Drill chuck

A drill chuck for holding a tapered end of a tubular drill bit. The chuck comprises a driving member having a tapered surface for frictional engagement with the tapered end of the drill bit, a first holding member mounted on the driving member and a second holding member mounted, in use, on the tubular drill bit. The second member has a substantially radial surface thereon for abutment with a surface 31 on the drill bit. The two holding members can be screwed together whereby abutment between the substantially radial surface on the second holding member and the surface on the drill bit urges the tapered end of the tubular drill bit into frictional driving contact with the tapered surface of the driving member.

The invention relates to a drill chuck and is particularly, but not 
exclusively, concerned with a drill chuck for coupling a drive member to a 
taper ended drill bit. 
In our UK Patent No 2263489, a hollow taper ended tubular drill bit is 
secured for rotation by gripping internal and external tapered surfaces of 
the drill bit between respective external and internal tapers on a driving 
member and a holding member in the form of a sleeve. In order to remove 
the drill bit from the driving member, the holding member is unscrewed. 
However, the unscrewing of the holding member involves overcoming the 
frictional grip between the internal taper on the holding member and the 
external taper on the drill bit. The forces involved require the use of a 
tool to overcome the frictional forces and the same tool is required to 
tighten the holding member afterwards when refitting the tool. 
The drill bit described in UK Patent No. 2263489 can be used for drilling 
into a concrete surface to form a bore therein or for generating a core 
sample from the ground. Once a drilling operation has been performed, the 
drilled-out material or core sample is removed from the drill bit after 
detaching the drill bit. Obviously, where a large number of holes is to be 
drilled, the detachment and re-attachment of the drill bit increases 
production time particularly as tools are required to release and 
re-tighten the holding member. An object of the present invention is to 
provide a chuck which enables such a drill bit to be detached and 
re-attached quickly and easily. 
According to one aspect of the invention there is provided a drill chuck 
for holding a tapered end of a tubular drill bit, the chuck comprising a 
driving member having a tapered surface for frictional engagement with the 
tapered end of the drill bit, a first holding member mounted on the 
driving member and a second holding member engageable with the tubular 
drill bit, the second holding member having a substantially radial surface 
thereon for abutment with a surface on the drill bit the two holding 
members being interconnectable by relative rotary movement whereby 
abutment between the substantially radial surface on the second holding 
member and the surface on the drill bit urges the tapered end of the 
tubular drill bit into frictional engagement with the tapered surface of 
the driving member. 
With such an arrangement, the use of the substantially radial surface means 
that it is not necessary to overcome friction between two tapered surfaces 
when rotating the second holding member making it much easier and quicker 
to change the drill bit. Moreover, the use of the first and second holding 
members is particularly advantageous in that, instead of using a tool, the 
user can grasp both holding members one in each hand and twist them in 
opposite directions for removal of the drill bit and when tightening the 
drill bit for use. 
In the preferred embodiment, the first holding member is rotatably mounted 
on the driving member and the second holding member may be rotatably 
mounted, in use, on the tubular drill bit. 
Preferably, one of the first holding member and driving member has a 
projection thereon for abutment with a surface on the other so that the 
drill bit and driving member will be drawn towards each other by 
interconnection of the two holding members. In the preferred embodiment, 
the projection is provided on the first holding member and may take the 
form of an annular flange. 
The projection may locate in a space between two surfaces on the driving 
member whereby the first holding member is held captive on the driving 
member. 
Preferably, the substantially radial surface on the second holding member 
is annular and the surface on the drill bit may also be annular. 
In the preferred embodiment, the first holding member and/or the second 
holding member comprise/comprises a sleeve. 
The first and second holding members may be interconnected by means of a 
screw thread so that the drill bit is drawn against the driving member by 
a relative rotary movement between the two holding members. The first 
holding member may be formed with an internal screw thread in such a case. 
The drill bit may be provided with an abutment surface against which a 
surface portion of the second holding member can be driven during 
disconnection of the two holding members so as to separate the tapered 
surface of the drill bit from the tapered surface of the driving member. 
According to a second aspect of the invention there is provided a drill 
chuck for holding a tapered end of a tubular drill bit, the chuck 
comprising a driving member having a tapered surface for frictional 
engagement with the tapered end of the drill bit and holding means for the 
drill bit, the holding means being movable into a holding position in 
which it holds the tapered end of the drill bit in frictional engagement 
with the tapered driving surface of the driving member and into a release 
position in which it separates the tapered end of the drill bit from the 
tapered surface of the driving member to enable the drill bit to be 
removed from the chuck. 
