Tuning machine with reduced backlash and end play

A tuning machine is provided with an adjustable bearing surface for eliminating mesh backlash and end play which gradually develope between the worm and worm gear over years of service. The worm is held against the worm gear by a pair of saddle bearings formed on a sliding retainer. When the bearing wear develops an unacceptable backlash or end play develops, the retainer is loosened and repositioned closer to the worm. In the new position the worm is returned to its original intimate engagement with the worm gear. Simultaneously, the worm, is axially centered due to opposed bevel surfaces on the worm and saddle bearings. The new worm to worm gear mesh is free of backlash and endplay.

TECHNICAL FIELD 
This invention relates to tuning machines for stringed instruments, and 
more particularly to tuning machines having a sliding worm retainer that 
is periodically adjustable for reducing backlash and end play. 
BACKGROUND 
Heretofore backlash was reduced in tuning machines by forcing the worm 
laterally into full mesh engagement with the worm gear. U.S. Pat. No. 
3,564,573 issued on Feb. 16, 1971 to Wustl, shows a worm spring urging the 
worm screw tightly against the worm gear. End play was reduced by trapping 
the worm axially between two stop structures. 
Heretofore end play was reduced in tuning machines by forcing the worm 
axially against a stop to prevent axial displacement during operation. 
U.S. Pat. No. 4,098,163 issued on July 4, 1978 to Kato, shows an 
adjustable axial sleeve mounted around the worm shaft. The sleeve is 
threaded and is positioned to pin the worm shaft against the housing. 
Axial movement (end play) is prevented by the housing at one end of the 
worm shaft and by the sleeve at the other end. These prior art devices do 
not permit the simultaneous reduction of both backlash and end play with a 
single adjustment. 
SUMMARY 
It is therefore an object of this invention to provide an improved tuning 
machine for stringed instruments. 
It is another object of this invention to provide such a tuning machine in 
which a single repositioning of the worm elements simultaneously reduces 
backlash and end play in the mesh between the worm and the worm gear mesh. 
It is a further object of this invention to provide such a tuning machine 
which may be periodically adjusted to remove backlash and endplay 
introduced by microscopic wear along the bearing interface. 
It is a further object of this invention to provide such a tuning machine 
in which the wear surfaces along the bearing interface are replaced with 
new surfaces by reversing the relationship of the bearing elements. 
It is a further object of this invention to provide such a tuning machine 
in which the repositioning motion is stabilized. 
It is a further object of this invention to provide such a tuning machine 
which is easy to assemble and to disassemble. 
It is a further object of this invention to provide such a tuning machine 
in which the bearing elements are lubricated. 
It is a further object of this invention to provide such a tuning machine 
in which the shaft bearing for the string roller is in intimate contact 
with a locating hole in the mounting plate. 
Briefly, these and other objects of the present invention are accomplished 
by providing a tuning machine for a stringed instrument. The tuning 
machine has a mounting plate for securing the tuning machine to a stringed 
instrument, and a string roller mounted on the plate for taking up string 
when turned in one direction and for letting out string when turned in the 
other direction. The tuning machine also has a worm gear mounted on the 
string roller with a worm in engagement with the worm gear. The worm has a 
shaft portion rotatable about an axis and a screw portion for causing the 
worm gear and the string roller to turn when the shaft portion is rotated. 
A worm retainer rotatably engages the shaft portion, and is slideably 
mounted on the plate for retaining the screw portion in engagement with 
the worm gear. The engagement simultaneously reduces lateral backlash and 
axial end play between the worm and the worm gear. A bearing between the 
worm retainer and the worm has a lateral component of force for reducing 
the lateral backlash and has an axial component of force for reducing the 
axial end play. A releasable lock releases and locks the worm retainer in 
engagement with the worm.

