Fence positioning apparatus

An apparatus for positioning a workpiece guiding fence relative to a rotary cutter projecting through the top surface of a work table, comprising a plurality of major components, primarily formed by aluminum extrusions, including a base element securable to the work table surface and having upstanding guiding ribs, an elongated hollow carriage slidably mounted on said ribs and defining a partially cylindrical elongated recess mounting an elongated lead screw. A fence is secured to one end of the carriage. A threaded segment is mounted on a force transmitting element which is moved laterally to engage the threaded segment with the lead screw by a pivoted camming lever having three positions. In the first position, the threaded segment is disengaged from the lead screw, permitting unrestricted longitudinal movement of the carriage relative to the base. In the second position, the threaded segment is engaged with the lead screw, permitting only incremental longitudinal movement of the carriage by rotation of the lead screw. In the third position, the threaded segment remains engaged with the lead screw and the force transmitting element exerts a clamping force on one of the supporting ribs on the base plate to lock the carriage against all movement during the cutting operation.

FIELD OF THE INVENTION 
This invention relates generally to an apparatus for accurately and 
repeatably positioning a workpiece relative to a rotary cutter projecting 
upwardly through a horizontal work bed. More specifically this invention 
constitutes improvements to the workpiece positioning and guiding 
apparatus disclosed in my prior U.S. Pat. No. 5,215,296, the disclosure of 
which is incorporated herein by reference. 
BACKGROUND OF THE INVENTION 
In my aforementioned U.S. Pat. No. 5,215,296, there is disclosed a 
positioning apparatus for a fence or guide which supports a workpiece for 
movement relative to a rotating cutter that projects upwardly through a 
horizontal work bed. Such apparatus achieved an accuracy of movement on 
the order of one 1/1000 (0.001) of an inch, but required a plurality of 
machined metal components together with six rollers secured to the inner 
walls of a positioning carriage and a pair of nylon rods mounted on a base 
element for mounting such positioning carriage on the base element for 
movement parallel to the work bed. A fine pitched, elongated, manually 
rotatable lead screw was mounted in the carriage to provide micrometer 
movement of the carriage, but such lead screw was rotatably supported in 
the carriage only by two small ball bearings respectively engaging the 
ends of the lead screw and held in position solely by a small spring 
imparting an axial force to one of the balls. Since the micrometer 
movement of the positioning carriage results from manually moving a 
threaded segment into radial engagement with the lead screw, there were 
ample opportunities for the lead screw to be laterally shifted or 
elastically bent by such applied force, thus resulting in a slight error 
in the longitudinal positioning of the carriage. 
Additionally, two separate manually operable devices were required to 
respectively effect engagement of the lead screw by the threaded segment 
and the clamping of the positioning carriage in the finally selected 
longitudinal position for guiding a workpiece into a desired engagement 
with the rotary cutter. 
Those skilled in the art of machine cutting of wood workpieces often have 
to align the center of the workpiece with the cutting axis. For example, 
in the forming of wooden boxes having interlocked pins and tails at each 
of the corners it is recognized that symmetrical placement of such pins 
and tails can only be accomplished by first positioning the workpiece with 
its center axis accurately aligned with the axis of the rotary cutter. 
Prior to this invention, such alignment could only be achieved by manual 
measurements followed by a plurality of trial cuts. 
SUMMARY OF THE INVENTION 
Accordingly, it is the object of this invention to provide an improved 
construction of a workpiece positioning apparatus that is more accurate 
and reliable than prior art designs, and, at the same time, is 
manufacturable with a substantially reduced cost. 
The two major components of a fence positioning apparatus embodying this 
invention constitute an elongated, generally planar base plate and an 
elongated, generally rectangular cross-section, hollow carriage, which is 
slidably mounted on the base plate for longitudinal movement. 
