Abstract:
A shipping strap assembly protects the isolator mechanism of a vibratory screening machine against exceeding its elastic limits. The isolator mechanism is pivotally connected between shafts on the machine frame and the machine basket. The protective assembly includes a distally narrowing boss on at least one of the shafts. A rigid strap has two apertures, one contoured to receive and ride on the boss and the other contoured to receive the other shaft, spaced to maintain the distance between the shaft axes within an elastic limit of the isolator mechanism. The narrowing boss provides leeway for easy manual alignment of the mechanism shafts with the strap apertures, and the narrowing boss and contour of the other aperture facilitate restoration toward its normal load length, of an elastically distorted mechanism.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to vibratory screening machines and more particularly concerns shipping straps used to protect the isolator mechanisms of a vibratory screening machine during transport of the machine from site to site. 
     Known isolator mechanisms include one or more coil springs or other types of resiliently expanding and contracting components, such as rubber-based belts, in lieu of the springs. The springs are commonly positioned at or near each of the four corners of the machine and suspend or support the basket of the machine from or on the machine base frame. Thus, the isolator mechanisms serve as pivoting linkages between the basket and frame. A typical known isolator mechanism is hereinafter described in detail. 
     Whatever the type of vibratory screening machine involved, its isolator mechanism and mass configuration will have a low resonance frequency. Unless the basket is locked down, the force fluctuations encountered during machine transport are close to its resonance point. These fluctuations often cause the basket to be displaced from the base frame to such an extent that the isolator mechanism will permanently stretch, the isolator mechanism “spring rate” may change, the basket may hang unevenly and, ultimately, the isolator mechanism will fail as its elastic limit is exceeded. As these deficiencies progress, the result will be increasing machine inefficiency and possibly total inoperability of the machine. The replacement of a defective isolator mechanism, assuming a replacement is on-hand, will typically require a half day of machine/drilling rig down time at a loss rate of likely more than $8,000 per day. 
     The known solution to these problems requires the use of a rigid shipping strap to “lock down” the isolator mechanism. A typical known shipping strap is hereinafter described in detail. The strap prevents any expansion or compression of the springs or equivalents during transport. This solution introduces problems of its own. 
     Prior to transport, if the springs are stretched beyond their normal load length, levers must be used to raise or lower the basket level to bring the springs to their normal load length so that the rigid strap can be aligned with the isolator mechanism. Once the springs are at their normal load length, the rigid strap can be installed on the isolator mechanism, but a separate tool is required to secure the strap and lock the mechanism down. In the locked-down status, the springs cannot expand at all and remain at their normal load length throughout transport. However, at the delivery site, a tool is again required to remove the strap from the mechanism. 
     Because of the owner&#39;s desire to achieve maximum the use of an expensive screening machine, there is generally a sense of urgency felt by rig hands to speed up the installation and removal of the machine from site to site. Rig downs are normally hectic and the tasks of installing and removing shipping straps are generally considered by rig hands to be a nuisance. Many rig hands simply do not want to take the time to perform the necessary tasks, especially when levering the basket into alignment with the straps is one of the necessary strap installation steps. If straps are not installed, they don&#39;t have to be removed. Since the tasks require separate tools and parts, for example a wrench and nuts, if the tools or parts are “lost” or “misplaced,” the shipping straps cannot be installed or removed and the shipping strap nuisance is thus avoided. But, eventually, when machines are moved without shipping straps, isolator mechanisms are stretched, shaker performance is poor and, ultimately, the isolator mechanisms fail totally and the machines will be inoperable until they are replaced. 
     It is, therefore, an object of this invention to provide a shipping strap assembly which eliminates the need of levers to bring isolator mechanisms to their normal loaded length before installation of the shipping strap. It is a further object of this invention to provide a shipping strap assembly which eliminates the need for tools to install or remove the shipping strap on or from an isolator mechanism. It is another object of this invention to provide a shipping strap assembly which eliminates the necessity for putting a machine basket in a locked-down condition for transport. Still another object of this invention is to provide a shipping strap assembly which eliminates the need for ever removing a shipping strap or installation part from the machine. It is also an object of this invention to provide a shipping strap assembly which reduces and simplifies the tasks involved in protecting an isolator mechanism from damage due to stretching. And it is an object of this invention to provide a shipping strap assembly which reduces the likelihood that machines will be transported without shipping straps. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention, a shipping strap assembly is provided that will protect the isolator mechanisms of vibratory screening machines against exceeding their elastic limits. 
     An isolator mechanism is pivotally connected to the machine frame by one shaft at one of its ends and to the machine basket by another shaft at its other end. The shafts are aligned on parallel axes defining a common plane. 
     Shipping Strap Assemblies Protecting Isolator Mechanism Elastic Limits 
     The protective shipping strap assembly of the present invention includes a distally narrowing boss on one of the shafts, the boss being radially aligned on the common plane and extending away from the other shaft for expandable isolator mechanisms and toward the other shaft for compressible isolator mechanisms. The rigid strap has two apertures therethrough aligned on parallel axes defining another common plane capable of coincident positioning with the common plane of the shaft axes. One of the apertures has a contour to receive and ride on the boss. The other aperture has a contour to receive the other shaft. The apertures are spaced at a distance such that, when the boss is fully received in the one aperture and the other shaft is received in the other aperture, a distance between the axes of the shafts is maintained within an elastic limit of the isolator mechanism. The contour of the other aperture can be adapted to define a range of distances between the axes of the shafts within an elastic limit of the isolator mechanism. 
     In a preferred embodiment, the protective shipping strap assembly of the present invention includes an extension of one of the isolator shafts along its axis. This first extension has a first boss defining a first guide path that lies in the common plane of the shaft axes, extends from a radially most-distal point at an axially proximal end of the first boss to a radially most-proximal point at an axially distal end of the first boss and is bounded between a pair of limiting axes parallel to the first shaft axis, one limiting axis through a corresponding one of each of the radially most-distal and most-proximal end points of the first boss. 
