UNDERPINNER MACHINE BACKGROUND OF THE INVENTION Moulding pieces for constructing frames, for paintings, photographs, and the like, are joined in various ways to form miter joints. One technique that is currently in widespread use utilizes a fastener, often in the form of a generally V-shaped nail, which is driven directly into the component frame pieces from the back and in a spanning or straddling relationship to the joint. A variety of such underpinning machines are commer- cially available and are disclosed in the prior art, which is typified by the following patent publications: U.S. No.

2,900,638, U.S. No. 4,436,234, U.S. No. 4,436,234, U.S. No.

4,572,420, U.S. No. 4,574,452, U.S. No. 4,817,965, U.S. No.

4,830,257, U.S. No. 5,390,842, EP 0 062 012 A2, EP 0 324 666 Al and EP 0 551 181 Al.

The underpinning machines of the prior art normally utilize a clamping arrangement for holding the workpieces in position.

Due to the character and magnitude of the driving force utilized, which is currently either manually or pneumatically generated, a high level of counteracting force is generally necessary to maintain the frame pieces in position, often being so great as to cause marring or other damage. Moreover, presently available underpinner machines do not provide optimal means for varying the position of the driving head relative to the secured frame pieces, as is necessary to accommodate frame pieces of different widths as well as to enable fasteners to be placed at two or more locations along a single joint, and the current machines tend to be unduly complex, excessively expensive, and somewhat inconvenient to operate.

SUMMARY OF THE INVENTION Accordingly, it is a broad object of the present invention to provide a novel underpinner machine in which reduced levels of clamping force are required for holding the workpieces in position during the fastening operation.

It is also a broad object of the invention is to provide a novel underpinner machine in which variation of the position of the driving head relative to supported frame pieces, is easily and conveniently achieved.

Other objects of the invention are to provide an under- pinner machine having the foregoing features and advantages which is, in addition, relatively incomplex and inexpensive to manu- facture, and facile and convenient to operate.

It has now been found that certain of the foregoing and related objects of the invention are readily attained by the provision of an underpinner machine comprising: a base having an overlying planar support surface; means for positioning a pair of workpiece members on the support surface in mutually abutted relationship, to form a miter joint; means for clamping the workpiece members in position; means for delivering fasteners to a drive location, beneath the workpiece support; a drive mechanism; an actuator; and means for controlling operation of the actuator. The drive mechanism includes a hammer having a head for driving engagement with the fasteners, and at least one mechanical spring disposed to act on and propel the hammer, the hammer head being disposed to intercept and engage a fastener and to drive it therebeyond. Functioning under the control means, the actuator is operatively engagable with the hammer for with- drawing the hammer head away from the drive location against the force of the springs employed, and is releasable from the hammer to permit the drive spring to propel it in the manner described.

In preferred embodiments the spring of the drive mechanism will be capable of delivering a force of at least about 45, and preferably 50 pounds per inch of deflection, and the arrangement will be such that deflection of at least about 2.5 inches (inclu- sive of any preloading) will occur at the point the hammer is released by the actuator. Most desirably, the spring will be of generally flat, rectangular cross section, and fabricated from a chrome/vanadium steel alloy. The clamp means will normally comprise a contact member, mounting structure that is movable toward and away from the support structure and that supports

the contact member thereover, and at least one coil spring that acts on the mounting structure to bias the contact member away from the support structure.

Certain objects of the invention are attained by the pro- vision of an impacter module comprised of the delivery means, the drive mechanism, and the actuator of the machine, all as- sembled within a common housing. In such instances, the machine will also include means for mounting the impacter module for movement along a path to selected positions, relative to the means for positioning. The machine will advantageously include locating means for disposing the impacter module at a multiplicity of selected positions. Such locating means will preferably com- prise cooperating locator components on the base and on the imp- acter module, the locator components begin interengagable in a multiplicity of relationships in which the spacing varies be- tween the impacter module and the locator component on the base.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a fragmentary perspective view of an under- pinner machine embodying the present invention, showing a pair of frame pieces positioned thereon for fastening at a miter joint; Figure 2 is a plan view of the machine of Figure 1; Figure 3 is a fragmentary front elevational view of the machine; Figure 4 is a fragmentary side elevation of the machine, with portions broken away to expose internal features; Figure 5 is a perspective view of the impacter module of the machine of the foregoing Figures, drawn to an enlarged scale and showing a magazine of fasteners in position for insertion into the housing of the module; Figure 6 is a fragmentary plan view showing the fastener discharge location of the impacter module depicted in Figure 5, drawn to a further enlarged scale; Figure 7 is a perspective view of a V-nail fastener adapted for being driven by the instant machine, drawn to a greatly enlarged scale;

