Note: Descriptions are shown in the official language in which they were submitted.
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CENTRELESS VALVE GRINDING
This invention relates generally to valve grinding
apparatus, and has to do specifically with a valve grinding
apparatus utilizing the principle of centreless grinding.
While centreless grinding techniques have been
used heretofore for the grinding of valves, for example
of the kind used in the automobile industry, these prior `~
uses have suffered from various drawbacks which it is an
aspect of this invention to overcome.
Among the prior art considered in connection with
~' 10 this application are the following:
; U.S. Patent 1,533,133 Nickau, issued April 14, 1925.
U.S. Patént 1,452,508, Hervig, issued April 24, 1923.
The drawbacks of the prio:r art relate to a lack
of flexibility in the design, and to certain specific fail-
ings which will become clearer in the light of the followingdisclosure.
Accordingly, this invention provides a valve grind~
.~ ing apparatus, comprising
two base rollers in side-by-side relation with
20 their axes parallel, ~~
` drive means for positively driving the base `~
rollers in the same direction so that their surface speeds
are the same,
a freely turning control roller centered above
the base rollers, with its axis in a plane paralIel ~o the
plane containing the axes of the base rollers,
control means a) for selectively raising and
.
~i lowering the control roller with respect to the base rollers, ~
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alll b) for selectively varying the angle o~ the co~trol
roller axis in said parallel plane, such that the control
roller can be angled to both sides of a central position
in which its axis is parallel with the axes of the base
roller,
support means spaced from the base rollers for
supporting one region of a valve stem when another region
thereof contacts the base roller, whereby the valve stem
extends parallel to the base roller axes,
a grinding wheel and means for driving the
same,
and stop means for establishing the maximum
permitted valve stem movement in the direction from the
support means toward the base rollers, said direction being
the rearward direction.
One embodiment of this invention is illustrated in :
; the accompanying drawings, in which like numerals denote
like parts throughout the several views, and in which:
Figure 1 is a perspective view of a complete
apparatus for grinding valves;
Figure 2 is a longitudinal sectional view through
a sub-frame which holds, controls and rotates the valve;
Figure 3, on the same drawing sheet with Figure 1,
is a sectional view taken at the l:ine 3~3 in Figure 2;
:~ 25 Figure 4, also on the same drawing sheet with
Figure 1, is a sectional view taken at the line 4-4 in
Figure 2;
Figure 5 is a simplified schematic diagram illustrat-
ing the various rollers, the drive system and related com-
~ 30 ponents in ~he sub-frame shown in Figure 2;
`. Figure 6 is a partly broken away view of the
~` base of the assembly of Figure 1, showing the internal
;~ mechanism;
Figure 7 is a sectional view taken at the line
."~ 35 7-7 of Figure 6; and
: Figure 8 is a sectional view taken at the line 8-8
in Figure 7.
Attention is first directed to Figure 1, which
shows a valve grinding apparatus generally at 10, which
4U includes a main frame 12 and a sub-frame 14. A grindi.ng
wheel 16 of conventional nature is mounted with respect to .
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the main frame 12, and can be rotated at high speed by an
electric motor (not shown). As can be seen in Figure 1,
the grinding wheel 16 is covered by a housing 17 except
for anaccess location 18, -through which the head of a
valve 20 can be ground.
The sub-frame will now be more particular described
with reference to Figures 2, 3, 4 and 5.
The schematic Figure 5 shows two base rollers 22
in side-by-side relation with their axes parallel, but
;10 spaced apart so that there is no frictional contact.
Drive means shown generally at 23 is provided for positively
driving the base rollers 22 in the same rotational direction,
in such a way that their surface speeds are the same. In
the embodiment illustrated in the drawings, the identity of
surface speeds is attained by making the two base rollers
22 of the same diameter, mounting them on two parallel
shafts 24, and rotating the two parallel shafts 24 at the
same speed by means of a belt drive which includes a :
belt 26, a drive pinion 27, and two identical driven pinions
29, mounted on the shafts 24 respectively. The drive
pinion 27 is rotated at a slow but constant speed by an
electric motor 30 working through a speed reduction mechanism
32 of conventional nature.
