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Description  |
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The invention relates to a fine-tuning peg which is suitable for use on a
stringed instrument and has means of fixing in order to hold the peg
firmly in the peg box of the stringed instrument, against being loosened
by the pull of the string, and which comprises a peg head, which is partly
hollow and can be firmly fixed at the peg box of the stringed instrument,
and a tuning wheel in the interior of the peg head as well as a neck part
with a tuning shaft, which is supported therein and is connected to the
tuning wheel in such a way that it can be turned by the latter, and a
string drum seated on the tuning shaft.
The known stringed instruments as a rule possess a peg box which has a
scroll and is delimited by the nut, at which the neck mounted on the sound
box of the instrument starts. In the case of a violin, for example, two
pegs each, by means of which the strings are tuned, are located on the
left and on the right, projecting into the peg box. With the customary
pegs, the clamping force on the cone, which is necessary to obtain a
secure hold, must be substantially larger than the pull, already in itself
considerable, of the string which is fitted on a string drum.
The ease with which these known pegs can be moved is generally inadequate
to make it possible for the person playing the instrument easily to effect
fine-tuning of a given string by adjusting, with the left hand, the lever
holding it, when the instrument is held in the usual way, while, at the
same time this string is bowed with the right hand as usual. Furthermore,
an additional pressure in the direction of the axis of the string drum is
necessary when turning the peg in order to prevent its becoming loose.
When bowing the string it is hardly possible, especially in the case of
violins and violas, to operate the additional fine-tuning devices which
have hitherto been proposed and comprise levers and/or screws. Tuners
which have a worm-wheel reduction and are known, in particular, for
plucked stringed instruments, have also been proposed for double basses.
They are, however, unsuitable for a violin, viola and cello, if only for
stylistic reasons.
The fine-tuning peg of the type described initially, such as has been
described by Georg Wolff in German Pat. Specification 677,242, also has a
tuning wheel which is supported in the peg head of the firmly clamped peg
and is seated directly on one end of the tuning shaft which is supported
in the peg shaft, and which tuning shaft can be moved axially therein and
has the shape of a threaded spindle.
Because of high friction losses, this known peg permits fine-tuning only
with the application of a relatively large force. Furthermore, since
re-tuning is only possible very coarsely by loosening the peg in the peg
box, it is necessary for fine-tuning to turn the tuning wheel by two
fingers gripping around both sides of the peg. There is also no device for
compensating the pull of the string. The only locking mechanism possible
in this case is a guide pin firmly clamped in a helical slot running
around the peg shaft.
It is true that, on turning in the tuning shaft, the string drum could be
moved axially in the direction away from the peg head, whilst tensioning
the string present on the drum with an increased effort, but the clamping
of the guide pin in the helical slot would in this case strongly impede
the turning-back of the string drum, and the movement of the string drum
following behind the threaded spindle, which latter is being screwed back,
would then be uncertain and irregular.
It is therefore an important object of the present invention to provide a
fine-tuning peg which makes it possible, whilst the instrument is securely
held in the normal way, easily to effect fine-tuning of a string, bowed by
the bow held in the other hand, with one finger of the hand holding the
instrument, a reliable response of the element carrying the string being
fully ensured in the case of both sharp tuning and flat tuning.
It is also an object of the invention to provide a fine-tuning peg of such
a type that it can, as desired, be mounted and removed from stringed
instruments of normal construction without modification of the latter.
It is a further object of the invention to provide a fine-tuning device
with great ease of movement, in which the string tension can be largely or
completely compensated by an adjustable counter-tension, so that small
changes in the tension of the string can easily be accomplished by
adjusting the tuning wheel with the end of one finger. In this adjustment,
the smallest possible change in the tension of the string should
correspond to a long path of the finger tip.