The holding means may be held captive on the drill bit in use. 
The holding means may comprise first and second holding members as 
aforesaid and, in such a case, the second holding member may be held 
captive on the drill bit. Where the second holding member has the 
aforesaid substantially radial surface thereon, means defining that 
surface may be held captive between spaced apart surfaces on the drill 
bit. One of the said surfaces on the drill bit may be the surface which 
co-operates with the second holding member to enable the drill bit to be 
drawn towards the driving member and the other surface may be the said 
abutment surface against which the surface portion of the second holding 
member can be driven during disconnection of the two holding members so as 
to separate the tapered surface of the drill bit from the tapered surface 
of the driving member. 
The first holding member may have an external surface formed with a contour 
produced, for example, by knurling to facilitate manual gripping of the 
first holding member. The second holding member may have an external 
surface which is similarly formed. 
According to a third aspect of the invention there is provided a drill 
chuck for holding a tapered end of a tubular drill bit, the chuck 
comprising a driving member having a tapered surface for frictional 
engagement with the tapered end of the drill bit, a first holding member 
mounted on the driving member and a second holding member engageable with 
the tubular drill bit, the two holding members being interconnectable by 
relative movement, preferably rotary movement, so as to urge the tapered 
end of the tubular drill bit into frictional engagement with the tapered 
surface of the driving member. 
According to a fourth aspect of the invention there is provided a drill 
chuck for holding a tapered end of a tubular drill bit, the chuck 
comprising a driving member having a tapered surface for frictional 
engagement with the tapered end of the tubular drill bit, a holding member 
mounted on the driving member having a substantially radial surface 
thereon for abutment with a surface on the drill bit whereby abutment 
between the substantially radial surface on the holding member and the 
surface on the drill bit urges the tapered end of the tubular drill bit 
into frictional driving contact with the tapered surface of the driving 
member. Preferably a first holding member is provided on the driving 
member and the aforesaid holding member having the substantially radial 
surface is a second holding member attachable by rotary movement to the 
first holding member. 
Other features as set out in any of the consistory clauses relating to the 
first or second aspect of the invention may apply to the third or fourth 
aspects of the invention.

Referring firstly to FIG. 1, a drill bit 10 comprises a steel circular 
cross section tube 12 having a plurality of circumferentially spaced tips 
11 at its lower end. The tips are preferably of a diamond impregnated 
type. It will be noted that the tips 11 define an internal diameter d1 
which is less than the internal diameter d2 of the tube 12. 
The upper end of the tube 12 is flared outwardly to define a tapered end 13 
having an internal tapered surface 14 and an external tapered surface 15. 
The internal tapered surface 14 locates on an external tapered surface 16 
formed on a rotary driving member 17. The driving member 17 is formed with 
a screw thread 18 at its upper end as viewed in FIG. 1 for location in a 
drive spindle of a drilling machine (not shown). The driving member 17 is 
formed with an internal bore 19 through which a drilling fluid flows to 
the lower end of the drill bit 10 when the bit is in use. 
A first holding member in the form of a first sleeve 20 is formed with an 
internal screw thread 20a. At one end of the sleeve 20 there is an 
inwardly directed projection in the form of an annular flange 21. The 
sleeve 20 is rotatably mounted on the driving member 17 and the flange 21 
is held captive between opposed annular surfaces defined by a shoulder 22 
on the driving member 17 and a washer 23 held in place by a spring 
retaining clip 24 which locates in a groove 24a in the driving member 17. 
A second holding member in the form of a second sleeve 30 is formed with an 
external screw thread 30a for threaded engagement with the screw thread 
20a of the first sleeve 20. The second sleeve 30 also has an inwardly 
directed projection in the form of an annular flange 31 at one end thereof 
defining a radial surface. The flange 31 is arranged to abut against an 
annular surface defined by a washer 32 which, in the case of the right 
hand half of FIG. 1, is positioned on the tube section 12 of the drill bit 
10 and is held in place by means of a spring retaining clip 33 in a groove 
33a, and, in the case of the left hand half of FIG. 1, is a taper 
frictional fit on the tapered surface 15 of the drill bit 10. The sleeve 
30 is rotatably mounted on the drill bit 10. 
