Difference between revisions of "VTube Reverse Calc from MIL-D-9898C Absolute Bender Data to Centerline XYZ Data"
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!Rule Explanation | !Rule Explanation | ||
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− | | Add or Subtract 180 to the Rotation if the Bend Hand Changes || The rotation at that bend must change by 180 degrees to take the bend plane direction change into account. | + | | Add or Subtract 180 to the Rotation if the Bend Hand Changes to CCW || The rotation at that bend must change by 180 degrees to take the bend plane direction change into account. |
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− | | Value Range || The rotations for this protocol are based on a 0 to 359.99-degree dial. Rotations are always a positive number in | + | | Valid Rotation Value Range || The rotations for this protocol are based on a 0 to 359.99-degree dial. Rotations are always a positive number in that range. Whether you add or subtract 180 depends on which method (adding or subtracting) gets you a positive number inside the valid positive range. (The only time rotations exceed 360 is for coiled parts - which is a special case for this protocol.) |
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− | | Propagate Rotation Changes || When the bend hand changes, it is necessary to | + | | Propagate Rotation Changes || When the bend hand changes to CCW, it is necessary to also change all following CCW bend rotations by 180 degrees. |
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− | | | + | | Propagation Stops When || However, the propagation of changes must stop when you come to a bend that switches back to CW. So, in the example case below, the last rotation is never changed. |
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− | ===Apply the | + | ===Apply the rules above to an example.=== |
{| | {| | ||
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| Bending switches to CCW at bend 3. || Adjust the bend 3 rotation of 216.9-degree rotation by 180 degrees. | | Bending switches to CCW at bend 3. || Adjust the bend 3 rotation of 216.9-degree rotation by 180 degrees. | ||
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− | | Determine + or - || 216.9 + 180 = 396.9, and 216.9 - 180 = 36.9<br><b>The answer is 36.9 because it fits within the 0 to 359.99 range.</b>. | + | | Determine +180 or -180 || 216.9 + 180 = 396.9, and 216.9 - 180 = 36.9<br><b>The answer is 36.9 because it fits within the 0 to 359.99 range.</b>. |
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| Bend 4 is still CCW, so change the rotation by 180|| Change the rotation from 306 to <b>126</b>. | | Bend 4 is still CCW, so change the rotation by 180|| Change the rotation from 306 to <b>126</b>. | ||
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<br><br> | <br><br> | ||
+ | [[image:mil-spec_cw_ccw_cw_bend_angle_in_VTube.png|1000px]] | ||
==Other Pages== | ==Other Pages== |
Latest revision as of 22:49, 8 July 2022
Contents |
General Principals for the 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. |
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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VTube Absolute LRA Data Rules
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Reverse Calc with Absolute LRA Data Requires an Accurate Cut Length
Reverse calculation requires an accurate cut length, so this dialog will display to allow you to enter a correct Cut Length before VTube finishes the calculation. This Cut Length value will overwrite the value in the Part Setup menu. |
Calculating the Last Length "LL" value
Notice in the MIL-D-9898C bender chart that there is no LAST LENGTH value. However, VTube includes a LL (Last Length) value in the last row.
If these three conditions are true, then you can use this feature to accurately calculate the LL value in this chart. |
Example of Switching from CW to CCW Bend Angles
This bender protocol assumes CLOCKWISE as the default bending direction. However, sometimes the part designer creates a tube shape where the bend hand changes from CW to CCW in the middle of the part. See the changing of bend hands in the two images on the right.
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Apply the rules above to an example.
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Other Pages
- See also VTube-LASER v2.7
- See also VTube-LASER
- See also VTube-STEP