This object is achieved by a fine-tuning peg of the type described
initially, which, in accordance with the invention, is characterized in
that the string drum is secured, during fine-tuning, against a shift in
the axial direction on the turning shaft, that a device for compensating
the pull of the string is connected to the tuning shaft, by means of which
device a pull, exerted on the tuning shaft by the string via the string
drum, is largely or completely compensated, and that a disengageable
locking mechanism is provided which secures the string drum against
turning, relative to the tuning shaft, in the sense of the direction of
the pull of the string, but permits a mutual twisting of the string drum
and the tuning shaft in the opposite direction, so that it becomes
possible to adjust the pre-tuning means.
Preferably, the connection between the shaft of the tuning wheel and the
tuning shaft can here consist of a wormgear accommodated in the interior
of the peg head.
The string drum with an extension which is suitable for adjustment by an
adjusting key preferably projects through the wall, facing away from the
peg head, of the peg box, and the disengageable locking mechanism
preferably prevents the string drum, after a string fastened thereon has
been tensioned, from turning back relative to the tuning shaft, whilst the
locking mechanism is engaged.
Furthermore, the locking mechanism can preferably comprise a locking string
element which is located on the tuning shaft and can be compressed or
narrowed in an axial direction, in order to release the locking mechanism.
The device for compensating the pull of the string can possess a
compensating spring which is placed around the tuning shaft, is supported
in a bush firmly seated on the tuning shaft and counteracts the pull of
the string on the tuning shaft.
A stop device which secures the peg head against unintended twisting can be
provided on the wall of the peg box. Preferably, this stop device can be
released by an axial movement of the peg head in the direction away from
the peg box and the peg head can thus be turned.
Moreover, the tuning wheel can preferably be seated on a tuning wheel shaft
which is supported, so that it can turn, in the peg head, transversely to
the longitudinal axis of the tuning shaft. An edge part of the tuning
wheel can here protrude through an orifice in the wall at the outer edge,
facing away from the peg box, of the peg head, so that it can be turned
from outside.
The locking mechanism can possess a first toothed rim, which is firmly
seated on the string drum, and a second toothed rim, which is firmly
inserted in the string drum and, during fine-tuning, positively engages
with the first toothed rim, this engagement being released, during
pre-tuning, by adjusting the string drum. In this case, the locking
mechanism can include a compression spring element which is supported, on
the one hand, on the tuning shaft and, on the other hand, on the toothed
rim and which puts a load on the latter in order to effect engagement.
The string drum can form, in its interior and around the tuning shaft, a
first annular chamber, into which a bush rigidly joined to the tuning
shaft projects, and a preferably cylindrical helical spring, biased for
clamping, in the ring chamber can make contact around the bush, one end of
the helical spring being joined to the string drum, and the joint of the
spring to the string drum is free from tension when no pull of the string
acts on the latter, and, when the string drum is turned for pre-tuning
which releases the tension of the string, the spring can be twisted via
its end so that the windings are extended, and can then freely slide on
the bush.
The worm-gears are known per se. Since they alone do not enable tuning to
be carried out with sufficient ease and especially require excessive
differences between the forces needed for sharp tuning and flat tuning,
the major part of the pull of the string advantageously is absorbed by the
said compensating spring element in the fine-tuning peg, according to the
invention, which includes a worm-gear in rotatable engagement with the
tuning shaft which is located inside the actual, non-rotatable peg.
Tensioning of the compensating spring element is here made possible by
pre-tuning with the aid of the abovementioned locking mechanism which can
be actuated by a key from the other end of the peg. In this way, the
tuning wheel which projects from the head part, similar to the handle of a
peg, of the fine-tuning peg according to the invention can now easily be
turned by the fingertip of the thumb of the left hand rolling over it,
while the other fingers support the scroll.
