CLAMP FOR A KEY CUTTING MACHINE

The present invention relates to an improved clamp for a key cutting machine.

Key cutting machines, also commonly called duplicating machines, are well known. A known type of such machines comprises a base on which a feeler is mounted to mechanically sense the notches of the notching pattern of an original key to be duplicated, together with a milling cutter to form similar notches on a blank key to be cut.

On the same base a movable structure is also mounted supporting two clamps, to which the original key to be duplicated and the blank key to be cut are fixed. The arrangement of the parts is such that the two keys are disposed with the axes of their respective shanks parallel and that when the original key faces the feeler the blank key faces the cutter.

In this manner, by moving the movable structure such that the feeler slides along the pattern notches of the original key the cutter forms, on the blank key, notches which are substantially identical to those of the original key in terms of position and depth.

In another known type of duplicating machine the movement of the blank key to be cut relative to the cutter is obtained mechanically on the basis of notching pattern data contained in a database. In this case, cutting the blank key does not require the physical presence of the original key as the notching data can be read off at a prior moment by a device separate from the duplicating machine, or can be made available via a previously memorized notching code. In all cases the blank key to be cut must at least be retained by a clamp in a position in front of a milling cutter and is moved relative to said

cutter such that this forms in the key edge the notches corresponding to the notching pattern to be provided.

Known clamps generally comprise two jaws, between which the key concerned is clamped. These jaws are mounted on a generally vertical pin and are maintained spaced apart by a spring. The pin has its upper portion threaded and on this a knob is screwed, which when operated by the operator causes the two jaws to move towards each other and clamp the interposed key.

A drawback of known clamps of this type is that if the knob is too loosely tightened the key does not become securely fixed and can vibrate during milling, such that in some cases it can even become detached from the clamp. These is hence a risk of cutter breakage and in any event an imperfect notching result. If instead the knob is too tightly tightened, the clamp can undergo early wear and the key be damaged, especially if made of soft material such as aluminium.

An object of the invention is to eliminate this drawback by making the operation of fixing a key to the duplicating machine clamp independent of the operator's ability and experience.

This and further objects which will be apparent from the ensuing description are attained according to the invention by an improved clamp for key cutting machines as described in claim 1 .

A preferred embodiment of the present invention is further described hereinafter with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a clamp according to the invention; Figure 2 shows it in frontal view in the direction M-Il of Figure 3; and Figure 3 is a vertical section therethrough on the line Ill-Ill of Figure 2.

As can be seen from the figures the clamp of the invention is applied to the structure of a duplicating machine, not shown in the drawings. It comprises a vertical pin 2, which is fixed to said structure and to which a base plate 4 is fixed, on which the square-based lower jaw 6 of the clamp rests. A lever 8 is also applied to the base plate 4 and interacts with the fixed jaw 6 to enable the clamp to be positioned in four different angular positions rotated through 90 to, in this manner arrange, the clamp for fixing keys of different profiles, in accordance with traditional techniques which do not form an aspect of the present invention. The clamp of the invention also comprises an upper jaw 10 which is also supported centrally by the pin 2 and together with the lower jaw defines four slots 12 for housing and fixing keys of different profile.

Between the two jaws 6 and 10 a coil 14 spring is disposed, acting in the sense of maintaining the upper jaw 10 spaced from the lower jaw 6 along the pin 2, to hence maintain the four slots 12 open.

The upper portion of the pin 2 comprises an outer thread on which a threaded sleeve 16 in the form of a cap is screwed, which depending on its different extent of screwing on the pin 2 urges the upper jaw 10 to a greater or lesser extent towards the lower jaw 6 against the elastic reaction of the spring 14.

With the cap 16 a sleeve 18 is associated, free to slide axially along the cap, but unable to rotate about it, it also comprising on its upper annular surface a frontal toothing with inclined teeth, which engage in the inclined teeth of the frontal toothing of another sleeve 20, rigid with an operating knob 22. This knob 22 is fixed to the upper threaded portion of the cap 16 by a nut

24 housed in a cavity 26 provided in the top of the knob 22 and closed by a plug 28.

A coil spring 30 interposed between the sleeve 18 and a lower flange 32 of the cap 16 maintains the two frontal toothed portions of the sleeves 18 and 20 elastically coupled together.

The clamp of the invention operates in the following manner.

During preliminary setting, the nut 24 is screwed down to a greater or lesser extent to load the spring 30 to the value required for the reaction torque of the dynamometric device comprising the spring 30 and the two toothed sleeves 18, 20 which are maintained coupled together by the spring.

After the pair of jaws 6, 10, maintained spaced apart by the spring 14, have been positioned on the pin 2 such as to make operative the chosen slot 12 corresponding to the key to be clamped, the key is positioned in the slot and the knob 22 operated. This action is transmitted via the dynamometric device to the cap 16, which is screwed onto the pin 2 to cause the upper jaw 10 to approach the jaw 6 and hence clamp the key.

The intensity of this clamping is given by the dynamic device, in the sense that after the upper jaw 10 has come into contact with the key, the reaction to further screwing of the cap 16 is controlled by the dynamic device, in the sense that until a certain value, the effect of the spring 30 prevails to maintain the two toothed sleeves 18, 20 coupled together, whereas when this value is exceeded the inclined teeth of the sleeves 18 and 20 slide over each other without causing further rotation of the cap 16 and hence without providing a further clamping effect on the key. In practice the torque transmitted by the knob 22 to the cap 16 and hence the intensity of the clamping on the key is related to the inclination of

the teeth of the sleeves 18 and 20 and to the preload of the spring 30. The inclination of the teeth is evidently fixed, whereas the preload of the spring 30 can be adjusted by screwing the nut 24 to a greater or lesser extent along the upper threaded portion of the cap 16. From the aforegoing it is apparent that the improved clamp according to the invention is particularly advantageous compared with traditional clamps for key cutting machines, in that it ensures a constant key clamping force without the risk of damaging the key and/or the milling cutter, independently of the ability and experience of the operator. Moreover it enables the value of this constant clamping force to be predefined, to adapt the clamp to the different possible key materials.