Figure 8A is a fragmentary side elevation of the impacter module assembled with other components of the machine, the module being shown in section to expose its internal features, and being drawn to a scale enlarged from that of Figure 5; Figure 8B is a cross sectional view of a generally flat, rectangular spring, drawn to a greatly enlarged scale, which is suitable for driving the hammer in the preferred embodiments of the machine; Figure 9 is a fragmentary plan view of a forward portion of the machine, depicting components of the impacter module positioning arrangement; Figure 10 is a fragmentary elevational view, showing the arrangement depicted in Figure 9; Figure 11 is a fragmentary perspective view showing compo- nents of the arrangement depicted in Figures 9 and 10, drawn to a further enlarged scale; Figure 12A is a fragmentary perspective view showing one of the fence members used for positioning frame pieces in the machine, associated adjustment elements being depicted in exploded relationship; Figure 12B is a fragmentary plan view, in partial section, drawn to an enlarged scale and showing the adjustment elements and fence member in assembly; and Figure 13 is a fragmentary elevational of a machine similar to that of the foregoing Figures, but in which a pneumatic actua- tion and clamping system is substituted for the mechanical system illustrated therein.

DETAILED DESCRIPTION OF THE PREFERRED AND ILLUSTRATED EMBODIMENTS Turning first to Figures 1 through 12 of the appended draw- ings, therein illustrated is a mechanically actuated underpinner machine embodying the present invention. The machine comprises a base or stand, generally designated by the numeral 10, which is attached a removable table, generally designated by the numeral 12. The table is formed to have an elevated platform, generally designated by the numeral 14, which is partially divided by a central slot 16 into two lateral portions 18, disposed in a right-

angular relationship to one another. Elongate fence members 20 are mounted along the rear margins of the platform portions 18, and are also disposed in a right-angular mutual relationship.

As can be seen, the fence members 20 serve to support two frame pieces "F," the adjacent end portions of which are cut to form a miter joint and are abutted against one another.

Each fence member 20 is pivotably attached to the underlying platform portion 18 by a screw 22, which passes through one of two apertures 36, 36', adjacent the inner end of the member 20, into engagement in an underlying threaded hole (not visible).

In the configuration illustrated, the fence member 20 disposed to the operator's right (i.e., at the top, in Figure 1) is at- tached by engaging the screw 22 in the aperture 36', which is closest to the end, whereas the member to the operators left is attached through the more inward aperture 36. The resultant overlap and spacing of the members 20 (see especially Figure 2) facilitates alignment of frame pieces to sharp corners despite imprecision in their miter cuts. By placing the mounting screws 22 in the endmost apertures 36' of both members 20, however, they can be pivoted to form angles other than 900 without interfer- ing with one another, thus enabling the assembly of "multisided" frames (typically having 5, 6 or 8 sides); use of the endmost apertures 36' in the 900 mode may also be preferred by some operators, to provide a gap for viewing of the miter joint.

Angle markings (not shown) will desirably be provided on the underlying platform surface for that purpose, to serve as guides for placing the frame pieces in proper orientations for any given frame configuration.