It will be understood that the criterion of having
the base rollers 22 rotate with the same surface speeds can
be attained even if the base rollers are of different diameters,
simply by adjusting the diameters of the driven pinions
29
As can be seen in Figure 5, a valve 33 can be
arranged with its stem 34 resting in the "V" defined by the
two base rollers 22, the valve stem being oriented parallel
with the shafts 24.
To maintain the valve stem 34 in frictional contact
with the surfaces of the base rollers 22, there is provided
a freely turning control roller 36 which is centred above
the base rollers 22, and which has its axis located in a
plane parallel to the plane containing the axes of the `
base rollers. In the embodiment shown, the axes of the
base rollers are identical with the axes of the shafts 24,
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and these axes are horizontal or substantially so, such that
a plane passing through both axes would be horizontal.
The freely turning control roller 3Ç has its axis also
in a parallel plane, but in the condition shown in
Figure 5 the axis of the control roller 36 is not parallel
with the axes of the base rollers 22. The control roller
36 is associated with mechanismr shortly to be described,
which allows it to be raised and lowered with respect to
the base rollers 22, and which allows it to swivel about
a vertical line, thereby varying the angle of the control
roller axis in its parallel plane, such that the control
roller 36 can be angled to both sides of the central position,
in which central position the control roller axis is parallel
with the axes of the base rollers 22.
lS Located forwardly (rightwardly in Figure 5) of
the base rollers 22 is support means 37 for supporting one
region of the valve stem 34 when another region thereof
contacts the base rollers 22. The support means is such that, `
when it is so located, the valve stem 34 extends parallel
to the base roller axesO More specifically, as seen in
Figure 5, the support means 37 includes two arcuate members
38 and 39 which together define a V-shaped groove 41 of which
the flanks 43 and 44 have the same curvature as the respec-
tive base rollers 22. The support means 37 ~urther includes
a hold-down member 46 whi.ch is supported above the apex of
.~! the groove 41 for vertical movement. Means (shortly to be
described) is provided for u.rging the hold-down member 46
downwardly against the valve stem 34 when the same is
supported in the groove 41.
Stop means shown generally at 48 are provided for
establishing the maximum permitted valve stem movement in the
direction from the support means 37 toward the base rollers
~2, this direction being referred to hereinafter as the
rearward direction (leftward in Figure 5).
The stop means 48 is seen in Figure 5 to .include
a stationary shaft 50 fixed with respect to the sub-frame
14, a barrel 52 slidable on the stationary shaft 50, and a
threaded locking member 53 constituting means adapted to
- ~ lock the barrel 52 to the shaft 50 at any selected location.
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More specif.ically, the threaded lock member 53 has a knurled
head 54 and a threaded shank 55, the latter being screwed into
a suitably tapped bore extending through the wall of the
barrel 52 at right angles to the axis thereof, such that
the threaded shank 55 can be tightened against the shaft
50.
The barrel 52 supports two stop members: a
permanent stop member 57 which is fixed to the barrel 52
and which has a region 58 adapted to be contacted by the
valve stem 34 when the latter is supported on the base
rollers 22 and moves rearwardly; and a temporary stop member
60 which is located forwardly of the permanent stop member
57, and which is pivoted with respect to the barrel 52.
The temporary stop member 60 is selectively pivotable between :
an interposed position (shown in broken lines) in which it
can be contacted by the valve stem 34, and a removed position
(shown in solid lines in Figure 5) in which the valve stem
34 can by-pass the temporary stop member 60 to contact the
permanent stop member 57.
As seen in Figure 5, the permanent stop member 57
is substantially rectangular in configuration, while the
temporary stop member 60 is somewhat elongated, with a
heavier portion extending in the direction of the contact
location with the valve stem 34, and a lighter portion extend-
ing oppositely thereto. The lighte:r portion includes a
depressible lever 62 which can be depressed manually in order
to raise the operative contact portion of the temporary
stop member 60 (that which would be contacted by the rear-
: ward end of the valve stem 34 if the temporary stop member
60 were located in the broken-line position shown in Figure
5).
