Difference between revisions of "VTube Reverse Calc from MIL-D-9898C Absolute Bender Data to Centerline XYZ Data"
(→Example of Switching from CW to CCW Bend Angles) |
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| Value Range || Rotations are always a positive number in the range of 0 to 359.99. 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.) | | Value Range || Rotations are always a positive number in the range of 0 to 359.99. 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 || It is necessary to propagate the 180-degree change through the rest of the rotations that follow the one you just changed. | + | | Propagate Rotation Changes || It is necessary to propagate the 180-degree change through the rest of the CCW rotations that follow the one you just changed - <b>until you come to a bend that switches back to CW</b>. |
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− | < | + | Apply these rules to the example chart shown here.<br><br> |
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{| class="wikitable" | {| class="wikitable" | ||
− | ! | + | !Case |
− | ! | + | !Handling |
|- | |- | ||
− | | | + | | Bending switches to CCW at bend 3. || Adjust the 216.9-degree rotation by 180 degrees. |
|- | |- | ||
− | | | + | | Determine + or - || 216.9 + 180 = 396.9<br>216.9 - 180 = 36.9<br>The answer is 36.9. |
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+ | | Bend 4 rotation || Change from 306 to 126. | ||
+ | |- | ||
+ | | Bend 5 rotation || Change from 359.7 to 179.7. | ||
+ | |- | ||
+ | | Bend 6 rotation || The bend hand switches back to CW, so leave the rotation unchanged. | ||
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− | <td>The rotation before bend 6</td> <td>changes from 89.9 to 89.9+180 = 269.9 | + | <td>The rotation before bend 6</td> <td>changes from 89.9 to 89.9+180 = 269.9</td> |
</tr> | </tr> | ||
Revision as of 21:58, 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 these rules to the example chart shown here.
Case | Handling |
---|---|
Bending switches to CCW at bend 3. | Adjust the 216.9-degree rotation by 180 degrees. |
Determine + or - | 216.9 + 180 = 396.9 216.9 - 180 = 36.9 The answer is 36.9. |
Bend 4 rotation | Change from 306 to 126. |
Bend 5 rotation | Change from 359.7 to 179.7. |
Bend 6 rotation | The bend hand switches back to CW, so leave the rotation unchanged. |
Because of rule 2 - | all the following rotations will need to be adjusted 180 degrees |
The rotation before bend 4 | changes from 306 to 306-180 = 126 |
The rotation before bend 5 | changes from 359.7 to 359.7-180 = 179.7 |
The rotation before bend 6 | changes from 89.9 to 89.9+180 = 269.9 |
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Other Pages
- See also VTube-LASER v2.7
- See also VTube-LASER
- See also VTube-STEP