The base plate is provided with screw holes for fixedly securing the base 
plate to the work bed with the length axis of the base plate generally 
aligned with a power driven rotary cutter which projects upwardly through 
the work bed. The base plate is provided on its top surface with a pair of 
longitudinally extending, integral, upstanding primary guide ribs, both of 
which define a downwardly facing surface overlying the top surface of the 
base plate. Additionally, a secondary integral elongated rib is provided 
on the top surface of the base plate outside of and parallel to the 
primary guide ribs. The secondary rib is provided for lateral adjustment 
of the carriage relative to the base plate and for mounting an upstanding 
spring plate, as will be described. 
An adjusting or clamping bar is provided which lies parallel and adjacent 
to a primary rib and has an inclined surface which can cooperate with a 
similarly inclined surface on the carriage to clamp the carriage against 
longitudinal movement relative to the base plate. 
The hollow carriage defines a bottom element, two laterally spaced 
upstanding side walls and a slightly inclined top wall connecting the 
sidewalls. On each longitudinal edge of the bottom wall, an integral 
longitudinal mounting rib is provided on said carriage which is 
operatively connectable with a respective one of the downwardly facing rib 
surfaces provided on the base plate. To effect lateral adjustment of the 
position of the carriage, an elongated adjusting bar of generally U-shaped 
cross section has one flange mounted under the downwardly facing surface 
of the base plate guide rib that is adjacent to the secondary rib on the 
base plate, and the other flange defines an angular downwardly facing 
surface which cooperates with the adjacent mounting rib on the carriage. 
Transversely disposed screws are threaded through the secondary rib to 
engage the adjusting bar, thus providing lateral adjustment of the 
carriage relative to the base plate to effect smooth longitudinal 
movements of the carriage relative to said base plate. The adjusting bar 
is also utilized to securely clamp the carriage to the base plate during 
the cutting operation, as will be described. 
An end plate is provided on one end of the carriage adjacent to said rotary 
cutter, and a conventional fence, similar to that disclosed in my prior 
U.S. Pat. No. 5,553,644, is secured to said one end plate in perpendicular 
relation to the carriage. As described in said patent, a workpiece is 
moved along such fence in abutting relation thereto to engage the rotary 
cutter. 
A plurality of parallel tracks are formed in the top surface of the 
carriage to permit printed tapes to be respectively mounted in said 
tracks. A transparent bar carrying a fine line cursor is mounted in 
transverse, overlying relationship to all of said tracks by two vertical 
posts secured to opposite sides of the base plate. 
Lastly, a third longitudinally extending rib is integrally formed on the 
top portion of one side wall of the carriage. Said third rib defines an 
elongated semi-cylindrical recess, preferably a few degrees greater than 
180 degrees in circumference, which provides a supportive rotatable 
mounting for an elongated finely threaded micrometer rod or lead screw. 
An adjusting knob is secured to one end of the lead screw to permit 
convenient manual angular shifting of the lead screw. A cooperating 
ratchet permits slight angular movements of the adjusting knob to be 
readily accomplished. The amount of angular shift of the lead screw is 
shown by printed indicia provided on a cylinder mounted on the threaded 
lead screw adjacent to the adjusting knob. Similar adjusting and indicia 
elements are disclosed in my aforementioned U.S. Pat. No. 5,215,296. 
To translate the minute angular adjustments of the lead screw into still 
smaller incremental longitudinal movements of the micrometer rod, a 
threaded segment is mounted on the free end of an upstanding leaf spring 
plate, which biases the threaded segment toward engagement with the lead 
screw. As mentioned, the spring plate has its bottom end secured to said 
secondary rib. 
A manually operable operating lever mechanism is provided, which is mounted 
on the base plate. Such lever is selectably positionable in three 
angularly spaced pivot positions. In the first position, the threaded 
segment is disengaged from the threaded lead screw against the bias of the 
spring plate. In the second position, the threaded segment is engaged with 
the threaded lead screw, thus rotation of the adjusting knob will produce 
a desired longitudinal movement of the carriage relative to the base 
plate, hence relative to the rotary cutter. In the third position of the 
lever mechanism, a cam surface is moved transversely on a force 
transmitting plate to shift the adjusting bar into clamping relation with 
the carriage, thus anchoring the carriage against any movement relative to 
the base plate, which is highly desirable during the cutting operation. 
