BACKGROUND OF THE INVENTION It is known in the art of electroplating to use frames on which are removably anchored plates or the like articles to be plated, for holding them while they are being submerged in large acid tanks or baths, e. g. for creating printed circuit boards.

In applicant's United States patent No 5, 904,820 issued May 18,1999, there was disclosed and claimed a holding clamp for releasably holding an article to be submerged in a liquid solution bath ahead of a submerged anode bar and to be electroplated therein. This patented holding clamp, destined to downwardly depend from an overlying cathode frame bar, comprises a first and a second elongated arm members made of an electrically conducting material and each defining a lower portion coated with a fluid-tight and electrically insulating sleeve, and an upper and a lower end, the first arm member to be fixedly attached to the cathode frame bar at its upper end, the second arm member being shorter than the first arm member and being pivotally attached to the first arm member and being pivotable between a first limit position in which the lower ends are spaced from one another and a second limit position in which the lower ends abut against one another, the first arm member having electrical current conduction means physically accessible at its lower end. Biasing means biases the arm members lower ends against one another, and a lever member pivotally attached to an intermediate section of the first arm member and located entirely above the first and second arm member sleeves at all times selectively forcibly pivotally biases the second arm member into the first limit

position against the action of the biasing means. In this way, the first and second arm members are destined to frictionally hold the article to be electroplated between their lower ends when the second arm member is in its second limit position, thus allowing current to be conducted through the conduction means into the article, with the first and second arm member lower portions destined to be submerged in the solution at the most partially up their sleeves.

Such a holding clamp device is very efficient for holding thin single layer planar articles. However, recent technical developments in the printed circuit boards have brought about thicker, multiple layer printed boards. Because of their greater overall thickness, the jaw studs of the prior art holding clamps are much more spread apart than before. Since the relative movement between the two jaws is a pivotal one about a circle of an arc, when the jaws are opened from their closed condition, the jaws do not remain parallel to one another and accordingly, the studs become eventually axially offset relative to one another. This means that electrical conduction between the studs from the two opposite jaws from a given clamp, becomes compromised in a progressively increasing fashion as the jaws are progressively pivoted away from one another.

A problem that appears once and a while is the vibrations generated by the conventional vibrators used in the acid bath tank, to remove air bubbles that may have struck to cavities on the circuit boards during their lowering into the volume of acid.

These vibrations may sometimes be important enough to bring about accidental progressive frictional release of the circuit board from the pair of studs between which the circuit board is taken in sandwich. This is undesirable.

OBJECTS OF THE INVENTION The gist of the present invention is therefore to improve upon applicant's United States patent No 5, 904,820, by providing means for relative movement of the pair of jaws from an article holding device, that will constantly maintain the pair of jaws parallel to one another during their relative movement to accommodate therebetween an article of varying thickness to be frictionally taken in sandwich therebetween.

A corollary object of the present invention is to address the requirements

for holding state of the art printed circuit boards over acid baths.

An important object of the invention is to overcome the vibration problem from acid bath vibrators that can accidentally release the circuit board from their sandwiching studs, as discussed in the preceding background of the invention paragraph, by providing an improved holding clamp for holding a thick planar article which holding clamp will not release its planar article from air-bubble dislodging vibrator borne forces.

General objects of this invention include: that the holding device be easy and quick to operate; and that the holding device require only one operation for installing or retrieving an article therefrom.

SUMMARY OF THE INVENTION In accordance with the objects of the invention, there is disclosed a holding clamp for releasably holding a thickened planar article to be submerged in a liquid solution bath ahead of a submerged anode bar and to be electroplated therein, said holding clamp destined to downwardly depend from an overlying cathode frame bar, said holding clamp comprising : a) an elongated main arm member, made from an electrically conducting material, and defining first and second opposite end portions; b) a pair of first and second tubular bar members, each defining an outer end portion coated with a fluid-tight and electrically insulating sleeve and an opposite inner end portion, each bar member outer end portion having a transverse terminal stud projecting therefrom, said first bar member anchored at its said inner end portion to said main arm member first end portion parallel thereto; c) a rail member, integral to an intermediate section of said main arm member and slidably engaged by said second bar member inner end portion, wherein said second bar member is maintained by said rail member parallel to said first bar and wherein said second bar member is movable relative to said first bar member while continuously remaining parallel thereto, while the pair of said terminal studs remain coaxially aligned; d) a first biasing member, continuously biasing said first and second bar members toward one another; and e) a second biasing member, for discretely biasing said second bar member away from said first bar member, against the continuous bias of said first biasing member.

