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Nov. 5, 1946.
'
'H_ F_ FRUTH
'
2,410,491
METHOD AND APPARATUS FOR GRINDING‘ SMALL OBJECTS _
Filed Jan. 6, 1944
'
4 Sheets-Sheet l
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INVENTOR.
Nov. 5, ‘1946;
2,410,491
H. F. FRUTH
METHOD AND APPARATUS FOR GRINDING SMALL OBJECTS
Filedv Jan. 6,' 1944
4 Sheets-Sheet 2
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INVENTOR.
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NOV. 5, 1946.
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H_ F, FRUTH
2,410,491
METHOD AND APPARATUS ‘FOR GRINDING SMALI] QBIJECTS
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Filed Jan. 6, 1944 "
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Nov. 5,‘ 1946.
H. F. FRUTH
2,410,491
METHOD AND APPARATUS FOR GRINDING SMALL OBJECTS
Filed Jan. 6, 1944
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2,410,491
METHOD AND APPARATUS FOR GRINDING
SMALL OBJECTS
Hal F. Fruth, Chicago, IlL, assignor to Galvin
Manufacturing Corporation, Chicago, 111., a
corporation of Illinois
Application January 6, 1944, Serial No. 517,175
7 Claims.
1
The present invention relates to methods and
apparatus for grinding small objects, and more
particularly, to improved methods and apparatus
for ?nish grinding the edges of piezoelectric
(Cl. 51-283)
2
which remain at the edges of the crystal have
a tendencyto break away, causing crystal dust
which remains on the surfaces of the crystals.
The dust particles 'will sometimes change the
crystals, in order to remove irregularities there 01 frequency of vibration of the crystal or cause
the vibration of the crystal to be entirely ar
from, to increase the activity thereof, and to
rested, which of course, is undesirable from an
produce polished edge surfaces thereon. This
operating standpoint. Another principal objec
application is a continuation in part of co-pend
tive in the edge grinding of the crystals, is that
ing application Serial No. 492,203, filed June 25,
of producing peak crystal activity. With con
1943, Hal F. Fruth, now Patent No. 2,387,136
ventional manual methods of edge grinding, ac
issued October 16, 1945.
tivity peaking of a crystal is difficult to obtain,
In the manufacture of certain articles or parts
with the result that for a given number of crys
which have relatively sharp edges formed at the
tal blanks, the percentage of waste due to insuf
intersections between the surfaces of each part
or article it is frequently desirable, if not essen 15 ficient activity of the ?nished crystals is exces
sively high.
tial, that the edges of the article be ground for
It is an object of the present invention there
the purpose of removing irregularities therefrom.
fore to provide improved methods and apparatus
Thus, in the manufacture of piezoelectric crystals
for ?nish grinding the edges of small objects
adapted for use in communication circuits and
more particularly, for use in crystal micro
or articles to remove edge discontinuities there
from.
'
phones, radio transmitting and receiving sys
It is another object of the invention to provide
tems and the like, the crystal blanks are cut
improved methods and apparatus for grinding
from the crystal stock, are ground to the dimen
piezoelectric crystals in an improved manner
sions required to provide the desired frequency
characteristics, and are then edge ground to 25 such that the disadvantages of the manual
grinding methods now commonly in use are ob
remove irregularities from the edges thereof.
viated, and an improved crystal structure hav
According to conventional practice, all ?nish
ing more stable operating characteristics. and
grinding operations are performed by hand, and
acceptacle activity is obtained.
are effected by bringing the desired surface or
edge to bear against an abrasive surface and 30 According to another object ofthe invention,
a controlled method of crystal grinding is pro
manually moving the bearing surface of the crys
vided, which may be utilized on a variable time
tal across the abrasive surface. These ?nished
basis with a minimum expenditure of manualv
grinding operations are performed in two steps,
labor, toedge grind small objects so that they
i. e. face grinding and edge grinding, either of
conform with precision accuracy to a predeter
which may be performed ahead of the other.
mined standard.
7
Both operations asv practiced by conventional
In accordance with a further object of the
manual methods, are tediously slow, and require
skilled labor in the performance thereof. Also, I invention‘, the objects are edge ground in batches
and in a manner such that face surface abrasion
in the ?nished grinding of crystals for use in
ultra-high frequency circuits, having a thickness 40 thereof is substantially eliminated.
It is a still further object of the invention to
of approximately '7 mills or less, the waste due
provide an improved method and apparatus for
to breakage during the ?nish grinding of .the
edge grinding piezoelectric crystals in batches at
crystals by hand is unduly high. Moreover, the '
high speeds and with a minimum expenditure
?nished crystals obtained by such grinding meth
ods are not entirely satisfactory in operation. 45 of labor.
According to a further object of the invention,
The operating di?iculties which have been ex
the edge grinding of a batch of crystals is ac
perienced are attributable in large part to the
complished Without any abrasion or grinding of fact that it is apparently impossible with con
the crystal faces.
ventional edge grinding methods to obtain crys
It is still another object of the invention to
tals which are free of edge irregularities. Under 50
provide "an improved method and improved ap
certain temperature conditions, those edge ir
paratus for ‘grinding a small object, in which the
regularities or discontinuities which are present
grinding time is reduced by centrifugally actu
in a ?nished crystal tend to produce spurious
ating‘ the object into engagement with a rela
vibrating frequencies which are di?icult to stop
when once started. Moreover, the minute points 55 tively movable abrasive surface, thereby to pro- ‘
2,410,491
3
duce a contact pressure between the object and
the surface which exceeds that producible by
gravity pull upon the object.
According to yet another and more speci?c
object of the invention, the grinding of the ob
4
are preferably made of glass, are arranged in the
form of a cone having a long axis coinciding with
the axis of rotation of the shaft I6. As thus ar
ranged, each tube“ may be considered as being
tilted with respect to the axis of rotation of the
ject is accomplished by alternately employing
shaft 58. Preferably, each tube is inclined at an
gravity force and centrifugal force to determine
angle of approximately twenty degrees relative to
the contact‘ pressure between the abrasive sur
the shaft I8. For the purpose of holding the
face and the contacting surface portions of the
tubes II upon the shaft IS in the described posi
object.