If the left-hand peg heads of the left-hand low strings G and D are mounted
in such a way that their tuning wheels point obliquely upward and forward,
that is to say towards the fingerboard, and the tuning wheels of the
right-hand strings A and E point downward and forward, at approximately
right angles to the former, this results in the very important advantage
that subjectively the same actuating direction always effects the sharp
tuning or flat tuning of all the fine-tuning pegs, that is to say a
pulling movement of the thumb preferably always serves for pulling up but
a pushing movement of the thumb serves for pushing back. This arrangement
also has the special advantage that, when the thumb changes from one side
of the peg box to the other, the other fingers of the left hand can always
remain in the same position in order to hold the instrument securely by
its scroll.
It is a further advantage that, in contrast to known lever fine-tuners, the
tuning range is not fundamentally limited. The form of the new peg can
also be readily matched to the stringed instrument, for example a violin,
and can be shaped in such a way that it does not conspicuously differ from
the customary wooden pegs.
Further details of the invention can be seen from the description, which
follows, of a preferred embodiment thereof by reference to the attached
drawing, in which
FIG. 1 shows, partially in axial section, a peg box with two fine-tuners
according to the invention, incorporated therein;
FIG. 2 shows a side view of the peg box part shown in FIG. 1, with a peg
head and a fine-tuner accommodated therein;
FIG. 3 shows a cross-section through a peg head in the plane indicated in
FIG. 1 by III -- III;
FIG. 4 shows a cross-section through a string drum in the plane indicated
in FIG. 1 by IV -- IV;
FIG. 5 shows an enlarged representation of a locking mechanism on the
tuning shaft, which interacts with the string drum, in the non-compressed
state and
FIG. 6 shows the same locking mechanism in the compressed state;
FIG. 7 shows a peg box with another embodiment of a fine-tuner incorporated
therein, partially in axial section and omitting the major part of the peg
head;
FIG. 8 shows a view of the side, facing the body of the instrument, of the
central part of the fine-tuner, located between the two box walls;
FIG. 9 shows a partial view through this central part along the plane
characterised in FIGS. 7 and 8 by IX -- IX;
FIG. 10 shows a partial view of the embodiment of the fine-tuner shown in
FIG. 7, along the plane indicated in FIG. 7 by X -- X;
FIG. 11 shows a similar cross-section, but along a plane indicated in FIG.
7 by XI -- XI, and
FIG. 12 shows a side view of the peg box with four fine-tuning pegs
according to the invention mounted thereon.
As can be seen from FIG. 1, two peg heads 2 and 3 are firmly built into the
peg box 1 of a violin or a similar stringed instrument, and specifically
the peg head 2 is built into the peg box wall 1a, which is on the right as
viewed by the violin player, and the peg head 3 is built into the box wall
1b on the left. Each of the peg heads 2, 3 must be built into the wall of
the peg box in such a way that they are secure against a shift in an axial
direction and also against rotation. It is necessary that the requisite
fastening elements can be adapted to deviations in the position of the
wall surfaces of the peg box, which never have accurate dimensions; the
normal inclined position of these wall surfaces must also be compensated
by corresponding shaping of the fastening agents. Securing plates 4, which
preferably are manufactured from glass-clear plastic material and thus are
hardly visible, serve to secure the peg heads against twisting. The
securing plates 4 make flat contact with the outer walls. They have a
wider end and a narrower end, the wider end surrounds the shaft 5 of the
peg 2 to be secured, whilst the conically tapered bush 6 of the adjacent
peg 3 protrudes through the narrower end of the securing plate 4. In this
way, the securing plates 4 themselves are secured against twisting or
turning on the outer surface of the box wall. Towards the wider end, the
securing plate 4 carries an extension 7 of frustoconical shape, which
protrudes into the hollow interior of a collar part 8, which has the shape
of an outwardly projecting truncated cone, on the shaft 5 of the peg head.
