Bend Connection

A Bend connection is formed between two objects when they are linked together by their end nodes. In some cases a successful bend intersection also requires the section sizes of the two objects to be matched so that the two objects fully terminate each other when they are intersected.

Fig: Valid bend intersection

There are two distinct cases of bend intersection that can occur. These are (1) Crossing intersections and (2) Inline intersections, as illustrated below. In the case of 'crossing' intersections it is usually essential to have matched section sizes for the bend intersection to be successful. In the 'inline' cases the objects can satisfactorily 'terminate' each other and form a successful intersection without the need for matching (although some types of matching can still be advisable).

For crossing intersections, if the objects are not matched then their intersection will be interpreted as a tee intersection instead of a bend, where the smaller object is teed on to the larger. Generally this is not a valid intersection because the tee occurs so close to the end of the larger object, but in some cases where multiple objects are joined by their end nodes it may be a valid design.

Fig: Invalid intersection (1.Outline 2.Cut)

The following image shows the same intersection with a third object added. The additional object is matched to the cone and therefore forms a valid bend intersection. The smaller cylinder can now be matching into the bend correctly to form a valid 3-way bend connection with the cylinder unmatched. In effect the cylinder is treated as a tee onto the two other parts together.

Fig: Bend intersection of 3 objects with an unmatched object

NOTE: to achieve a successful intersection in the above case it is necessary to adjust one of the more complex 'Weld options'. In this case just the 'Termination Level' option is raised to '2nd'. Normally the termination level is set to 'None' because most designs are fully matched and the termination checking for fully matched objects is redundant. For large designs the termination setting can slow down the speed of the intersection calculation so the default setting of 'None' is nothing more than a time saving measure. For designs with few parts this is generally not a problem so the termination level can be raised for all designs until the calculation speed becomes an issue.

Inline bend intersections are in some ways much more flexible that crossing intersections because the objects fully terminate each other irrespective of their section sizes. This applies to all section shapes (see example below). Note that inline does not necessarily mean that the object center lines are lined up. There may be some difference in their orientation but the taper (or flare) of the objects may still mean that they are an inline case. Often by reducing the taper of one of the objects the intersection changes from an inline case to crossing case.

Fig: Inline intersection - cone to rectangle.

There are one or two special considerations to make for inline object intersections which may still mean that it is preferable to perform some kind of section size matching of the objects. First of all the most common inline intersection is where the center lines are exactly aligned. Often in these cases the the section shapes of the objects at their ajoining ends are the same. In these cases there is a common requirement to simply match the two faces to be the same size and shape. This is called face matching.

Secondly in the case of inline circular object intersections (cones and cylinders) it may be desireable to match the objects. The advantage is that the intersection gives a straight cut when viewed from the side, whereas if the objects remain unmatched the side view of the intersection appears curved.

Fig: Bend circular - matched straight, unmatched curved.

In the case of circular matching sections the objects are not 'face matched' to achieve the straight cut, they are matched using something called the 'common central sphere' (CCS - only applicable for circular sections). This can be overridden and face matching used instead but the face match may product the curved line. Also the CCS match has a great advantage that any number of circular sectioned objects (cones and cylinders) can be intersected at the same point and each mutually terminates all the other. Ths means 1. all cut lines are straight and 2. there is no need to raise the complex options such as the 'termination level' option (discussed above) to achieve a successful intersection.

Finally Sheet Lightning s capable the most complex bend intersection. The matching facilities work for all sections enabling objects of entirely different shape to successfully terminate each other in the bend.