Unfolding of polybeams - Common problems

Environment

Not environment-specific

Introduction

Unfolding is the term used in Tekla Structures when a polybeam is made ‘flat’ for the purpose of creating drawings aimed at manufacturing.
In some situations, unfolding of polybeams is not successful. These instances can usually be identified if:

An unfolded single part drawing is empty, when you turn on Unfolding: Yes (‘Single-part drawing properties’ dialog box > View > Attributes > Unfolded: Yes).
There are some error messages in the log file (Tools > Display log file > Session History), for example:
- “Solid error: Glueing solids failed”
- “Solid polybeam error: Cannot create frame point”
- “Solid error: Creating one of the glued solids failed”, etc.
A polybeam turns into a ‘line’, as shown below. This usually happens if the radius chosen for the chamfer is too large, or the geometry of the polybeam points is invalid.

Incorrect unfolding can also be the cause of incorrect NC files.

Note: This document does not cover how a polybeam is unfolded (that is, which unfolding parameters are used, through which bending radius a polybeam is unfolded, etc).

Cuts at the same level as chamfer solid edges

This error usually occurs when using curved chamfers in polybeams. Curved chamfers are made of solid edges. Since Tekla Structures 17.1, you can use the command ‘Draw Selected solids with all edges’ (available from the ‘Options’ > ‘Customize’ toolbar editing dialog box) to visualize the edges. If the edge of a cut is at the same level to any of these solid edges, then you will get solid errors and the polybeam will not be unfolded correctly. See below.

Cuts' planes 'flush' with part planes

This error is commonly seen when using 'Cut using other parts'. Example below:

In this L-shaped plate (created using a polybeam), the cut is cutting the lower side completely, so the face of the part cut is at exactly the same level (‘flush’) to the vertical plate face, as shown below.

This will normally give solid errors. The correct way to model these cuts is to model the face of the cut away from the face of the plate, by a minimum of 0.3 mm, as shown in the picture below.

If erroneous part cuts are created by components, they should be reported to Tekla Global Helpdesk.

Polybeams curving in two directions (3D polybeams)

Polybeam unfolding is not supported in 3D cases, such as shown below.

However, sometimes it is not so obvious that a polybeam is folding in more than one plane, as in the example below. If you see the side view, we can see that one of the handles has been moved a certain distance “off-plane”, as shown below.

Tekla Structures is mostly able to unfold these types of polybeams. However, the end results, such as length, might not be as expected. The most obvious error though, is that there will be no unfolding line in the drawings, or it would be in an incorrect position.

Tips for troubleshooting polybeam unfolding problems

The way to solve these problems is to identify what is causing the unfolding to fail. Usually, this is a cut, but it can be other things such as the size of a curved chamfer radius. These tips could help:

You can choose to see the shape of the chamfers by setting advanced options: Model View : XS_DRAW_CHAMFERS_HANDLES= CHAMFERS_AND_HANDLES.

Tekla Structures shows the status of polybeam chamfers using the following colors:

If you see solid error messages in the Session history log, you can select the error line, right-click, and select options such as ‘Zoom > Zoom selected’ or ‘Fit Work Area to Selected Parts’ to easily identify the problematic part.
To see the solid edges which make up the curved chamfers, you can bring to your toolbars the button “Draw selected solids with all edges”, from the Tools > Customize… menu.