Preferably, the collar part 8 is knurled on its annular conical inner wall
and can thus be pressed, providing securing against twisting, into the
conical annular surface of the extension 7, which preferably is
manufactured from a somewhat softer material than the shaft of the peg, by
tightening the tightening nut 9 which is screwed by means of the thread 9a
onto the bush 10 which is firmly inserted into the shaft 5 of the peg
head, an elastic washer 9b resting on the inside of the box wall 1a. This
washer 9b has, on the side facing the sound box, a sufficiently greater
thickness than on the opposite side, in order to compensate the
inclination of the box wall. The outer surface of the washer 9b here has a
rounded profile, against which the nut 9, which has a hollow shape with a
conically chamfered inner ring surface, rests. In a peg hole 11 of the
opposite box wall 1b, the bush 6 is supported, so that it cannot be
turned, in alignment with the peg shaft 5. The center of a tuning shaft 12
and one of its ends are supported in the interior of the shaft 5 of the
peg head and of the peg head 2 itself, respectively, and its other end is
supported in the bush 6. The gearing mechanism of the fine-tuner is now
built into the peg head 2.
This mechanism includes the tuning wheel 14 (FIG. 3) which is borne by the
tuning wheel shaft 13 and projects through the orifice 2a in the wall of
the peg head 2, the inside of which is hollow. To facilitate operation,
the tuning wheel 14 preferably has a knurled rim 14a. Furthermore, the
worm 15 which engages with a crown wheel 16 on that end of the tuning
shaft 12 which projects into the peg head 2, is seated on the shaft 13 of
the tuning wheel. A string drum 17 which extends into the bush 6 by a
sleeve part 18 surrounding the tuning shaft 12 and is supported, so that
it can turn, in the bush by means of a ball-bearing 19, is loosely seated
on the tuning shaft 12 in the central range thereof between the two peg
box walls is 1a and 1b. The free end of the sleeve part 18, which projects
into an outwardly opening recess 6a of the bush 6, ends in a hexagon 18a
which fits a pre-tuning key (not shown). With the aid of the pre-tuning
key, the string drum 17 can be turned relative to the tuning shaft 12 and
a string 20 fastened thereon can be pre-tensioned.
Preferably, the string 20 not only is threaded in, but is also additionally
pre-secured by a transverse screw 21 to such an extent that a few smoothly
adjacent windings of the string suffice for a secure hold thereof on the
string drum 17 (FIG. 4). In this way, the usual mere threading of the
string into the orifice 22 in the string drum 17, followed by multiple
cross-over windings of the string, is avoided.
After the said pre-tensioning of the string, the drum is secured against
turning back by a locking mechanism 23 which is in itself known and which
is pressed in the direction towards the bush 6 by a set of locking springs
24, which is supported in a bush 10 inserted into the cavity 5a of the peg
shaft 5. A ball-bearing 25 which is firmly seated on the tuning shaft 12
and which can be turned relative to the inner wall of the cavity 5a in the
region of the bush 10 of the peg shaft 5, serves as the abutment for the
set of locking springs 24.
As shown in the enlarged representation in FIG. 5, the locking mechanism
consists of two mutually engaging toothed rim members 30 and 31, the
former of which is rigidly joined to the tuning shaft 12, whilst the
second is firmly inserted into the string drum 17. Mutual engagement of
the two toothed rim members is effected by the set of locking springs 24,
the set of springs 24 which is supported on the ball-bearing 25 pressing
the toothed rim member 31, joined to the string drum 17, of the locking
mechanism 23 into the toothed rim member 30 joined to the tuning shaft 12.
The set of springs 24 consists of a number of annular springs, and each
curved annular spring 24a is supported on a flat annular spring 24b,
whilst one of the outermost annular springs of the set, which are both
curved, is supported on the ball-bearing 25 and the other is supported on
the toothed rim member 31 joined to the string drum 17.
When the string drum 17 is adjusted clockwise (as viewed from the peg head
2) by means of a key fitting the hexagon 18a so that the set of springs 24
is compressed, the toothed rim member 31 slides out of engagement with the
toothed rim member 30 which latter is held in place, against twisting, by
the worm 15 via the crown wheel 16 and the tuning shaft 12. During this
procedure, the string 20 is tensioned. After the key has been withdrawn,
the string 20 tries to turn the string drum 17 back counterclockwise, but
the set of springs 24 now presses the toothed rim member 31 into locking
engagement with the toothed rim member 30 on the tuning shaft 12.
