Saw chain grinder

A grinder for sharpening saw chain cutting teeth includes a base, an arcuate guide arranged on the base, a power-driven rotary grinding wheel mounted on a pivotal motor arm movable with a mounting bracket along the arcuate guide and a releasable, self-centering clamp for holding a segment of a saw chain in position beneath the grinding wheel. The clamp includes laterally opposed elongate bars which support a saw chain and which are each simultaneously displaceable at equal rates toward a preselected datum line. The preselected datum line intersects a fixed, reference axis about which the mounting bracket is angularly displaced. Because the elongate bars are movable equally with respect to the preselected datum line, the lengthwise centerline of a saw chain will always be maintained substantially aligned on the preselected datum line regardless of the width of the chain. The arcuate guide is an elongate bar having an arcuate guide track which receives the motor arm mounting bracket. The arcuate guide is pivotal about a pivot axis so that the mounting bracket may be angularly displaced along the arcuate guide and offset at varying distances from the reference axis.

BACKGROUND OF THE INVENTION 
The present invention relates to saw chain sharpening apparatus, and more 
particularly to those forms of saw chain sharpening apparatus using a 
power-driven rotary grinding wheel mounted on a motor arm, the motor arm 
being shiftable so that the grinding wheel may be positioned for 
sharpening right and left-hand cutting teeth of a saw chain without 
removing the saw chain from a clamping device. The present invention is 
directed to improvements in such apparatus, and more particularly is 
concerned with providing a self-centering saw chain clamping device which 
will substantially align and maintain, independently of width, a saw 
chain's lengthwise centerline on a preselected datum line. Also, the 
present invention is directed towards providing an improved configuration 
for offsetting a grinding wheel with respect to the preselected datum 
line. 
Saw chain grinding apparatus which employ a power-driven rotary grinding 
wheel mounted on a motor arm movable along a base-mounted arcuate guide 
are known in the art. These devices typically employ a base mounted saw 
chain clamping or gripping construction which is used to maintain a 
segment of a saw chain in position for sharpening by the grinding wheel. 
Associated with the clamping or gripping device is an indexing arm or 
finger which serves to prevent a saw chain cutting tooth from being moved 
in one direction while the grinder is used to sharpen the tooth. The 
grinding wheel, being movable along an arcuate slot, may be first 
positioned at a preselected location on the arcuate guide for sharpening 
the right-hand cutting teeth. The wheel is then moved along the arcuate 
guide to a second position for sharpening the left-hand cutting teeth. The 
saw chain is indexed along the gripping or clamping device without the 
necessity of removal therefrom. 
A problem present with the prior art saw chain grinding apparatus as 
described above resides in the fact that the length-wise centerline of a 
saw chain will not be maintained at a fixed location with respect to the 
grinding wheel if saw chains of differing widths are successively used in 
the apparatus. In sharpening right and left-hand cutter elements, it is 
important that each element be ground uniformly throughout the length of 
the saw chain. In the prior art, such uniformity was ensured for a saw 
chain of a particular width by setting the grinder at the factory or by 
providing clamps which had to be reset for each chain width to be 
sharpened. However, if an operator in the field desired to sharpen a saw 
chain having a width different from that accommodated by the factory 
setting the operator took the chance of imprecisely setting the apparatus. 
The present invention overcomes the aforementioned problem by providing a 
self-centering clamping device which substantially aligns and maintains 
the lengthwise centerline of a saw chain on a preselected datum line 
without regard to the saw chain's width. The preselected datum line is 
intersected by a fixed, reference axis which is the axis about which the 
motor arm mounting bracket is angularly displaced along the arcuate guide. 
Because a saw chain's lengthwise centerline is substantially aligned and 
maintained along the preselected datum line, and because such datum line 
intersects a reference axis, the position of the grinding wheel with 
respect to either right or left-hand cutter elements of a saw chain 
supported in the self-centering clamping device is maintained constant. 
Thus, it may be readily appreciated that a sharpening operation will 
proceed uniformly on the cutting elements. 