The opposite end of each fence member 20 is secured by an eccentric adjustment assembly, generally designated by the numeral 24 and illustrated in detail in Figures 12A and 12B. More particularly, the eccentric assembly 24 comprises a rotor having an upper cylinder portion 26 and a lower cylinder portion 28, the lower cylinder portion 28 having its axis eccentrically dis- posed relative to the axis of upper cylinder portion 26. The lower cylinder portion 28 of the rotor is seated in a short oblong slot 30 formed through the outer end portion of the fence member

20, and a clamping screw 32 extends through the bore 27 and into engagement in the threaded hole 34 formed in the underlying stage portion 18; the bore 27 lies on the axis of the upper cylinder portion 26. A flange element 38 circumscribes the base of the upper cylinder portion 26, where it joins the lower portion 28, and has a small pointer mark 40 embossed into its surface. As will be appreciated, turning the rotor (for the facilitation of which the surface of the upper portion may be serrated or otherwise roughened) will cause the associated fence member 20 to pivot slightly about the screw 22, thereby enabling limited adjustment of its angular relationship to the other member 20, and thus permitting firm back-up support of frame pieces that are slightly out-of-square (due, for example, to imprecise cutting of the end bevels, warpage, etc.). The pointer mark 40 cooperates with the reference mark 42 on the fence member 20 to indicate the positions at which an exact 90-degree relationship would exist between the two members 20.

The same eccentric assembly 24 can be engaged, in the manner described, within each of the longer oblong slots 31 formed in the fence members 20, to thereby enable fine-tuning adjustment of orientation when the fence members are configured for multisid- ed frame construction, as mentioned above. A series of threaded apertures 33 (only one of which is visible) are provided in the underlying platform surface to engage the clamping screw 32 for establishing the gross angular relationships for the several configurations for which the machine is adapted.

It will be noted that the back face of each fence member 20 is curved, rather than being flat like the front face. By rotating the fence member 1800 about their longitudinal axes, the curved surfaces can be employed to make line contact with an outer surface of a frame piece that is not uniform or that is not adequately square with the back surface (which rests on the platform portion 18).

The mechanism for holding the frame pieces in position against the fence members 20, and against the force of the un- derlying hammer that is used to drive the fastening nails (as

will be described in detail hereinbelow), includes a crosspiece 44 having a transparent safety plate 46 extending forwardly therefrom over the location at which the nails are driven. A clamping screw 48 passes downwardly through the safety plate 46 and the crosspiece 44, into engagement with a nut 49 which is in turn received within a channel 51 that is formed upwardly into, and extends longitudinally along, a support bar 50; slot 54 is provided to permit passage of the clamping screw 48, and a distance scale 56 extends along one side margin of the slot.

The support bar 50 mounts a depending contact foot, which consists of a right angular, V-shaped portion 52 and a planar portion 53, and is normally fabricated from a resiliently de- formable elastomeric material; typically, the material will have a durometer value of about 40 to 50 (on the A scale), but a harder material (e.g., 80 to 90 durometer) may be used to minimize bounce when the workpieces are relatively hard. The foot serves to engage the frame pieces F, to urge and secure them against the fence members 20 and the platform portions 18. The support bar 50 is mounted for slidable movement in the forward and rearward directions, as constrained by the down-wardly open channel 45 in which it is seated, so as to enable optimal placement of the contact foot; the scale 56 enables presetting of the position of the contact foot 52, if so desired.

Although not illustrated, the contact foot is mounted on pins that depend from the support bar 50 and into passages that extend, from top-to-bottom, through the foot. The pins fricti- onally hold the foot in place, and permit its facile inversion.

When the frame pieces are disposed at a 900 angle, the foot will be oriented to present its V-shaped portion 52 for contact, as illustrated. When other configurations are to be constructed, however, the foot would be inverted on the supporting pins to present the planar portion 53 for contact with the frame pieces.

The crosspiece 44 of the clamping mechanism is affixed to the upper end portions of a pair of parallel rods 58, which pass through openings (not visible) in the table 12 and protrude into the space therebeneath, within the base 10. The rods 58 are oriented at an angle (typically 15°) to vertical, to enable the

contact foot to apply a rearward (as well as a downward) force component when brought to bear upon the pieces F. A coil spring 60 (typically rated at a strength of about 5 to 10 pounds per inch) surrounds each rod 58 and bears operatively upon the table surface and the crosspiece 44, to urge the latter upwardly away from the table 14. As can be seen in Figures 4 and 8, a sheave 62 is rotably mounted upon a shaft 64, which extends between the lower end portions of the two rods 58.