During the compression in the direction towards the peg head 2, the flat
annular springs 24b in the set of springs 24 are deformed, whilst the
pre-formed, curved springs 24a are flattened to a corresponding extent
(FIG. 6).
One end 26 of a balancing spring 29 surrounding the tuning shaft 12 is
inserted in a recess 26a of the ball-bearing 25, whilst its other end 27
is inserted in a second recess 27a in the end wall 28 of the cavity 5a of
the shaft 5 of the peg head. This balancing spring 29 tends to reset the
tuning shaft 12 against the pull of the string into its position relative
to the peg 2, when the string is not under tension. For a release, the
locking mechanism 23 can be disengaged by axial pressure with the key and
the compression, thus resulting, of the set of locking springs 24.
Pre-tuning starts with the balancing spring 29 at first only slightly
tensioned, by first tightening the string 20 somewhat with the aid of the
pre-tuning key turning the string drum 17, whereupon the string is tuned
down again, that is to say somewhat relaxed again, by turning the tuning
wheel 14, the rotation of which is transferred via the worm 15 to the
crown wheel 16 and hence to the tuning shaft 12. By the adjustment of the
tuning wheel 14 which does not move too easily, the balancing spring 29 is
tensioned without overloading the entire gear mechanism, since the pull of
the string and the tension of the balancing spring 29 are always
approximately in balance even if the pre-tuning process and tuning down
process is repeated during the gradually progressing tuning. In final
tuning, the ratio (pull of the string) : (tension of the spring) in itself
can then be selected as desired, but preferably in such a way that this
ratio on the one hand corresponds to the natural perception whilst tuning,
but on the other hand also keeps the gear mechanism free from play.
In order to make the tuning of the strings as easy as possible, the
frictional resistance to turning must be reduced to a minimum. This
purpose is served by supporting the tuning shaft 12 and the string drum 17
in the ball-bearings 19 and 25 and also in the ball-bearing 40 which is
firmly built into the end wall 41, of the peg shaft 5, situated in the
hollow interior of the peg head and on which the crown wheel 16 runs. The
bearings 19 and 25 which are most highly stressed by pressure here lie as
close as possible to the insides of the walls 1b and 1a respectively of
the peg box 1.
In the second embodiment of the fine-tuning peg according to the invention
the fixing device comprises a string drum 117, the sleeve part 118 of
which projects outwards through the left-hand box wall 1b and the
projecting part of which has a hexagonal shape. The hexagon of the sleeve
part 118 serves for pre-tuning in the same manner as the hexagon 18a in
the first embodiment.
The string drum 117 is secured against turning back in the direction of the
pull of the string by the locking spring 34 which is situated in an
annular chamber 33 within the string drum 117 around a bush 125,
accommodated in the latter and rigidly joined to the tuning shaft 12, and
the flattened end 35 of which projects into the groove 36 of a locking
spring holder 37. The latter is seated in a recess 38 of the string drum
117, extending transversely to the axis of the drum.
The locking spring 34 is seated on the bush 125 and has a slight bias which
increases as the spring starts to turn, if this turning of the spring is
effected via the string drum 117 starting at the end 35 of the spring in
the direction in which the spring is wound onto the bush 125, so that the
spring 34 and the bush 125 jam and produce locking; the spring 34 can then
easily be turned on the bush 125 in the opposite direction since the
initial friction between the bush 125 and the spring 34 has the effect
that the windings of the latter expand easily and hence reduce the
friction.