The prior art saw chain sharpening apparatus also presents another problem 
in that the apparatus must be adjusted through various complicated 
mechanism to sharpen cutting teeth other than the so-called Oregon type 
teeth. For instance, it is common to use a grinding apparatus to sharpen 
micro, semi or super chisel-type saw chain teeth. In order to sharpen such 
chisel-type teeth, it is necessary to grind such a tooth across the full 
width thereof. Such full width sharpening requires that the centerline of 
a rotary grinding wheel be adjusted with respect to the centerline of a 
supported saw chain length. In order to alter the position of a grinding 
wheel's centerline with respect to the lengthwise centerline of a 
supported saw chain, as when changing from sharpening Oregon cutter teeth 
to sharpening chisel-type teeth, it is desirable to provide axes offset 
from the reference axis about which the motor arm mounting bracket 
travels. By providing such offset axes, the relative positions of a 
centerline of a grinding wheel and the lengthwise centerline of a saw 
chain may be appropriately adjusted. 
SUMMARY OF THE INVENTION 
The present invention provides a saw chain sharpening or grinding apparatus 
which includes a novel self-centering saw chain clamping device for 
substantially aligning and maintaining, independently of saw chain width, 
a saw chain's lengthwise centerline on a preselected datum line. The datum 
line intersects a reference axis about which pivots a positioning arm. The 
positioning arm controls orientation of the mounting bracket as it is 
shifted along the arcuate guide. Additionally, the present invention 
provides that the arcuate guide bar be pivotally mounted on a base so that 
the offset of the centerline of a grinding wheel with respect to the saw 
chain centerline may be varied. 
An object of the present invention is to provide a saw chain sharpening 
apparatus in which the saw chain clamping device is self-centering and 
arranged to substantially align and maintain, independently of saw chain 
width, the lengthwise centerline of a saw chain along a preselected datum 
line so that saw chains of different widths may be successively sharpened 
without complicated adjustments to the apparatus. 
Another object of the present invention is to provide an improved saw chain 
sharpening apparatus in which an arcuate guide track is formed in a 
base-mounted arcuate guide bar, the arcuate bar being pivotal about an 
axis so that the centerline of a rotary grinding wheel may be offset with 
respect to the preselected datum line. By providing pivotal movement of an 
arcuate guide bar, the selected degree of offset may be maintained 
precisely when grinding either right- or left-hand cutting teeth of the 
micro, semi or super (round file) chisel-type chain. This offset allows 
for the proper top plate cutting angle to be ground across the full width 
of the top plate of a cutter tooth or link. 
Yet another object of the present invention is to provide a means by which 
proper orientation of the mounting bracket relative to the reference axis 
may be accurately maintained. To this end, the positioning arm which 
connects the mounting bracket to the reference axis is provided with a 
slidable connection between one end thereof and the mounting bracket. It 
may be readily appreciated that if the arcuate guide bar is pivoted so 
that the mounting bracket is movable therealong about an axis other than 
the reference axis, some provision for permitting movement between the 
positioning arm and mounting bracket is required. The present invention 
includes a sliding connection between the mounting bracket and the 
positioning arm so that such movement can occur while maintaining proper 
orientation of the mounting bracket and elements mounted therein relative 
to the reference axis. 
Additional objects of the present invention reside in the specific 
construction of the exemplary apparatus hereinafter particularly described 
in the specification and shown in the several drawings.

DETAILED DESCRIPTION OF THE INVENTION 
With reference directed initially to FIG. 1 of the drawings, a saw chain 
grinding apparatus in accordance with the present invention is generally 
indicated at 10. Saw chain grinder 10 includes a base section indicated at 
12 and a motor arm assembly 14. 
Base section 12 includes a base plate 16 which serves as a support for saw 
chain grinder components to be hereinafter described. Base 16 is formed 
with raised seats 16a, 16b upon which an arcuate guide means, or bar, 18 
rests when assembled thereupon. Arcuate guide bar 18 is formed with an 
arcuate slot, or track, 18a therein and is pivotally connected to an upper 
surface of base 16 by means of a pivot bar shaft 22. A flanged bearing 24 
is secured to base 16 and supports pivot bar shaft 22 which is connected 
by screws 22a to arcuate guide bar 18 intermediate opposite ends of slot 
18a. Such connection provides a pivot axis about which guide bar 18 may be 
swung parallel to the upper surface of base 16. 