Preferably, said first biasing means includes at least one pair of coil springs, hookingly interconnecting said first and second bar members. Also, said second biasing member could include an arcuate cantilever member defining an engagement leg and an opposite actuation leg, said engagement leg extending between said first and second bar members within their common plane, and a pivotal linkage assembly integral to said main arm member and pivotally mounting an intermediate section of said arcuate cantilever member; wherein upon actuation of said actuation leg to move the latter away from said main arm member, pivotal motion of said cantilever member will bring about frictional engagement of said cantilever member engagement leg against said second bar member for displacement of the latter away from said first bar member.

Said cantilever member engagement leg preferably includes a bevelled tip.

According to a first embodiment of the invention, there is further provided an elongated handle, operatively mounted to said pivotal linkage assembly for facilitating actuation of said actuation leg. Said second biasing member could then include an arcuate cantilever member defining an engagement leg and an opposite actuation leg, said engagement leg extending between said first and second bar members within their common plane, an elongated elbowed handle member integrally carried by said actuation leg coextensively thereto, and a straight link arm pivotally mounted to an intermediate section of said main arm member and pivotally mounting an intermediate section of said handle member; wherein upon actuation of said handle to move the latter toward said main arm member, there will be brought about frictional engagement of said cantilever member engagement leg against said second bar member for displacement of the latter away from said first bar member.

This invention also relates to an alternate embodiment of holding clamp, for releasably holding an article to be submerged in a liquid solution bath ahead of a submerged anode bar and to be electroplated therein, said holding clamp destined to downwardly depend from an overlying cathode frame bar, said holding clamp comprising: a) an elongated main arm member, made from an electrically conducting material, and defining first and second opposite end portions ; b) a pair of first and second tubular bar members, each defining an outer end portion coated with a fluid-tight and

electrically insulating sleeve and an opposite inner end portion, each bar member outer end portion having a transverse terminal stud projecting therefrom, said first bar member anchored at its said inner end portion to said main arm member first end portion parallel thereto; c) an endless screw member, integral to an intermediate section of said main arm member and to said second bar member inner end portion, said endless screw member maintaining said first and second bar members parallel to each other, and said second bar member being movable relative to said first bar member while continuously remaining parallel thereto, while the pair of said terminal studs remain coaxially aligned; and d) a biasing member, for discretely actuating said endless screw member for biasing said second bar member away from or toward said first bar member.

Preferably, said biasing member is an enlarged wheel, carried at a free end portion of said endless screw member, said wheel being manually rotatable by an operator.

The invention also extends more generally to a holding clamp device, for releasably holding a thick planar article over ground, comprising: a) an elongated main arm member, defining first and second opposite end portions; b) a pair of first and second tubular bar members, each defining an outer end portion and an opposite inner end portion, c) a rail member, integral to an intermediate section of said main arm member and slidably engaged by said second bar member inner end portion, wherein said second bar member is maintained by said rail member parallel to said first bar and wherein said second bar member is movable relative to said first bar member while continuously remaining parallel thereto, d) a first biasing member, continuously biasing said first and second bar members toward one another; and e) a second biasing member, for discretely biasing said second bar member away from said first bar member, against the continuous bias of said first biasing member.

