Overview

VTube now offers three ways to compensate for bend elongation: Simple %, Multiple %, and Interpolated Distances. You choose one per part in the new Elongation Setup window. Interpolated setups can be saved in a shared library and reused across projects.

When the tube is bent, the material stretches along the outside of the bend. The finished part, therefore, comes out slightly longer than its nominal centerline length. To land on the right finished length, VTube shortens each bend arc by an elongation amount when it calculates the cut length.

The nominal arc length of each bend comes from its centerline radius (CLR) and its bend angle

The elongation method decides how much is taken off that arc. The compensated arcs feed the cut length and the straight positions used when the part is unbent. Only CLR and bend angle are used. OD, wall, and material are not part of the calculation.

The three elongation methods

Use Simple % when one value works for the whole part, Multiple % to control elongation uniquely for each bend, and Interpolated elongation distances when you have measured elongation at several bend angles.

How Interpolated Distances are looked up

Each row says how much length to remove for a bend of that angle. For angles between two rows, VTube interpolates a new value.

Example: your table has 45° = 0.020 in and 90° = 0.040 in. A 60° bend uses 0.027 in.

• One row only: that distance is used for every bend.
• Below the smallest or above the largest angle: VTube continues the slope of the two nearest rows. Include rows that cover your smallest and largest bend angles.
• Row order: rows do not need to be in angle order. VTube sorts them for the calculation.
• Duplicate angles: avoid entering the same angle more than once.

Percentages in Simple % and Multiple % run from 0 to 100. A higher percentage makes each bend arc shorter.

Choosing and setting up a method

All three methods are set in the Elongation Setup window. It opens on the tab for the method currently in use.

Open Elongation Setup

Use any of these:

• In the Part Setup grid, click the value cell of the Tube Elongation % row.
• Right-click the Part Setup grid and choose Multi-Elongation Percentage Setup.
• Right-click the XYZ grid and choose Multi-Elongation Percentage Setup.

This works in both the main window and the Measure window. If your system uses UAC, you may be asked for the Part Setup password.

Simple %

1. Open the Simple % tab.
2. Check Use the SINGLE tube elongation percentage in part setup.
3. Type the percentage in Tube Elongation, then press Enter.
4. Click Close.

Multiple %

1. Open the Multiple % tab.
2. Check Use the MULTIPLE tube elongation percentages.
3. In the grid, type a percentage in the Elong% column for each bend.
4. Click Close.

Interpolated Distances

1. Open the Interpolated Distances tab.
2. Check Use Interpolated Bend Elongations based on bend angles.
3. Enter a name in Elongation Setup Name, for example the material, diameter or bender.
4. Build the table in one of two ways:
   • Click Get New Setup from Interpolated Setup Library and pick a saved setup (see the next section).
   • Or enter rows yourself: type each Angle (degrees) and Elong Dis. Use Add, Insert, Up, Down, Delete and Undo, or right-click the grid.
5. Check the Unit column. Distances are entered in the units shown there (in or mm). Click the M/I button in the window header to switch units.
6. Click Close.

Only one method is active at a time. Checking one box clears the other two.

Check the result

• The Tube Elongation % row in Part Setup shows the active method, for example Simple 3%, Multi - Unique Per Bend or Interpolated - 304SS 1.5in - Data Points: 4. Simple percentages are rounded to a whole number here only; the full value is still used.
• If Automatic Calc Cut Length Type is AutoCalc ON + Elong Comp, the cut length is recalculated when you close Elongation Setup. The viewport header reads CUT LENGTH recalculated with Elongation Compensation followed by the method.
• AutoCalc ON Nominal ignores elongation. With AutoCalc OFF, right-click Part Setup and choose Recalculate Cut Length from the XYZ Data - WITH Elongation Compensation.
• Reports can show the method with the Tube Elongation Calc Type field, as in the Bender Data report.

Using the Interpolated Bend Elongation Library

The library stores named angle/elongation tables so you can reuse them in every project. It is saved as InterpolatedBendElongationLibrary.xml in the VTube configuration folder. Every change is saved as soon as you make it.

Each library entry has a Name and a list of Angle / Elong Dis data points. Entries do not store material, OD, or CLR, so put those details in the name, for example, 304SS 1.500 x 0.065 3.0 CLR.

Build and maintain the library

1. On the main toolbar, click System Options.
2. Open the Global Level Lists tab and click Edit Interpolated Elongation Setup Library.
3. In Library Entries, right-click and choose Add Row to create an entry. Type its Name.
4. With the entry selected, right-click in Angle / Elongation Datapoints of the Selected Library Entry and choose Add Row for each datapoint. Enter the Angle and Elong Dis.
5. Use Insert Row, Delete Row, or Clear all Rows to make changes. VTube asks before anything is deleted.
6. Click Close.

The Datapoints column shows how many rows each entry has. The M/I button switches the displayed units between inch and mm; stored values are not changed.

Apply a library entry to a part

1. Open Elongation Setup and go to the Interpolated Distances tab.
2. Click Get New Setup from Interpolated Setup Library.
3. Select an entry and click TO Part Setup, or double-click the entry.

VTube copies the name and datapoints into the part and switches the part to Interpolated Distances. You can undo this in one step.

The part keeps its own copy. Editing the table in Elongation Setup does not change the library, and later library edits do not change parts that already used the entry.

Share a library between computers

• Export Library saves the whole library to an .xml file you choose.
• Import Library loads an .xml file. If the library already has entries, choose Replace to overwrite them or Append to add the imported entries to the end.

Import and Export are available when the library is opened from System Options.

Tips and FAQ

I copied a percentage from the Material Table, but the cut length did not change. Copying from the Material Table, the Springback Table or the TubeCalc Elongation Converter sets the Simple % value only. It does not switch methods. If the part uses Multiple % or Interpolated Distances, open Elongation Setup and check Use the SINGLE tube elongation percentage in part setup.

My cut length ignores elongation. Check Automatic Calc Cut Length Type in Part Setup. AutoCalc ON Nominal does not apply elongation; choose AutoCalc ON + Elong Comp.

Part Setup shows Simple 3%, but I entered 2.75. The Part Setup cell rounds for display. VTube calculates with 2.75.

A bend outside my table's angle range looks wrong. VTube extends the slope of the two nearest rows beyond the table, with no warning. Add rows at or beyond your smallest and largest bend angles.

I have elongation from TubeCalc as a distance per degree. Right-click Part Setup in the Measure window and choose Convert TubeCalc Elongation to VTube Elongation. Enter the distance per degree and the CLR, click Calculate, then Copy Calculated Value to Part Setup. Alternatively, enter it as Interpolated Distances: multiply the distance per degree by each angle.

Can I calculate elongation from a measured part? Yes. In the Measure window, right-click Part Setup and choose Recalculate Tube Elongation % from Measured Length minus Cut Length. This sets the Simple % value.

Do older project files still work? Yes. Parts saved with the older multi-elongation option open as Multiple %. All other older parts open as Simple %.

Tips

• Record elongation data from test bends at the angles you bend most often.
• Name library entries so anyone can tell which material, size, CLR, and bender they belong to.
• Export the library as a backup, and import it into other VTube stations so everyone uses the same data.