10 tions therefor, a supporting structure is provided
It is a further object of the invention to pro
which comprises a small disc I4 mounted adja
vide an improved method of edge grinding a
cent the bracket l2 for rotation with the shaft,
batch of piezo-electric crystals to impart sub
and a large disc I5 which is disposed adjacent the
stantially peak activity to an exceedingly high
opposite bracket !3. The latter disc is provided
percentage of the crystals in the batch.
15 with a hub l~5a which may be utilized in set-screw
In accordance with yet another object of the
mounting the disc upon the shaft is for rotation
invention, the crystal activity peaking is obtained
therewith.
by repeatedly subjecting decreasing portions of
As best shown in Fig. 1 of the drawings, a nut
the crystals of a batch to random edge grind op
23 is used to clamp the disc I5 against the ?anged
erations for predetermined time intervals which
end 22a of a sleeve 22 which is splined or key
respectively correspond to expected activity peak
connected to the shaft IS, the nut 23 being
ing of certain crystals Within the batch, and by
threaded onto, the threaded outer surface of this
removing the acceptably peaked crystals from
sleeve in order to clamp the disc I4 against the
the batch at the end of each grinding operation.
sleeve ?ange 22a. With this arrangement, the
The invention, both as to its organization and
disc I4, as viewed in Fig. 1 of the drawings, may
method of operation, together with further ob
be moved to the left away from the disc I 5 for the
jects and advantages thereof, will best be under
purpose of removing the tubes I! from between
stood by reference to the speci?cation taken in
the two discs hi and I 5. The opposite ends of
connection with the accompanying drawings, in
each grinding tube I I are closed by means of rub
which:
ber stoppers 26a and 2Ia which are both utilized
Fig. 1 is a side view of improved edge grinding
in rigidly supporting the associated tube upon
apparatus which is characterized by the features
the two discs I4‘ and I5. More in detail, the sup
of the present invention and may be utilized to
port is completed by respectively providing the
practice the improved method of grinding crystal
blanks or the like;
Fig, 2 is an end sectional view of the apparatus
shown in Fig. 1;
Fig. 3 is an end view of a portion of the appa
ratus shown in Fig. 1;
_
Fig. 4- is a circuit diagram illustrating the ar
rangement of the circuit for energizing the driv
ing motor of the apparatus shown in Fig. 1;
Fig. 5. is a fragmentary sectional View illustrat
ing the disposition of crystals within one of the
edge grinding tubes embodied in the apparatus
shown in Fig. 1;
stoppers ‘Mia and 2m with bent metal stems 20
~- and 2| which are adapted to be received within
oppositely disposed holes provided at the periph
cries. of the discs L5 and I4 respectively. Thus
the upper one of the grinding tubes I I as shown
in Fig. 1 of the drawings, is provided at its right
40 end with a stopper 20a having ?xedly secured
thereto a stem 28' which enters an opening pro
vided' in the side of the disc I5 at the upper pe
ripheral portion thereof. At its left end, this tube
is closed by means of a stopper 25a having ?xedly
secured‘thereto a stem ZI which enters an open
ing in the upper peripheral portion of the disc
Fig. 6 is an end sectional View of the grinding
Id. The other grinding tubes I I of the apparatus
tube shown in Fig. 5;
are likewise supported between different periph
Fig. 7 is a characteristic crystal activity curve
eral portions of the two discs I4 and I5. With
indicating the» activity of a typical crystal plotted 5.0 this arrangement, the tubes may be readily de
as a function of edge grinding time;
tached from the supporting discs by moving the
Fig. 8 is a fragmentary sectional view illustrat
disc [4' to the left in the above-explained man
ing the manner in which the crystal faces are
ner, thereby to permit withdrawal of the stems
coated in order to prevent face abrasion thereof
2!. individual to the various tubes from the open
during the edge grinding operations;
ings provided at the periphery of this disc.
Fig. 9 is a side view illustrating a modi?ed ar
A variable speed driving motor 30, which is
rangement of the edge grinding apparatus;
mounted upon the base I0, is provided for impart
Fig. 1c is an end. view partially in section illus
ing rotary movement to- the shaft I6 and the
trating the movable parts of the apparatus shown
grinding tubes I I supported thereon. This motor
in Fig. 9;
60 is equipped with a double ended rotor shaft 29,
Fig. 11 is a view schematically illustrating the
one end of which carries a pulley 28 which is
driving arrangement for the apparatus shown in
connected by a driving belt 2? to drive a second
Figs. 9 and 10; and
pulley 26 rigidly mounted upon the left end of
Fig. 12 is a side view illustrating means for tilt
the shaft I6. The opposite end of the rotor shaft
ing the apparatus shown in Figs 9 and 10.
29 is mechanically connected to drive a speed re~
Referring now to the drawings, and more par
ducing gear box 3!‘ having a take-01f shaft 32
ticularly to Figs. 1, 2, 3 and 4 thereof, the im
which mounts a crank disc 33. This disc is pin
proved edge grinding apparatus there illustrated
connected by means of a pin 35 to one end of
comprises a base It having two upstanding
crank arm 34 which is utilized to pivot a rheostat
bracket pieces I2 and I3 rigidly mounted thereon 70 wiper arm 36 back and forth between two ex
at spaced apart points therealong. These bracket
treme positions. More specifically, the arm 36 is
pieces are respectively provided with bearings I B
pivotally supported by means of an axis pin 37
and it which rotatably support a shaft It‘ upon
and is pivotally connected to the actuating end
which a plurality of edge grinding tubes II are
of the crank arm 34 by means of an aXis pin
mounted. More speci?cally, the tubes II, which
38. At its opposite end, the arm 36 carries a
3
2,410,491
wiper 39 which is arranged to be moved back
at slow speeds, the crystal is slid around the-en-i
and forth over a resistor element 49 in response
to pivotal movement of the arm 36 between the
tire inner circumference of the tube during each
revolution of the tube about the shaft it. Thus
it will .be understood that during rotation of the
tubes H, the batch of crystals supported within
extreme angular positions thereof.