The invention also relates to a holding clamp for releasably holding a thickened planar article to be submerged in a liquid solution bath ahead of a submerged anode bar and to be electroplated therein, said holding clamp destined to downwardly depend from an overlying cathode frame bar, said holding clamp comprising: a) an elongated main arm member, made from an electrically conducting material, and defining first and second opposite end portions; b) a pair of first and second tubular bar

members, each defining an outer end portion coated with a fluid-tight and electrically insulating sleeve and an opposite inner end portion, each bar member outer end portion having a transverse terminal stud projecting therefrom, said first bar member anchored at its said inner end portion to said main arm member first end portion parallel thereto; c) a rail member, integral to an intermediate section of said main arm member and slidably engaged by said second bar member inner end portion, wherein said second bar member is maintained by said rail member parallel to said first bar and wherein said second bar member is movable relative to said first bar member while continuously remaining parallel thereto, while the pair of said terminal studs are directed toward one another and remain coaxially aligned; d) a first biasing member, cooperating with said rail member and continuously biasing said first and second bar members toward one another; and e) a second biasing member, for discretely biasing said second bar member away from said first bar member, against the continuous bias of said first biasing member; said second biasing member including an arcuate cantilever member defining an engagement leg, an intermediate actuation leg transverse to said engagement leg, a handle bar opposite said engagement leg and extending generally away from said first and second bar members and integral and transverse to said actuation leg, said engagement leg extending between said first and second bar members within their common plane, and a pivotal mount integral to said main arm member and pivotally carrying a section of said arcuate cantilever member intermediate said engagement and actuation legs, said pivot mount defining a pivotal axis orthogonal to the plane intersecting said first and second bar members; wherein said engagement leg of cantilever member is engageable with said second bar member inner end portion, so that upon push actuation of said handle bar toward said main arm member, pivotal motion of said cantilever member brings about frictional engagement of said cantilever member engagement leg about said second bar member and displacement of the latter away from said first bar member.

Preferably, said first biasing means includes two pairs of coil springs, hookingly interconnecting said first and second bar members on opposite sides of said cantilever member engagement leg.

Preferably also, said cantilever member engagement leg includes a free end bevelled tip portion. A carriage, would be integrally mounted to said second bar

member inner end portion, and an open cavity member, projecting from said first bar member outer end portion, said carriage sized for sliding engagement into said open cavity member, said cantilever member bevelled tip end portion frictionally slidingly engaging directly said carriage member upon pushing force being applied against said handle bar.

A bulge could also be located on an intermediate section of said cantilever member, said cantilever member bulge abutting against said main arm member at a limit released condition of said cantilever member when said studs abut one another.

DESCRIPTION OF THE DRAWINGS In the annexed drawings: Figure 1, is a front elevational sectional view of an acid bath showing an overhanging horizontally supported cathode bar holding a number of downwardly depending holding clamps supporting circuit boards to be electroplated according to a first embodiment of the invention; Figure 2, is an enlarged perspective view of a first embodiment of holding clamp, with its jaws in closed condition; Figure 3, is a view similar to figure 2, but showing the jaws in their opened condition after pivotal action of the central lever under manual bias from the operator; Figures 4 and 5, are plan views of the holding clamp in their conditions of figures 2 and 3, respectively; Figure 6, is partly broken view at an enlarged scale of the area circumscribed by ellipse 6 of figure 5;

Figure 7, is an enlarged view of the area taken within ellipse 7 of figure 8; Figure 8, is a cross-sectional view of the closed jaws from figure 4; Figure 9, is an exploded view of the first embodiment of holding claim from figures 1-8; Figure 10, is a view similar to figure 2 but for a second embodiment of holding clamp, with its jaws again in closed condition; Figure 11, is a view similar to figure 10, but showing the jaws in their opened condition after pivotal action of the central lever under manual bias from the operator; Figures 12 and 13, are plan views of the holding clamp in their conditions of figures 10 and 11, respectively; Figure 14, is an exploded view of the second embodiment of holding claim from figures 9-13; Figure 15, is a plan view of an alternate third embodiment of holding clamp; Figure 16 is an exploded view of still another embodiment of holding clamp; Figure 17 is a perspective view of the assembled holding clamp, with the jaws in their closed default condition, and showing the actuator lever handle in its diverging position away from the main arm; Figure 18 is a view of the holding clamp similar to figure 17, but with the

jaws spread apart and with the actuator lever handle brought toward the main base arm; Figures 19 and 20 are plan views of the clamp of figures 17 and 18, respectively; and Figure 21 is a partly broken perspective view of the clamp with the jaws thereof being open, at a larger scale than figure 18, and with party of the casing thereof being broken for clarity of the view of the cantilever arm.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Figure 1, shows a liquid solution bath or tank 20, with a top mouth 20a and a bottom wall 20b and which contains an acid solution 22. A frame 24 overhangs the top mouth 20a of acid tank 20. Frame 24 comprises a flight bar acting as a negatively charged cathode bar 26. From cathode bar 26 downwardly depend a number of holding clamps 28 according to a first embodiment of the invention, and illustrated in figures 2 to 9. Holding clamps 28 are each adapted to hold a thickened planar article 30 to be electroplated, usually of a flat rectangular thick plate as shown in the drawings, through mouth 20a and into acid batch 20 but spacedly over the bottom wall 20b of the tank 20.

