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~ v Sept. l0, 1946.
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_R GQ|TD5¢HM|DT
2,407,604
PERCUSSION TooL
Fi'iedFeb. 16, 1944
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Sept- 10, 1946-
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R. GoLDscHMlDT "
2,407,604
PERCUSSION TOOL
Filed Feb. _16, 1944
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2,467,504
Patented Sept» 10, 1946
UNITED STATES PATENT OFFICE
2,407,604
PERCUSSION kTOOL
Rudolph Goldschmidt, Sheffield, England
Application February 16, 1944, Serial No. 522,681
In Great Britain March 5, 1943
'14 Claims.
»
(Cl. .'125-33)
1
This invention relates to mechanically-oper
ated percussion tools, such for example as power
hammers, riveters and paving-breakers.
An object of this invention is to provide a per
cussion tool which is relatively light and compact
2
be carried round and move longitudinally with
the striker, but is free to move radially with re
spect to the striker under the influence of cen
trifugal force, while its axis is kept parallel to
that of the motor shaft |by the restraint afforded
by the surfaces of the pockets in which the
grooves 33 are formed; The extent of the radial
movement of the rollers is determined by the
,inner surface of the ybody, on which circumferen
and which .is economical in power consumption.
A vfurther object is to provide such a tool which
can be readily designed to give blows of any de
sired frequency and energy.
Another object is to provide an electrically 10 tially yridged portions 3B ofthem bear continu
ously while the tool is operating; Y I
` ' .
operated tool having the above-mentioned ad
The outer end portion of the body (i. e. the end
vantages.
portion `remote from the tool-bit holder 23) con
Another object is to .enable a percussion .tool
tains a nrst race 35 of truncated conical form
to be operated b-y a high-speed rotary motor
disposed with its smaller end adjacent to the
without reduction gearing.
motor. ` When the striker is rotating within the
Another object `is to enable a percussion tool,
smaller end of the race 35, the radial thrust of
such as a riveter, which is intended forinter
the rollers 3l causes a reactionv which accelerates
mittent use, to store during .an idle period kinetic
energy which is usefully employed during the «
the striker inwards towards the tool-bit holder.
20 The lower end face oi the striker may -be convex
at 36 to cao-operate with a concave annular sur
Further objects and features -of the invention
subsequent working period.
will be apparent from the following description
of an example thereof as applied to a hand tool
face 31 fonthe tool-bit holder.
'
`
Immediately adjacent to the larger end of the
iirst race 35 is a second race 38, the object of
and given with reference to the accompanying
25 which Vis -to impart to the striker, after its impact
diagrammatic drawings, `in which:
with the tool-bit holdenan ac-celeration in the
Fig. 1 is a longitudinal section through the tool,
outward direction suiîicient ot return it to the
Fig. 2 is a section on the line 2-2 in Fig. 1J
smaller end of the first race, while causing only
a relatively slight retardation of` the inwardv
movement `of the striker as it passes through the
Figs. 4 and 5 show respectively two alternative
second race towards the end of its in-stroke.
forms of this detail,
With this object in View, the second race is pro
Fig. 6 is a section on the line B-B in Fig. 1, i
vided with two diametri'cally opposed helical
Fig. 7 is an explanatory diagram,
paths of such asection that in any plane normal
Fig. 8 is a section on the line 8--8 in Fig. 1,
Figs. 9, 10 and 11 are respectively sections .on C.,‘ Ll to the axis of the motor shaft this race, which
Fig. 3 is an elevation of a detail, as viewed in
the plane of Fig. 1,
the lines 9_9, lil-ID and II--~II in Fig. 8,
Fig. 12 is an explanatory diagram, and
Fig. 13 is a section on the line I 3--l3 in Fig. 12.