The described rheostat facilities are utilized
to vary the speed of operation of the driving
motor 39 back and forth over a predetermined
speed range. To this end and as best shown
in Fig. 4: of the drawings, the motor 36 is ar
ranged to be energized from a source of cur
rent indicated by the bracketed terminals £52 over
a circuit which includes the in-circuited portion
each tube are slid back and forth within the
tube and at the same time are moved around
the inner surface of the tube.
As indicated above, the purpose of the motor
controlled rhecstatic facilities comprising the re
sistor t9 and the wiper 39 is that of varying the
speed of operation of the motor 39 over a wide
of the resistor 49, the wiper 39, and the contacts
speed range. To this end, the wiper 39 is driven
of a manually operable “on” and “off” switch M.
back and forth across the resistor 139 under the
In utilizing the above described apparatus for 15 in?uence of the driving force exerted thereon‘
the purpose of grinding the edges of piezoelectric
through the gear box 3f, the crank disc 33, and
crystals, the crystals are disposed within the tubes
the crank arm 31%. As this Wiper is moved in a
H. To produce random changes in the position
direction for increasing the resistance of the cir
of each crystal relative to the tube within which
cuit for energizing the motor 39, the speed of
it is con?ned, a baffle or obstruction 43 is pro 20 rotation of this motor decreases to correspond
vided at one or more points along each tube.
ingly decrease the speed of rotation of the grind
Each ba?le may comprise a small strip of ad
ing tubes II about the shaft i6. Conversely, as
hesive tape extending longitudinally of the tube
the wiper 39 is moved in the opposite direction
in the manner shown in Figs. 5 and 6 of the
to decrease the resistance of the motor energiz
drawings. Depending upon the type of random 25 ing circuit, the speed of rotation of the motor 30
movement of the crystals which is desired, the
is increased to produce a correspondingv increase
ba?'le strips may be positioned at different points
in the speed of rotation of the tubes H about
intermediate the ends of each tube H, or may
the shaft l6. Preferably, the permissible resist
be provided only at the ends of each tube.
ance change of the resistor 49 due to the move
In the operation of the apparatus shown in 30 ment of the wiper 39 thereacross is such that
Figs. 1, 2, 3, 4, 5 and 6 of the drawings, each
the speed of rotation of the tubes H about the
of the tubes H is loaded with a charge of cry
shaft I6 is varied back and forth between an
stals and abrasive material, in the manner more
upper limit of 500R. P. M. and a lower limit of
fully explained‘below, after which the tubes are
25 R. P. M. In this regard it will be noted that
stoppered, and are mounted between the two discs
as the motor 3% speeds up, movement of the
l4 and IS. The switch 41 may now be operated
wiper 39 across the resistor 49 is accelerated to
for the purpose of energizing the driving motor
increase the rate of motor speed up. Conversely,
39. When operation of the driving motor is
as the motor speed is decreased from the upper
thus initiated, each tube H, in its tilted position
limit of the speed range, movement of the wiper
relative to the axis of rotation of the shaft I6,
39 across the resistor G9 is decelerated to decrease
is rotated about this axis to de?ne the surface
the rate at which the motor slows down. As a
of a cone. In the normal use of the apparatus,
result, any selected period of high speed rota
the base I0 is supported upon a horizontal sur
tion of the tubes ll about the shaft i6 is rel
face so that the shaft lt occupies a substantially
atively short when compared with the remaining
horizontal position. Accordingly, as each tube 45 period of slow speed rotation of the tubes about
II is rotated about this shaft, it is alternately
the shaft.
tilted in opposite directions with respect to the
As the speed of rotation of each tube ll about
horizontal, whereby the crystals disposed there
the shaft 56 is increased, the increased centrif
within tend to slide back and forth longitudinally
ugal force acting upon the crystals con?ned
of the tube. The maximum tendency of the cry
therewithin tends with increasing effectiveness to
stals to slide to the left within a con?ning tube
move the crystals to the right ends of the tubes
ll obviously occurs when this tube is rotated to
as viewed in Fig. l of the drawings, and lessens
a position directly above the shaft l6. Con
the tendency of the crystals in the tube to move
versely, the maximum tendency for a tube con
to the left when the tube is rotatedto a position
?ned batch of crystals to move from the left end
directly above the shaft l6. As a result, the zone
of the tube toward the right end thereof occurs
of longitudinal movement of the crystals within
when the tube occupies a position directly below
each tube is decreasingly narrowed and is in
the shaft l6. Intermediate the extreme positions
creasingly shifted toward the right end of the
indicated, each tube is obviously tilted at a lesser
tube as the speed of rotation of the tube about
angle with respect to the horizontal, with the
the shaft i6 is increased. At a predetermined
result that the de?ned tendency of the crystals
critical'speed located somewhere within the de
to slide in one direction or the other longitudi
?ned limits of the speed range, the centrifugal
nally of the tubes is lessened. Under the condi
force acting upon the crystals within each tube
tions now under consideration, this sliding action
becomes sufficient to throw the crystals radially
of the crystals is alone produced by gravity pull 65 outward from the shaft it against the outermost
upon the crystals. Gravity pull upon each cry
portion of the inner surface of the tube. As the
stal also causes relative circumferential move
speed of rotation of the tubes H is increased
ment between the inner surface of the support
above this critical value, the increasing centrif
ing tube and the crystal. Thus each tube is
ugal force acting upon each crystal serves in-'
effectively rotated through one revolution about
creasingly to enhance the contact pressure be
its own longitudinal axis during each revolution
tween the crystal and the abrasively coated inner
of the tube about the shaft [6. Further, gravity
surfaces of its supporting tubes at the points of
pull upon each crystal tends to hold the crystal
engagement therebetween. This increase in con
against the bottom portion of its con?ning tube,
tact pressure between each crystal and the en
with the result that so long as the tube is rotated 75 gaging tube surface, which pressure may vexceed;
7
2,410,491
by ten or ?fteen times the pressure produci'ble
by gravity pull upon the crystal, is obtained with
outv eliminating relative sliding movement be
tween each crystal and the engaging surface of
the tube. Such. relative sliding movement is,
however, con?ned to movement of the crystals
‘ longitudinally of their con?ning tubes, since once
8
the. periods of high speed rotation of the grinding
tubes. Thus by so doing, effective abrading of the
crystals is obtained during the predominant por
tion of each complete speed cycle period.