Thus a single lever mechanism performs the functions of two separate 
elements employed in my aforementioned U.S. Pat. No. 5,215,296 and effects 
a further reduction in manufacturing cost. 
The preferred apparatus for mounting the three-position operating lever 
comprises a U-shaped mounting bracket firmly mounted to the base plate 
with screws and having a pair of upstanding lateral flanges. Each 
upstanding flange has two laterally spaced, transversely elongated holes 
respectively, an inner elongated hole and an outer elongated hole, with 
the inner and outer elongated holes being respectively aligned from flange 
to flange. The inner pair of elongated holes mounts a cylindrical pivot 
pin that runs through an elongated, longitudinal, semi-cylindrical recess 
integrally formed in the operating lever and thus defines a laterally 
shiftable axis of rotation of the operating lever. The outer pair of 
elongated holes is for mounting a pin which mounts cylindrical rollers 
which cooperate with two integrally formed cam surfaces on the operating 
lever, as described below. 
The operating lever comprises a generally planar, upper grasping portion 
which is integrally formed with two spaced, lower curved portions. The 
first curved portion defines a partial cylindrical recess which is 
traversed by the pivot pin mounted in the inner pair of elongated holes in 
the vertical flange portions of the mounting bracket. The first curved 
portion also defines a cam surface which cooperates with the cylindrical 
rollers. The second curved portion defines a second cam surface which 
cooperates with the previously mentioned cylindrical rollers. Such cam 
surfaces position the operating lever in each of its aforementioned three 
pivotal positions, thus effecting the aforementioned movements of the 
threaded segment into engagement with the lead screw and moving a force 
plate (described below) into clamping engagement with the adjusting bar. 
A means for applying the clamping force to the carriage is provided by a 
generally rectangular and upstanding force plate located between the 
adjusting bar and the secondary rib. The force plate has a longitudinal, 
partial cylindrical recess and a central vertical slot substantially 
perpendicular to and traversing the recess. The top edge of the force 
plate is connected to the top edge of the upstanding spring plate that 
also has a vertical slot. Thus the threaded segment is also secured to the 
force plate. 
The force plate is connected to the operating lever by a transversely 
oriented link having two ends, with a hole in each end. The first end of 
the link passes through the vertical slot of the spring plate and into the 
vertical slot of the force plate, with the hole in the first end of the 
link concentrically aligned with the semi-cylindrical recess of the force 
plate. The link is pivotally secured to the force plate by a force plate 
pin running through the partial cylindrical recess of the force plate and 
the hole in the first end of the linkage. Similarly, the second end of the 
link runs through a slot in the operating lever and is pivotally mounted 
to such lever by the pivot pin running through the partial-cylindrical 
recess in the operating lever and traversing the hole in a second end of 
the link. 
In the first lever position, the previously mentioned threaded segment, 
which is mounted on the force plate is disengaged from the lead screw and 
the force plate is disengaged from the adjusting bar under the bias of the 
spring plate such that the carriage may freely slide longitudinally with 
respect to the base plate. In the second lever position, the spring plate 
moves the threaded segment into engagement with the lead screw, but the 
force plate is still disengaged from the adjusting bar so that the 
longitudinal position of the carriage relative to the base plate may be 
finely adjusted by rotation of the lead screw. In the third lever 
position, the threaded segment remains engaged with the lead screw and the 
force plate is engaged with, and imparts a lateral clamping force on, the 
adjusting bar, which in turn transmits the clamping force to the adjacent 
one of the longitudinally extending ribs on the bottom wall of the 
carriage to lock the carriage to the base plate to facilitate cutting 
operations. 