Referring now to Figures 1, 2 and 3, the control
means for selectively raising and lowering the control roller
36 and for varying the angle of its axis, is seen to include
a guide cylinder 64 to the top of which is bolted an end
plate 65 (boltsnot visible). As seen, the guide cylinder
64 is centred above the base rollers 22 and has its axis
vertical, i.e. at right angles to the plane containing the
:. axes of the base rollers 22, which in the embodiment illu-
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stra~ed is horizontal. A piston 67 is slidable in the
guide cylinder 64, and the piston supports the control
roller 36.
Looking at Figure 2, the guide cylinder 64 is
threadedly engaged with a lower end b]ock 68, and the
latter has two downwardly extending arms 69 in which
are supported conventional ball bearings 70, the ball
bearings supporting for rotation a shaft 72, which in
turn supports the control roller 36 through a bushing
74. The piston 67 which supports the control roller
36 can reciprocate vertically within the guide cylinder
64, and can also rotate to a limited extent about its own
axis within the guide cylinder 64.
Threadedly engaged in the wall of the piston 67,
and extending perpendicularly to the axis of the same is
a lever 76, which projects away from the piston through
an opening 77 in the cylinder 64. The opening 77 has a
greater circumferential extent than the diameter of the
lever 76, and also extends vertically over a distance
greater than the diameter of the lever 76. In actual fact,
the opening 77 is approximately rectangular, or could be
described more accurately as a rectangle laid upon the
surface of the cylinder 64, and having rounded corners.
Because the opening 77 has a greater width than the lever
25 76, limited rotational movement of the piston 67 about its .
own axis within the cylinder 64 is permitted. Because the
opening 77 has a greater vertical extent than the diameter
of the lever 76, vertical movement of the piston 67 within
the cylinder 67 is possible.
Urging the piston 67 resiliently toward its upper-
most position is a coil spring 79. The coil spring 79 is
secured at its lower end to a shaft 80 located in a recess
81 in the lower end block 68. The upper end of the spring
;~ 79 is hooked around a shaft 83 which is secured with respect
to the end plate 65. Integral with the end plate 65 is a
coaxial, downwardly extending tubular portion 84, which has
. an upper part of smaller diameter than the.inside diameter
of the piston 67, and a lower part 85 which is received
~ snugly but slidably within the inner bore 86 of the piston 67,
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with O-ring-type sealin~ mea~s 87 for effecting a seal.
The end plate 65 has a central tapped bore 86
therethrough, into which a plug 88 is threaded. A seal is
effected between the plug 88 and the end plate 65 by means
of an O-ring member 90. The plug 88 is centrally open at
91 and is tapped to receive a conventional connector 92 to
which a pressurized air supply can be fed to the space within
the tubular portion 84 (where the spring 79 is located).
It will be appreciated that an increase in fluid pressure
within the tubular portion 84 will eventually be able to
overcome the urging of the spring 79, and will force the
piston 67 to move downwardly, along with the lower end block
68 and the control roller 36.
The spring 79 is also able to exert a torque upon the
pistons 67 with respect to the guide cylinder 64, by suitably
angling the shafts80 and 83. In practice, this torque tension
is arranged in such a way that the piston 67 is turned as far
as possible in the direction which will result in the control
roller 36 causing the valve stem 34 to shift rearwardly
toward the stop means 48. When the operator wishes to push
the valve stem forwardly out of the sub-frame, or to cause it
to "ride even" without being pushed either forwardly or
rearwardly, he simply adjusts the position of the lever 76
to the corresponding location. To cause the valve stem to
"ride even", the lever 76 would be placed in the middle
location of the opening 77, so that the axis of the control
roller 36 lies parallel with the axes o~ the base rollers 22.
To push the valve stem 34 forwardly out of the gripping
apparatus, the lever 76 is moved to the opposite side of the
opening 77, so that the angulation of the control roller 36
is opposite to that which it normally assumes under the
torque exerted by the spring 79.