Referring to Figs. 1, 2 and 3, the tool includes
a tubular body 20, an electric motor 2i fixed to
a ñange 22 at the outer end of the body, and a
tool-bit holder 23 slidably guided in an .inner end
cap 24 of the body for limited movement along
the axis of the motor shaft 25. A striker includes
a flywheel 26 which is slidably engaged with a ‘
splined extension 25A of the motor shaft. An
extension 27 of the tool-bit holder 23 is provided
with a journal 28 slidably ñtted in a bore 29 in
the lower end of theshaft 25A in such a manner
as to permit the longitudinal movement of the
will hereinafter be termed the “dynamic screw,”
everywhere presents a concave surface to the
rollers, which is the condition determining con
tinuous contact between the rollers and the dy
namic screw.
The preferred cross section of the dynamic
screw varies from a circle adjacent to and regis
tering exactly with the larger end of the race 35,
through ovals (e. g. Fig. 6), of more or less ellip
tical form, having the same major axis and minor
axes which progressively decrease towardsvthe
inner end of the dynamic screw. The major axis
of the oval at any section is angularly displaced
about the axis of the motor shaft, in the direction
opposite to the direction of rotation of this shaft,
with respect to the major axis of the oval at any
section nearer the outer end of the dynamic
screw, so that the hand of the helical paths de
tool-bit holder. In the periphery of the striker
are two diametrically-opposed pockets 30 each
accommodating a hardened steel roller 3i which
fined by the parts of successive ovals adjacent to
has two co-axial pins 32 guided in radial slots 33
in the striker; the roller is thus constrained to 56 the ends of their major axes is opposite to the
,
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2,407,604
3
4
hand of the helixes traced out Lby the rollers dur
ing the in-stroke of the striker.
has spent its axial momentum in the blow upon
Fig. 7 represents diagrammatically on a re
duced scale a -developed view of the inner surface
of the dynamic screw. The two helical paths
4are similar and each is produced by a family of
helical grooves the centre lines of which inter
from the latter, the dynamic coupling between
sect at A and the pitch angles of whichl range
the tool-bit holder, and even if there is no recoil
the striker and the screw increases to a value
such that the screw is eñective in accelerating the
striker outwards in readiness for another cycle.
« This effect will be explained with reference to
Figs. 12 and 13. In the development of the screw
shown in Fig. 12, line G denotes the bottom of a
example 7° and 9° respectively), so that the 10 groove, and line R the top of the dividing ridge
grooved paths Ibecome progressively wider to
» on the inner side of this groove. For the sake
wards the outer end of the dynamic screw, whileV ' ’ of simplicity the slope S between the lines G and
the height of the lands between the grooved pathsY
YPi. willV be regarded as having the uniform gradient
' `between the limits ßi and ,32 (which maybe for
decreases towards the outer end owing to the
merging of these paths into each other. Such a>
screw can be machined on a screw-«cutting lathe
having a milling attachment, with the aid ois' 7
milling cutter having a suitably profiled periphery
and employed to cut in succession the several '
grooves of thesaid family forming each path. Y
At the inner end of the dynamic screw 38 there
is preferably a short race 39 the bore of which
has an oval section which is> the same as the sec
tion of the inner end of the dynamic screw 38
but which is not helical. The major axes of these
two sections are relatively displaced through a
small angle,v e. g. 15° as shown in Fig. 8 (where
for the sake of> clearnes's the ovals are 'shown in
exaggerated form), while the adjacent edges _of
the two parts 38 and 39 are rounded, as shown in
Figs. 9, 10 and 11. The race 39 is provided with a
y circumferential groove 49.
«1i4 (Fig. 13). The roller 3l contacts the dynamic
screw at the bottom of the groove at the point
A in Fig.l 12 and passes onto the slope S. A cen
trifugal force E' urges the roller 3| radially out
wards against the slope S, and the axial com
ponent C=F tan qi, of the force acting between
the roller and the screw accelerates the striker
outwards so that the roller describes a path P.
If no is the velocity of whirl ofthe point of con
tact between roller and slope S, the final trans
latory velocity outwards attained at the intersec
tion of lines G and P is 11:00 tan 2ß, friction being
neglected. It is usually preferable t0 arrange _that
the path P shall, as shown, leave the slope S at its
outer_edge; thoughV in some circumstances the
path P may cross the ridge R and enter the next
succeeding helical groove.