Frame 24 is movable between a lower and an upper limit position, as known in the art. In its upper limit position, the articles 30 clear the mouth 20a of the acid bath 10 and the liquid acid volume 22, while in its lower limit position, the clamps 28 extend through mouth 20a and the articles 30 are entirely submerged into the liquid acid volume 22 but spacedly over bottom wall 20b.

When powering means (not shown) are activated, a voltage difference is generated between the cathode element and the anode element, and current is transmitted from the anode element through the acid in the bath, the article, the holding clamp to the cathode bar. This way, the positively charged ions composing the metallic (copper, gold or another suitable metal) anode element are conveyed by the acid solution-being used as a carrier means-and fix themselves to the article 30 outer surface, thus effectively

electroplating article 30.

The first embodiment of holding clamp 28 is illustrated in figures 2 to 9.

As best shown in figures 5 and 9, holding clamp includes an elongated clamp arm 32 having at one end a fastening band assembly 33, for transverse attachment of the horizontal support element (as already discussed in applicant prior U. S. patent No 5 904 820, supra, and a pair of integral spaced elongated brackets 34,36, extending transversely from an intermediate section of clamp arm 32 wherein a short end portion thereof 32a remains, and being in spaced register with one another. Each bracket 34,36, includes on a fraction of its interior planar face 34a, 36a, an inturned groove 34b, 36b in facing register with one another, and an outer free end portion 34c, 36c, opposite main arm 32.

A spacer member 37 (fig 9) is mounted between the outer free end portions 34c, 36c, of brackets 34,36. A first stud support tubular bar 38 is fixedly anchored by bolts 40,40a, at one inner end portion thereof 38a to the clamp arm end portion 32a parallel thereto. A second stud support tubular bar 42 is fixedly anchored by bolts 44,44a, at one inner end portion thereof 42a to a carriage member 46 This tubular bar end portion 42a is engaged into a complementary open channel section 46a made in the carriage member 46. Carriage member 46 includes a transverse U-shape end tubular slider member 48, sized for slidable complementary engagement through the mouth formed between the free end portions 34c, 36c, of transverse brackets 34,36, and into and along the cross-sectionally U-shape grooves 34b, 36b of the clamp arm transverse brackets 34,36, towards main arm 32, wherein tubulars bars 38 and 42 remain parallel to one another. Accordingly, as carriage member 46 slides along the rails formed by bracket grooves 34b, 36b, second stud support tubular bar 42 is movable relative to stationary first stud support tubular bar 38, while both bars 38,42 remain parallel to one another at all times.

Each tubular bar 38,42 is as generally described in applicant's U. S. patent No 5,904, 820, supra, and thus further includes (figure 8) an outer end portion 38b, 42b, covered by a corrosion-resistant, fluid-tight and electrically insulating protective sheath 50, opposite inner end portions 38a, 42a; and a cylindroid stud 52,54, projecting inwardly transversely from the corresponding free end 38c, 42c, of sheathed end portion

38b, 42b, the studs 52,54, being coaxially aligned. As suggested in figures 2 and 4, biasing means 56 are provided to continuously bias tubular arms 38,42 toward one another, and thus, the free inner ends 52a, 54a of the cylindroid studs 52,54, coaxially against one another (typically taking a planar board article 30 in sandwich therebetween).

Preferably, biasing means 56 preferably includes two pairs of coil springs 58,60, 62,64 ; one end 58a, 60a, 62a, 64a, of these four coil springs hook around integral ears 66,68, 70, 72, transversely projecting from carriage member 46 orthogonally to slider 48, while the opposite end 58b, 60b, 62b, 64b of these four coil springs hook around integral ears 74, 76,78, 80 projecting transversely from the end portion 32a of the clamp main arm 32.