     The protective shipping strap assembly of the present invention also includes an extension of the other isolator shaft along its axis. This second extension has a second boss defining a second guide path that lies in the common plane of the shaft axes, extends from a radial point at an axially proximal end of the second boss to another radial point at an axially distal end of the second boss and is bounded between another pair of limiting axes parallel to the second shaft axis, one limiting axis through a corresponding one of each of the end radial points of the second boss. The proximal end radial point is not more radially distal than the distal end radial point. 
     The first and second guide paths are outward of their respective first and second axes for expandable isolator mechanisms and inward of their respective first and second axes for compressible isolator mechanisms. 
     The protective shipping strap assembly of the present invention also includes a rigid strap with first and second apertures extending through corresponding first and second end portions of the strap. The first and second apertures are each aligned on corresponding longitudinal axes that define a second common plane. The common plane of the aperture axes can be positioned to coincide with the common plane of the shaft axes. The first aperture is contoured to receive the first boss and has contact points that are coordinated for abutting juxtaposition with the radially most-distal and most-proximal points on the first guide path when the first boss is fully received in the first aperture. The second aperture is contoured to receive the second boss and has contact points that are coordinated for contemporaneous abutting juxtaposition with corresponding radial points on the second guide path of the second boss when the second boss is fully received in the second aperture. The distances between corresponding contact points of the first and second apertures are within an elastic limit of the isolator mechanism. 
     The distances between corresponding contact points of the first and second apertures of the strap can be selected to limit a range of motion of the second boss relative to the first boss within the elastic limit of the isolator mechanism. The distances between corresponding contact points of the first and second apertures can be selected to prevent motion of the second boss relative to the first boss. 
     If the distal end portion of the first extension has a constant radius not greater than the radius to the radially most-proximal point at the axially distal end of the first boss and has a threaded distal end, then a nut threaded on the threaded distal end of the first extension can be used to tighten and loosen the first aperture into and out of abutting juxtaposition with the radially most-distal and most-proximal points on the first guide path, thus maintaining the distance between the first and second guide paths within the elastic limit of the isolator mechanism. In this embodiment also, the distances between corresponding contact points of the first and second apertures of the strap can be selected to limit the range of motion of the second boss relative to the first boss within the elastic limit of the isolator mechanism or the distances between corresponding contact points of the first and second apertures can be selected to prevent motion of the second boss relative to the first boss. 
     The first guide path, the second guide path or both guide paths may include at least one load-interfacing portion parallel to the first axis and the first aperture of the strap may include corresponding load-interfacing portions parallel to the first aperture longitudinal axis. In this embodiment, the first guide path may further include at least one non-load-interfacing portion aligned at least one angle to the first axis and the first aperture of the strap may include corresponding non-load-interfacing portions aligned at corresponding angles to the first aperture longitudinal axis. 
     Preferably, the shipping strap assembly will have a concentric cylindro-conical boss on one shaft and a cylindrical boss proximate on the other shaft and the shipping strap will have corresponding cylindro-conical and cylindrical apertures, the distance between the apertures being equal to the distance between the two shafts with the isolator mechanism at a normal loaded length. The cylindro-conical aperture is tapered for complemental juxtaposition against the boss on the one of the two shafts and the cylindrical aperture has a diameter sized to provide an annulus around the other of the two shafts. A nut threaded on the one shaft is used to tighten and loosen the cylindro-conical aperture into and out of complemental juxtaposition against the boss. Thus, when the cylindro-conical aperture and the boss are in complemental juxtaposition, a distance between the two shafts is maintained at a normal loaded length of the mechanism. The trailing end of the nut may have a handle adapted for tool-free manual operation. The taper of the cylindro-conical aperture and the diameter of the cylindrical aperture are coordinated to permit the cylindrical aperture to be disengaged from the other shaft without removing the nut from the one shaft. The cylindro-conical boss may have a conical mid-portion between leading and trailing end portions, a conical portion trailing a cylindrical portion or a conical portion leading a cylindrical portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings in which: 
         FIG. 1  is a perspective assembly view of a prior art isolator mechanism and shipping strap; 
         FIG. 2  is a one line representation of a shipping strap assembly according to the invention; 
         FIGS. 3A-3G  are one line representations of various embodiments of the boss of an isolator mechanism shaft extension according to the invention; 
         FIG. 4  is a cross-sectional assembly view of a shipping strap assembly according to the invention taken in a plane common to the isolator mechanism shaft and strap aperture axes; 
         FIGS. 5A-5D  are cross-sectional assembly views of several concentrically symmetrical embodiments of the shipping strap assembly according to the invention taken in a plane common to the isolator mechanism shaft and strap aperture axes; 
         FIGS. 6A-6B  are cross-sectional views of the shipping strap assembly embodiments of  FIGS. 5A and 5B , respectively, with the straps partially installed on the isolator mechanism shaft extensions; and 
         FIG. 7  is a cross-sectional view of the shipping strap assembly embodiment of  FIGS. 5B and 6B  with the strap fully installed on the isolator mechanism shaft extensions. 
     
    
    
     While the invention will be described in connection with preferred embodiments thereof, it will be understood that it is not intended to limit the invention to those embodiments or to the details of the construction or arrangement of parts illustrated in the accompanying drawings. 
     DETAILED DESCRIPTION 
     The present shipping strap assembly is described in relation to presently known isolator mechanisms which permit the vibratory motion of the baskets of vibratory screening machines. As explained above, those isolator mechanisms are protected by known shipping straps which lock down the isolator mechanisms in a non-expanding and non-contracting condition. 
     Prior Art Isolator Mechanisms and Lock-Down Shipping Straps: 
     Looking at  FIG. 1 , a prior art shipping strap Z is shown in association with a prior art isolator mechanism I of a vibratory screening machine V. 