`
The translatory velocity so imparted to the
striker is sufficient to return it to the race 35,
the tapered surface of which ¿constrains the roll
The races 35 and 39 and the dynamic screw
38 are locked in the tubular body 20 of the tool
ers to move inwards against the centrifugal forces
by means of >an externally*screw-threaded ring 35 acting on them and thus arrests th’e translatory
4| engaged in the end ofthe body and bearing
part of the motion of the striker. Thereafter
against a flanged portion 42 of the inner end
the rollers, continuing to> press upon the conical
cap 24, which in turn Vbears against the race 39.
surface of the race, Vcooperate with the latter
The races, the dynamic/screw and the rollers 3|
Yto force the striker out again so that the striker
are hardened and ground to a high surface finish. 40 leaves the race 35 with a translatory velocity
The tool-bit holder 23 is associated with a
which, if friction is neglected, will be equal to
spring 43 compressed between the end of a coun
that with which it entered the race 35. Thus the
f . terbore 44 in the end cap 24 anda guide ring 45
cycle will repeat automatically.
Y
retained by a snapring 46y engaged on thetool
The race 38 forms a starting and idling zone
bit holder which is thereby resiliently biased to
lwards the position shown. '
The operation of the tool will now be described,
starting from the condition in which the striker
26 is being rotated at normal speed in the direc
tion ofthe arrow in Fig. 1 and is within the upper
. part of the race 35. The rollers 34 rotating with
the striker are urged radially outwards by cen
trifugal force and co-operate with the diverging
race 35. 'I‘he axial components of the forces act
ing between the race and thel rollers accelerate
, the striker inwards.
When the rollers 3| leave the inner end of the
race 35, the momentum of the striker carries it
into the dynamic screw. The helixes now described by the rollers are of the opposite hand
to the helical paths in the dynamic screw, so that
the rollers move more or less transversely to these
paths; under these circumstances, since the
threads of the screw and the ridged portions 34
of the rollers are of smoothly curved profile, therel
is only a very loose dynamic coupling between the
striker and the screw and the retardation of the
inward movement of the striker is relatively
slight,
The tool bit being in contact with work, the
tool-bit holder will be raised to a position such
that its surface 31 is against the inner end of the
shaft 25A, Consequently the striker will strikeV
for the rollers 3|, in which thev striker can> be
brought up to normal speed when the motor is
switched on and before the tool is set to work.
The groove 40 forms a track round which the
rollers can run idly. When the tool is set to work
after th’e motor has run up to speed, outward
movement of the tool-bit holder 23 as the tool
is engaged with the work causes the striker to be
displaced outwards until the ridged portions 34
of the rollers engage the sinuous groove formed
by the roundededges of the race 39 and the dy
namic screw, as shown in Figs. 9, 10 and 11. This
sinuous groove operates to project the striker
into the dynamic screw in such a way that the
ridged portions of th'e rollers enter the helical
paths at spots so selected that the points of
contact between the rollers and the race willfol
low substantially the ideal path P (Fig. 12).
The frequency of the movement of the striker
is controllable by varying its total weight, the
weight and profile of the rollers, the dimensions
of the race 35 and the pitch and form of the
dynamic screw; and this frequency can easily
be made a small fraction ofthe speed of revolu
tion of the motor, which may be as high as
10,000 R.. P. M. in a hand tool.
In intermittent service, such as riveting, the
motor may be allowed to run continuously, since
the power consumption is low while' the tool is
idling. During idleintervals the motor speed
gaged in the dynamic screw. When. the striker 75 may be allowed to rise, and the energy thereby
the tool-bit holder while the rollers3| are en
2,407,604
5
stored in the rotary masses „is usefully employed
in the nekty working periodïas the motorspeed
drops' with increasing load. This possibility of
energy storage enables a small and light motor
to be used. A motor having a drooping torque
speed characteristic, e. g. a series motor, is par
ticularly suitable for this application.
The mechanical parts can be kept well lubri
cated by splash by introducing a small quantity
of oil within the tubular body 2B, which- is of
oil-tight construction.
