VTube Reverse Calc from MIL-D-9898C Absolute Bender Data to Centerline XYZ Data

This military spec bender chart data chart can converted by VTube-STEP and VTube-LASER in the LRA grid section of the Part Data menu. This specification was created decades ago when CONRAC benders were popular with the US Air Force. It was made inactive according to NOTICE 1 on January 21, 1986. No new designs are created with this spec. CONRAC benders have been obsolete for decades, but legacy tube shape data is still stored with this specification.

General Principals for the Military Specification

ABSOLUTE LENGTHS

This bender data spec uses ABSOLUTE LENGTHS between bends as if they were derived from a tape-measure attached to the Feed axis of a bender. CONRAC benders sometimes had tape measures riveted along the rail of the carriage that moves along the length of the bender. The lengths indicate where each bend begins.

ABSOLUTE ROTATIONS

According to the spec, the bender data uses ABSOLUTE ROTATION data (twist angle between the planes of the bends). It is absolute because it always depends on the rotations in all preceding bends accumulated. The dial on an absolute rotation spindle reads from 0 to 360. If a rotation does not change from one bend to the next, then the rotation value remains at the degree position that it was at in the previous bend. For example, if a rotation is at 270 degrees, and the next bend has no rotation relative to this bend, then the rotation dial stays at 270 for the next bend. Every rotation value depends on the proceeding rotation values. This is why it is referred to as "absolute".

DRAW BENDING

Although it seems to be ambiguous in the specification, most of the part data from this specification assumes DRAW bending versus COMPRESSION bending - which means the LENGTH values move the carriage so that the tube is positioned at the start of each bend (for clamping and drawing around the bend die that rotates with the bend arm) rather than the end of each bend (for clamping with rollers or wipers and compressing around the bend die that does not rotate with the bend arm).

VTube Absolute LRA Grids

The Absolute LRA grids are in both STEP and LASER modes of VTube. They are automatically calculated when you import a model or enter centerline XYZ data. You can Reverse Calc to XYZ data from Absolute LRA data by entering data in the Absolute LRA grids in either VTube-STEP and VTube-LASER. Be sure to keep the mouse in the grid while you are entering new data to prevent the XYZ to LRA calculator from overwriting your entries.. The LAST length value is always the length of the last straight of the tube. All other lengths should start with larger values, then decrease as you move down the tube. None of the lengths should be larger than the Cut Length - or negative incremental length values may be calculated. The rotation values are always within a range of 0 to 360 degrees. If you enter any negative value, then it will automatically be converted to its equivalent in the 360 range. For example, -45 degree will be converted to +315 degrees 360 + -45

Reverse Calc with Absolute LRA Data

Press the Reverse Calc button above the grid to recalculate new centerline XYZ data. This specification requires an accurate CUT LENGTH, so a Cut Length dialog will display to allow you to enter a correct Cut Length before it finishes the calculation.