Ears 66,68, extend in a direction opposite ears 70,72 ; while ears 74,76, extend in a direction opposite ears 78,80, wherein, as best illustrated in figures 2 and 3, the coil springs 58-64 clear the passageway of the carriage member 46 between the two tubular bars 38,42. Accordingly, coil springs 58-64 continuously biases the opposite pair of otherwise spaced studs 52,54, to firmly coaxially abut against each other, while the tubular bars 38,42, remain consequently spaced from one another and parallel to one another. As the tubular bars 38,42, are forcibly spread apart to put a planar board article 30 in between the studs 52,54, the coil springs 58-64 are stretched (figure 3) from their initial released condition (figure 2).

According to the specific features of the present invention, and as clearly shown in figure 9, a generally V-shape cantilever member 82 is mounted between the two spaced brackets 34,36, for relative movement therebetween. Cantilever member 82 includes a bore 82a at its intermediate apex, and brackets 34,36, include a pair of registering bores 34d, 36d, extending through their ungrooved planar faces 34a, 36a, wherein a half-threaded bolt 84 extends through bores 82a, 34d, 36d, for pivotally interconnecting the cantilever member 82 to the brackets 34,36. Bores 34d, 36d, are proximate arm 32, so that cantilever member 82 clear the carriage slider 48 at all times.

Cantilever member 82 further includes a first leg 86 having a bevelled tip 86a, extending in between stud bars 38,42, and a second opposite leg 88, extending away from stud bars 38,42 and diverging from main arm 32. Cantilever member outer leg 88 is maneuverable to pivot cantilever member inner leg 86 in between the two stud holding bars 38,42, and to spread apart the latter against the bias of the coil springs 58-64, since the bevelled tip

86a of first leg 86 is slidingly frictionally engageable against the smooth external face 46b (figure 4) of carriage member 46 opposite U-shape channel 46.

To facilitate actuation of cantilever leg 88, there is provided a manual lever handle bar 90. Elongated handle bar 90 includes a bored recess 90a at its inner end portion, for free engagement by the free end portion of cantilever leg 88 which transversely integrally carries a first innermost finger 92 for pivotal engagement with the opposite bores of the recess 90a. In addition, a pair of link rods 94,96, (fig 2) pivotally interconnect a pivot mount 98 at an intermediate section of handle bar 90, and another pivot mount 100 on a bracket 102 extending transversely inwardly from an intermediate section of the clamp main arm 32 and in general transverse register with pivot mount 98.

Therefore, as the handle bar 90 is pivoted from its released condition illustrated in figure 2, away from main arm 32 toward its loaded condition illustrated in figure 3, the bevelled end 86a of cantilever arm 82 slidingly abuts against carriage member 46 and the latter and associated stud bar 42 is brought into motion away from stud bar 38 against the bias of coil springs 58-64.

Preferably, a transverse stopper pin 104 (fig 9) is provided to V-cantilever arm 82 intermediate bore 82a and pivot mount 92, to prevent accidental movement of stud bar 42 away from stud bar 38 beyond a set relative distance therebetween, by coming to transversely abut against the link rods 94,96 should the handle bar 90 be pivoted away beyond a set threshold as suggested in figure 5 of the drawings.

A second embodiment of holding clamp device is shown as 28'in figures 10-14 of the drawings. All corresponding elements with the first embodiment will be primed. In this second embodiment of the invention, the main components remain substantially the same, including the V-shape cantilever arm 82', the carriage member 46', the two pairs of biasing coil springs 58', 60', 62', 64', the main elongated arm 32'and the two sheathed stud supporting bars 38', 42'. However, instead of having the maneuvering handle (90, first embodiment) pivoted outward away from arm 32 to spread apart the stud carrying bars (38,42, first embodiment, figure 3), in the present embodiment, the operating linkage assembly for the cantilever arm 82'is inverted, so that-as illustrated in figure 11, it is as the handle bar 90'is pivoted toward main elongated clamp arm 32'that the stud carrying bars 38', 42', become progressively spread apart.