As mentioned above, it is highly desirable that a workpiece positioning 
apparatus be capable of locating the center of the workpiece in precise 
alignment with the axis of the rotary cutter to produce, for example, 
accurate centering spacing of pins and tails cut on the opposed edges of 
two workpieces to form a box corner. In accordance with this invention, 
the required positioning of the carriage is accomplished with the aid of a 
looped cord which is mounted on the exterior of the hollow carriage by 
being trained over two pulleys respectively journalled on pins pressed 
into opposite ends of the carriage. The two ends of the cord are connected 
to the mounting bracket of the manually operable lever mechanism. One of 
such connections includes a tension spring. The top flight of the looped 
cord lies in one of the longitudinal tracks formed in the top surface of 
the carriage and passes under the aforementioned transparent bar carrying 
a fine line cursor. 
A pointer is frictionally secured to the top flight of the cord loop, which 
pointer is called in our trade, the "rabbit". With the aforedescribed 
construction, the rabbit is moved by the carriage, but the rabbit covers 
twice the distance traveled by the carriage. With this apparatus, the 
center of the rotary cutter may be precisely aligned with the center of 
the workpiece by manual movements of the rabbit relative to a dimensional 
scale inserted in another of said tracks which has printed indicia 
corresponding to the diameter or width range of rotary cutters that will 
be used. The manual method for achieving such alignment will be described 
in detail in the subsequent Detailed Description of the Invention. 
An outstanding advantage of this invention is that five major components of 
the fence positioning apparatus, namely the base plate, the carriage, the 
adjusting bar the operating lever, and the force plate may be formed of 
aluminum or a rigid plastic by an extrusion process, thus eliminating all 
machining operations ordinarily required to produce the various ribs, 
slots and bolt receiving recesses heretofore described, except to cut the 
extrusion to the desired length, and cut slots or thread a few holes, thus 
effecting a substantial reduction in manufacturing cost. 
Further objects and advantages of the invention will be readily apparent to 
those skilled in the art from the following detailed description, taken in 
conjunction with the annexed sheets of drawings showing a preferred 
embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to the drawings there is shown a fence positioning apparatus 1 
embodying this invention. Apparatus 1 comprises a horizontal base plate 10 
of rectangular configuration and having vertical holes 10a for reception 
of screws or bolts 10c (FIG. 1A) for securing the base plate 10 to the top 
surface 2a of a work table 2. A rotary cutting tool 3 driven by a suitable 
motor (not shown) projects upwardly through top surface 2a of table 2 and 
the base plate 10 is secured to the work table 2 with its longitudinal 
axis aligned with and intersecting the rotary axis of cutting tool 2. 
A fence carrying carriage 20 is provided comprising an elongated hollow 
element formed by extrusion of a suitable metal or rigid plastic. Carriage 
20 has a generally rectangular cross-sectional configuration defined by a 
bottom wall 20a, two upstanding side walls 20b and 20c and a slightly 
inclined top wall 20d connecting the top portions of side walls 20a and 
20b (FIG. 2A). All of said walls are integrally formed by a conventional 
extrusion process. 
As best shown in FIG. 2A, the top surface 10b of base plate 10 is formed 
with three integral upstanding parallel ribs 11a, 11b and 11c which are 
parallel to the length axis of base plate 10. Rib 11a projects upwardly 
from the top surface 10b of base plate 10 at an angle, thus defining a 
downwardly facing inclined surface 11d. The adjacent rib 11b is of angular 
cross-section and thus defines a downwardly facing surface 11e. The third 
rib 11c is close to rib 11b and is vertical. 
The left hand edge of side wall 20b of carriage 20 has an integral side 
projection 20e which surrounds the upper portion of base plate rib 11a. 