In FIGS. 7 and 8, the locking spring 34 is shown with a winding in the
sense of a left-handed thread. This means that, when the string 20 is
tensioned, the drum 117 must be turned clockwise, as viewed from the
right, that is to say from the peg head 2. Accordingly, the drum 117 must
be locked in the opposite direction against the bush 125 joined to the
tuning shaft 12, since the windings of the spring 34 over the bush 125 are
wound up by the drum via the end 35 of the spring in the sense of
narrowing the windings and are thus jammed on the bush 125. If, however,
the drum 117 is turned by the pre-tuning key itself in the abovementioned
direction of tensioning the spring, it then takes the end 35 of the string
along in the sense of relaxing the spring, that is to say expanding the
windings, so that the spring 34 can then freely slide on the bush 125.
One end 26 of the balancing spring 29 engages with the recess 126a of the
bush 125 and its other end 27 is supported in the recess 27a of the peg
head 2 in the same way as in the first embodiment.
In the instant embodiment, the fastening, secure against turning, of the
fine-tuning peg in the peg box wall is effected in a manner similar to
that shown in the embodiment of FIGS. 1 to 6.
It is, however, desirable to loosen the fine-tuning peg from its fastening
in the peg box wall to such an extent that it can also be turned around
the axis of the tuning shaft, in particular for the purpose of changing a
string.
In the embodiment according to FIGS. 1 to 6, it would be necessary to
loosen the tightening nut 9 for this purpose. In the embodiment according
to FIGS. 7 to 11, however, this is effected in a simpler manner by axially
pulling the peg head 2 in the direction out of the peg box 1, and
specifically against the action of a compression spring 39 which is
located in the interspace between the sleeve part 118 and a threaded bush
106 surrounding the latter and which is compressed by a collar 42 fixed to
the tuning shaft 12, when the latter undergoes a limited axial movement as
a result of the pull on the peg head 2. The cylinder 105 which is rigidly
joined to the neck 108 of the peg head 2 then slides, in a crown bush 110
inserted into the peg box wall 1a, so far outwards that the crown segments
110a, 110b, 110c and 110d lose engagement with the recesses 108a, 108b,
108c and 108d opposite thereto (FIG. 11). The peg head 2 can now be turned
in any desired direction until one of its recesses 108a to 108d again
coincides with one of the crown segments 110a to 110d of the crown bush
110, and when the peg head 2 is then released, the spring 39 effects a
firm seating of the peg head on the peg box 1, the crown segments engaging
with the corresponding recesses of the peg head.
Fundamentally, the fastening, secure against turning, of the crown bush 110
in the peg box wall 1a takes place in accordance with the principle of
clamping on a cone, as is customary with wooden pegs, but with the
difference that a firmer joint is obtained in this case, it being no
longer necessary, in contrast to the previously known pegs, that the bush
110 can still be turned. On the contrary, adhesives should therefore be
used in this case in place of the customary slip lubrications. If a firm
bond is omitted, in order to be able to replace the crown bush 110, a
prior bushing of the peg hole 11, which is free from lubricant, with a
solution of a soft resin has proved useful. The security against turning
can also be further increased by providing the outer surface of the crown
bush 110 with a fine, sharp knurling. Of course, a well-matched fit it
also a prerequisite in this case. Since the peg holes 11 in stringed
instruments are not yet standardized, this can be achieved, when the new
fine-tuning pegs are built afterwards into old violins, either by
re-reaming the peg holes to the intended dimension or by also supplying
crown bushes with stepped outer dimensions. The latter is possible because
a very narrow dimensional tolerance is not required when the crown bush
110 is firmly pressed in, although care must be taken that the
dimensioning of the crown segments 110a to 110d, which slightly project
beyond the peg box wall in order to engage with the peg shaft 105, is
approximately correct. A special screwing tool can be used for pulling the
crown bush 110 out again, without using force.