Figs. 4 and 5 show two alternative forms of
striker. In Fig. 4 the rollers 31A are rotatable in
hollow rectangular carrier blocks ¿il which are
slidably guided in pockets 30A in the striker
26A. In Fig. 5 balls SEB are provided instead of
rollers and are a working fit in pockets SEB in
th'e striker 25B. Rollers are generally preferable,
sincev their profile can be adapted to design re
quirements, whereas the radius of balls is iiXed 20
by the mass desired.
'
I claim:
1. A percussion tool including a rotary driving
member, a diverging tubular race co-aXial with
said driving member, a second tubular race ad- -
of its stroke in which the h'and of the helixes
traced out by said masses is opposite to the hand
of said helical path, and means for‘reversing
the direction of translation of said striker at the
other end of itsstroke, the shape of said interior
surface being such as to impose on said masses
when in Contact with .every point on said surface
an acceleration having a component towards said
axis, irrespective of the axial velocity of said
striker.
A
4. A percussion tool including a rotary driv
ing member, a striker co-aXial with and 'con
strained to rotate with said driving member and
reciprocable along the axis of rotation of >said
member, a tubular race co-aXial with said >driv
ing member and having helical'fpaths on its Yin--
terior surface, said striker carrying centrifugal
rolling elements constrained to rotate and re
ciprocate therewith >and capable of moving at
least in part radially with respect to said axis
while rolling round said interior surface, an abut
ment member positioned to be struck by said
striker atl the end of its stroke in which the
hand of the heliXes traced out by said masses is
opposite to the hand of said helical paths, and
jacent to the larger end of said diverging race
>and having helical paths on its interior surface,
a striker co-aXial with and constrained to rotate
means for reversing th'e direction of translation
of said striker at the other end of its stroke, the
forming the kinetic `energy of rotation of said
striker into striking energy of translation of said
striker, and van abutment member capable of
locity of said striker.
shape of said interior surface and of said rolling
elements being such as to impose on said rolling
with said driving member and reciprocable along
said axis, said striker having centrifugalmasses 30 elements when` in contact with every point on
said surface an acceleration having a component
constrained to rotate with it and capable of
towards said axis, irrespective of the axial ve
co-operating with said helical paths for trans
‘
5. A percussion tool including a rotary driving
member, a diverging tubular race co-aXial with
said driving member, a second tubular race ad
arresting such translatory movement of said
jacent to the larger end of said diverging race
striker while said striker is within said second
and having helical paths on its interior surface,
race, said helical paths being of opposite hand to
a striker co-aXial with and constrained to ro
the helixes traced out by said masses during the
translatory movement of said striker towards 40 tate with said driving member and reciprocable
along said axis, said striker having centrifugal
said abutment member.
rollers constrained to rotate and reciprocate with
2. A percussion tool including a rotary driving
shaft, a tubular body, a striker connected for
rotation with said shaft and capable of recipro
eating longitudinally within said body along the
axis of said shaft into engagement with a toolbit holder >slidably mounted in the inner end of
'said body, said striker having a plurality of cen
trifugal masses uniformly distributed around it
and constrained to rotate and reciprocate with
it, but capable of moving at least in part radially
with respect to th`e striker, the interior surface
'of said body forming near its outer end a race
for said masses, which diverges in the inward di
rection for the purpose of accelerating the striker
on its iii-stroke, the interior surface of said body
forming beyond the inner end of said diverging
race a second race providing helical paths for
influencing the motion of said masses for the
purpose of accelerating the striker on its out
stroke, and the hand of said helical paths being
opposite to the hand of the helixes traced out by
it while rolling round the interior surfaces of
said races, said rollers co-operating with said
helical paths for transforming the kinetic energy
of rotation of said striker into striking energy of
translation of said striker, and an abutment
member capable of arresting `such translatory
movement of said striker while said striker is
within said second race, said helical paths being
of opposite hand to the helixes traced out by
said rollers during the stroke of said striker to
wards said abutment.V
6. A percussion tool including a tubular body,
lan electric motor at one end of and co-axial with
said body, a tool-bit holder slidably mounted co
Xially with and in the other end of said body,
said motor having a shaft extending co-aXially
within said body, a bearing between the end of
said shaft and said tool«bi`t holder, a striker
mounted on and constrained to rotate with said
shaft and reciprocable within said body for co
operation with said tool-bit holder, said striker
having centrifugal masses constrained to rotate
