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

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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.

Bendxyz militaryspec.jpg

Conrac bender horizontal.png


Contents

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.

Tape measure.png



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".

Conrac rotation dial.png



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).




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