Also shown in Figure 2 is the means for raising and
lowering the hold-down member 46 with respect to the groove
41. This means includes an air cylinder 93, and an air line
94, both of conventional construction.
Turning briefly to Figure 4, the support means 37
is drawn in greater detail, and is seen to include a frame
member 95, which supports the members 38 and 39 in such a
way as to define the groove 41. The frame member 95 has a
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base 97 which has a conventional dovetail securement
arrangement 99 so that it can be secured at various
forward or rearward positions with respect to the base rollers
22. More specifically, the sub-frame includes a base member
101, having a dovetail ridge 103, and the base portion 97
of the frame member 95 defines a recess adapted to enclose
the dovetail ridge 103. Part of the enclosure involves a
wedge member 104 adapted to be urged rightwardly or left-
wardly (in Fi~ure 4) by a threaded member 106. Further
details of this construction are not necessary, since the
construction is identical to that on present-day machine
tools, such as lathes.
At the top of the frame member 95 is located a
horizontal plate 105 to which is secured the lower end of
the air cylinder 93.
Attention is now directed to Figures 1, 2, 6, 7
and 8, for a description of the way in which the sub-
frame 14 is mounted to the main frame 12, and can be moved
in various ways with respect thereto.
As can be seen in Figure 1, the sub-frame 14 is
mounted on an arcuate slideway 108 f which is affixed atop
a rocker link 110, which will be described more fully
subsequently.
The base plate 101 of the sub-frame 14 is keyed in
dovetail fashion to the arcuate slideway 108 in exactly the
same manner as the keying shown at 99 in Figure 4. More
specifically, the arcuate slideway 108 defines an arcuate
dovetail ridge which is received in a matching arcuate
dovetail slot in the underside of the base plate 101, and
30 a suitable wedge 112 controlled by a threaded member 114 is
adapted to lock the base plate 101 in any desired location
with respect to the arcuate slideway 108. A surface 115
of the arcuate slideway 108 is calibrated, and a pointer
117 serves to indicate particular points in the calibration,
so that the operator can move the sub-frame 14 away from a
given calibrated setting, and back again, with certainty
that the precise same setting will be attained. As the sub-
frame 14 is moved along the arcuate slideway 108 it rotates
about a theoretical point close to the typical position of
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a valve head when the same is contained in and held by the
sub-frame 14. By adjusting the sub-frame 14 with respect to
the arcuate slideway 108, the precise grind angle on the
sealing surface of the valve can be varied between 5 and 47.
The rocker link 110 is adapted to rock longitudinally
of a slot 118 cut in the top of a base housing 119, the slot
118 extending parallel to the plane of rotation of the
grinding wheel 16. Thus, as the rocker link 110 moves toward
and away from the grinding wheel 16, the entire sub-frame 14
is also carried toward and away from the grinding wheel 16.
In the "away" position, a valve contained in the sub-frame
14 can be easily removed and replaced without dangerous
contact with the grinding wheel 16.
When the operator is grinding a series of identical
valves having identical lengths, it is of advantage time-wise
to be able to move the sub-frame 14 away from the grinding
wheel 16 in order to exchange valves, and then return the
sub-frame 14 to operative position with respect to the
grinding wheel 16, in such a way that the sub-frame 14 always
returns to precisely the same position. However, since
valve lengths differ, it is also of advantage to be able to
rapidly adjust the position of the sub-frame 14 with respect
to the grinding wheel 16, when it has attained this "inner"
position (i.e. when the rocker link 110 has moved inwardly
as close as it can get to the grinding wheel 16). The
mechanism which allows this combination of repeatability
and adjustability will now be described with reference to
Figures 6, 7 and 8.
As can be sean in Figure 6, the rocker link 110 is
secured at its lower end to a shaft 120 which is journalled
for rotation in two opposed brace plates 121 secured to the
inside of the base housing 119. Also secured to the shaft
120 is a link 123 spaced ~rom the rocker link 110 and fixed
with respect thereto thro~gh a cross piece 124 spaced above
the shaft 120.