A novel aspect of the present machine resides in its uti- lization of an integrated impacter unit or module, which con- stitutes the means by which the fasteners are delivered and driven into the frame pieces. As is best seen in Figures 5, 6, and 8, the impacter module consists of a housing, generally designat- ing the numeral 66, which contains a hammer assembly, generally designated by the numeral 68, and an actuator assembly, generally designated by the numeral 70. The hammer assembly 68 includes a head 72, received within a hardened steel nail guide sleeve 88 mounted in the housing 66, which head is (as can best be seen in Figure 6) configured to engage and drive a fastener, generally designated by the numeral 80 (and best seen in Figure 7).

More particularly, the upper end portion of the head 72 is formed with a V-shaped ridge element 73, which extends slightly above a planar land element 75. This structure ensures that the head (properly adjusted to bring the top of the ridge 73 element flush with or very slightly below the end surface of the guide sleeve 88) will drive the nail to a depth slightly beneath the surface of the wood from which the frame pieces are made, with the land element 75 serving to prevent excessive penetration.

At the base of the hammer head 72 is a first collar 74, from which is spaced a second collar 77 that operatively engages one end of the drive spring 76; a washer 79 of tough, impact- absorbing synthetic resinous material, such as polyure- thane, is interposed between the spring and the collar 77. The spring 76 is mounted upon an intermediate shaft portion 82 of the hammer assembly 68, and has its opposite end bearing upon a second polyurethane washer 79 and a metal retaining washer

84. The lower end of the shaft 82 extends from the cylinder portion 78 outwardly of the housing 66, through a bushing 85, and is threaded to engage a nut 86; the nut 86 can be adjusted to established precisely the desired relative position of the ridge element 73 at the end of the drive stroke. A rubber bumper 83 is interposed between the nut 86 (and its associated washer) and the adjacent end of the housing, to absorb shock and impact.

Notwithstanding the presence of the bumper 83, the two washers 79 serve an important function in protecting the drive spring 76 against damage and breakage, absorbing vibration and in other- wise improving overall operation of the machine.

It might be pointed out here that basic novelty resides in the use of a spring for driving the hammer of the instant machine. The high impact produced, which is generated through the abrupt and very rapid release of the stored spring energy, enables the workpieces to withstand the driving force of the hammer with relatively light clamping force applied, with the nail efficiently absorbing a high proportion of the energy deliv- ered), which in turn minimizes marring and other damage to the frame pieces (such damage being of particular concern, of course, when the frame pieces are made of a relatively soft wood variety, or covered with plastic).

In order to provide the required kinetic characteristics, coupled with the good life-cycle durability that is necessary as a practical matter, and given practical space limitations, it has been found to be highly desirable to employ, as the drive spring 76, a coil spring of generally flat rectangular cross section, as indicated in Figure 8B. Such springs are typically employed as so-called "die springs," and are usually fabricated from chrome-vanadium or a comparable steel alloy. By way of functional characteristics, the drive spring 76 should have a rating of a least about 45 pounds per inch of deflection, to produce a driving force of at least about 100 pounds (by virtue of any prestressing, together with the dynamic deflection that occurs in operation of the hammer assembly).

The actuator, or trigger assembly, is contained within a second cylinder portion 90 of the housing, which is disposed

adjacent to, and in lateral communication with, the cylinder portion 78. The assembly 70 consists of a head 92 disposed within a bronze bushing 93 and mounted upon the upper end of a shaft 94, about which shaft extends a coil spring 96; the spring bears at its opposite end upon the head 92 and a hardened metal washer 98, which washer is disposed against a bushing 99 seated within a passage at the lower end of the cylinder portion 90. The shaft 94 is connected to a yoke 100, which in turn rotably mounts a sheave 102 on a removable pin 103; ready disassembly of the sheave 102 facilitates removal of the impacter module from the machine.

Contained within the head 92 of the actuator assembly is a pawl 104, which is pivotably mounted at its upper end by a pin 106 and is biased outwardly of the head 92, toward the hammer assembly 68, by a small coil spring 108; a second pin 116 serves to limit such outward movement. In its extended position, a nose portion 110 of the pawl 104 projects into the cylinder portion 78; preparatory to actuation, the nose portion 110 lies at a level above, and in registration with, the collar 74 of the hammer assembly.