In order to fit the drill bit 10 into the chuck in frictional driving 
engagement with the drive member 17, screw threads 20a, 30a of the first 
and second sleeves 20, 30 are screwed together manually and tightened. By 
means of abutment between the flange 21 of the first sleeve 20 and the 
washer 23 of the drive member 17, and abutment between the flange 31 of 
the second sleeve 30 and the washer 32 of the drill bit 10, the screwing 
together of the first and second sleeves 20, 30 causes the tapered surface 
14 of the drill bit 10 and the tapered surface 16 of the drive member 17 
to be urged together. 
The angle of taper a of the surfaces 14, 16 is preferably selected to 
ensure that drive can be transmitted frictionally from the driving member 
17 to the drill bit 10 via the surfaces. A suitable angle of taper is 
slightly greater than 15 degrees, eg 15.5 degrees which will also enable 
the drill bit 10 to be manually detached from the tapered surface 16 of 
the driving member 17 after the sleeve 30 has been unscrewed. 
In use, the drill bit 10 is driven into the ground so as to generate a core 
sample. When sufficient depth has been reached, the drill bit 10 is 
extracted from the ground along with the core sample which is positioned 
freely within the tube 12. However, the diameter of the core will be 
approximately the same as the internal diameter d1 defined by the tips 11 
and will normally be difficult to remove from the lower end of the drill 
bit 10. However, with the present invention, it is a simple matter to 
unscrew the sleeves 20, 30 manually by holding them in both hands to 
enable the flared upper end of the drill bit 10 to be disconnected from 
the driving member 17. The drill bit 10 can then be inverted so that the 
core sample will slide out of the tapered end of the drill bit 10 for 
retrieval. When rotating the sleeve 30, it is much easier to overcome the 
friction between the flange 31 and the washer 32 than between two 
frictionally engaged tapered surfaces as in our UK No. 2263489. 
The chuck of FIGS. 2 and 3 includes all of the features of the chuck in 
FIG. 1. In addition, a washer 34 is restrained on the tube 12 by means of 
a spring retaining clip 35 in a groove 35a. The flange 31 is held captive 
between the washers 32, 34 and again, the sleeve 30 can be rotated on the 
drill bit 10. Accordingly, on unscrewing the sleeves 20, 30 one from the 
other, the sleeves abut respectively against shoulder 22 of the driving 
member 17 and washer 35 on the drill bit 10 whereby sufficient unscrewing 
movement will break the frictional grip between the tapered surfaces 
14,16. 
By using a system as in FIG. 2 which will give a positive force for 
breaking apart the two tapered surfaces 14, 16, the taper angle t can be 
made more shallow than hitherto thereby improving the frictional drive 
capability between the driving member 17 and the drill bit 10. With a more 
shallow angle of taper t, eg 15.degree., the two sleeves 20, 30 do not 
need to be screwed together as tightly as in FIG. 1 to obtain the same 
frictional grip between the drill bit 10 and the driving member 17 making 
it even easier to remove and re-fit the drill bit manually. 
The tube 12 may be selected from a range of diameters. By placing the 
washer 32 at a position axially of the drill bit which is appropriate to 
the particular diameter, the drill chuck of the present invention is 
capable of receiving drill bits of a range of diameters. FIGS. 1 and 2 
show two alternative positions of the washer 32. 
Reference is now made to FIG. 4 in which parts corresponding to parts in 
FIG. 2 carry the same reference numerals. FIG. 4 shows the way in which 
the upper end of the tube 12 can be provided with a separate internally 
tapered tubular section 44 of annular cross section which has a 
cylindrical bore 45 in which the tube 12 is welded or brazed. The tube 12 
has a shoulder 46 thereon which is equivalent to the washer 32 in FIG. 2 
and the second sleeve 30 has a snap ring 48 mounted in a groove 50 in the 
sleeve 30 which provides a radial surface on the sleeve 30 equivalent to 
that provided by the flange 31 in FIG. 2. The tubular section 44 carries a 
washer 34 and spring retaining clip 35 in the same manner as the tube 12 
in FIG. 2. By using the tubular section 44, it is not necessary to flare 
the tube 12 outwardly to provide the tapered end 13. However, for large 
scale production, the use of the flared tube 12 is preferred as it avoids 
the use of a separate element which needs to be attached to the tube. 
It is envisaged that the sleeves 20, 30 may be machined from a suitable 
plastic material or a metal. 
A particular advantage of the present invention is that tools are not 
required to separate the drill bit 10 from the drive member 17. To assist 
manual rotation of the sleeves 20, 30 the two sleeves may have knurled 
outer surfaces 40, 41 which help a user to grip the sleeves one in each 
hand and twist them to release the drill bit 10.