     The isolator mechanism I shown is a pivoting linkage of two parallel expansion coil springs C. Each spring C is fixed at one end to an upper sleeve S U  and at the other end to a lower sleeve S L . The sleeves S U  and S L  are pivotally mounted on upper and lower tubes T U  and T L  which extend through upper and lower pairs of ears E U  and E L  on the frame F and basket K of the vibratory screening machine V, respectively. Bolts B extend through washers W and nuts N 1  on the threaded ends of the bolts B to secure the sleeves S U  and S L  between their respective ears E U  and E L . 
     For the prior art arrangement shown in  FIG. 1 , the isolator mechanism I is used to hang the basket K from the upper ears E U  of the machine frame F. Thus, the weight of the basket K and its contents (not shown) tend toward expanding the coil springs C. Alternatively, isolator mechanism I could be used to support the basket K on the frame F on the isolator mechanism I. If so, the weight of the basket K and its contents (not shown) would tend toward compressing the coil springs C. 
     Continuing to looking at  FIG. 1 , if the prior art nuisance tasks hereinbefore discussed were first properly performed, the prior art shipping strap Z could then be installed to lock down the prior art isolator mechanism I. In the locked down condition, the gaskets G on the strap Z surround the nuts N 1  and abut the ears E U  and E L . The apertures A through the strap Z fit snugly on the bolts B, preventing all expansion or compression of the coil springs C. Additional nuts N 2  with washers W tightened down on the bolts B secure the strap Z against the exposed ends of the tubes T U  and T L  so that the isolator mechanism I is free to pivot but cannot be expanded or compressed. 
     However, still looking at  FIG. 1 , if the springs C have stretched or shortened at all, even within their elastic limit, the upper and lower apertures A U  and A L  in the strap Z cannot be simultaneously in alignment with their respective bolts B. Therefore, the strap Z cannot be installed on the isolator mechanism I for transport without levering the basket K to bring the aperture A L  into the necessary alignment with its bolt B. Furthermore, after transport, in order to put the machine V into its normal operation, it is necessary to totally disconnect the strap Z and the nuts N 2  and their washers W from the isolator mechanism I and hope that they, and the tools used for the purpose, will later arrive at the next destination of the machine V. 
     Shipping Strap Assemblies Protecting Isolator Mechanism Elastic Limits: 
     According to the invention, a shipping strap assembly is provided which can protect an isolator mechanism against exceeding its elastic limit. Looking at  FIG. 2 , the protective shipping strap assembly  10  of the present invention includes a first longitudinal distal extension  20  of one of the isolator shafts, a second longitudinal distal extension  60  of the other isolator shaft and a rigid strap. 
     One Extension 
     The first extension  20  has a boss  30  defining a guide path  31  that lies in the common plane defined by the longitudinal shaft axes X 1  and X 2 . The guide path  31  extends from a point  33  that is radially most-distal from the axis X 1  at an axially proximal end  35  of the boss  30  to a point  37  that is radially most-proximal to the axis X 1  at an axially distal end  39  of the boss  30 . The terms axially proximal and axially distal are herein used in relation to distances from the isolator mechanism I. The terms radially proximal and radially distal are herein used in relation to distances from their longitudinal axes of origin X 1  and X 2 . The guide path  31  is also bounded between a pair of limiting axes  43  and  47  parallel to the shaft axis X 1 . One limiting axis  43  extends through the radially most-distal point  33  of the boss  30  and the other limiting axis  47  extends through the most-proximal end point  37  of the boss  30 . In the assembly  10  shown, the guide path  31  extends downwardly from the radially most-distal point  33  to the radially most-proximal point  37  in a straight line path  31  and at an angle  49 . As shown, the radial distance  53  from the shaft axis X 1  to the radially most-distal point  33  is greater than the radial distance  57  from the shaft axis X 1  to the radially most-proximal point  37  by a distance  59 . 
     The Other Extension 
     The other extension  60  has a boss  70  defining another guide path  71  that lies in the common plane defined by the shaft axes X 1  and X 2 . As shown, this guide path  71  extends from a radial point  73  at an axially proximal end  75  of the second boss  70  to another radial point  77  at an axially distal end  79  of the second boss  70 . This guide path  71  is also bounded between another pair of limiting axes  83  and  87  parallel to the second shaft axis X 2 . One limiting axis  83  extends through the axially proximal radial point  73  and the other limiting axis  87  extends through the axially distal radial point  77  of its boss  70 . In the assembly  10  as shown, the guide path  71  extends upwardly from the axially proximal radial point  73  to the axially distal radial point  77  in a straight line path  71  at an angle  89 . 
     As shown, the radial distance  93  from the shaft axis X 2  to the axially proximal radial point  73  is greater than the radial distance  97  from the shaft axis X 2  to the axially distal radial point  77  by a distance  99 . However, the axially proximal radial point  73  of the second boss  70  need not be more radially distal from the shaft axis X 2  than the axially distal radial point  77 . The angle  89  and distance  99  could be 0°. 
     The Rigid Strap 
     The rigid strap  110  has a first aperture  130  extending through a corresponding first end portion of the strap  110  and a second aperture  170  extending through a corresponding second end portion of the strap  110 . The first and second apertures  130  and  170  are each aligned on corresponding longitudinal axes Y 1  and Y 2  that define a second common plane. The common plane defined by the aperture axes Y 1  and Y 2  can be positioned to coincide with the common plane of the shaft axes Y 1  and Y 2 . As shown, the first and second apertures  130  and  170  are contoured to receive the first and second bosses  30  and  70 , respectively. However, while the common planes may be positioned to coincide, the aperture axes Y 1  and Y 2  may or may not be simultaneously coincident with the shaft axes X 1  and X 2 . 