As will be appreciated, the application of downward force to the sheave 102 will bring the carbide insert (unnumbered) at the tip of the nose portion 110 of the pawl 104 into engagement with the top of the hammer assembly collar 74, thus drawing the hammer head 72 downwardly as the actuator assembly continues to descend. When the actuator head 92 reaches the tripping pin 112 (received within aligned holes 113 in the housing 66), the pin will ride upon the surface 114 of the nose portion 110, camming the pawl 104 inwardly and thereby effecting release of the hammer assembly. This will of course enable the drive spring 76 to thrust the hammer head upwardly into contact the V-nail 80, and thus to drive the nail into the overlying frame pieces F.

A supply or V-nails 80 is provided to the driving location from a magazine, generally designated by the numeral 118. As can be seen, a line of nested nails 80 is contained within the elongate chamber 119 of the magazine housing 122, which also contains a slidable pushing piece 120 disposed behind the fas-

teners. The bottom side of the housing 122 is formed with a slot, thus permitting the finger 124 of a follower 126 to extend into the chamber 119 and into engagement with the pushing element 120. The base of the follower 126 is slidably received within an elongate track 128 in the housing 66, which is also slotted at 129 to accommodate the finger 124. A coiled, constant-force "clock" spring 130 is maintained by a spool 131, mounted on a crosswise anchor 133, within a recess 134 formed at the inner end of the track 128. The opposite end of the spring 130 is attached to the base of the follower 126, as is a pull-cord 136.

It will be appreciated that withdrawal of the follower 126 is effected by pulling the cord 136 rearwardly (as indicated by the arrow in Figure 5); doing so will ultimately draw the follower into the offset section 138 of the track 128, effectively lowering the finger 124 out of contact with the pushing element 120 and permitting ready withdrawal of the entire magazine 118 from the receiving chamber 67 of the housing 66. The follower 126 serves of course to urge the nails 80 through the lateral opening 89 in the guide sleeve 88, to present the leading nail in the path of the hammer head 72.

A pair of rectilinear channels 140 (one of which is visible in Figures 4 and 6) are formed into the outer surfaces of the housing 66, which cooperate with mating ribs 141 (only one of which is shown) that project inwardly from confronting surfaces of the lateral platform portions 18, to permit slidable movement of the entire impacter module, from back-to-front, within the machine table 12. Displacement of the module is effected by use of a handle assembly, generally designated by the numeral 142, which includes an arm 156 pivotably attached to the module housing 66 by a crosspin 144. The arm 156 is formed with a de- pending lug portion 158, from which extend, in opposite lateral directions, lower and upper fingers 160, 164, and intermediate pins 162, the fingers and pins constituting laterally projecting portions of through-rods engaged in the lug portion 158.

A locator assembly, generally designated by the numeral 146, is affixed at the front of the table 12 and cooperates with the handle assembly 142 to enable selective positioning of the

impacter module for driving the fastening nails into the frame pieces at one or more desired locations. More specifically, the locator assembly 146 consists of a plate 148 that is fastened to the table surface and is longitudinally slotted at 150, the margins of which slot 150 are defined by rows of teeth 152 and the forward end of which terminates in an enlarged section 154.

The section 154 is dimensioned and configured to permit passage of the lug 158, including the lower fingers 160 and the pins 162; the upper fingers 164 are however sufficiently long to prevent their passage through the slot section 154. Once insert- ed, the lower fingers 160 will engage the bottom of the plate 148, and will thereby prevent withdrawal of the lug 158 in any position along the length of the slot 150, except at the enlarged section 154. The pins 162 are dimensioned and located to mesh with the teeth 152, and it will be appreciated single pins (rather than pairs) can be employed if preferred, such pins desirably being formed with flat surfaces for most positive engagement.

The position of the pins 162 at a level intermediate the fingers 160, 164 is such that they can be elevated from between the teeth (as indicated by the phantom line representation of Figure 10) for free translation of the handle assembly, and hence of the impacter module. Needless to say, lowering the pins 162 into selected recesses will positively locate the impacter module at a selected position.