The left hand edge of bottom wall 20a has an integral projection 20f that 
slidably cooperates with downwardly facing inclined surface 11d of rib 
11a. The bottom surface 20g of projection 20f slides on the top surface 
10b of base plate 10. The right hand edge of carriage bottom wall 20a is 
horizontal and slides on the top surface of base plate rib 11b. 
To secure carriage 20 to base plate 10 for smooth longitudinal sliding 
movements, an elongated adjusting and clamping bar 22 is provided having a 
horizontal projection 22a which fits beneath the downwardly facing surface 
11e of the base plate rib 11b, and a downwardly facing inclined side 
surface 22b that overlies a similarly inclined surface portion 20u formed 
on the right hand side wall 20c of carriage 20. A pair of longitudinally 
spaced bolts ilk, shown in FIG. 7, traverse rib 11c of plate 10 and 
contact clamping bar 22 to adjust its lateral position relative to rib 
11b. Thus, carriage 20 is secured to base plate 10, but is freely 
longitudinally slidable relative to the base plate 10, hence can be 
smoothly moved toward or away from the axis of cutting tool 3. 
A first end plate 23a (FIG. 1) is secured by bolts (not shown) in 
transverse relationship to the end of carriage 20 that is adjacent the 
cutting tool 3. A conventional workpiece supporting fence 24 (FIG. 1A), 
similar to that shown in the above referred to U.S. Pat. No. 5,553,644, is 
then secured to end plate 23a, hence is disposed in perpendicular 
relationship to the length axis of carriage 20. Such fence is then movable 
to a selected position relative to the cutting tool 3 by movement of 
carriage 20 relative to base plate 10. 
A second end plate 23b is secured by bolts (not shown), to the other end of 
carriage 20 for a purpose to be described. To facilitate the provision of 
bolt holes for mounting the end plates 23a and 23b, the carriage 20 is 
formed with integral projections defining partial cylindrical recesses 25 
(FIG. 2A) extending the length of carriage 20 which are only threaded at 
their ends. 
The carriage 20 is further provided with an integral lateral projection 20h 
adjacent the junction of the right hand side wall 20c and top wall 20d 
which defines an elongated partial cylindrical recess 20j for supporting a 
finely threaded lead screw 26. The partial circular recess 20j has a 
peripheral extent of more than 180.degree., so that the lead screw 26 can 
only be inserted in such recess by axial movement and is secured in the 
recess between the two end plates 23a and 23b, as will be described. 
A bearing ball 26a (FIG. 3) is provided at the end of lead screw 26. A 
threaded ball socket 23c permits adjustment of the axial force on the lead 
screw 26 to support the lead screw 26 between the respective end plate 23a 
and 23b. A metal clip 26g is inserted in each end of partial cylindrical 
recess 20j to impart a light bias of lead screw 26 against the inner wall 
of recess 20j. 
Manual rotation of lead screw 26 is conveniently accomplished by an 
enlarged knob 26b secured to one end of lead screw 26. Knob 26b has 
peripherally spaced ratchet teeth 26c formed thereon and a spring detent 
26d (FIG. 3) cooperates therewith to permit small incremental rotational 
movements of lead screw 26 which result in even smaller longitudinal 
movements (as low as 0.001 inches) of the carriage 20 toward and away from 
the rotary cutting tool. A portion of knob 26b projects through a cut out 
20k transversely cut through top wall 20d and projection 20h. If desired, 
a conventional thrust washer 26f may be inserted between knob 26b and the 
wall of the cutout 20k in carriage 20. 
Manual rotation of lead screw 26 is converted into small increments of 
axial movement of the carriage 20 relative to the base plate 10, hence, 
toward and away from the rotary cutting tool 3, by a threaded segment 26s 
(FIG. 2A) which is adjustably mounted on the base plate 10 by an actuating 
mechanism 30 to be described, which effects the radial movement of 
threaded segment 26s from a position of non-engagement with the lead screw 
26 (FIG. 2A) to a position of engagement with the threads of the lead 
screw 26 (FIGS. 2B and 2C). 