A motor arm mounting bracket 26 is arranged to be slidably received on 
arcuate guide slot 18 for travel therealong. Mounting bracket 26 includes 
an extension 26a and lugs 26b, the function of which will be later 
described. A lock handle 29 having a cam surface is connected to a pin 29a 
for insertion through lock spring 29b and aperture 26c. With reference to 
FIG. 10, it can be seen that pin 29a depends through aperture 26c and is 
secured to a cap 20. Cap 20 includes an outer periphery 20a arranged to 
contact against lip sections 18b when lock handle 29 is disposed in 
locking position. When lock handle 29 is pivoted to a nonlocking position, 
pin 29a is permitted to move downwardly so that periphery 20a does not 
frictionally engage sections 18b. Thus, mounting bracket 26 may be 
selectively positioned and locked along arcuate guide bar 18. Pin 29a is 
arranged to slide in slot 18a when lock handle 29 is disengaged from 
contact against spring 29b. 
Extension 26a is inserted through a second arcuate guide slot 28 in the 
base when the device is assembled (see FIG. 8). A pivot connection 30 
defines a reference axis and is arranged on an underside of base 16 to 
permit connection thereto of an elongate rigid positioning arm 32. The 
other end of positioning arm 32 is slidably received within a bearing 34 
which, in turn, is mounted in a sleeve 26d connected to extension 26a. 
Positioning arm 32 orients mounting bracket 26 so that it will be 
maintained with a preselected face directed toward the reference axis when 
bracket 26 is moved along guide bar 18. For reasons to be hereinafter 
described, it is required that positioning arm 32 be slidably connected to 
mounting bracket 26. 
Motor arm assembly 14 includes a motor arm 36 which supports a motor 38 
drivingly connected by means of a belt and pulley arrangement to a rotary 
power-driven grinding wheel 39. Arm assembly 14 incorporates a shroud 42 
for operator protection. Motor arm 36 further includes a handle 36a. Arm 
assembly 14 further includes threaded lugs such as shown at 36b (one is 
hidden) which will be mounted to flanges 26b of motor arm bracket 26 in 
the assembled configuration. When motor arm 36 is so mounted, (see FIGS. 7 
and 8) it will be arranged at an angle obliquely to the plane of base 16. 
Appropriate bolts 27 and nuts are provided for pivotally connecting motor 
arm assembly 14 to bracket 16 and providing a pivot axis extending through 
bolts 27 about which the motor arm assembly may be moved toward and away 
from the base 16. 
A saw chain clamping mechanism in accordance with the present invention is 
generally designated at 40. Clamping device 40 includes two elongate, 
laterally opposed members, or bars, 42, 44 which are mounted for movement 
toward and away from one another on a pair of shoulder screws 43. Shoulder 
screws 43 extend through spaced bores 45 in elongate bars 42, 44 and are 
threadedly connected to lugs 46, 47 on base 16. 
As is seen in FIGS. 1, 4 and 4a, an elongate clamp screw 48, having a 
shoulder 48a and threaded segments 48b and 48c is inserted through aligned 
bores 42a, 44a in elongate clamping bars 42 and 44. Threaded segment 48b 
extends through the threaded bore of a clamp nut 50 and threaded segment 
48c is received in an accommodating threaded bore in a clamp block 52. 
Threaded segment 48c is threadedly engaged with like threads in clamp 
block 52 while the threads on segment 48b are threadedly engaged with 
clamp nut 50. Clamp block 52 is secured to base 16 by means of screws 51. 
A plate 17 is provided for mounting. For reasons to be hereinafter 
described, clamp nut 50 is allowed to travel along clamp screw 48 relative 
to base 16 as such screw is rotated for further engagement with clamp 
block 52. Clamp screw 48 is provided with a knob 48d to facilitate 
rotation thereof. 
A feed adjustment screw assembly 54 is threadedly secured through support 
53 and is further provided with a tightening wing nut 54a. Disposed 
through a slot 28a in base 16 is a feed arm assembly 56 which is pivotally 
connected to an underside of base 16. A pawl 58 is pivotally connected by 
means of a bolt 59 to feed arm assembly 56. The function of feed 
adjustment screw assembly 54 and feed arm assembly 56 will be described 
later. 