GENERAL DESCRIPTION (FIGS. 1A and 1B) 
The tuning machine of FIG. 1 includes mounting plate 10 for securing the 
machine to the instrument (shown in dashed lines), string roller 30 and 
worm gear 40, rotating worm 50 for turning the string roller, and sliding 
retainer 20 for holding the worm into engagement with the worm gear. The 
sliding retainer bears against the worm along first bearing interface 22:1 
at one end of the worm screw and second bearing interface 22:2 at the 
other end of the worm screw. As the bearing surfaces slowly wear over 
years of service, the sliding retainer may be periodically loosened from 
the mounting plate and pushed forward to a new position slightly closer to 
the worm. The pushing force simultaneously applies both a lateral force 
and an axial force to the worm at the bearing interfaces for removing both 
the backlash and end play in the worm to worm gear mesh. 
MOUNTING PLATE 10 (FIGS. 2A and 2B) 
The mounting plate is secured to the head of the stringed instrument by a 
suitable fastening device such as mounting screws 12:S which pass through 
mounting holes 12:H in the plate for engaging the head material (shown in 
dashed lines). Thrust collar 14:C extends from the back of the mounting 
plate into the head material for anchoring the plate against the combined 
tension in the strings of the instrument. The anchoring by the thrust 
collar provides stress relief for the mounting screws. In addition, the 
thrust collar prevents the string roller from rubbing against the bore 
through the instrument material. The string roller maintains intimate 
contact with the thrust collar at roller bearing aperture 14:A. 
The mounting plate has a stationary pedestal 16:P for raising the sliding 
retainer in relation to the worm. A suitable stabilizing structure is 
provided between the stationary pedestal and the sliding retainer for 
defining the direction of the slide movement and for maintaining a linear 
slide movement in a straight line. Stabilizing groove 16:G formed in the 
top of the pedestal engages a corresponding stabilizing tongue 26:T 
extending from the bottom of the sliding retainer (see FIG. 3). The tongue 
is guided by the groove for directing the motion of the retainer towards 
the worm in a straight line. 
SLIDING RETAINER 20 (FIGS. 3A, 3B, 3C, and 3D) 
Sliding retainer 20 is secured to pedestal 16:P in the retaining position 
by a suitable securing device such as adjusting or locking screws 24 
(shown in FIGS. 1A and 1B). The locking screws pass through slide slots 
26:S in the retainer and engage threaded holes 16:H in the pedestal (shown 
in FIG. 2A). The retainer may be repositioned periodically to adjust for 
wear of the bearing surfaces along the bearing interfaces. Locking screws 
24 are loosened and the retainer pushed toward the worm to re-establish 
full engagement between the worm and the worm gear. In order to change a 
worm or worm gear, screws 24 may be removed and the retainer lifted away. 
Sliding retainer has a pair of suitable trunions or bearing surfaces such 
as a first saddle trunion 22:1 and a second saddle trunion 22:2 spaced 
from the first trunion. The trunions project from the front of the 
retainer for engaging the worm along shaft portions 56:1 and 56:2 (shown 
in FIG. 4A). 
STRING ROLLER 30-WORM GEAR 40 (FIGS. 1A and 1B) 
String roller 30 has a neck end 32 which passes through roller aperture 
14:A in the mounting plate from the back or head side. Worm gear 40 is 
fastened to the neck end of the roller by a suitable device such as end 
screw 42. The worm gear is held in mesh with the worm by the sliding 
retainer. The worm bearing surfaces may be lubricated by a suitable 
lubricating means such as lubricant well 20:W formed in the saddle bearing 
surface of each trunion. 
Shank 52:S of the worm terminates in bonding pin 52:P for receiving a 
suitable turning device such as manual tuning key 52:K. Turning the key 
rotates the worm about worm axis 52:Ax causing the worm gear and the 
string roller to turn. 
The string roller has a winding end 34 which extends through the head of 
the instrument. The string of the musical instrument is wound onto the 
winding end. The string is "tuned up" or tightened when the tuning key is 
turned in one direction causing the roller to take up more string. The 
string is "tuned down" or loosened when the tuning key is turned in the 
other direction causing the roller to let out some string. 
WORM 50 (FIGS. 4A and 4B) 
Worm 50 includes screw portion 54 formed on the worm shaft between first 
shaft portion 56:1 and second shaft portion 56:2. The first shaft portion 
has an annular V shaped centering groove or channel 58:G therearound with 
beveled side walls 58:W for receiving the first trunion of the sliding 
retainer. The sides of the first trunion are correspondingly beveled and 
bear against the channel side walls. The second shaft portion is a 
cylinder for bearing against the second trunion of the sliding retainer. 