     As seen in  FIG. 2 , the first aperture  130  has a contact line  131  that lies in the common plane defined by the aperture axes Y 1  and Y 2 . The contact line  131  extends from a radially most-distal point  133  at an axially proximal end  135  of the first aperture  130  to a radially most-proximal point  137  at an axially distal end  139  of the aperture  130 . With respect to the strap  110 , the terms axially proximal and axially distal are also used in relation to the isolator mechanism I. The contact line  131  is also bounded between a pair of limiting axes  143  and  147  parallel to the aperture axis Y 1 . One limiting axis  143  extends through the radially most-distal point  133  of the aperture  130  and the other limiting axis  147  extends through the most-proximal end point  137  of the aperture  130 . In the assembly  10  shown, the contact line  131  extends downwardly from the radially most-distal point  133  to the radially most-proximal point  137  in a straight line at an angle  149 . As shown, the radial distance  153  from the shaft axis Y 1  to the radially most-distal point  133  is greater than the radial distance  157  from the shaft axis Y 1  to the radially most-proximal point  137  by a distance  159 . 
     The second aperture  170  has a contact line  171  that lies in the common plane defined by the aperture axes Y 1  and Y 2 . The contact line  171  extends from a radial point  173  at an axially proximal end  175  of the second aperture  170  to another radial point  177  at an axially distal end  179  of the second aperture  170 . This contact line  171  is also bounded between another pair of limiting axes  183  and  187  parallel to the second aperture axis Y 2 . One limiting axis  183  extends through the axially proximal radial point  173  and the other limiting axis  187  extends through the axially distal radial point  177  of its aperture  170 . In the assembly  10  as shown, the contact line  171  extends upwardly from the axially proximal radial point  173  to the axially distal radial point  177  in a straight line at an angle  189 . 
     As shown, the radial distance  193  from the aperture axis Y 2  to the axially proximal radial point  173  is greater than the radial distance  197  from the aperture axis Y 2  to the axially distal radial point  177  by a distance  199 . However, the axially proximal radial point  173  of the second aperture  170  need not be more radially distal from the axis Y 2  than the axially distal radial point  177 . Thus, the angle  189  and distance  199  could be 0°. 
     Angular Positioning of the Bosses in Relation to their Axes of Origin 
     As illustrated in  FIG. 2  in solid lines, in expanding isolator mechanism applications, the isolator mechanism I will stretch in response to the force applied by the load suspended below the isolator mechanism I. Therefore, the guide paths  31  and  71  of the first and second bosses  30  and  70  and the contact lines  131  and  171  of the first and second apertures  130  and  170  will lie outward of their respective first and second shaft and aperture axes X 1  and X 2  and Y 1  and Y 2 . However, as is also illustrated in  FIG. 2  in dashed lines, in compressing isolator mechanism I applications, the isolator mechanism will be compressed in response to the force applied by the load supported above the isolator mechanism I. Therefore, the guide paths  31  and  71  of the first and second bosses  30  and  70  and the contact lines  131  and  171  of the first and second apertures  130  and  170  will lie inward of their respective first and second shaft and aperture axes X 1  and X 2  and Y 1  and Y 2 . As shown, the inward guide path and contact lines are in the common planes of their axes X 1  and X 2  and Y 1  and Y 2 , 180° apart. 
     Axis Alignment Enablement 
     Continuing to look at  FIG. 2 , since the isolator mechanism I is a resilient device, over time the normal load distance  23  between the shaft axes X 1  and X 2  may stretch or compress, as indicated by directional arrows  25 , within their elastic limit, depending on whether the isolator mechanism I is a resiliently expanding or compressing device. Therefore, at the time of installation of the substantially inelastic strap  110  on the isolator I, it may not be possible to simultaneously align the shaft axes X 1  and X 2  with their respective strap aperture axes Y 1  and Y 2 . 
     However, since the angles  49  and  149  are greater than 0° and, therefore, the radius  57  of the boss  30  at its axially distal end  39  is smaller than the radius  153  of the first aperture  130  at its axially proximal end  135 , the strap apertures  130  and  170  can be aligned with their respective isolator mechanism bosses  30  and  70  regardless of whether the axes X 1  and X 2  are aligned. As long as the distance  23  between the axes X 1  and X 2  has not increased or decreased by more than the difference  59  in radial distance between the axially distal and proximal guide line points  37  and  33 , the strap apertures  130  and  170  can still be aligned with their respective isolator mechanism bosses  30  and  70  regardless of whether the axes X 1  and X 2  are aligned. Thus, the principle can be applied to one boss  30  and its corresponding aperture  130 . 
     This principle may, but need not necessarily, be applied in a given application to both the first boss  30  and aperture  130  as discussed above and also to the second boss  70  and second aperture  170  by use of angles  89  and  189  that are greater than 0°. As long as the distance  23  between the axes X 1  and X 2  has not increased or decreased by more than the sum of the differences  59  and  99  in radial distance between the axially distal and proximal guide line points  37  and  33  and  77  and  73 , respectively, the strap apertures  130  and  170  can be aligned with their respective isolator mechanism bosses  30  and  70  regardless of whether the axes X 1  and X 2  are aligned. 
     Moreover, the simultaneous alignment of the bosses  30  and  70  with the apertures  130  and  170  can be further aided even if the second guide path and contact line angles  89  and  189  are 0°. If so, the radial distances  53  and  57  are substantially equal and the radial distances  193  and  197  are equal but, if the radial distances  53  and  57  are less than the radial distances  193  and  197 , a gap  99  will separate the second guide path and contact lines  71  and  171 , providing leeway for alignment of the second boss  70  and the second aperture  170 . 
     Normal Load Length Restoration Enabled by One Boss/Aperture Gap 
     As long as the combined distances  59  and  99  are within the elastic limits of the isolator mechanism I, if the bosses  30  or  30  and  70  are not yet fully nested in their respective apertures  130  or  130  and  170  when initial contact is made between both bosses  30  and  70  and their respective apertures  130  and  170 , continued axial movement toward full nesting will either draw expanded isolator mechanism shafts closer together or spread compressed isolator mechanism shafts further apart. 
