This invention refers to a drill construction-

Conventional drills in general have a cylindrical, unhardened portion which is provided to be held by the chuck of a drilling machine or the like. There also exist drills having a Morses cone to fit into a corresponding socket of a drilling machine or the like.

To prevent the drill from skidding the drill has to be securely held by the chuck and the latter thus has to be effectively tightened. Since a proper tightening of a chuck necessitates a certain care and time it is often neglected and the result is that the drill and/or the chuck is often damaged by a drill rotating in the chuck.

One object of the invention is thus to eliminate these disadvantages in providing a drill which is effectively prevented from skidding also when the chuck has not been tightened as completely as would be necessary with a conventional drill.

Another object is to provide a drill construction including a Morses cone socket enabling the use of relatively cheap drills with the ad¬ vantages of the Morses cone equipment.

Still further objects will be apparent from the attached specification and with reference to the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to fig. 1 numeral 1 designates a twist drill which is of a .conventional design in that it comprises a spiral shaped portion 2 ending in a drill bit 3 and a cylindrical attachment 4. Additionally the drill according to fig. 1 and fig. 2 has three equ distantly spaced longitudinal grooves 5 extending from the free end of the attachment portion 4 and ending in a tapered portion 6. The tapered portions 6 incur no costs to provide when a grinding wheel is used to provide the grooves 5. The shape of the tapered portions is de- termined by the profile and radius of the grinding wheel.

Since conventional drill chucks have three equidistantly spaced jaws eac having a tip shaped to hold the drill and since the grooves 5 have a section complementary to the tip sections of said jaws it is evident that the drill will be effectively prevented from skidding in the chuck also when the chuck is not tightened as much as would be necessary in respect of conventionally designed drills.

It is now common practice to make drills having a variety of drill diameters with a unitary dimension of the attachment 4. For instance a diameter of T/2" of the attachement is used for drills from about 12 mm diameter to 24 mm diameter. This practice makes it very cheap to design the drills according to the invention since making the. grooves necessitates no alteration of grinding data from one drill dimension to another.

In professional work drills being provided with Morses cone are frequently used due to the effective holding of the drill and to the rapid way of shifting drills. However, such drills are expensive.

According to this invention a drill construction offering all the advantages of the conventional Morses cone constructions but at much lower costs and with less bulky drills have- been achieved.

To obtain this result a modified Morses cone according to fig. 3 is used with a drill according to fig. 1. The modified Morses cone in fig. 3 7 has like conventional Morses ^" cones an outer tapered surface 8. It further has an inner surface 9 which, however, in this case is not tapered but cylindrical. Like conventional Morses cones it further has a planar upper portion 10 and a through elongated opening 11 serving as part of an arrangement to replace drills.

Thus, the first difference between the modified Morses cone 7 and a conventional one resides in the fact that the new Morses cone has a substantially cylindrical inner surface. A second difference is that the new Morses' cone has three equidistantly spaced longitudinal splines or ridges 12 each of which having- a tapered end portion 13 complementary to the end portions 6 (fig. 1) of the grooves 5 of the drill 1.

By inserting a drill 1 into the new Morses cone 7 the drill is attached to the cone by means of friction between the tapered portions 6 and 13. It is to be noted that the friction need only be sufficient to prevent the drill 1 from falling down when the drill is stading still or rotating. Of course it is possible to increase the grip by designing the cylindrical inner surface such that it in the region where the upper portion (fig. 4) of the drill is housed is tapered into a surface having a slightly reduced diameter and of course any kind of arresting means may be used to obtain the desired effect of just holding the drill in place. For instance it is possible to provide the Morses cone 7 with axially extending slots to obtain a gripping.

As soon as the drill is inserted in the described manner the drilling operations can take place and it is obvious that the pressure exerted upon the drill by the drilling operation further increases the grip between the drill and the Morses cone.

Although any kind of ejecting device can be used to remove the drill the frequently used method of inserting a wedge into the dpening 11 will in most cases be the most attractive one.

Instead of arranging a number of Morses cones according to fig. 3 it is also possible to use only one such modified cone, i.e. one having a dimension to fit into the actual drilling machine. The Morses cones of smaller diameter can in such case be replaced by sockets having a cylindrical outer surface with grooves corresponding to the grooves 5 of the drills and with internal ridges.

It is apparent that the drills 1 can be used without restrictions in chucks, turret bushings, Morses cones modified according to fig. 3 and so forth and it is also apparent that such drills are much cheaper and less bulky than drills havingintegral Morses cones.

It is evident that the diameter of the inner surface 9 is so close to the diameter of the attachment portion 4 of the drill that the drill will be correctly centered when introduced in the modified Morses cone or the sockets just mentioned.