The carriage 20 is further provided with a plurality of parallel, 
longitudinally extending T-slots 20m, 20n, 20o, 20p, and 20q in its top 
surface 20d. Such slots are employed for mounting elongated plastic strips 
28 (FIG. 1) carrying printing of dimensions or cutting positions of the 
carriage 20 relative to the rotary cutting tool 3, as will be described. A 
dovetailed slot 20r is formed in a lateral projection 20t formed as an 
extension of carriage top wall 20d. This slot slidably mounts an indicator 
40 as will be described. 
To effect a measured longitudinal displacement of the carriage 20, an 
annular scale 26e is wrapped around the end of lead screw 26. The 
dimensions of scale 26e may be either degrees of rotation or thousandths 
of an inch displacements of carriage 20. 
An accurate selection of movement of carriage 20 relative to the base plate 
10 may also be obtained by the cooperation of a sighting line 12a on a 
transverse transparent sighting bar 12 with dimensions or carriage 
position indicia provided on the elongated strips 28. Sighting bar 12 is 
mounted at its opposite ends on upstanding pedestals 13a and 13b. Pedestal 
13a is secured to one side of base plate 10 by suitable bolts 13c. 
Pedestal 13b can be an extension of bracket flange 27c, as will be 
described. Preferably, sighting line 12a comprises two vertically aligned 
lines respectively provided on the top and bottom surfaces of sighting bar 
12. 
As previously mentioned, the threaded segment 26s is engaged with the lead 
screw 26 when the operating lever 31 of the actuating mechanism 30 is in 
the two lowered positions shown in FIGS. 2B and 2C. The threaded segment 
26s is disengaged from the lead screw 26 when the control lever 31 is in 
its uppermost position. The carriage 20 is then freed for longitudinal 
sliding movement relative to the base plate 10. 
The preferred apparatus 30 for mounting the three position control lever 31 
comprises a generally U-shaped mounting bracket (FIG. 7) having a base 
portion 30a and upstanding, longitudinally spaced vertical flange portions 
30b and 30c. If desired, flange portion 30c may be extended upwardly to 
form the pedestal 27c. Base portion 30a is secured to base plate 10 by 
suitable screws 30d. Each upstanding flange 30b and 30c is provided with 
two laterally spaced holes, respectively, an inner hole 30e and an outer 
hole 30f, with said holes being respectively longitudinally aligned and 
transversely elongated. 
The operating lever 31 has a planar, upper grasping portion 31a and two 
integrally formed, vertically spaced curved lower portions 31b and 31c 
(FIG. 6A). The upper curved portion 31b, which is approximately 
perpendicular to portion 31a, defines a partial cylindrical, longitudinal 
recess 31d which snugly surrounds a pivot pin 30g which is mounted in 
elongated inner holes 30e of bracket 30a. The outer holes 30f mount a pin 
30h (FIG. 7) which rotatably mounts two rollers 30j which are engaged by a 
first cam surface 31g formed on the outer curved lower portion 31c of 
operating lever 31, or by a second cam surface 31k formed on the inner 
curved portion 31b. In the upper or disengaged position of the operating 
lever 31 as shown in FIG. 2A, the arcuate surface 31v (FIG. 9), at the 
merger of first and second cam surface 31g and 31k, is in the contact with 
rollers 30j thus limiting the upward movement of the operating lever 31. 
As best shown in FIG. 9 the two cam surfaces are formed as several 
connected, variously radiused curved, and flat surfaces. The cusp 31r, at 
the juncture of surfaces 31v and 31m, provides the slope reversal required 
to detent the lever 31 in the upper position. Likewise, the cusp 31s at 
the juncture of surfaces 31n and 31t provides detent action in the lowered 
position shown in FIG. 2C. Intermediate flat surfaces 31p and 31q 
cooperate to minimize free play in the middle position shown in FIG. 2B. 