Above the cross piece 12~, bridging sha~s125 and
126 support a bearing housing 128, containing a bearing which
; permits rotation but not longitudinal movement of a shaft
130 on the rightward end of which a hand-wheel 131 is affixed.
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The bridging shafts 125 and 126 permit rotation
of the bearing housing 128 about the common a~es of the
bridging shafts.
At its leftward end, the shaft 130 has external
threads 133 engaginga composite stop 135 adapted to engage
a trunion 136 supported on a rotatable shaft 138 jour.nall~d in
the brace plates 121. The furthest leftward end of the
shaft 130 passes through the trunion 136 by virtue of a
central bore in the latter, which has an inner diameter
larger than the outer diameter of the threads, so that no
engagement between the shaft 130 and the trunion 136
takes place.
For a more detailed explanation of the working
of the composite stop 135 and the trunion 136, attention
is directed to Figure 7.
In Figure 7, it can be seen that the comp~site
stop 135 consists of a forward member 140 and a rearward
member 141, both of them cylindrical in outer configuration,
and both of them in threaded engagement with the shaft 130.
The rearward member 141 has two antipodal recesses 143 on
its rearward face 145, and the trunion 136 has two matching
forwardly directed protuberances 147 which are adapted to
engage the recesses 143 when the shaft 130 is moved to the
rear (leftwardly in Figure 7), ther~by establishing a furthest
:25 rearward position for the shaft 130, and a corresponding
furthest rearward position for the rocker link 110 in the
. arcuate slideway 108.
.~` When the shaft 130 is in its furthest rearward
position, with the protuberances 147 engaged with the recesses
143, the said engagement prevents rotation of the composite
stop 135, and rotation of the shaft 130 by means of the
hand-wheel 131 will cause the shaft 130 to move forwardly
or rearwardly with respect to the trunion 136, thus incre-
mentally adjusting the position of the bearing housing 12~,
. 35 the rocker link 110, the arcuate slideway 108, and the
sub-frame 14.
When the shaft 130 is moved forwardly (rightwardly
; in Figure 7) away from the trunion 136, no restraint is
exerted on the rearward member 141 against rotation, and
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~ny turning of -the shaft 130 will tend to rotate the
composlte stop 135 along with it. To ensure tha-t these
two rotate together whenever the protuberances 147 are
out of engagement with the recesses 143, the two members
141 and 140 of the composite stop 135 are spring-biased
apart by virtue of two antipodal coil compression springs
149 located in suitable aligned bores in the members 140
and 141.
At locations spaced 90 from the springs 149 are
guide pins 151 which lie in aligned bores of smaller
diameter than the bores for the compression coil springs
149. Thus, the action of the coil springs 149 urges the
respective members 140 and 141 away from each other,
in order to "bind" the threaded engagement of each of the
members with the threads of the shaft 130. This binding
thus increases the frictional contact between the composite
stop 135 and the shaft 130, whereby rotation of the latter
will necessarily cause rotation of the former.
By virtue of the provisions just described, it will
be understood that, whenever the rocker link 110 rocks
forwardly (clockwise in the view of Figure 6), due to forward
movement of the bearing housing 12~ and shaft 130, any
accidental bumping against the hancl-wheel and change in its
rotational position will not change the longitudinal
25 position of the composite stop 135 on the shaft 130, so that
when the rocker link 110 is returned to its furthest inward
position (furthest counter-clockwise in Figure 6), the same
innermost position will be established.
In order to cause the rocker link 110 and the arcuate
30 slideway 108 to rock away from the grinding wheel 16 (clock-
wise in Figure 6), there is provided a Y-linkage consisting
of three links pivotally connected together at a central
axis 153, the three links including a lower link 154, a
rearward upper link 155, and a forward upper link 156. The
35 lower link 154 has a fork 158 at the top, through which a
shaft 160 passes. The inner ends of the upper links 155 and
156 are pivotally connected to the shaft 160. i
The lower link 154 extends generally downwardly to
a pivot arrangement 162, where it is connected to one end
40 of a lever 163 having a foot pedal 164 at the other end. ~-
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The lever 163 e~tends outwardly through a vertically elongated
slot 165 in the base housing 119. The lever 163 is pivoted
at an intermediate location by virtue of brackets 167
secured to a member 168 in turn secured to the bottom wall
of the base housing 119.
