TubeCAD allows you to calculation elongation (the stretching of the arc during draw bending) with two formulas.

Both formulas require some experimentation on the part of the user in order to determine the best variable setup for each process. The two formulas are:

1. OD-based Formula
2. Arc-length Multiplier Formula

The Arc-length formula simply multiplies the arc-length by a value slightly less than 1 to derive a new arc-length. The OD-based formula is more sophisticated in that it takes into account the diameter of the tube in question.

Customers tell us repeatedly that the OD-based formula works best. Based upon this feedback from several customers, we recommend that you choose the OD-based formula.

Several years ago, one of our customers approached us with this proposal: "If you include our formula, then we will purchase your TubeCAD." We agreed and incorporated their formula into our reports.

The variable in this formula is a very small value that is derived from testing. The contributor of this formula had built up a database of values based upon unique tube diameters, which he guarded as a proprietary to his company. We recommend to each customer that they build their own proprietary values for use in this formula.

You can find the elongation value for any unique OD by performing a length test on your tube or pipe before and after bending. For example, if you are draw bending, then the elongation will usually end up in the last length. It will be longer due to total elongation. You could create a single 90-degree bend and measure the extra stock in the end of the tube. (It is very simple to predict the non-elongated length on this configuration before you start bending.) You may find, for example, that a value 0.001 works well for 1-inch tubing. New tests should be performed for different OD configurations.

TubeCAD users can setup the command by entering the ELONG command at the command line in TubeCAD.

1. Choose option 1 (Set elongation formula switch.)
2. Choose option 0 (zero) to select the OD-Radius formula.
3. Choose option 2 to view the formula and enter the unique variable.
4. Choose option 0 to exit the menu.