In the modi?ed arrangement of the apparatus
shown in Figs. 9, l0, l1 and 12 of the drawings,
the grinding tubes 55 are journalled within bear
lugs 51 and 58 which are supported within oppo
the crystals are thrown outwardly against the
sitely disposed openings arranged around the
inner surfaces of the tubes, the, tendency for the
tubes to rotate around the crystals is eliminated. 10 outer peripheries of two spaced apart supporting
Sliding movement of the crystals longitudinally
discs 53 and 154. These discs are set screw mount
of the tubes is controlled by the changing effect
ed by means of set screws 53a and 54a upon a
of gravity'pull upon the crystals. Thus as each
rotatable shaft 55 which is journalled within
bearing members to; and 52a carried by up
tube is moved. from a substantially horizontal
position to a position beneath theshaft i5 and 15 standing bracket pieces 5| and 52, respectively.
The identi?ed bracket pieces are rigidly mounted
then back to a horizontal position, the centrif
upon a base member ‘5t. Stoppers 53 are used to
ugal and gravity forces add or combine to in
close the ends of the grinding tubes. Collars 60
crease the contact pressure and to increase the
tendency to slide each crystal within the tube
and El, set screw mounted upon each tube 56
upon opposite sides of the disc 5d, are utilized to
towards the right end of the tube. On the other
prevent end play of the tubes 56 relative to their
hand, as each tube is moved from a substantially
supporting discs 53 and 54. For the purpose of
horizontal position to a position above the shaft
rotating the shaft 55 thereby to rotate the tubes
I6 and then back to a horizontal position, the net
56 about this shaft, a driving motor 61 is pro
force tending to more each crystal within the
vided which is mounted upon the right end of
tube towards the right end of the tube is repre
the base member 50 in the manner shown in
sented by the difference between the centrifugal
Fig. 12 of the drawings. This motor is belt
force acting upon the crystal and the gravity
connected to drive the shaft 55 by means of the
force acting upon the crystal. Accordingly each
pulleys l2 and 65 and the belt 66. Rotation of
crystal may be held back somewhat in its move
the tubes 56 relative to the stationary parts of
ment toward the upwardly tilting right end of
the apparatus is also utilized to rotate these tubes
its supporting tube. The net result is that each
relative to their supporting discs 53 and 54. To
crystal is slid longitudinally of its con?ning tube
this end, each tube, as viewed in Fig. 9 of the
during each revolution of the tube about the shaft
drawings, carries an enlarged driving pulley 62
[6. Finally, the crystals are all stacked against
at the right end thereof. These pulleys are set
each other at the right ends of their respective
screw mounted, or otherwise ?xedly secured to
con?ning tubes.
their respective supporting tubes, and are pro
As the speed of rotation of the tubes ll about
vided with belt grooves which are in alignment
the shaft I6 is decreased, the crystals are held
transversely of the structure and are also aligned
at the right ends of their respective supporting
with a belt groove 5% cut around the bearing
tubes under the in?uence of ‘centrifugal force
tube 5264 within which the shaft 55 is journalled.
until such time as the speed of rotation of the
A belt 54 which is disposed within the groove
tubes is lowered to the critical value at which
52b and passes around the outer peripheral por
the gravity pull upon the crystals exceeds the
tions of the several pulleys 52 in the manner
centrifugal force acting upon the crystals. Below
shown in Fig. 10 of the drawings, is utilized to
this critical speed, the crystals are only held in
rotate the pulleys and the tubes 55 relative to
contact with the inner surfaces of the tubes by
the supporting discs 53 and 54 in response to
gravity pull with the result that sliding move
rotation of the named parts about the shaft 55.
ment of the crystals longitudinally and circum
In order to insure random grinding of crystals
ferentially of the tubes is resumed.
disposed within the grinding tubes 56, the base
From the foregoing explanation it will be un
58 is tiltably supported by means of an axis rod
derstood that at tube speeds below the critical
'54 and spaced apart bearing brackets ‘l5 upon a
value at which the centrifugal forces acting upon
second base member 16. A slow speed motor 11,
the crystals exceed gravity pull upon the crystals,
mounted upon the base member 16, is provided
the contact pressure with which the crystals are
for tilting the base 55 and the parts carried
held in engagement with the inner surfaces of
thereby back and forth about the axis rod 14,
their con?ning tubes is determined solely by grav
whereby the grinding tubes, 56 are alternately
ity pull upon the crystals. At tube speeds in
tilted in different directions relative to the hori
excess of the critical value, the centrifugal forces
zontal. More speci?cally, the rotor shaft of the
acting upon the crystals determine the contact
motor ‘i? is provided with a crank disc 18 which
pressures between the crystals and their support
is crank connected by means of a crank 19 and
ing surfaces, and may exceed by several times
the axis pins 80 and 8! to the right end of the
the contact pressures producible by gravity pull
base 50.
'
alone. When the latter condition prevails, the
As
best
shown
in
Fig.
11
of
the
drawings,
the
abrading action is much more rapid, due to the
greater contact pressures between the crystals 65 motor ‘i7 is arranged to be energized from a
current source indicated by the bracketed termi
and their abrading surfaces. It will also be un
rials
‘13 over a circuit which includes the contacts
derstood that after the critical speed of tube
of an “on-off” switch ‘H. The motor 61 is con
rotation is exceeded, only a short time interval
nected for energization from this source over a
is required to move all of the crystals to the right
ends of their respective supporting tubes, and 70 circuit which also includes the contacts of the
switch ‘H and the contacts of a communicating
that once the crystals are stacked against each
device. This device comprises a rotary conduc
other at the rightends of the tubes no further
tive disc 65, an insulating segment 69 which pro
abrading action occurs. It is for this reason that
vides a non-conductive segment at the disc pe
the described rheostatic control facilities for the
motor 30 are deliberately arranged to shorten 75 riphery, and a brush ‘HI Wipingly engaging the
2,410,491v
9
10
periphery of the disc. The disc may be actu
ated at a slow speed by any suitable driving
this reason that the commutating device com
prising the time actuated commutating disc 68
and the wiping brush 10 is provided. Thus, when
this disc is rotated to a position wherein the brush
engages the insulating segment 6%, the circuit for
means so that the operating circuit for the motor
6? is intermittently opened in the manner de
scribed below.