3. A percussion tool including a rotary driving
member, a striker co-axial with and constrained (i5 with it and movable at least in part radially with
respect to said axis while co-operating with the
to Vrotate with said driving member and recip
interior surface of said body, said interior surface
rocable along the axis of rotation of said mem
having grcoved helical paths in the portion there
ber, a tubular race co-aXial with said driving
of that cci-operates with said masses when said
member and having helical paths on its interior
striker is impacting said tool~bit holder, the hand
surface, said striker comprising centrifugal
of said helical paths being opposite to that of the
masses constrained to rotate and reciprocate with
paths traced by said masses while said striker ap
it and capable of moving at least in part radially
proaches said tool~bit holder, and means for re
with respect to said axis while co-operating with
versing the direction of the translatory motion
said interior surface, an abutment member posi
Cf said striker while it is in th‘e neighborhood
tioned «to be struck by said’striker at the end
said masses during the in-stroke of the striker.
2,407,604.
7
of the' end of said bodyadjacent Vto said motor
and thereby returning saidv striker into said
grooved portion.
,
'
7. A percussion tool including a tubular body,
an electric motor at one end of and co-axial with
said body, a tool-bit holder slidably mounted co
axially with> and in the„other end of said body,
said motor having a shaft extending co-axially
within'said body, a bearing between the end of
8
member, a striker co-axial with and constrained
to rotate with saiddriving member and recipro->
cable along the axis of rotation of said member,
a tubular race co-axial with said driving member
and having h'elical paths on its interior surface,
saidstriker comprising centrifugal masses> con
strained to rotate and reciprocate with it and
capable vof moving at least in part radially with
respect to said axis while co-operating with said
said shaft and said tool-bit holder, and a striker 10 interior surface, an abutment member for co
mounted on and constrained to rotate with said
operation with said striker while it is in a posi
shaft and reciprocable within said body for co
operation with said tool-bit h'older, said striker
tion such that said masses are traversing said
helical paths, and means for reversing the direc
having centrifugal rolling elements constrained
tion of translatory motion of said striker while it
to rotate with it and movable at least in part 15 is remote from said abutment member, the shape
radially with respect to said axis while co-oper
of said interior surface’being such that cross
ating with the interior surface of said body, said
sections thereof taken in succession in the direc
interior surface -díverging from the end nearer to
tion towards said abutment member are ovals of
said motorand merging into a portion having
approximately elliptical form, of which the ratio
grooved helical paths so disposed as to co-operate 20 of major axis to minor axis increases in said di
with said rolling elements when said striker is
rection, while the major axis of the oval at any
impacting said tool-bit holder, the hand of said
section is angularly displaced about said axis, in
helical paths being opposite to that of th'e paths
the direction opposite to the direction of rota
traced by said rolling elements while said striker
tion of said driving member, with respect to' the
approaches said tool-bit holder.
25 major axis ofthe oval at any section more re
8. A percussion tool including a tub-ular body,
mote from said abutment member.
a rotary driving member, a striker in said body
11. A percussion tool including a tubular body,
coeaxial with and constrained to rotate with said
a driving shaft substantially co-axial with said
driving member and reciprocable along the axis
body, a centrifugal mass constrained to rotate
of rotation of said member, said striker compris 30 with said shaft but movable parallel and radially
ing centrifugal masses constrained to rotate and
with respect to the axis of said shaft, said body
reciprocate with it but movable at least in part
having on its interior surface a helical groove
radially with respect to said axis, an abutment
with which' said mass co-operates'under the in
member slidably carried in said body co-axially
fluence of centrifugal force to produce any axial
with said striker for co-operation with said strik 35 thrust, means on said body for' taking the mo
er, the interior surface of said body providing
mentum of said mass in one axial direction and
an idling track for said masses when said striker
means for reversing the direction of. translatory
is in contact with said abutment member and
motion of said mass after its .displacement in the
when said abutment member'is extended, and
other axial direction, the shapes of said mass and
said interior surface also having shallow helical
said groove being'such that the dynamic coupling
grooves on the side of said idling track remote
between them is higher when the helical path of
from said striker for co-operation with said
the mass is of the same hand as said helical
masses so as to accelerate said striker in the
groove than when the helical path of the mass
direction away from said abutment member, and
is of the opposite hand to the helical groove.