Turning now to FIGS. 2-4a, features of clamping mechanism 40 will be more 
particularly described. FIG. 2 is a top view of base 16 with motor arm 
assembly 14 removed for clarity. Arcuate guide means 18 is shown in solid 
line in FIG. 2 in one operating position and in dot-dashed outline swung 
about pivot bar shaft 22 to a different operating portion as will be 
described below. Mounting bracket 26 is shown in solid outline in FIG. 2 
positioned for sharpening a left-hand cutter link. The dotted outline of 
mounting bracket 26 shown on the left represents the position for 
sharpening right-hand cutter links. Base 16 includes a zero reference mark 
at 16c and further includes scales to either side thereof for showing the 
amount of angular displacement of mounting bracket 26 either to the left 
or right of zero reference 16c. It is to be noted that the pivot point 30 
intersects a preselected datum line 31 which is that line along which the 
lengthwise centerline of a saw chain will be disposed when the chain is to 
be sharpened. In FIG. 2, clamping mechanism 40 is shown closed to grip a 
saw chain therein. 
In FIG. 3, a bottom view of the apparatus more clearly illustrates 
positioning arm 32 which orients mounting bracket 26 so that it will be 
maintained with a preselected face directed toward reference axis 30. 
With reference now directed to FIG. 4, the specific operation of the 
clamping mechanism 40 will be described. As heretofore stated, it is 
desirable to maintain the lengthwise centerline of a saw chain, regardless 
of saw chain width, on a preselected datum line. Such a datum line is 
shown at 31 in FIGS. 2 and 3 and lies in a plane 31a, such plane being 
parallel to elongate bars 42, 44 and disposed intermediate thereof. The 
present invention provides that clamping mechanism 40 will maintain and 
substantially align a saw chain's lengthwise centerline along datum line 
31, by providing a construction in which elongate bars 42, 44 will move 
simultaneously toward the preselected datum line at equal rates. To 
accomplish such, the present invention utilizes the dual threaded clamp 
screw 48 which extends loosely through apertures 42a, 44a in the elongate 
clamping bars 42, 44. Segment 48c of clamp screw 48 has threads which are 
formed with one-half the lead of those threads on concentric segment 48b. 
Threads 48c engage receiving threads in clamp block 52 while threads 48b 
engage receiving threads in clamp nut 50. Threads 48c will not threadably 
engage the threads in clamp nut 50. 
The threads on segments 48b, 48c are so formed that upon rotation of the 
screw to cause it to screw further into clamp block 52 (and move to the 
right in FIGS. 4 and 4a) the threads on segment 48b produce movement of 
clamp nut 50 away from block 52 (to the left in FIGS. 4, 4a). Considering 
the construction shown in FIG. 4a, with the elongate clamping bars 
initially open to receive a saw chain, a clockwise rotation of screw 48 
will cause threads 48c to move into further engagement with clamp block 
52. During such a rotation, shoulder portion 48a will displace elongate 
clamping bar 42 to the right. Clamp nut 50 will simultaneously move to the 
left thereby displacing elongate clamping bar 44 to the left. Because the 
threads on segment 48b have twice the lead of the threads on segment 48c, 
elongate clamping bars 42, 44 move at equal rates toward datum line 31. 
Thus, it can be appreciated that if clamping mechanism 40 is initially 
disposed in a position such as shown in FIG. 4a and a saw chain is placed 
within the opening of elongate bars 42, 44, such bars may be 
simultaneously displaced toward preselected datum line 31 to clamp such 
saw chain segment, regardless of its width, in a position substantially 
aligned on the preselected datum line. Such is the result shown in FIG. 4a 
wherein a saw chain segment 49 has its guide links 49a securely held 
between clamping bars 42, 44. 