Since the seating of the small peg end (sleeve part 118) does not need to
be secured against turning, an approximate matching of the dimensions
suffices here. The element used in this case for equalizing the dimensions
is a split clamping bush 43 which has an internal thread and a wide
longitudinal slit and, in the state when it has been taken out of the peg
box wall 1b, that is to say in the relaxed state, has a diameter somewhat
greater than corresponds to the outer thread of the threaded bush 106. The
effect of this is that it must be compressed, when it is inserted into the
peg box wall 1b, and thus already jams in the peg hole 11 under a certain
external pressure. Firstly, this facilitates an accurate adjustment of the
axial position of the fine-tuning peg, since the threaded bush 106 can be
displaced in the clamping bush 43 by screwing using a clamping key which
grips it from its inside, and secondly, this makes it easier to overcome
small deviations in dimensions, because a fit between the two threaded
parts is not necessary here.
After the fine-tuning peg has been axially adjusted, the clamping bush 43
must be locked in its position by the nut 104 via the threaded bush 106,
its flange 44 abutting against the inside of the left-hand box wall 1b. In
particular, this is necessary also because, when the peg head 2 is pulled
forward in order to disengage the neck 108 and the crown bush 110, the
pressure of the compression spring 39, which is then compressed, bears on
the threaded bush 106. However, since the position of the outer wall is
not perpendicular, but somewhat inclined to the axis of the tuning shaft
12, an intermediate disc 45 is required which compensates this
irregularity and is spherically rounded on the side of the nut and the
axis of which necessarily assumes, under the action of the internal
conical surface 104a of the nut 104, a position perpendicular to the
outside of the box wall 1b.
Since the axial pull on the peg head 2 must be transmitted via the tuning
shaft 12 to the string drum 117, the latter is secured against axial
displacement, at its sleeve part 118 which is provided with a hexagon, by
a pin 46 which is inserted, and firmly seated, in a recess 12a of the end
face of the tuning shaft 12.
In order to avoid the unreliable mere threading-in of the strings, which is
followed by multiple cross-over windings, the string 20 is pre-secured, as
in the first embodiment, by a transverse screw 21 in the orifice 22 to
such an extent that at most a few smoothly adjacent windings then suffice
for a secure hold of the string. In order to present a better hold of the
string, even for these windings, on the string drum 117, the latter is
provided with flat, concentric guide grooves 47. If the diameter of the
latter slightly narrows towards the peg head 2, this results in a raised
rim 48 at that end of the string drum 117 which faces the peg head 2, and
this rim 48 effectively prevents the troublesome scraping of the last
winding on the box wall 1a. Particularly regular windings result if the
guide groove 47 itself is wound helically.
The locking spring holder 37 in the form of a slit cylinder (FIG. 9) is
seated in a recess 38 of the string drum 117 opposite the transverse screw
21. This holder is necessary in order to ensure a secure and
distortion-free fastening of the locking spring 34, and this in turn is an
important pre-requisite if the spring is to function perfectly and, above
all, with little play. This is so because a firm seating, which is
accurately parallel to the axis and moreover free from play, of the
flattened fastening end 35 of the spring 34 in a narrow drilled locating
hole can hardly be achieved technically, and even less can a precise
coincidence, without transition, of the angling-off of the spring end 35
with the end of the curvature of the last winding of the spring 34 be
expected, and this would indeed be a condition if the position of the
drilled locating hole were to coincide with the diameter of the spring.
All these difficulties are avoided by placing, according to the invention,
the spring end 35 in the groove 36 of the rotatable locking spring holder
37. In this case, the spring end 35 can then point outwards within wide
limits.
as shown in FIGS. 7 and 8; likewise, the angular deviations transverse
thereto are automatically compensated by turning the cylindrical locking
spring holder 37 in the recess 38. A laterally flat tapering of the spring
end 35 makes it easier to thread it into the groove 36. Additionally,
however, an axial locking of the spring end 35 also is necessary. This can
easily be achieved by filling the groove 36 with a hot-melt cement or a
solder or adhesive. If in this case the spring end 35 has been shaped to
point outwards, as shown, or deformed in another way, its locking in
position is ensured even if no reliable surface bond with the filler is
obtained.
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