means in said body co-operating with said striker 45
12. A percussion tool including a tubular body,
to reverse the direction of its translatory motion
a driving shaft substantially co-axial 'with said
when` said striker is remote from said abutment
body, a centrifugal mass constrained to rotate
member. »
with said shaft but movable parallel and radially
9. A percussion tool including a tubular body,l
with respect to the axis of said shaft, said body
a rotary driving member, a striker in said body 50 having on its interior surface a helical groove
co-axial with and constrained to rotate with
with' which said mass co-operates under the in
said driving member and reciprocable along the
fluence of centrifugal force to produce an axial
axis of rotation of said member, said striker com
thrust, and a frusto-conical portion having its
prising centrifugal masses constrained to rotate
larger end adjacent to said groove, the shapes
and reciprocate with it but movable at least in 55 of said mass and said groove being such that
part radially with respect to said axis, an abut
the dynamic coupling between them is higher
ment member slidably carried in said body co
when the helical path of the mass is of the same
axially with said striker for co-operation with
hand as said helical groove than when th'e heli
said striker, th‘e interior surface of said body
cal path of the mass is of the opposite hand to
having ñrstly an idling track for said masses 60 the heli-cal groove, and such higher dynamic cou
when said striker is in contact with said abut
pling producing on said mass a thrust in the axial
ment member and when said abutment mem
direction opposite to that produced on said mass
ber is extended, secondly shallow helical grooves
on the side of said idling track remote from said
striker for co-operation with said masses so as to
accelerate said striker in the direction away from
said abutment member and thirdly a sinuous
circumferential groove between said helical
grooves and said idling track and placed to re
ceive said masses on retraction of said abutment
member, and means in said body co-operating
with said striker to reverse the direction of its
translatory motion when said striker is remote
fromV said abutment member.
'
by said frusto-conical portion.
13. A percussion tool including a tubular body,
a driving shaft substantially co-axial with said
body, a centrifugal mass constrained to rotate
with said shaft but movable parallel and radi
ally with~ respect to the axis of said shaft, said
body having on its interior surface a helical
groove with which said _mass co-operates under
the inñuence of centrifugal force to produce an
axial thrust, a frusto-conical portion having its
larger end adjacent to said groove,'and a cylin
drical portion on the side of said groove remote
10. A percussion tool including a rotary driving 75
from said frusto-conical portion, the shapes of
2,407,604
10
dynamic coupling between them is higher when
cluding a centrifugal mass constrained to follow
the rotation and translation of said striker and
the h‘elical path of the mass is of the same hand
as said helical groove than when the helical path
of the mass is of the opposite hand to the helical
groove, and such higher dynamic coupling pro
ugal force on the interior surface of said body, at
least part of said surface having a helical form
such as to cause a screwing effect by which part
ducing on said mass a thrust in the axial direc
of the rotary motion of said striker is converted .
said mass and said groove being such that the
capable of bearing under the inñuence of centrif
into translatory motion in an axial direction, and
means for reversing the said translatory motion
said frusto-conical portion.
14. In a percussion tool, a tubular body, a 10 of the striker, so that undel` the alternating ef
fects of said helical surface and said reversing
rotatable striker Within said body and capable of
means said striker will reciprocate continuously.
translation along th‘e axis thereof a motor driv
RUDOLF GOLDSCHMIDT.
ably connected to said striker, said striker in
tion opposite to that produced on said mass by
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