In considering the operation of the apparatus
shown in Figs. 9, 10 and 11 of the drawings it
energizing the driving motor t'l is obviously in
terrupted. As a result, the rotary movement of
will be understood that to load the tubes 55 with
the grinding tubes 56 relative to the supporting
charges of crystals and abrasive material, the
discs and about the shaft 55 is decelerated to a
apparatus is tilted about the rod ‘is, the stoppers 10 standstill. When the speed of rotation of the
63 are removed from‘the tubes at the uppermost
tubes 56 about the shaft 55 is reduced to a pre
ends thereof, and measured charges of crystals
determined value, to correspondingly decrease
the centrifugal forces acting upon the crystals
and abrasive material are then introduced into
the various tubes. After the tubes are thus
con?ned within the tubes, these forces are ex
loaded, the stoppers 63 may be re-inserted in the
ceeded by gravitational forces acting upon the
open ends of the tubes, following which the ap
crystals, with the result that the crystals fall
paratus is fully conditioned to perform the de
down to engage the bottom surfaces of the re
sired grinding operation. To initiate this opera
spective tubes within whichthey are con?ned.
tion, the switch ‘H is operated to its closed circuit
As the crystals within each tube fall, they are
position to energize the motor ‘ll and to complete 20 obviously tumbled about, with the result that the
a circuit through the commutating disc 55 and
positions thereof within the tube are changed
the engaging wiper 78 for energizing the driving
at random. After a predetermined time interval
motor iii‘. In operating, this motor serves to
required for the insulating segment 59 to traverse
rotate the tubes 55 about the shaft 55 in an obvi
the wiper 15, the operating circuit for the driving
ous manner. The motor ‘ll concurrently oper
motor 67 is re-completed, thereby to reinitiate
ates to tilt the apparatus back and forth about
rotation of the tubes about the shaft 55 and
the aXis rod 14. Coincident with the rotation of
relative to the two supporting discs. As the speed
the tubes 56 about the shaft 55, the belt 64 in its
of rotation of the tubes about the shaft 55 is
engagement with the belt glove 52b of the sta
accelerated to the normal value, the crystals with
tionary bearing hub 52a functions to rotate each 30 in each tube are again thrown outwardly under
of the tubes relative to the supporting discs 53
the influence of the centrifugal forces acting
and 5/3 at a reduced speed which is determined by
thereon. Incident to the movement of, the
the relative diameters of the pulleys 52 and the
crystals which occurs within the tubes during the
bearing hub 52a.
tube decelerating and accelerating periods, the
In this embodiment of the apparatus, the motor 35 positions ofthe crystals are changed at random,
6? is operated at a speed which will insure that
‘thereby substantially to insure that new surface
the crystals con?ned within each grinding tube
portions of each crystal will be brought into con
53 are thrown radially outward from the shaft
tact with the inner surface of the tube within
55 under the influence of centrifugal force to
which the crystal iscon?ned. - It will thus be
engage the ever changing portion of the inner 40 understood that the commutating devicecoma
surface of the tube which is farthest removed
from the axis of rotation of the shaft 55. Prefer
ably this speed is suf?ciently high to provide a
contact pressure between the inner surface of
prising the disc 58 and the wiper ‘iii, in its operae
tion periodically to de-energize the driving motor
61, insures that if the grinding operation ‘is con
tinued for a reasonable period of time all pos
each grinding tube and the contacting surfaces 45 sible contacting surfaces of each crystal will at
of the crystals con?ned therewithin, exceeding
one time or another be brought into engagement
by ten or ?fteen times the contact pressure which
with the inner surface of the tube within which
is alone producible by gravity pull upon the
the crystal is con?ned.
_
crystals. This high contact pressure insures rapid
The desired random grinding of the crystal
grinding, and the centrifugal force producing the 50 surfaces is further obtained through the opera
same serves to prevent the crystals from being ro
tion of the tilting. motor ‘ll’. With this motor
tated with the tubes around the longitudinal axes
operating ‘concurrently with the driving motor
of rotation of the tubes. Relative sliding move
67, the grinding tubes 55 are tilted in ?rst one
ment required to produce the desiredabrading
direction and then the other relative to the hori-action is brought about by the rotation of each ' zontal. As a result, the crystals ‘within each I
grinding tube 55 relative to the supporting discs
grinding tube 56 will obviously slide longitudinally
53 and 56. Thus, as the crystals within each
of the tube both when centrifugally actuated to
tube are held by centrifugal force against the
engage the inner surface of the tube and when
surfaces of the con?ning tube farthest removed
gravity actuated to engagethis surface. During
from the shaft 55, the rotation of the tube rela 60 the decelerating and accelerating periods the
tive to the two supporting discs serves to ‘move
sliding movement of the'crystals longitudinally
the inner surface of the tube around the crystals,
of the tubes 55 may be utilized to change at ran
and centrifugal force acts in the manner ex
dom the positions of the crystals within the tubes.
plained above to prevent rotation of the crystals
To this end, ba?le strips 43 of the character de
with this surface. Preferably the grinding tubes
scribed above and shown in Figs. 5 and 6 of the
56 are rotated relative to the supporting discs
drawings may be provided in each grinding tube
53 and 54 at only a fraction of the speed of rota
tion of the tubes about the shaft 55, thereby to
prevent too rapid abrasion of the crystals.
As will be evident from the above explanation,
once the crystals are centrifugally actuated into
engagement with the inner surfaces of their con
?ning tubes, the contacting surfaces of each
crystal will not ordinarily be changed until the
centrifugal actuating force is removed. It is for
at one or more points along the inner surface
thereof to produce the desired crystal position
change.