     Assume an application in which the angles  89  and  189  of the second boss guide path  71  and the second aperture contact line  171  are equal to 0° and the radial distances  93  and  97  are substantially equal to the radial distances  193  and  197 . Once the boss  70  enters snugly into the aperture  170  and the proximal contact point  133  of the first aperture  130  comes into contact with the guide path  31  of the first boss  30 , further movement toward full nesting will either draw expanded isolator mechanism shafts closer together or spread compressed isolator mechanism shafts further apart. However, sliding the strap aperture  170  snugly onto the boss  70  may be difficult. 
     Assume another application in which the angles  89  and  189  of the second boss guide path  71  and the second aperture contact line  171  are equal to 0° and the radial distances  93  and  97  are less than the radial distances  193  and  197 , providing a gap  99  between the boss  70  and the aperture  170 . Once again, after the second boss  70  enters into the second aperture  170  and the proximal contact point  133  of the first aperture  130  comes into contact with the guide path  31  of the first boss  30 . Unless it should coincidentally occur, further movement toward full nesting will eventually cause the second aperture  170  to come into contact with the second boss  70 . Thereafter, further movement toward full nesting will either draw expanded isolator mechanism shafts closer together or spread compressed isolator mechanism shafts further apart. The gap  99  between the boss  70  and aperture  170  will make it easier to slide the strap aperture  170  over the boss  70  while still providing the desired drawing of the expanded isolator mechanism shaft extensions  20  and  60  closer together or spreading of the compressed isolator mechanism shaft extensions  20  and  60  further apart. Furthermore, the size of the gap  99  can be selected to facilitate alignment of the boss  70  and aperture  170 , to facilitate drawing expanded isolator mechanism shaft extensions  20  and  60  closer together or spreading compressed isolator mechanism shaft extensions  20  and  60  further apart or to facilitate both alignment and drawing/spreading. However, the gap  99  must be selected such that the isolator mechanism I does not stretch beyond its elastic limit. 
     Assume yet another application in which the angles  89  and  189  of the second boss guide path  71  and the second aperture contact line  171  are not equal to 0° and the radial distances to the second guide line  71  are less than the radial distances to the second contact line  171 , providing a gap  99  between the boss  70  and the aperture  170 . Once again, after the second boss  70  enters into the second aperture  170  and the proximal contact point  133  of the first aperture  130  comes into contact with the guide path  31  of the first boss  30 . Unless it should coincidentally occur, further movement toward full nesting will eventually cause the second aperture  170  to come into contact with the second boss  70 . Thereafter, further movement toward full nesting will either draw expanded isolator mechanism shafts closer together or spread compressed isolator mechanism shafts further apart. The gap  99  between the boss  70  and aperture  170  will make it easier to slide the strap aperture  170  over the boss  70  while still providing the desired drawing of the expanded isolator mechanism shaft extensions  20  and  60  closer together or spreading of the compressed isolator mechanism shaft extensions  20  and  60  further apart. Furthermore, the size of the gap  99  can be selected to facilitate alignment of the boss  70  and aperture  170 , to facilitate drawing expanded isolator mechanism shaft extensions  20  and  60  closer together or spreading compressed isolator mechanism shaft extensions  20  and  60  further apart or to facilitate both alignment and drawing/spreading. However, the gap  99  must be selected such that the isolator mechanism I does not stretch beyond its elastic limit. 
     Variations in the Shapes of Bosses and Apertures 
     As shown in  FIG. 2 , the first and second apertures  130  and  170  have substantially identical shapes as the first and second bosses  30  and  70  that they respectively receive. The term “substantially identical” when used herein in reference to shapes is intended to allow for that slight variation in dimensions necessary for the full nesting of the bosses  30  and  70  in their respective apertures  130  and  170 . The term “substantially identical” used in reference to points, and particularly in reference to axially most proximal and distal points, is intended to allow for that slight variation in dimensions necessary to permit abutting the axially most proximal and distal guide path points  33  and  37  on the first boss  30  with their respective most proximal and distal contact points  133  and  137  on the first aperture  130  and to permit abutting the axially most proximal and distal guide path points  73  and  77  on the second boss  70  with their respective most proximal and distal contact points  173  and  177  on the second aperture  170 . 
     The configuration of the guide paths  31  and  71  of the bosses  30  and  70  need not necessarily be single straight lines as shown in  FIG. 2 . Looking at  FIGS. 3A-3F , the guide paths  31  and  71  may include one or more straight load-bearing segments  32  and  72  substantially parallel to the shaft axes X 1  and X 2  and one or more straight non-load-bearing segments  38  and  78  angled with respect to the shaft axes X 1  and X 2 , respectively. The substantially parallel segments  32  or  72  are considered load-bearing because, when fully engaged, they tend to maintain a constant axial relationship between the bosses  30  and  70  and the apertures  130  and  170 . The angled segments  38  and  78  are considered non-load-bearing because, when fully engaged, they tend to cause the apertures  130  and  170  to shift distally along the bosses  30  and  70 . While the angled segments  38  and  78  can also carry loads, they do not do so as efficiently. 
     In  FIG. 3A , a single straight line non-load-bearing segment  38  or  78 , like the guide paths  31  and  71  of  FIG. 2 , is illustrated. In  FIG. 3B , a single straight line non-load-bearing segment  38  or  78  is distally followed by a single straight line load-bearing segment  32  or  72 . In  FIG. 3C , a single straight line load-bearing segment  32  or  72  is distally followed by a single straight line non-load-bearing segment  38  or  78 . In  FIG. 3D , a single straight line non-load-bearing segment  38  or  78  is proximally preceded and distally followed by single straight line load-bearing segments  32  or  72 . In  FIG. 3E , a single straight line load-bearing segment  32  or  72  is proximally preceded and distally followed by single straight line non-load-bearing segments  38  or  78 . In  FIG. 3F , a single straight line load-bearing segment  32  or  72  is illustrated. 