It will thus be appreciated -that downward pressure
on the foot pedal 164 causes upward movement of the lower
link 154, and upward pressure on the lower ends of the
upper links 155 and 156.
As can be seen in Figure 6, the rearward upper link
155 has its upper rearward end pivotally connected to the
shaft 138, and since the latter is fixed with respect to
brace plates 121, the upper pivoted end of the rearward
upper link 155 cannot move.
The upper forward end of the other upper link 156
is pivoted to the bridging shaft 126, the latter of course
:. being movable forwardly and rearwardly due to the fact that
the links 110 and 121 are rotatable about their lower ends.
Hence, downward pressure on the foot pedal 164 causes
the shaft 160 to be raised, which increases the angle defined
between the upper links 155 and 156, and forces the upper
: forward end of the forward upper link 156 to move rightwardly,
thus rotating the rocker link 110 in the clockwise direction
as seen in Figure 6, thus carrying the arcuate slideway 108
and the sub-frame 14 away from th~ grinding wheel 16.
It can now be seen that the apparatus herein
.~ described incorporates a high degree of flexibility and man-
oeuvrability by virtue of several o~ the provisions. Firstly,
the control roller 36, unlike the control rollers in the
prior art devices, can be selectively swivelled in a
horizontal plane, to change the angle of its a~is with respect
to the base rollers 22, thereby adjusting the longitudinal
forces applied to the valve stem 34, and reversing them where
this is required. Secondly, in the ~rior art exempli-
fied by Hervig, U.S. 1,452,508, only the upper angulated
roller is driven, providing only a single driving contact
with the valve stem 34, which contact is a theoretical line.
In the apparatus described herein, two of the three rollers
are driven (the base rollers 22), and this increases the
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frictional gxip agalnst the valve stem 34. It is preferred
that all rollers be made of a tough but somewhat resilient
material, for example nylon, in order to attain an area of
contact, rather than a mere theoretical line as would be
the case with metallic rollers. Another advantage arising
from the provision of resilient rather than metallic
rollers is that it avoids the tendency of metal filings or
chips to un-center the valve shaft by entering between
the shaft and a non-resilient metallic roller. The resilient
rollers simply yield to "absorb" the metal filing.
A further advantage relates to the support means
37 forwardly of the roller assembly, which support means
simulates the surfaces of the base rollers 22, without
requiring actual rollers to be provided. Naturally, freely
running rollers could be positioned where the support means
37 is located, but the extra expense of providing shafts,
etc. for such rollers is avoided by the construction pro-
vided herein. Additionally, by avoiding rolling supports,
it is not possible for metal filings and chips to enter
between the valve shaft and the supports. Any such filings
etc. are simply "wiped off" at the contact between the
shaft and the stationary support. E'urthermore, it will be
appreciated that, by making the flanks 43 and 44 of the ~
members 38 and 39 of the support means 37 a match for the '
surfaces of the rollers 22, valve stems of different
diameters may be ground, and their axes will still remain
precisely parallel with the shafts2~ of the base rollers 22,
although being raised or lowered to some extent with
respect to the shafts24.
Another advantage relates to allowing the stone .