,
‘
The present improved method of edge grinding,
as practiced by utilizing either embodiment of the
improved apparatus described above, may con-v
veniently be considered in its application to the
finish grinding of the edges of piezoelectric quartz
crystals. As previously indicated, such crystals
2,410,491
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are initially sliced from the mother crystal, fol
lowing which they are diced to the approximate
Water soluble glue is employed as the coating
desired dimensions and are then rough ground
more nearly to conform to the desired rectangle
dimensions on a grinding wheel. After the rough
grinding operations are completed, two finish
grinding operations are required, namely, the
grinding of the crystal faces to the desired thick
material, this particular product having the de
sired advantages of being easily applicable to the
crystal faces and of being easily removable there
from after the edge grinding operation is com
pleted. Thus in order to remove the glue from
the crystal faces it is only necessary to dip the
ness for the purpose of obtaining the desired
crystals in boiling water after the edge grinding
operation is completed. It is noted, however, that
resonant frequency characteristics, and the edge
10 adhesively coated paper strips, scotch tape or the
grinding of the crystals for the purposes of ii.
creasing the activity thereof and of removing
edge discontinuities therefrom. These two ?nish
grinding operations may be performed in any de
sired order, but both are necessary in order to
obtain a satisfactory crystal having satisfactory
operating characteristics. In the usual crystal
structure, the crystal length is somewhat greater
than the crystal width. These dimensions are
taken into account in determining the inner di
ameters of the tubes ll or 56 which are utilized
in the two embodiments of the above disclosed
apparatus. More speci?cally, the purpose of the
edge grinding operation is that of producing a
rounded chamfer or bevel at the junction point
between each pair of intersecting surfaces of
each crystal. Accordingly, the diameter of each
tube H or 56 is properly chosen to produce th
desired average chamfer radius at the edges de
?ning theintersections between the crystal sur
faces. Thus to provide a relatively broad cham
fer it is necessary that the tube diameters rather
closely approximatethe longest dimension of each
crystal. On the other hand, to produce a. sharp
ohamfer the tube diameter should be relatively
large as compared with the longest dimension of
each crystal. Preferably the tube diameters asv
related to the dimensions of the crystals are about
as shown in Fig. 6 of the drawings.
As there
illustrated, the diameter of the illustrated grind
ing tube l I or 56 is so chosen that when a crystal
like, may be applied to the crystal faces to per
form the protective function with equal success.
The provision of such a coating or covering posi
tively precludes face grinding of the crystals dur
ing the edge grinding operation. In addition, the
coating applied to the faces of each crystal in
creases the mass of the crystal, thereby to increase
the contact pressure between the edges of the
crystal and the abrasive grinding surface and
thus enhance the abrading action. If extremely
fast grinding is desired, each crystal face cover~
ing may take the form of a small metal wafer or
plate of lesser length and width than the crystal,
which is adhesively secured to the central portion
of the crystal face by a water soluble glue. Such
face coverings produce a marked increase in the
mass of each crystal, with an accompanying in
crease in the speed of edge abrasion.
As indicated above, to condition either embodi
ment of the disclosed apparatus for a grinding
operation the tubes l I or 56 are each loaded with
a batch of crystals and a charge of abrasive ma
terial. The abrasive material may comprise a
small amount of diamond powder or boron car
bide, the particular grinding speed being deter
mined to a large extent by the size of the grind
ing particles employed. Thus, if rapid grinding
is desired diamond powder of No. 100' to 150
screen mesh may be used. On the other hand, if
less rapid grinding and a higher polish of the
ohamfer surfaces is to be obtained, No. 320 to
is supported at its edges with its long axis extend
No. 400 screen mesh grinding material may be
ing longitudinally of the tube, ‘a second crystal
utilized. The amount of grinding material used
may be supported thereabove with the long axis
in each tube will, of course, depend upon the di
thereof extending transversely of the tube and
mensions of the tube. For example, when tubes
having a length of about 60 inches and an in
with the adjacent surfaces of the two superim
posed crystals in spaced apart relationship. With
ternal diameter of 1.0625 inches are employed,
satisfactory grinding is obtained if approximately
this arrangement, the upper crystal is prevented
two carats of No. 1G0 to 150 screen mesh diamond
from changing the contact pressure between the
inner surface of the tube and the contacting 50 powder is used in each tube. On the other hand,
if the ?ner grinding powder of from N0. 320 to
edges of the crystal, and the presence of the
No. 400 screen mesh is employed, approximately
lower crystal beneath the upper crystal is pre
two to three carats of the grinding material
vented from reducing the contact pressure be
should be used in each tube.
tween the inner surface of the tube and the en
gaging edges of the upper crystal. Moreover, the 55 After each grinding tube is loaded with a
described relative diminishing of the tube diam
batch of crystals and a charge of abrasive ma
eters and the length and width of the crystals
terial in the manner just explained, operation of
the driving means of either embodiment of the
minimizes face abrasion of the crystals as the
edge grinding operation proceeds. In this regard
apparatus may be started for the purpose of ini
it is noted that if the ?nish grinding of the crystal 60 tiating the edge grinding operation. The abrad
faces to impart a predetermined frequency char
ing action which occurs when the ?rst embodi
acter thereto is completed before the edge grind
ment of the disclosed apparatus is used may ac~
ing operation .is started, further crystal face
curately be considered as being divided into two
parts, i. e. that which is produced when gravity
grinding should, if possible, be entirely eliminated
during the edge grinding operation in order posi 65 pull alone determines the contact pressure be
tively to prevent the resonant frequencies of the
tween the edges of each crystal and the abra
crystals from being changed. In order to mini
sively coated inner surface of its con?ning tube,
and that which occurs when the crystals are cen
mize such crystal face abrasion during the edge
trifugally actuated to bring the edges thereof to
grinding operation the faces of each crystal may
be coated or otherwise covered before the edge 70 bear against the abrasively coated inner surfaces
of the grinding tubes. During those intervals
grinding operation is started. This coating may
when gravity pull upon the crystals predomi
take the form illustrated in Fig. 8 of the draw
nates, i. e. the periods when the grinding tubes
ings, wherein the faces of a crystal fragment I?