     For any of the guide paths  31  and  71  illustrated in  FIGS. 3A-3F , any straight line non-load bearing segment  38  or  78  can be replaced by an irregular non-load-bearing segment  38 ′ or  78 ′, such as is exemplified in  FIG. 3G , provided the irregular contours of the segments  38 ′ and  78 ′ permit their respective bosses  30  or  70  to be fully received in their respective apertures  130  and  170  with their respective axially proximal and distal guide path points  33  and  37  and  73  and  77  and contact line points  133  and  137  and  173  and  177  in abutment. 
     Considering  FIGS. 2 and 3A-3G  taken together, in any embodiment of the shipping strap assembly, the contours of the contact lines  131  and  171  of the apertures  130  and  170  will be coordinated to cooperate with the contours of the guide paths  31  and  71  of the bosses  30  and  70 . The first aperture  130  has contact points  133  and  137  that are coordinated for abutting juxtaposition with the radially most-distal and most-proximal points  33  and  37  on the first guide path  31  when the first boss  30  is fully received in the first aperture  130  and the second aperture  170  is contoured to receive the second boss  70  and has contact points  137  and  177  that are coordinated for contemporaneous abutting juxtaposition with corresponding radial points  73  and  77  on the second guide path  71  of the second boss  70  when the second boss  70  is fully received in the second aperture  170 . 
     Axial Spacing Distances Related to Isolator Mechanism Elastic Limits 
     Furthermore, as best seen in  FIG. 2 , the distance  125  between corresponding contact points  137  and  177  of the first and second apertures must be within the elastic limit of the isolator mechanism I. That distance  125  can be selected to limit a range of motion of the second boss  70  relative to the first boss  30  within the elastic limit of the isolator mechanism I or can be selected to prevent motion of the second boss  70  relative to the first boss  30 . 
     Concentrically Symmetrical Embodiments of the Shipping Strap Assembly: 
     Now turning to  FIG. 4 , a concentrically symmetric embodiment of the shipping strap assembly  200  includes shaft extensions  210  and  240  and a strap  270 . The extensions  210  and  240  extend distally from, and are aligned on the axes X 1  and X 2  of, the shafts of an isolator mechanism I and include bosses  220  and  250 , respectively. The shipping strap  270  is a rigid member with apertures  280  and  290  through its end portions  271  and  273 . 
     The bosses  220  and  250  of the extensions  210  and  240  illustrated in  FIG. 4  are defined by the 360° rotation of the guide paths  31  and  71  of  FIGS. 3D and 3F  about the axes X 1  and X 2 , respectively. Thus, the boss  220  has a large diameter proximal cylindrical portion  221 , a conical portion  223  and a small diameter distal cylindrical portion  225 , all concentrically and symmetrically aligned on the axis X 1  and the boss  250  is cylindrical and aligned on the axis X 2 . 
     Similarly, the strap apertures  280  and  290  illustrated in  FIG. 4  are aligned on the axes Y 1  and Y 2  of the strap  270 . The apertures  280  and  290  are also defined by the 360° rotation of the guide paths  31  and  71  of  FIGS. 3D and 3F  about the axes Y 1  and Y 2 , respectively. Thus, the aperture  280  has a large diameter proximal cylindrical portion  281 , a conical portion  283  and a small diameter distal cylindrical portion  285 , all concentrically and symmetrically aligned on the axis Y 1  and the aperture  290  is cylindrical and aligned on the axis Y 2 . 
     However, the bosses  220  and/or  250  and the apertures  280  and/or  290  can be defined by generating any guide path consistent with the examples explained in relation to  FIGS. 3A-3G  about the axes X 1  and/or X 2 , and Y 1  and/or Y 2 , respectively, provided cooperable bosses and apertures are compatible as earlier explained herein. The first boss  220  and cooperable aperture  280  in the embodiment of  FIG. 4  include both cylindrical and conical portions and are, therefore, sometimes referred to as cylindro-conical. Such an identification is appropriate to any of the configurations of  FIGS. 3B-3E  while the configurations of  FIGS. 3A and 3F  are conical and cylindrical, respectively. 
     Moving in a distal direction from the isolator mechanism I, the first extension  210  includes a landing flange  211 , the boss  220  and a threaded distal end portion  230 . A nut  231  will be threaded onto the distal end portion  230 . The flange  211  serves as a landing area against an upper ear E U  of the frame F of the vibratory machine V shown in  FIG. 1 . The first extension  210  may be an integral part of, or an add-on fixed to, the first shaft of the isolator mechanism I. 
     Again moving in a distal direction from the isolator mechanism I, the second extension  240  includes a landing flange  241 , the boss  250  and a threaded distal end portion  260 . The flange  241  serves as a landing area against a lower ear E L  of the basket K of the vibratory machine V shown in  FIG. 1 . Optionally, a nut  261  can be threaded onto the threaded distal end portion  260  of the second extension  240  to hold the second extension  240  and the isolator mechanism I together. As shown, the outer diameter of the nut  261  does not overlap the outer diameter of the shaft extension  240 . The second extension  240  may be an integral part of, or an add-on fixed to, the second shaft of the isolator mechanism I. 
     The distance  291  between the axes Y 1  and Y 2  of the apertures  280  and  290  is equal to the distance  251  between the axes X 1  and X 2  of the shafts of the isolator mechanism I when the isolator mechanism I is at a normal loaded length. As shown in  FIG. 4 , the shaft axis distance  251  has a slight stretch  253  beyond its normal loaded length due to permanent deformation of the isolator mechanism I so that, when the shaft axes X 1  and X 2  are aligned, the second shaft is still within the range of alignment with the second aperture  290 . The cylindro-conical boss  220  on the first shaft extension  210  and the cylindro-conical aperture  280  through the strap  270  are complemental so that, when the boss  220  is fully nested in the aperture  280 , the circumferences generated by the points  33 ,  34 ,  36  and  37  and the surfaces generated by the lines  38 ,  32  and  38  of  FIG. 3D  are substantially coincident. The cylindrical boss  250  on the second shaft extension  240  and the cylindrical aperture  290  through the strap  270  have an annulus  263  therebetween which is preferably centered on the axes X 2  and Y 2  when the isolator mechanism I is at a normal loaded length and, as shown, is not centered because of the stretch  253 . Still, as will hereinafter be seen in relation to  FIG. 6B , the annulus  263  is sized so that, when the cylindro-conical boss  220  is fully seated in the cylindro-conical aperture  280  and the cylindrical boss  250  is fully inserted into the cylindrical aperture  290 , the isolator mechanism I and strap  270  are in the shipping configuration and the isolator mechanism I cannot extend beyond its elastic limit. 
