METAL CUTTING DRILLThis invention relates to a metal cutting drill particularly but not exclusively a so-called short hole drill.
It is known to provide such metal cutting drills of a two-part construction comprising a cutting head, usually incorporating at least one replaceable carbide insert, releasably attachable to a drill body having a shank securable in a machine tool. The two-part construction provides the advantage that when the head end, which is prone to damage, becomes damaged, the head only is replaced as the drill body is perfectly servicable. However, relatively complex means have in the past been employed for securing a head to a body, necessitating, amongst other things, a removal of metal and hence weakening of the body and/or head, which in turn has placed a restriction on the ability to use the two-part concept for smaller diameter drills.
A basic object of the present invention is to provide an improved metal cutting drill of the two-part kind.
According to the present invention there is provided a metal cutting drill comprising a head releasably and coaxially attachable to one end of a body about the longitudinal axis of rotation of the drill, with the other end of the body being securable in the chuck of a machine tool; mutually engageable abutment faces on both the head and the body; and at least one connection screw operable about an axis parallel to the longitudinal axis of the drill to secure the head to, or release the head from, the body, with the or each screw being hollow and co-axial with a conventionally-provided coolant bore, whereby the or each screw serves not only for connection and release of the head to and from the body, but also for conveying the coolant.
As, conventionally, two coolant bores in opposing sectors would be provided in both the head and the body, two hollow screws would be provided, one associated with each coolant bore.
The concept of providing screws co-axial with the coolant bores results in the connection means between the head and the body requiring minimum space and therefore permits the construction of two-part metal cutting drills in the smaller diameters e.g. 25 mm, that have not previously been achievable.
Preferably, a pin of the head (or body) engages a blind socket of the body (or head) to control axial forces.
The pin may be co-axial with the rotational, longitudinal axis, of the drill, or may be offset, the latter ensuring that a head is always attached to the body in the correct disposition.
Preferably, the abutment faces are serrated to control radial separation.
To enable the screws to be effective the coolant bores in the head and/or body are tapped, and in a preferred arrangement both screws are double acting and may be rotated e.g. by an Allen key, extended into the conventional discharge apertures of the coolant bores of the head.
Alternatively, the screws may be single acting screwed into the tapped bores of the body, with a modified screw head to retain the drill head by engaging a plain counterbore in the drill head.
One example of metal cutting drill in accordance with the invention will now be described in greater detail, by reference to the accompanying drawings, in which:- Figure 1 is a side elevation of a drill in accordance with the invention with the head shown separated from the body;Figure 2 is a view in the direction of arrow A ofFigure 1;Figure 3 is a view in the direction of arrow B ofFigure 1;Figure 4 is a view in the direction of arrow C ofFigure 3; andFigure 5 details serrations.
In the drawings a metal cutting drill 1 comprises a head 2 releasably and co-axially attachable to one end 3 of a body 4 about the longitudinal axis 5 of rotation of the drill.
The other end 6 of the body 4 terminates in a spigot 7 securable in the chuck of a machine tool. Mutually engageable abutment faces 8, 9 respectively on both the head 2 and the body 4 are provided with inter-engageable serrations 10 as detailed in Figure 5. The spigot 7 is provided with a co-axial, coolant inlet bore 11 terminating at its inner end in a transverse distribution bore 12 intersecting a pair of parallel coolant bores 13 located 1800 apart in the body 4 and extending to the face 9, and a short distance inwardly from the serrated abutment face 9, each bore 13 is tapped at 14.
The head 2 is provided with a pair of coolant bores 15 co-axial with the bores 13, each bore 15 also being tapped at 16 for a short distance inwardly from the serrated abutment face 8. The bores 15 continue to an opposite end face 17 of the head 2, at which location a plurality of industry-standard carbide cutting inserts 18 are provided. From the face 9 a pin 19, co-axial with axis 5, extends for location in a blind receiving bore 20 at the face 8 of the head 2.
The head 2 is releasably secured to the body 4 by a pair of hollow screws 21 rotatable about axis 22 of the bores 13 and 15. The screws 21 are double acting with one portion 23 to screw into the tapped portion 14 of one bore 13 of the body 4 separated by a neck 24 from another portion 25 to screw into the tapped portion 16 of an aligned bore 15 of the head 2. Screw rotation to attach, or detach, a head 2 from a body 4 is conveniently by passing an Allen key into the bores 15 from the face 17.