A typical sharpening operation for the so-called Oregon, or chipper-type, 
cutter link will now be described with reference to FIGS. 5-9. With the 
motor arm and grinding wheel raised as shown in FIG. 7, a saw chain, such 
as chain 60, is placed in seated position along elongate bars 42, 44 as 
shown in FIG. 5. A rear edge of cutting tooth 61 is moved to the right as 
viewed in FIG. 5 against pawl 58. Clamp screw 48 then is rotated clockwise 
to simultaneously displace elongate clamping bars 42, 44 toward datum line 
31 so that saw chain 60 may be rigidly secured between the elongate 
clamping bars with cutting tooth 61 in position for sharpening. The 
position of pawl 58 is adjusted by operation of feed adjustment screw 
assembly 54 which may be shifted to vary the position of pawl 58. As shown 
in FIG. 5, rotary grinding wheel 39 then is moved downwardly so as to 
sharpen cutter link 61. FIG. 7 shows saw chain grinder apparatus 10 in a 
raised position before rotary grinding wheel 39 is lowered for sharpening 
a left-hand cutter link. 
In FIG. 6, the sharpening of a right-hand cutter link 51a is shown. Before 
the right-hand cutter links are sharpened, saw chain 60 is indexed along 
clamping bars 42, 44 until all the left-hand cutter links are sharpened. 
Lock handle 29 is released to permit pin 29a to move downwardly so that 
cap 20 does not frictionally engage lip sections 18b. Thereinafter, motor 
arm assembly 14 is angularly displaced along arcuate guide bar 18 to a 
preselected top plate cutting angle as shown in FIG. 8. FIG. 6 is a 
partial view shown looking in from the rear of base 16 and shows rotary 
grinding wheel 39 sharpening a right-hand cutter link 61a. 
A chipper cutter link is shown in FIG. 9. It can be seen that a top plate 
angle such as indicated at A will be specified for a given saw chain. The 
top plate angle is set on the base 16 by moving mounting bracket 26 so 
that an indicator 26f on extension 26a points to a preselected angle 
indicator mark on either side of reference 16c. 
It is often desirable to be able to position the grinding wheel with its 
center offset to one side or the other of the centerline of the saw chain 
held in clamping assembly 40. For instance, micro, semi or super (round 
file) chisel-type cutter links need to have a top plate cutting angle 
ground across the full width. In order to accurately offset the centerline 
of grinding wheel 39 with respect to the preselected datum line, arcuate 
guide means 18 is pivoted about pivot bar shaft 20 either in the direction 
of arrows B or C in FIG. 2. As shown in FIG. 2, guide bar 18 has been 
shifted to that position shown in dot-dashed outline. Mounting bracket 26 
will now be movable along guide bar 18 about a new axis which is offset 
from reference axis 30. In order for mounting bracket 26 to be so moved, 
bearing 34 is slidable in sleeve 26d. 
A releasable locking mechanism is provided so that guide bar 18 may be 
pivoted and then locked in position. A lock handle 19 having a cam surface 
is connected by means of a pin 19a to a clamp screw 19b. Clamp screw 19b 
is inserted through a lock spring 19c and aperture 18b in guide bar 18. 
Further, clamp screw 19b is disposed through an apertured indicator 21 and 
is held by means of a threaded cap 25 within elongate slot 23a. Elongate 
slot 23a is formed in scale 23 which is secured to base 16. Cap 25 is 
provided with an outer periphery 25a which frictionally engages an 
underside portion of base 16 when lock handle 19 is moved so that its cam 
surface contacts lock spring 19c. Thus, it can be seen that when lock 
handle 19 is released, clamp screw 19b may be moved along elongate slot 
23a to thereby pivot guide bar 18 about pivot bar shaft 22. Indicator 21 
is provided with a reference mark 21a which may be read against marks 23b 
on scale 23 to display the amount of offset. 
When it is desired to provide an offset between the centerline of rotary 
grinding wheel 39 and preselected datum line 31, lock handle 19 is 
released from a locking position so that arcuate guide means 18 may be 
pivoted about pivot bar shaft 20 in the directions of arrows B or C as 
shown in FIG. 2. For purposes of illustration, assume that mounting 
bracket 26 is positioned to the left of zero reference 16c as shown by the 
dotted lines in FIG. 2. If bar 18 is pivoted about pivot point 20 in the 
direction of arrow B, the face of grinding wheel 39 will be moved further 
across the width of a right-hand cutting link and thus be offset in a 
direction away from the viewer in FIG. 6. The right-hand cutter link may 
now be ground across its full width. Mounting bracket 26 may be then moved 
an equal distance to the right of zero reference 16c so that a left-hand 
cutter link may be ground across its full width. 