     Looking at  FIG. 4 , to achieve the shipping configuration, the cylindro-conical and cylindrical apertures  280  and  290  of the strap  270  are first generally aligned with the cylindrical extensions  210  and  240  of the isolator mechanism shafts, approximately on their respective axes X 1  and X 2 . The annulus  263  shown allows some leeway, and the large diameter cylindrical portion  281  of the strap aperture  280  affords much greater leeway, for initially sliding the strap  270  onto the extensions  210  and  240  of the isolator mechanism I. 
     Once general alignment is achieved, sliding of the strap  270  onto the extensions  210  and  240  proceeds. If the initial alignment is not perfect, the large diameter cylindrical portion  281  of the strap aperture  280  will cooperate with the conical middle portion  223  of the boss  220  to bring the cylindro-conical strap aperture  280  into registration and eventually into abutment with the boss  220 . At the same time, the strap  270  comes into abutment with the flanges  211  and  241  of the extensions  210  and  240  of the isolator mechanism I. 
     Once the threaded distal end portion of the extension  210  is emerging through the cylindro-conical aperture  280  of the strap  270 , the nut  231  can be threaded onto the threaded distal end portion  230  of the extension  210  and manually tightened to drive the strap  270  toward the flange  211 . Thus, the cylindro-conical boss  220  and strap aperture  280  are brought into complemental juxtaposition. The preferred nut  231  has a body  233  with an internally threaded portion of length  237  slightly less than the length of the distal end portion  230  of the first extension  210 . Thus, the nut  231  binds up on the shaft  230  in a locking manner. 
     Some other concentrically symmetrical embodiments of the shipping strap assembly are illustrated in  FIGS. 5A-5D . The operating principles above described apply to the embodiments of  FIGS. 5A-5D . 
     In  FIG. 5A , the shipping strap assembly  300  includes shaft extensions  310  and  340  with bosses  320  and  350 , respectively, and a strap  370  with apertures  380  and  390 . The bosses  320  and  350  and apertures  380  and  390  are defined by the 360° rotation of the guide paths  31  and  71  of  FIGS. 3A and 3F  about the axes X 1  and X 2  and Y 1  and Y 2 , respectively. Thus, the first boss  320  and aperture  380  have only conical portions  323  and  383  concentrically and symmetrically aligned on the axes X 1  and Y 1 , respectively, and the second boss  350  and aperture  390  are cylindrical and aligned on the axes X 2  and Y 2 , respectively. As will hereinafter be seen in relation to  FIG. 6A , the cylindrical boss  350  on the second shaft extension  340  and the cylindrical aperture  390  through the strap  370  have an annulus  363  therebetween sized so that, when the conical boss  320  is fully seated in the conical aperture  380  and the cylindrical boss  350  is fully inserted into the cylindrical aperture  390 , the isolator mechanism I and the strap  370  are in the shipping configuration and the isolator mechanism I cannot extend beyond its elastic limit. The nut  331  will be threaded onto the distal end portion  330  of the first extension  310 . The flanges  311  and  313  serve as landing areas against upper and lower ears E U  and E L  of the frame F and basket K of the vibratory machine V shown in  FIG. 1 . The extension  310  and  340  may be integral parts of, or add-ons fixed to, the shafts of the isolator mechanism I. 
     In  FIG. 5B , the shipping strap assembly  400  includes shaft extensions  410  and  440  with bosses  420  and  450 , respectively, and a strap  470  with apertures  480  and  490 . The bosses  420  and  450  and apertures  480  and  490  are defined by the 360° rotation of the guide paths  31  and  71  of  FIGS. 3B and 3F  about the axes X 1  and X 2  and Y 1  and Y 2 , respectively. Thus, the first boss  420  and aperture  480  have proximal conical portions  423  and  483  and small diameter distal cylindrical portions  425  and  485 , all concentrically and symmetrically aligned on the axes X 1  and Y 1 , respectively, and the second boss  450  and aperture  490  are cylindrical and aligned on the axes X 2  and Y 2 , respectively. The cylindrical boss  450  on the second shaft extension  440  and the cylindrical aperture  490  through the strap  470  have an annulus  463  therebetween sized so that, when the cylindro-conical boss  420  is fully seated in the cylindro-conical aperture  480  and the cylindrical boss  450  is fully inserted into the cylindrical aperture  490 , the isolator mechanism I and the strap  470  are in the shipping configuration and the isolator mechanism I cannot extend beyond its elastic limit. A nut  431  will be threaded onto the distal end portion  430  of the first extension  410 . The flanges  411  and  413  serve as landing areas against upper and lower ears E U  and E L  of the frame F and basket K of the vibratory machine V shown in  FIG. 1 . The extensions  410  and  440  may be an integral parts of, or add-ons fixed to, the shafts of the isolator mechanism I. 
