TREPAN D'ATTAQUE POUR OUTIL A PERCUSSION

CUTTING BIT FOR PERCUSSION TOOL

Abrégé anglais

ABSTRACT


A percussive tool is provided with a bit which
comprises a shank, by which the bit is held in the tool, and
a flexible blade made from a springy metal such as bainitic
steel or phosphor bronze. 1.5mm has been found to be a
particularly satisfactory thickness for the tip portion of the
blade. Deposits of plaster, cement, caked oil and other
deposits all of which can be highly resistant to removal by
rigid-bladed bits from surfaces on which they have become
hardened have proved surprisingly easy to remove using a
springy metal blade. The new blade is also very effective
in removing tiles which have been cemented to a surface.

Revendications

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A percussive tool equipped with a cutting bit comprising a shank
held by one end in the tool and a blade secured to the other end of the shank
so that the blade extends in substantially the same direction as the shank,
said blade being made from a springy metal.


2. A percussive tool as claimed in claim 1, wherein the blade is
made from bainitic steel.


3. A percussive tool as claimed in claim 1 wherein the blade is
made from phosphor-bronze.


4. A percussive tool as claimed in claim 1 wherein the blade has a
thickness not exceeding 5mm.


5. A percussive tool as claimed in claim 4 wherein the tip portion
of the bit has a thickness of 1.5mm.


6. A percussive tool as claimed in any one of claims 1, 4 and 5
wherein the plane of the blade is inclined to the lengthwise axis of the shank.


7. A percussive tool as claimed in claim 1 wherein the blade is made
separately from and is secured to the shank.



8. A percussive tool as claimed in claim 7 wherein one end of the
shank carries a yoke to which is secured the rear edge of the blade.


9. A percussive tool as claimed in claim 8 wherein at least one
gasket is interposed between the rear edge portion of the blade and the yoke.

Description

~O~i4Z53
This invention relates to percussive tools i.e. motorized tools
which operate to apply impact forces to a holder for a tool-bit.
According to this invention there is provided a percussive tool
equipped with a cutting bit comprising a shank held by one end in the tool
and a blade secured to the other end of the shank so that the blade extends
in substantially the same direction as the shank, said blade being made
from a springy metal.
Bainitic steel and phosphor-bronze have been found to be
particularly suitable materials for the blade. The thickness of the blade
is preferably 5mm. or less if a single thickness of material is used, but
the blade may be of laminated form in some cases. 1.5mm has been found to
be a particularly effective thickness for the tip portion of the blade.
Such a cutting bit used in con~unction with a percussive tool has
been found to be remarkably effective, for reasons which are not clear, in
ren~ving dropped plaster and concrete, paint, caked oil and other
deposits, and tiles from floors, walls and ceilings.
In certain applications the blade may be inclined to the shank,
e.g. at an angle of 30, to provide a clearance for the body of the
~- cutting tool, as where the bit is used to cut silage and hay disposed in
a stack.
m e blade m~y be brazed or welded to the shank but it is
preferred to make the blade detachable from the shank. For this purpose,
the said one end of the shank may be formed as a yoke to embrace an edge
s of the blade, the blade being secured by one or more rivets or threaded
: bolts extending throu~h the blade and the yoke. m us one blade may be
exchanged for another and a gasket or gaskets may be disposed between the
blade and the yoke to reduce the risks of fatigue failure and high-
frequency noise. In order to avoid the gasket or gaskets becoming lost it
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10642S3

or they may be adhesively secured to the blade.
One embodiment of the invention will now be described by way of
example with reference to the accompanying drawings in which:
: Figure 1 shows in elevation a cutting bit for a percussive tool
according to the invention;
Figure 2 is a side elevation of the bit partly sectioned on
` line 2-2 of Figure l; and
Figures 3 and 4 are respectively front and rear end views of the
bit shown in Figures 1 and 2.




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Referring to the drawings, the bit comprises a
shank 10 having a blade 11 secured to one end thereof. To
hold the blade a yoke 12 is secured on a self-locking
tapered s?igot 13 on the end of the shank, the spigot being
; driven into a correspondingly tapered socket in the yoke.
In the illust~ated construction the blade is rectangular and
is clamped in a rebate in the yoke by a plate 14, two bolts 15
extending through holes in the plate, blade and yoke and being
secured by nuts 16. Heavy duty gaskets 17 are adhesively
bonded to both sides of the blade between the plate 14 and
the yoke to reduce the risks of fatigue-failure and high-
frequency noise.
The blade is made from bainitic steel or from phosphor-
bronze and is thus relatively springy by comparison with the
usual type of cutting or chisel bit where the shank and a
heavy rigid blade are forged integrally with each other from a
tough steel.
In an alternative construction, the yoke has instead of
the rebate and plate 14 a slot into which the back edge
portion of the blade fits. In this construction also, heavy
duty gaskets, made for example from red fibre, are secured by
an adhesive to the faces of the blades where it fits in the
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slot. The blade is secured in the slot by bolts and nuts as

in the illustrated arrangement.
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1~642S3
~ e releasable attachment of the yoke to the shank enables different
lengths and types of shank to be used lnterchangeably, but the yoke may be
for~ed integrally with the shank or may be brazed or welded or press-fitted
to the shank. The yoke may be a steel forging or a spheroidal graphite iron
casting.
In addition to its use in con~unction with a percusslve tool for
removing concrete and plaster droppings, tiles, paint and caked oil from
floors, walls and ceilings, the bit may have a sharpened blade and be used
for cutting such materials as silage and hay for feeding farm animals. The
bit can be used with any type of percllssive tool including those, known as
buzz drills, which em~loy high frequency, low energy vibrations.
Where the bit is to be used for cutting silage or hay disposed in
a stack the blade may be inclined to the general lengthwise dimension of the
shank, i.e. to the direction of the percussion or vibration, at an angle which
should not exceed 30, to provide a clearance for the body of the percussive
tool. m e blade can be so disposed for example by forming a bend in the
shank near its forward end, by arranging the yoke at an angle to the shank,
or by inserting packing pieces of appropriate forn between the yoke and the
b1Idb.




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