Strips

For the development the plate is divided into a number of strips by partitioning the plate along the baseline into intervals of equal length. Each strip is restricted by two planar strip curves (the end strips by edges 1 and 3, respectively). There are three options to control the plane of the strip curves:

• To be located in a principal plane (normally the principal plane that is ‘most’ perpendicular to the baseline curve).

• To be perpendicular to the baseline in the point of intersection with it (that means, the strip plane is defined by a point on the baseline and the normal of the baseline in this point).

• To be distributed along edge 2 and edge 4 with the same relative distance as between the points along the baseline. In this case the plane is defined by three points on edges 2 and 4 and the baseline (provided they are not collinear).

The figures below illustrate what the strips will look like when developed for one and the same plate with use of these three options.

For most plates the end result will be practically the same independent of the option selected but in certain cases selecting the right option may give a better result (or even be the only option that gives a result at all).

Conditions for any strip curve are:

• It must intersect the baseline and the edges 2 and 4 in exactly one point.

• It must not intersect any other strip curve (or the edges 1 and 3).

The program will automatically adjust the plane of the strip curves to fulfill these conditions to the extent possible.

Thus a fundamental restriction is that both of edges 2 and 4 must have a single and well defined intersection with each strip curve. for example, suppose that for the plate below the strip planes have been selected to be principal planes. (The program will always make certain that ‘extra’ strip curves are added through the knuckle points along edges 2 and 4, if required).

At the knuckle point (KN) the edge 4 is not unique with respect to the strip curve at this position (there are two knuckle points in the same position along the baseline!) and there is a risk that the plate will be improperly developed. In this case there is a simple way to overcome the problem by selecting the strip option Perpendicular Baseline with a result as shown in the figure below.

If the edges have very special characteristics or violate the rules above it may be better to develop the plate with a simpler geometry from an ‘envelope’ and then subtract some information by aid of a generalised hole. The plate below is not possible to treat as suggested in the figure above since inevitably some strip planes will have more than one intersection point with edge 4.