     In  FIG. 5C , the shipping strap assembly  500  includes shaft extensions  510  and  540  with bosses  520  and  550 , respectively, and a strap  570  with apertures  580  and  590 . The bosses  520  and  550  and apertures  580  and  590  are defined by the 360° rotation of the guide paths  31  and  71  of  FIGS. 3C and 3F  about the axes X 1  and X 2  and Y 1  and Y 2 , respectively. Thus, the first boss  520  and aperture  580  have proximal cylindrical portions  521  and  581  and small diameter distal conical portions  523  and  583  concentrically and symmetrically aligned on the axes X 1  and Y 1 , respectively, and the second boss  550  and aperture  590  are cylindrical and aligned on the axes X 2  and Y 2 , respectively. The cylindrical boss  550  on the second shaft extension  540  and the cylindrical aperture  590  through the strap  570  have an annulus  563  therebetween sized so that, when the cylindro-conical boss  520  is fully seated in the cylindro-conical aperture  580  and the cylindrical boss  550  is fully inserted into the cylindrical aperture  590 , the isolator mechanism I and the strap  570  are in the shipping configuration and the isolator mechanism I cannot extend beyond its elastic limit. The nut  531  will be threaded onto the distal end portion  530  of the first extension  510 . The flanges  511  and  513  serve as landing areas against upper and lower ears E U  and E L  of the frame F and basket K of the vibratory machine V shown in  FIG. 1 . The extensions  510  and  540  may be integral parts of, or add-ons fixed to, the shafts of the isolator mechanism I. 
     In  FIG. 5D , the shipping strap assembly  600  includes shaft extensions  610  and  640  with bosses  620  and  650 , respectively, and a strap  670  with apertures  680  and  690 . The bosses  620  and  650  and apertures  680  and  690  are defined by the 360° to rotation of the guide paths  31  and  71  of  FIG. 3F  about the axes X 1  and X 2  and Y 1  and Y 2 , respectively. The bosses  620  and  650  and apertures  680  and  690  have only cylindrical portions  621  and  651  and  681  and  691  concentrically and symmetrically aligned on the axes X 1 , and Y 1  and X 2  and Y 2 , respectively. The cylindrical boss  620  on the first shaft extension  100  and the cylindrical aperture  680  through the strap  670  are of substantially equal diameter. The cylindrical boss  650  on the second shaft extension  640  and the cylindrical aperture  690  through the strap  670  have an annulus  663  therebetween sized so that, when the first cylindrical boss  620  is snuggle and fully seated in the conical aperture  680  and the second cylindrical boss  650  is fully inserted into the cylindrical aperture  690 , the isolator mechanism I and the strap  670  are in the shipping configuration and the isolator mechanism I cannot extend beyond its elastic limit. The nut  631  will be threaded onto the distal end portion  630  of the first extension  610 . The flanges  611  and  613  serve as landing areas against upper and lower ears E U  and E L  of the frame F and basket K of the vibratory machine V shown in  FIG. 1 . The extensions  610  and  640  may be integral parts of, or add-ons fixed to, the shafts of the isolator mechanism I. In this configuration, no axial alignment leeway or isolator mechanism length restoration are afforded by the first boss  620  and aperture  680 . However, the annulus  663  does afford axial alignment leeway and a range of motion of the isolator mechanism second shaft extension  640  within the second strap aperture  640  within the elastic limits of the isolator mechanism I. While the first boss  620  and strap aperture  680  are locked down, the isolator mechanism I is not. 
     Turning now to  FIGS. 6A and 6B , which correspond to the embodiments of  FIGS. 5A and 5B , respectively, the taper angles  339  and  439  of the cooperable conical portions  323  and  423  and  383  and  483  of the bosses  320  and  420  and apertures  380  and  480 , respectively, and/or the size of the annuli  363  and  463  between the isolator mechanism shafts and their corresponding shipping strap apertures  390  and  490  can be predetermined to facilitate installation of the shipping straps  370  and  470  and the use of the shipping strap assemblies  300  and  400  to restore an isolator mechanism toward its normal load condition length. 
     Looking at  FIG. 7 , the shipping strap  470  of  FIGS. 5B and 6B  is fully installed on the isolator mechanism. The strap  470  is snuggly sandwiched between the upper flange  411  and the nut  431 . The strap  470  also abuts the lower flange  413 . The strap  470  is fully raised by the cooperating conical portions  423  and  483  of the upper boss  20  and the aperture  480 , restoring the isolator mechanism toward its normal load condition length. 
     Advantages: 
     The use of a shipping strap assembly with at least one at least partially conical boss and cooperable aperture facilitates installation of the shipping strap on the isolator mechanism without need for manipulating the basket of the vibratory screening machine. 
     Furthermore, the use of a shipping strap assembly with at least one at least partially conical boss and cooperable aperture facilitates use of the shipping strap assembly to restore an isolator mechanism, the length of which has been displaced from its normal load condition. 
     Also, the use of a shipping strap assembly providing an annulus between a shaft of the isolator mechanism and its corresponding shipping strap aperture facilitates installation of the shipping strap on the isolator mechanism without need for manipulating the basket of the vibratory screening machine. The annulus being less than the elastic limit, the isolator mechanism is protected against stretching. 
     And the use of a shipping strap assembly with at least one at least partially conical boss and cooperable aperture facilitates installation of the shipping strap on the isolator mechanism without the need for manipulating the basket of the vibratory screening machine. 
     The taper angle of the cooperable conical portions of the boss and aperture and/or the size of the annulus between the isolator mechanism shaft and its corresponding shipping strap aperture can be predetermined to enhance the above noted capabilities of the shipping strap assembly. 
     Preferably, the lengths of the shaft extensions, the tapers of the cooperable conical boss and aperture portions, if any, and the size of the annulus, if any, are also coordinated to permit disengagement of the strap from the isolator mechanism without ever disengaging the operating nut from the threaded extension of its shaft. In this case, the threaded extension can further be adapted to prevent removal of the operating nut from the threaded extension of its shaft, thereby assuring that neither the strap nor the nut can be lost. 
     Thus, it is apparent that there has been provided, in accordance with the invention, a vibratory screening machine shipping strap assembly that fully satisfies the objects, aims and advantages set forth above. While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art and in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications and variations as fall within the spirit of the appended claims.