More particularly, the improvements brought about are directed at the cantilever arm 82', the transverse brackets 34', 36', and the linkage arm 94'. Cantilever member 82'is now integral to and generally coextensive with handle bar 90'by the outer end of its leg 88'. Cantilever leg 88'extends in between a pair of ears 110,112, that <BR> <BR> transversely depend from the brackets 34', 36', . Ears 110,112, extend away from stud bars 38', 42', and are bored so as to pivotally receive the pivot finger 92'of cantilever member leg 88'. Handle bar 90'includes an intermediate elbowed section 90'a, and an inner portion 90'b adjacent cantilever member 82'and comprising an ovoidal slot 114.

Slot 114 is freely engaged by a short thinned section 116a of a half-threaded bolt 116, the opposite end of bolt 116 extending through a registering bore 118 made in the clamp main arm 32'. A pin 120 is mounted transversely through thinned bolt section 116a, so as to enable free limited sliding motion of bolt section 116 along ovoidal slot 114 of handle bar 90' ; while a tension spring and nut assembly 122,124, is mounted to bolt 116 on the side of bar 32'opposite handle 90'.

In operation, the linkage bolt 116 maintains handle 90'and V-cantilever arm 82'in their released condition, due to the bias of the four large compression springs 58'-64'but against the bias of the single small tension spring 122. As sequentially suggested in figures 12 and 13, as the handle 90'is pushed toward arm 32', the integral cantilever arm 82'frictionally slides against carriage member 46'thus concurrently displacing carriage member 46'and stud arm 42'away from stationary stud bar 38', against the bias of the coil springs 58'-64'but yielding for a small part to the bias of the bolt spring 122.

A third embodiment of article support device is schematically illustrated as 28"in figure 15 of the drawings. Corresponding elements relative to the first embodiment will be double primed. In this third embodiment, the movable stud carrying bar 42"is connected to the stationary stud carrying bar 38", simply by a pair of scisor linkage assemblies 130 (only one scisor linkage is shown in the figure). The five pivotal axes 132,134, 136,138, 140 of the linkages from the scisor linkage assembly 130 are all orthogonal to the plane extending through both stud carrying bars 38", 42". Relative movement of movable stud carrying bar 42"is controlled simply by an endless screw shaft member 142, being operatively connected to the scisor linkage assembly

intermediate pivot mount 140. An enlarged rotatable wheel 144 is carried at the outer end of the shaft member 142, for facilitating rotation of the integral endless screw and therefore relative displacement of movable stud bar 42".

The still other alternate embodiment of holding clamp 210 according to the present invention is illustrated in figures 16-21. Holding clamp 210 includes an elongated main clamp arm 212 having at one end a fastening band assembly 214, for transverse attachment of the horizontal support element.

A first stud support tubular bar 216 is fixedly transversely anchored by bolts 218, at one inner end portion thereof 216a, to the clamp arm end portion 212a parallel thereto.

A second stud support tubular bar 220 is fixedly anchored by bolts 222, at one inner end portion thereof 220a to a carriage member 224. This tubular bar end portion 220a is engaged into a complementary open channel section 224a made in the carriage member 224.

Each tubular bar 216,220, further includes an outer end portion 216b, 220b, covered by a corrosion-resistant, fluid-tight and electrically insulating protective sheath 225, opposite inner end portions 216a, 220a; and a cylindroid stud 226,228, respectively, projecting inwardly transversely from the corresponding free end 216b, 220b, of sheathed end portion 225, the studs 226,228, being coaxially aligned and directed toward one another.

Biasing means 230 are provided to continuously bias tubular arms 216,220, toward one another, and thus, the free inner ends 216b, 220b, of the cylindroid studs 226, 228, respectively, coaxially against one another (typically taking a planar board article in sandwich therebetween). Preferably, biasing means 230 includes two pairs of coil springs 232,234, and 236,238, one end of which hook around two pairs of opposite ears 240,242 and 244,246, which transversely project from carriage member 224 orthogonally to the plane intersecting the two tubular stud bars 216,220, while the opposite end of these four coil springs 232-238 hook around two pairs of opposite ears 248,250 and 252,254, projecting transversely from the end portion 212a of the clamp main arm 212 and parallel to ears 240-246. Ears 240,242 extend in a direction opposite ears 244,246, while ears 248,250, extend in a direction opposite ears 252,254. It is noted that coil springs 232-238 continuously bias the opposite pair of otherwise spaced

studs 226,228, to firmly coaxially abut against each other, while the tubular bars 216, 220, remain consequently spaced from one another and parallel to one another. As the tubular bars 216,220, are forcibly spread apart to put a planar board article in between the studs 226,228, the coil springs 232-238 are stretched (figure 20) from their initial released condition (figure 19).