The threaded segment 26s is rigidly secured by suitable bolts 26c to the 
upper portion of a force plate 33 which has a curved medial portion 33a 
(FIG. 8) and a vertical portion 33e positioned adjacent the latching bar 
22. An actuating link 38 has one end pivotally secured to the center of a 
pivot pin 30g by passing through a slot 31h (FIG. 6A) in the upper curved 
portion 31b of the operating lever 31. The other end of link 38 is 
pivotally secured to the center of a pin 33b which longitudinally 
traverses a partial cylindrical recess 33c provided in the lower portion 
33a of the force plate 33 (FIG. 8). A slot 33d in the center of the lower 
portion 33a of the force plate 33 permits such connection to be made. 
For a purpose to be later described, a transversely inward spring bias on 
both ends of pin 30h is desirable. Such spring bias is applied by a pair 
of angularly shaped brackets 35 having two flanges. Each bracket 35 has 
one flange secured to a respective end of pin 30h by a spring clip 35d and 
the second flanges are respectively secured in abutting relation to rib 
11c by bolts 35a which respectively traverse the second bracket flanges 
and are threadably engaged with rib 11c. The spring bias is applied by two 
compression springs 35b which respectively surround bolts 35a and are 
compressed between the bolt heads and the adjacent surface of the second 
flanges of brackets 35. 
The force plate 33 is supported by a generally vertical spring plate 34 
which has its lower edge portions secured to rib 11c by a pair of bolts 
34a (FIG. 7) traversing plate 34. Spring plate 34 thus opposes outward 
transverse movement of force plate 33 and, if not acted upon by other 
elements, biases threaded segment 26s into intimate engagement with the 
lead screw 26 as shown in FIG. 6B. In this middle position, the pin 30h is 
held against the inner end of elongated holes 30f by the right angle 
brackets 35 acted upon by springs 35b (FIG. 7), and the pin 30g is in a 
static location dictated by the stationary force plate 33 and the link 38. 
The handle 31 therefore seeks a relaxed position where the rollers 30j 
float in the transitional regions 31p and 31q between the first and second 
cam surfaces (FIGS. 6B and 9). In this state, carriage 20 is movable only 
by rotation of the knob 26b on lead screw 26. 
Whenever the handle 31 is moved to the upright position (FIG. 6A) from the 
neutral position (FIG. 6B), the decreasing radius portion of the first cam 
surface 31g works with the rollers 30j, rotating on pin 30h, to pull the 
threaded segment 26s away from the lead screw 26. Since the pin 30h is 
initially forced against the inner end of elongated holes 30f by the right 
angle brackets 35 acted upon by springs 35b, the entire handle is 
translated away from the lead screw as it is rotated to the upright 
position. Once the roller has passed the cusp 31r (FIG. 9), the prevailing 
restoring force of the resilient plate causes the roller to seek contact 
with, and stop against, surface 31v. During the above motion, a small 
protruding ridge 33f along the lower edge of the force plate 33, in 
contact with the rib 11c, provides a fulcrum for the force plate, as a 3rd 
class lever, to multiply the translational movement, of the handle, and 
consequently the link, resulting in generous clearance between the 
threaded segment and the lead screw. 
Downward pivotal motion of control lever 31 from the middle or neutral 
position (FIG. 2B) to the position illustrated in FIG. 2C, serves to clamp 
and lock the carriage against any movement relative to the base plate 10, 
which is highly beneficial during the cutting operation. As the motion 
begins, a curved cam surface 31n (FIG. 9) with increasing radius relative 
to the axis of pin 30g, works with rollers 30j to cause link 38 to move 
force plate 33 inward toward the adjusting bar 22. When all clearance has 
been removed between relevant surfaces of the carriage 20, base plate 10, 
adjusting bar 22, and the lower end of force plate 33, further translation 
of pivot pin 30g is halted. Because the rollers have traversed only about 
one half the rise in cam surface 31n at this point, further motion forces 
the pin 30h to move outward within the elongated slots 30f thereby 
carrying the angle brackets 35 along and compressing springs 35b against 
retaining nuts 35a. When the cusp 31s passes the rollers 30j, a torque is 
developed on the handle that assists its downward motion until arrested by 
contact between a handle extension 31u and the horizontal base 30a of the 
U-shaped mounting bracket. As can be seen in FIG. 2C, the total clamping 
force applied to the force plate 33, by means of link 38 and pin 33b, is 
divided between the threaded segment 26s engagement of the lead screw and 
the adjusting bar 22 with the greater portion, by ratio of the distances, 
applied to the adjusting bar 22. 