The bearing pressure between the worm and the trunions results in lateral 
and axial force components which reduce the backlash and end play in the 
worm to worm gear mesh. 
The initial contact between the channel sidewalls and the first trunion 
centers the worm axially in relation to the trunion. After centering, the 
first trunion and the sidewalls are in full engagement and the worm is 
prevented from shifting axially (no end play). The full engagement 
produces offsetting axial force components +Ax and -Ax (shown in FIG. 4B) 
which eliminate end play. The full engagement also produces a first 
lateral force component R which pushes the worm in engagement with the 
worm gear. A second trunion engages the surface of bearing cylinder 58:C 
on the second shaft portion and produces a second lateral force spaced 
from the first lateral force. The two lateral forces push the worm into 
intimate engagement with the worm gear (no backlash). 
PERIODIC ADJUSTMENT--WEAR GAP G (FIGS. 4A and 4B) 
Preferably, the trunions are made of a softer material than the shaft 
portions and take most of the bearing wear as the worm is rotated for 
tuning. The tip of the first trunion does not extend to the floor of the 
centering channel. A wear gap G between tip and floor provides for bearing 
surface wear. 
Over long periods of service, the bearing surfaces show microscopic wear. 
The sides of the first trunion wear against the sidewalls of the channel 
and the tip of the second trunion wears against the bearing cylinder. This 
slow wear gradually introduces tiny amounts of backlash and end play in 
the worm to worm gear mesh which can drastically interfere with proper 
tuning of the strings. Periodically the retainer is repositioned forward 
to reestablish an intimate meshing. Each forward adjustment of the 
retainer closes the wear gap slightly because the tip of the first trunion 
does not wear against the floor of the centering channel. 
REVERSIBLE RETAINER 20 (FIG. 3) 
In the embodiment of FIGS. 1 through 3 the saddle trunions are identical 
having the same length, bevel angle and width at the tip. The diameter of 
the centering channel is slightly less than the diameter of the bearing 
cylinder to provide the wear gap. After many adjustments of the retainer 
the wear gap may approach zero. The retainer may be reversed thereby 
bringing unused wear surfaces into use. Back-to-back stabilizing tongues 
26:T are provided on opposite sides of the sliding retainer to permit 
reverse mounting of the retainer. 
SPECIFIC EMBODIMENT 
The following particulars of a tuning machine are given as an illustrative 
example. 
String Roller 30--plastic 
Worm Gear 40--brass or bronze 
Worm 50--steel 
Channel 58:G--0.156 inches (0.396 cm) diameter; 30 degree included angle; 
width at bottom 0.050 inches (0.127 cm) 
Bearing Cylinder 58:C--0.171 inches (0.434 cm) diameter 
Sliding Retainer 20 plastic 
Trunions 22--0.170 inches (0.432 cm) diameter; tip width 0.068 mils (0.173 
cm); 30 degree included angle 
The values, dimensions, and material given above are not intended as 
defining the limitations of the invention. Numerous other applications and 
configurations are possible. 
INDUSTRIAL APPLICABILITY 
It will be apparent to those skilled in the art that the objects of this 
invention have been achieved by providing a worm retainer which 
simultaneously reduces backlash and end play in the mesh between the worm 
and the worm gear mesh. The worm retainer may be periodically adjusted to 
remove backlash and end play introduced by microscopic wear along the 
bearing interface. The wear surfaces along the bearing interface may be 
replaced with new surfaces by reversing the relationship of the bearing 
elements. The worm retainer has a tongue and groove interface with the 
mounting plate for stabilizing the repositioning displacement of the 
retainer. The tuning machine is easy to assemble and to disassemble by 
removing the worm retainer. A lubrication well is provided along the 
bearing elements for lubricating the interface. 
CONCLUSION 
Clearly various changes may be made in the structure and embodiments shown 
herein without departing from the concept of the invention. Further, 
features of the embodiments shown in the various Figures may be employed 
with the embodiments of the other Figures. 
Therefore, the scope of the invention is to be determined by the 
terminology of the following claims and the legal equivalents thereof.