Because guide bar 18 is arcuate, if mounting bracket 26 is moved to equal 
angle positions on opposite sides of zero reference 16c, the amount of 
offset will be the same when grinding either a right or left-hand cutter 
link. Thus, to set the degree of offset is greatly simplified. 
Explaining briefly a sequence of operation for the apparatus thus 
described, and assuming that it is desired to sharpen chain teeth in which 
an offset of the grinding wheel is required, locking handle 19 is first 
released to permit swinging of arcuate guide 18 to a desired position as 
indicated by the relationship between reference mark 21a on indicator bar 
21 movable with one end of guide bar 18 and its relationship to the scale 
marks 23b on scale 23. The relationship between such indicator and scale 
is used to select the amount of offset which will be provided for the 
grinding wheel relative to the datum line for the saw chain. After this 
offset is established, locking handle 19 is secured to lock the guide bar 
in position. 
Chain holding bars 42, 44 then are opened as illustrated in FIG. 4a to 
receive a saw chain therebetween, the saw chain is inserted as illustrated 
in FIG. 4 and the screw 48 is operated to bring bars 42, 44 into position 
to support a section of the chain but not to clamp it tightly therein. The 
saw chain then is moved to the right as illustrated in FIG. 5 into a 
position in which a chain tooth to be sharpened has its rear edge abutting 
pawl 58. This positions the saw chain for grinding and then screw 48 is 
further tightened to bring clamp bars 42, 44 into secure clamping relation 
against opposite sides of the saw chain as shown in FIG. 4. As previously 
described, with the clamp bars thus held tightly against the saw chain the 
centerline of the saw chain is aligned on datum line 31 and resting within 
plane 31a between the clamp bars. 
To sharpen a left-hand tooth, the mounting bracket is swung to the position 
illustrated in solid outline in FIG. 2 to a specified degree of angular 
offset from the zero reference mark 16c. This is accomplished by loosening 
locking handle 29 to allow sliding movement of the mounting bracket along 
guide bar 18. Upon arriving at the proper angular position, the clamping 
handle is relocked. Throughout such swinging of the mounting bracket and 
motor arm, positioning arm 32, disposed beneath the base 16 maintains a 
proper orientation of the mounting bracket 26, motor arm 36 and grinding 
wheel 39 whereby they are directed at central pivot point 30. The sliding 
connection between positioning arm 32 and the mounting bracket 26 permits 
the mounting bracket to move toward selected offset positions with the 
preset positioning of arcuate guide bar 18. Thus, assuming guide bar 18 
has been swung in the direction of arrow B in FIG. 2, when the mounting 
bracket is in the position illustrated in solid outline in FIG. 2, the 
grinding wheel will be offset from datum line 31 in a direction toward 
guide bar 18. 
With the mounting bracket and chain thus locked in position, the first 
tooth is sharpened as illustrated in FIG. 5 by swinging the grinding wheel 
into grinding relationship with the tooth. After this tooth is ground, 
clamp screw 48 is loosened, the chain is moved forwardly until the next 
left-hand tooth is adjacent pawl 58 and may be positioned thereagainst 
after which screw 48 is tightened. The grinding operation then is 
performed on all of alternate links along the chain to thereby sharpen all 
of the left-hand cutter teeth on the chain. 
Subsequently, to sharpening all of the right-hand teeth on the chain, 
locking lever 29 is released, mounting bracket 26 is swung to the position 
illustrated in dot-dashed outline in FIG. 2, and is locked in a position 
in equal angular displacement to the left of zero reference mark 16c as it 
previously occupied on the right hand side of zero marking 16c. In this 
position and with the arcuate guide bar 18 still swung to and locked in 
the position in the direction of arrow B, the grinding wheel will be 
offset away from the viewer as illustrated in FIG. 6. The above explained 
operation for sharpening teeth then is performed on the right-hand teeth 
distributed alternately along the length of the chain. 
While the invention has been particularly shown and described with 
reference to the foregoing preferred embodiment thereof, it will be 
understood by those skilled in the art that other changes in form and 
detail may be made therein without departing from the spirit and scope of 
the invention as defined in the appended claims.