Two rows of apertures 166 are formed in the plate 148 along the opposite sides of the slot 150, each aperture being dimension- ed to receive the cylindrical tip (not shown) of one of the square stop posts 168. The posts 168 can thus be employed to selectively define positions along the locator plate 148, and thereby to enable presetting of positions to which the impacter module is to be moved for repetitive driving of fasteners. As suggested by the phantom line representations in Figure 9, two of the posts 168 are set to determine alternative driving positions between which the module can be shifted.

Operation of the machine is best described with reference to Figures 4 and 8A. As can be seen, a pedal, generally desig- nated by the numeral 170, is pivotably mounted on shaft 172

adjacent the back of the machine base 10, and extends forwardly for access by the operator (it might be noted however that the pedal 170 can be reversed, for mounting on the bar 180 rather than shaft 172, to enable operation from the rear of the machine, if preferred). A cable 174, having a turnbuckle assembly 173 attached at one end, is secured to a pin 175, and passes therefrom about the sheave 62, the pulley 176 (mounted on the pedal 170), and the sheave 102, finally being secured at its opposite end to a pin 178 on the pedal. Depressing the pedal from the full- line position shown (upward movement therebeyond being limited by a crosswise bar 180, which mounts a plastic cushioning sleeve 181) will effect downward movement of the clamping mechanism against the force of the coil springs 60, to bring the lower contact foot portion 52 into engagement with the frame pieces F. When further movement of the clamping mechanism is thereby prevented (and the pedal 170 is in the phantom line position "1"), continued force on the pedal will cause the cable 174 to draw the actuator assembly 70, and in turn the hammer assembly 68, downwardly against the force of the springs 96 and 76. (It might be noted that although some displacement of the actuator assembly will usually occur initially, against the force of spring 96 alone, acting together the springs 76, 96 exert a higher level of resistance to movement than do the springs 60.) At phantom line pedal position "2," the pawl 110 of the actuator head 92 has been disengaged from the collar 74 by the tripping pin 112, and the hammer assembly 68 has been thrust upwardly for driving a nail presented to the head 72 through the lateral opening 89 of the nail guide 88, in the manner previously described.

Turning now to Figure 13, the machine illustrated therein is comparable in all respects to that of Figures 1 through 12, with the exception that movement of the clamping mechanism and the actuator assembly is effected by pneumatic motors, generally designated by the numerals 182 and 184, respectively, rather than by springs. It is to be emphasized however that the hammer assembly in this embodiment of the invention is driven by a mechanical spring, functioning in a the manner described with reference to the earlier Figures.

The pneumatic system of the machine of Figure 13 includes a two-position switch, diagrammatically illustrated and generally designated by the numeral 186, which is connected by lines 188 and 190 to the motors 182, 184, respectively, and by line 192 to a pressurized air supply. Depressing the foot plate 194 will initially pressurize the cylinder of motor 182 (through switch effect "1"), which will act through the linkage 196 to lower the clamping components; the needle valve 183 in the line 188 can be adjusted to vary the clamping speed. Upon attaining a fully clamped condition, depressing the foot plate 194 further (to actuate switch effect "2") will cause the cylinder 184 to be pressurized, thereby operating the actuator assembly 70 and in turn the hammer assembly 68, to drive a nail in the manner described.

One advantage that is afforded in the pneumatic machine resides in its ability to permit clamping force to be maintained while actuating the hammer two or more times. This enables the position of the impacter module to be changed, and/or the stacking of nails (i.e., driving one nail behind another), without need for releasing the frame pieces. Doing so merely requires the operator to elevate his foot to the extent necessary to deactivate effect "2" of the switch 186, without lifting it sufficiently to deactivate effect "1." Thus, it can be seen that the present invention provides a novel underpinner machine in which reduced levels of clamping force are required for holding the workpieces in position during the fastening operation, and in which variation of the position of the driving head, relative to the supported frame pieces, is easily and conveniently achieved. The machine is, in addition, relatively incomplex and inexpensive to manufacture, and it is facile and convenient to operate.