washer nut and of the shaft end has a pitch angle of 4 - 8°, more preferred 5 - 7°, most preferred 6°, and
that the rotation direction of the grindstone is such that the washer nut will be tightened against the grindstone at rotation of the grindstone.
In this way the joint is in effect self-tightening after a manual mounting of the washer nut into contact with the grindstone, but the great pitch angle will still enable the joint to be easily loosened by hand.
In a practical embodiment with the advantages of the invention, the thread of the washer nut and of the shaft end has a pitch of 4 mm at a shaft diameter of 12 mm, leading to a pitch angle of 5.8°.
The thread has preferably at least two entrances.
For securing a good frictional engagement between the washer nut and the side of the grindstone, the washer nut may have a chamfered surface at its side facing the grindstone. The washer nut preferably has a knurled periphery in order to enhance the manual handling thereof.
Brief Description of the Drawing
The invention will be described in further detail under reference to the accompanying drawing, in which
Fig 1 is a section through a known attachment arrangement for a grindstone and
Fig 2 is a corresponding section through an attachment arrangement according to the invention.
Description of Embodiments
A disc-shaped grindstone 1 has a central through hole, preferably provided with a bushing 2. The grindstone 1 is releasably attached to a rotatable shaft 3 in a grinding machine by means of an attachment arrangement to be described.
A conventional such arrangement is illustrated in Fig 1. An inner washer 4 is supported against a shoulder on the shaft 3. An outer washer 5 is arranged at the other side of the grindstone 1 , and a conventional nut 6 is mounted on a conventional thread at the end of the shaft 3.
In a practical case, the diameter of the shaft 3 may be 12 mm, and the standardized thread at the end of the shaft may have a pitch of 1.5 mm. With the geometrical relationship between diameter and pitch of a thread, this means that the pitch angle of the thread is some 2.3°.
The nut 6 is tightened by means of a spanner or wrench, and in order to obtain the necessary tightening torque it may be necessary to hit the spanner or wrench with a hammer or the like.
The friction between the different surfaces involved determines the transferred torque, which is impossible to determine on beforehand.
There is a certain tightening effect between the nut 6 and the washer 5, but it is not reliable because the washer may easily rotate in relation to the nut. It is thus necessary to tighten the joint heavily in order to secure that the grindstone 1 does not get loose on its shaft 3. A negative consequence of the tightening is that it will be difficult to unwind the nut at a later replacement of the grindstone 1.
Depending on the rotational direction of the grindstone 1 in relation to the winding direction of the nut 6, there will be a tendency either to tighten the joint further or to loosen the joint at rotation of the grindstone 1. This tendency is, however, not reliable and can not be assessed. An attachment arrangement according to the invention is shown in Fig 2. The following parts can be recognized from the conventional arrangement shown in Fig 1 : the grindstone 1, the bushing 2, the shaft 3, and the inner washer 4, but the thread at the end of the shaft 3 is different.
Here, the outer washer 5 is abolished, and the nut 6 is replaced by a washer nut
7.
The cooperating threads on the end of the shaft 3 and in the washer nut 7 have a greater pitch and thus a greater pitch angle than the threads used in the conventional arrangement of Fig 1, where the pitch is 1.5 mm with a shaft diameter of 12 mm. In the arrangement according to the invention it is preferred to employ a pitch of 4 mm with the same shaft diameter, leading to a pitch angle of 5.8°, but a favorable effect may be obtained with a pitch in the span of 3-5 mm. Also, each thread has two entrances.
Practical tests have shown that favorable results will be obtained with pitch angles in the span 4 - 8°, more preferred in the span 5 - 7°.
The thread direction is such that the rotation of the grindstone 1 will automatically tighten the joint without the use of any external force or tool, provided that the washer nut 7 has been manually brought into engagement with the grindstone 1. The handling of the washer nut will be enhanced by a knurled periphery thereof.
The friction engagement is enhanced by the provision of a chamfered surface at the internal surface of the washer nut 7.
Due to the great pitch it will be easy to dismount the washer nut 7 by a moderate manual twist at the replacement of a worn-out grindstone 1. However, the dismounting may require that the otherwise freely rotatable shaft 3 is held against rotation. A grinding machine of this kind often has one grindstone and one honing wheel at either end of the same shaft. The dismounting can be performed in that the honing wheel (with the shaft) is held with one hand and the grindstone is rotated in the dismounting direction with the other hand.
Modifications are possible within the scope of the appended claims.
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