As illustrated in figure 16 of the drawings, carriage 224 is cross-sectionally H- shape, with two opposite flat plates 256,258, integrally interconnected by an intermediate transverse web 260, so that two opposite U-shape channels 224a, 224b, are formed. Ears 240,242, integrally project from plate 256 away from plate 258, and ears 244,246 integrally project from plate 258 away from plate 256. Movable stud bar inner portion 220a snugly fits flatly inside U-channel 224a, with bolts 222 extending transversely through bores in portion 220a and through bores in web 260.

A pair of rectangular arms 262,264, transversely integrally project from opposite sides of the main stationary bar inner portion 212a, in registering parallel fashion relative to one another. The transverse gap between arms 262,264, is slightly greater than the total outer distance between the carriage two opposite plates 256,258, so that the carriage 224 be freely movable through this gap lengthwisely of arms 262,264 toward or away from arm 212. Moreover, the width of the rectangular arms 262,264, is slightly smaller than the inner distance between ears 240 and 242, and between ears 244 and 246, respectively, so that the free end portion of each elongated arm 262,264, can guidingly pass freely between the two corresponding opposite pairs of ears as the carriage 224 moves through the gap lengthwisely between elongated arms 262 and 264. Coil springs 232-238 bias carriage 224 into this channel gap between arms 262 and 264, toward main arm inner portion 212a.

Preferably, a shaft 266 transversely joins the free end of elongated arms 262,264, so that carriage 224 be trapped between shaft 266 and main arm inner portion 212a without any possibility of carriage 224 accidentally escaping endwisely from the gap or "open casing"between arms 262 and 264.

A manual cantilever arm assembly 268 is provided to forcibly bias carriage 224 away from arm inner portion 212a, against the bias of coil springs 232-238. Assembly 268 includes a pivot mount 270, installed transversely to main arm 212 proximate to the

inner portion thereof. Pivot mount 270 defines a pivotal axis 270'extending orthogonally to the plane intersecting stud arms 216,220. An arcuate cantilever arm 272 is pivotally engaged by its apex pivot section 272a to pivot mount 270, for pivotal displacement of cantilever arm generally within the plane of stud bars 216,220. Tapered leg 274 of cantilever arm 272 extends transversely through and into the channel between elongated arms 262 and 264, and in between carriage 224 and main arm inner end portion 212a. A handle 276 transversely projects from the other leg 278 of cantilever arm 272, in a direction generally opposite that of tapered leg 274.

In use, by manually pushing handle 276 pivotally around pivot mount 270 toward the intermediate section of main arm 212, the tapered leg 274 of cantilever arm is pivoted in the opposite direction to come to frictionally slidingly bear against web 260 of carriage 224. By further pushing handle 276 inwardly, cantilever arm leg 274 pushes carriage 224 slidingly away from bar 212, and thus, spreads apart studs 226 and 228. However, studs 226 and 228, even when spread apart, constantly remain coaxial to one another, in view of the operational layout between movable stud arm 220, carriage 224, slider bars 262,264, and main arm 212.

As shown in figure 19, the cantilever arm tapered leg extends into the gap between plates 262 and 264, transversely beyond coil springs 234,238, but sheet of coil springs 232, 236.

Preferably, cantilever arm 272 includes an intermediate bulge 280, proximate its apex pivotal point 272a, wherein this bulge 280 comes to abut against main bar 212 once handle 270 is released to its limit position (shown in figure 19) farthest from main bar 212, thus forming a stopper defining a limit position of handle 270. Bulge 280 thus abuts on main bar 212 in the closed condition of stud bars 216,220, but facilitate the lever action of handle 276 when stud bars 216,220, are to be spread apart.