The aforementioned spring moderated over-travel provides predictable 
clamp-up forces in spite of the common production variability in 
thickness, parallelism, and twist inherent in the extrusion process and 
resulting components. 
The operation of the fence positioning device described is conventional 
except for one unique feature of Applicants' invention. Referring to FIG. 
5, there is shown a plastic centering tape 28a mounted in the T slot 20q. 
Adjacent to T slot 20q is a dovetailed longitudinal slot 20r. An indicator 
40, called by us a rabbit, is slidably mounted in slot 20r. Rabbit 40 is 
in turn secured to a cord 41 which has its opposite ends secured by one or 
two springs 41a to opposite ends of the mounting bracket 30a. Cord 41 
forms a tight loop extending the full length of carriage 20 by being 
trained around two pulleys 42 respectively mounted on inwardly projecting 
pins 42a mounted on the side wall 20d of carriage 20 FIG. 3). Thus sliding 
movement of rabbit 40 produces movement of carriage 20 in the same 
direction, but only for one half of the movement of the rabbit 40. 
The plastic tape 28a carries indicia corresponding to the range of 
diameters of cutters 3 to be employed. A very difficult wood cutting 
operation is the symmetrical cutting of interlocking pins and tails on two 
wood pieces to form a corner. To achieve this, the fence must be 
accurately located relative to the axis of the rotating cutter 3 so that 
the exact center line of the workpiece passes through the cutter axis. 
With the apparatus of this invention, such requirement is readily 
accomplished. The longitudinal position of carriage 20 is adjusted so that 
the workpiece supporting surface of the fence 24 is just touching the 
cutter diameter. The special centering tape 28a is then moved in its 
supporting slot so that the cutter diameter indicia line on the tape 28a 
is aligned with the sighting line 12a of cursor 12. The fence 24 is 
withdrawn from the cutter by sliding movement of the carriage 20. The 
workpiece is then inserted between the fence 24 and the cutter 3 where it 
makes light contact with both. Without further movement of the carriage 
20, the rabbit pointer 40 is then moved, by sliding along its cable, into 
alignment with the zero on the centering tape, which is marked by a carrot 
symbol. The workpiece is then withdrawn and the carriage 20 is moved 
toward the cutter until the rabbit pointer indicia is directly under the 
cursor line 12a. This last action moves the carriage, hence the fence, 
toward the cutter a distance of one half the workpiece width due to the 
two-to-one ratio of rabbit movement to carriage movement. Thus, the 
centerline of the workpiece, when placed against the fence, is exactly 
aligned with the axis of the rotary cutter without requiring a single 
measurement. 
If the alignment of the rabbit with the cursor is not exact, the fence can 
be moved, in 0.001 inch increments, by shifting the operating lever 31 to 
its middle position and then rotating the knob 26b on the lead screw 26. 
The fence is then locked in that position by pivoting the operating or 
control lever 31 downwardly to assume the carriage locking position shown 
in FIG. 2C. 
A conventional cutting tape may then be inserted in one of the T-slots on 
the top surface 20d of carriage 20 and utilized to successively position 
the carriage 20 to accurately cut the desired pins and tails on the 
workpiece. 
Obvious modifications of this invention will occur to those skilled in the 
art and all such modifications are deemed to fall within the scope of the 
annexed claims.