16 to grind the valve at its own speed dependent upon the
pressure between the valve face and the stone, this pressure
being established by the angulation of the control roller
36 and the air pressure controlling vertical pressure on the
roller 36. In actual practice, the force urging the valve
stem rearwardly is mainly controlled by adjusting the air
` pressure, since this can be set at a level corresponding
to the size of the valve and the area of the face. The
control roller 36 would usually be allowed to swing to the
fully angulated position corresponding to rearward movement
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of the valve stem. In the case of the instant invention,
the temporary stop 60 is first left in the operative
position (broken lines in Figure 5), as the valve 34 is
inserted. The insertion takes place with the control
roller 36 raised upwardly by the spring 79, due to the
absence of air pressure being applied to the central
cavity containing the spring 79. The control roller 36
is then lowered and the apparatus is switched on. As the
base rollers 22 rotate, the valve stem 34 is gradually drawn
rearwardly until its rearward end strikes the temporary
stop 60. At this time, the arcuate slideway is in its
furthest inward position, which is such as to cause the face
of the valve to be adjacent to but not in contact with
the outer side edge 170 of the grinding wheel 16. When
: 15 the rearward end of the valve stem 34 has made contact with
the temporary stop 60, the lever 62 is manually depressed,
to remove the temporary ~top 60 from
contact with the valve stem 34. The continued rotation of
the base memhers 22, combined with the angulation of the
control roller 36 then attempts to carry the valve stem 34
further rearwardly toward contact with the permanent stop
57. However, before contact takes place, the face of the
valve to be ground (shown at 172 in Figure 2) will contact
the grinding surface 170 of the gr.inding wheel 16, and
grinding will commence. As material is removed from the
face 172 of the valve, the entire valve is allowed gradually
to move rearwardly, and eventually contact will take place
with the permanent stop 57. When this has occurred, the
face 172 will be evenly and completely ground.
In order to "polish" the face 172, the lever 76
can be moved to a middle position, so that the axis of
~ control roller 36 is parallel with the axes of the base
.~ rollers 22, and thi.s will allow the valve to simply
"float" against the grinding wheel 16, which will have the
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effect of polishing the face 172. The latter procedure
could be u~ilized before the valve stem had abutted against
the permanent stop 57. Conversely, "polishing" will also
take place after the valve stem has contacted the permanent
stop 57, since no further rearward movement is then
possible, and the valve face will simply "float" against the
grinding wheel 16.
In order to change valves for the next grinding,
the lever 76 is first moved to its furthest counter-
clockwise position as seen from above (to the side of the
opening 77 opposite from the position shown in Figures 3),
and this will move the valve rightwardly or forwardly,
which will have the effect of separating the face 172 of
the valve from the grinding surface 170 of the grinding
wheel 16. At this point, downward pressure with the foot
on the foot pedal 164 will swing the entire sub-frame 14
outwardly away from the grinding wheel 16, thus allowing ~,
the operator to exchange valves. This is done by turning
off the air pressure in the compartment containing the
coil spring 79, and simultaneously releasing the air pressure
in the air cylinder 93. This will allow the hold-down member
. 46 and the control roller 36 to move upwardly, allowing the
operator simply to pick up the valve, remove it forwardly
out of engage~ent, and then put the next valve into place.
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Prior to putting the next valve into place, the
operator will allow the temporary stop 60 to fall back
down into its broken line position shown in Figure 5, so
that, initially, the new valve will not be drawn all the
way back into grinding position with respect to the grind-
ing wheel. When the next valve has been laid upon the
base rollers 22, the operator activates the air pressure
means to lower the control roller 36 and the hold-down
means 46, whereby the valve is gripped. Rotation of the
base rollers 22 then gradually carries the new valve
rearwardly toward the temporary stop 60, which it eventually
contacts. In this position (or prior to the contact between
the valve stem 34 and the temporary stop 60) the operator
allows the sub-fram~ to move inwardly toward the grinding
wheel, by releasing pressure on the foot pedal 164. Once
the sub-frame and the supported valve have reached the
innermost position, the operator presses down on the lever
62 to remove the temporary stop 60 from interfering
position, and the valve is gradually drawn rearwardly
toward the fixed stop 57. As before, prior to contact
with the fixed stop, grinding of the valve face commences.
In Figure 6, a shock absorbing element 175 of
conventional construction has been provided between the
base housing 119 and an intermediate location on the lower
link 154. This avoids "slamming" of the sub-frame 14 into
its innermost and outermost positions.
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