H are being rotated at slow speed, each crystal
are shown as being coated with thin layers Fig
and I lb of a protective material. Preferably a 75 within each tube is slid back and forth longi
2,410,491
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tudinally of the tube over the inner abrasive
From the above explanation it wil1 be under
coated surface thereof. Concurrently therewith
stood that the edge grinding of the crystals dis
and due to the rotation of the tubes about the
posed within the tubes H is, during slow speed
shaft IS, the inner surface of each grinding tube
rotation of these tubes about the shaft‘ l6, pro
is slid around the contacting edge surfaces of 5 duced with a completely random action; that is,
each crystal which it houses. As this sliding
the back and forth movement of the crystals with
movement proceeds, the crystals tend to align
respect to the abrasive surfaces do not follow any
themselves along the length of their respective
predetermined or ascertainable pattern, but dif
enclosing tubes with only the straight edge sec
fers for each crystal. When, however, the speed
tions thereof bearing against the inner surfaces
of rotation of the tubes ll about the shaft I6 is
of the enclosing tubes. The abrasive material is
increased to a point such that the crystals are
‘ of course soon spread over the inner surface of
centrifugally actuated to engage the abrasive sur
each tube to produce an abrasive surface against
faces relative sliding movement of the crystal
which the edge surfaces of the crystals bear. Due
edges circumferentially of the tubes is stopped
to the abrasive action of this material, the high
in the manner previously explained, the relative
points of the crystals are cut away as the crys
sliding movement being confined exclusively to
tals are slid relative to the surfaces of their
movement of the crystals longitudinally of the
enclosing tubes. In this connection it is pointed
tubes within which they are confined. It is dur
out that the movement of the crystal edges longi
ing this portion of each tube speed cycle that
tudinally of the tubes prevents transverse
the high contact pressure and resulting rapid
scratches from being produced in the chamfered
abrasion of the crystal edges are obtained. Dur
surfaces which are soon formed at the edges of
ing each such period, moreover, the particular set
each crystal. Similarly, the sliding of thecrys~
of edges of each crystal which bear against the
tals circumferentially of the abrasive surfaces
inner surface of the enclosing tube remain un
against which they bear prevents the chamfered
changed. As between successive high speed pe
surfaces from being scratched longitudinally, in~
riods, however, the random movement of the
cident to the sliding of the crystals back and
crystals within the tubes su?ices to produce the
forth within their enclosing tubes.
desired change in the position of each crystal
Preferably the angle of inclination of each tube
necessary to bring a different set of edges into
l I with respect to the horizontal shaft H3 is such
contact with the abrading surface during the suc
that when the tubes are being rotated about this
seeding high contact pressure grinding period
shaft at slow speed, a crystal disposed at the ele
On an average basis, therefore, all eight edges of
vated end of a tube will just slide to the other end
each crystal are in a given time interval cham
of the tube before the angle of inclination of the
fered or ground to almost precisely the same ex
tube is reversed. More speci?cally, the lengths ‘1 tent.
of the tubes are preferably such that when the
When the embodiment of the apparatus dis
angle of inclination is approximately 20 degrees,
closed in Figs. 9, 10 and 11 of the drawings is uti
the desired full length sliding movement of a
lized to perform the edge grinding operation, the
crystal longitudinally of its con?ning tube is ob
action is substantially similar to that just de
tained. The longitudinal movement of the crys
scribed with reference to the ?rst disclosed em
tals along the tubes during the periods of slow
bodiment of the apparatus. In the second em
speed rotation of the tubes about the shaft it is
bodiment of the apparatus, however, the trans
also utilized to change the positions of the crys
verse grinding of the crystal edges is produced
tals within the tubes so that different edge sec
both during the periods of low contact pressure
tions thereof are brought to bear against the 45 grinding and the periods of high contact pressure
abrasively coated inner surfaces of the tubes.
grinding. Thus, since the tubes 55 are at all
To consider one aspect of the crystal tumbling
times positively rotated relative to their support
movement, it may be assumed that the uppermost
ing discs 53 and 5d, relative movement of the crys
crystal as shown in Fig. 6 of the drawings is slid
tal edges oircumferentially of the inner grinding
into a position where it is transversely aligned
surfaces of the tubes is produced so long as the
with the baffle strip 43. As the illustrated tube l l
motor Bl is operating. This insures rapid abra
in which this crystal is disposed is rotated
sion of the crystal edges and also provides for the
through one revolution about the shaft it, one
cutting of these edges along the two paths of
edge of the strip 63 engages one side of the crys
abrasion, i. e. transversely and longitudinally of
tal so that during continued rotation of the tube
the crystal edges, so long as the abrading action is
the crystal is'turned over to reverse the edges
being carried on. Otherwise, the abrading action
thereof which bear against the abrasively coated
obtained with the second disclosed embodiment of
inner surface of the tube. The crystal is not
the apparatus is exactly the same as described
only turned over so that alternately faces thereof
above.
face downwardly, but in addition is turned end 00
As indicated above, the edge grinding of the
for end so that all eight edges of the crystal are
crystals is not only for the purpose of removing
at one time or another brought to ,bear against
discontinuities of the crystal edges to enhance the
the abrasively coated inner surface of the tube.
stability of operation thereof, but is also for the
Incident to the turning of the crystals end for
purpose of increasing the activity of each crystal
end the corner edges thereof are also subjected 65 to an acceptable value. It has been found that
to the action of the abrasive material so that they
when the activity of a crystal is plotted as a func
too become smoothly rounded. The particular
tion of edge grinding time, a sawtooth character
set of oppositely disposed edges of the particular
istic curve having a number of peaks and valleys
crystal under consideration which remain in con
is obtained. A typical curve of this character,
tact with the abrasively coated surface of the
plotted from experimental data, is'indicated at A
tube during the longitudinal sliding movement of
in Fig. 7 of the drawings. From aconsideration
the crystal through the tube depends upon the
of this curve it will be noted that the activity of
particular position at which the crystal is brought
the particular crystal in question peaks at the
to rest after it is moved out of transverse align
points B, C and D, respectively‘corresponding to
ment with the ba?le strip 43.
75 4, l2 and 28 hours of edge grinding time, utiliz
2,410,491
15
16
ing random edge grinding wherein the contact
pressures are alone determined by gravity pull
the method of edge grinding the crystals of a
given batch to produce substantially peak ac
valleys
upon the
representing
crystal. Between
non-acceptable
these peak
crystal
points
activ
tivity for the major portion of the crystals in
said batch, which comprises concurrently sup
porting each of the crystals of the batch along a
pair of opposed edges upon abrasive material
ity. On an empirical basis it has also been found
that for a given batch of crystals, approximately
25 per cent of the batch are possessed of substan
tially matching activity~edge grinding time peaks
representing
initial predetermined
acceptable edge
crystalgrinding
activity after
interval.
within a tube, rotating the tube at a speed so that
the abrasive material moves relative to the
crystals thereon, and in such manner subjecting
10 all of the crystals of said batch to an edge grind
Further, it has been found that roughly 25 per
ing operation for a selected time interval corre
cent of theremaining non-acceptable crystals of
sponding to expected activity peaking of at least '
the batch have substantially matching activity
a portion of said crystals, separating the accept
peaks at a second point farther along the time
ably peaked crystals from the batch, subjecting
axis of their characteristic curves. This activity 15 successively smaller portions of the remaining
peak matching of the remaining non~acceptable
crystals to repeated corresponding edge grinding
operations for selected time intervals respectively
percentage
crystals of the
basis
batch
as the
proceeds
characteristic
on about curves
the
of
corresponding to expected activity peaking of
the individual crystals and are further compared
said successively smaller portions of said remain
on a continued edge grinding time basis.
ing crystals, and removing the acceptably peaked
In practicing the present improved methods of
crystal edge grinding to obtain ?nished crystals
crystals from the remainder between successive
ones of the repeated such grinding operations in
having acceptable activity, successively smaller
portions of the crystals of a given batch are re
peatedly subjected to edge grinding operations of
the character described above for predetermined
time intervals. More speci?cally, the entire batch
of crystals is initially edge ground for a period
ranging from four to six hours, following which
the crystals are segregated from the abrasive ma‘“
terial, cleaned and tested for activity. Those
crystals, approximating 25 per cent of the batch.
having acceptable activity are separated from the
batch and are not subjected to further edge grind
ing. The remaining non-acceptable crystals of .
the batch are subjected to a further edge grind
ing operation for an additional period of from
four to six hours, following which the activity
testing step is repeated for the purpose of again
picking out the crystals which have been edge
ground to possess acceptable activity. This proc
ess of repeatedly edge grinding the non-accept—
able crystals on a timed basis and of separating
the
of each
acceptable
grinding
crystals
operation,
from the
is batch
continued
at theuntil
such time as the predominant portion of the crys
tals have been edge ground to possess the desired
activity. It has been found that by extending
this process over a sufficiently long period of time,
approximately 95 per cent of the crystals in a
given batch may be successfully ground to possess
the desired activity.
.
the tube.
V
3. The method of grinding the edges of an ob
ject which comprises supporting said object
along its opposite edges upon the abrasively
coated inner surface of an elongated tubular
member, centrifugally actuating said object so
that its edges are held in pressure engagement
with said surface, and moving said member to
abrade the edges of said object transversely
thereof and to move the ends of said member al
ternately above and below the center of said
member, thereby to slide said object back and
forth longitudinally of said member and thus
abrade the edges of said object longitudinally
thereof.
4. The method of grinding the edges of an ob
ject which comprises, supporting said object
along its opposite edges upon the abrasively
coated inner surface of an elongated member,
centrifugally actuating said object so that its
edges are forced into pressure engagement with
said surface, moving said member to abrade the
edges of said object transversely thereof, inter
mittently decreasing the centrifugal force acting
upon said object, and gravitationally actuating
said object to shift the position thereof relative
to said surface each time the centrifugal force
acting upon said object is decreased, whereby dif
ferent opposed edges of said object are brought
into contact with said surface.
5. The method of grinding an object which
comprises, supporting said object upon the ab
While different embodiments of the invention
have‘ been disclosed, it will be understood that
various modi?cations may be made therein which
rasively coated inner surface of an elongated tu
are within the true spirit and scope of the inven“
bular member which is tilted relative to an axis of
tion.
rotation, rotating said tubular member about said
I claim:
axis to slide said object back and forth longitu
1. The method of grinding an object which
dinally of said tubular member, varying the speed
comprises supporting said object upon the ab 60 of rotation of said tubular member back and
rasively coated inner surface of‘ an elongated tu
forth between a lower limit at which said object
bular member which is tilted relative to an axis
is‘ freely slidable longitudinally of said member
of rotation, rotating said tubular member about
and an’ upper limit at which said object is cen
said axis to slide said object back and forth lon
trifugally restrained at the end of said tube fur
gitudinally of said tubular member, and varying
thest removed from said axis, and contacting said
the speed of rotation of said tubular member
object with a point ?xed relative to said surface
back and forth between a lower limit at which
during said relative sliding movement, thereby
said object is freely slidable longitudinally of said
member and an upper limit at which said object
is centrifugally restrained at'the end of said tube
furthest removed radially from said axis of roe
tation.
2. In the manufacture of piezoelectric crystals
to change at random the edges of said object
which bear against said surface.
6. The method of grinding the edges of an ob
ject which comprises, supporting said object
along its opposite edges upon the abrasively
coated inner surface of an elongated tubular
each having a number ofactivity peaks which
member, centrifugally actuating'said object so
are separated along an edge grinding time axis, 75 that its edges are held in pressure engagement
2,410,491
17
18
with said surface, moving said member to abradev
the edges of said object transversely thereof and
the edges of said object transversely thereof and
to move the ends of said member alternately
above and below the center of said member,
above and below the center ‘of said member,
thereby to slide said object back and forth lon
gitudinally of said member and thus abrade the
thereby to slide said object back and forth lon
gitudinally of said member and thus abrade the
edges of said object longitudinally thereof, and
intermittently changing, the edges of said object
to move the ends of said member alternately
edges of said object longitudinally thereof, inter
mittently decreasing the centrifugal force act
ing to produce pressure engagement between the
edges of said object and said surface, and
which are brought to bear against said surface
by said centrifugal actuation of said object.
10 gravitationally shifting the position of said ob
ject relative to said surface during at least a
7. The method of grinding the edges of an ob
portion of the intervals when said centrifugal
force is decreased, thereby to change the edges of
said object which are brought to bear against
coated inner surface of an elongated tubular
member, centrifugally actuating said object so 15 said surface by said centrifugal actuation of said
object.
that its edges are held in pressure engagement
HAL F. FRUTH.
with said surface, moving said member to abrade
ject which comprises, supporting said object
along its opposite edges upon the abrasively
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