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CAD, CAM and shop data exchange · Lesson 2 of 4

CAD, CAM and shop data exchange: materials, standards and design constraints

The conventions every exchanged drawing has to state (units, coordinate frame, angle convention, model space, layers and dimension definition points), how precision is handled, and the AFS limits and folder behaviour the file does not carry.

You will be able to: Identify the units, coordinate frame, angle convention, layer and dimension rules an exchanged drawing must declare, and the AFS fabrication limits a profile must meet before it can be sent.

11 min · 11 slides · 8 questions

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Slide 1 of 11

Units must be declared

Autodesk's DXF header codes for $INSUNITS include 1 Inches, 2 Feet, 4 Millimeters, 5 Centimeters and 6 Meters.

Autodesk describes $INSUNITS as the default drawing units for AutoCAD DesignCenter blocks. AFS's CAD reader reports it as the drawing unit; it can be 0, Unitless, so confirm the unit against a known dimension.

NIST Handbook 44 defines 1 inch = 25.4 millimeters exactly.

Units codes and the 25.4 factorA table of the DXF header units codes: 0 unitless, 1 inches, 2 feet, 4 millimeters, 5 centimeters, 6 meters, with code 0 outlined as a warning. Below, three bars on a log scale in inches: a 2 inch leg read correctly; the same number read as millimetres, 0.0787 inch; and a metric 50.8 read as inches, which crosses the dashed line at AFS's 48 inch maximum girth.DXF header units codes ($INSUNITS)code 0Unitlesscode 1Inchescode 2Feetcode 4Millimeterscode 5Centimeterscode 6MetersCode 0 tells you nothing: confirm with a knowndimension. 1 in = 25.4 mm exactly (NIST).One leg, three readings (log scale, inches)2 in, read correctly“2” read as mm = 0.0787 in“50.8” read as inches48 in0.01 in0.1 in1 in10 in100 indashed line: AFS maximum girth, 48 in

A table of DXF units codes with code 0, unitless, outlined as a warning, and three bars on a log scale: a 2 inch leg read correctly, the same number read as millimetres (0.0787 inch), and a metric 50.8 read as inches, which crosses the 48 inch line.

Units codes from Autodesk's DXF Reference; 1 in = 25.4 mm exactly (NIST Handbook 44). The dashed line is AFS's 48 in maximum girth.

Sources

Videos for this lesson

What this video shows: RAS, a folder maker, shows its software importing a DXF that gives the blank and bend lines; the angles are added by hand, then the bending sequence is programmed. Not AFS's equipment.

Video: Multibend-Center: Programmierung mit dxf-Datei | Multibend-Center: Programming with dxf file by RAS Reinhardt Maschinenbau GmbH, on YouTube. AFS checked its description against this lesson.

What this video shows: AMS Controls shows its control bending to a nominal angle, measuring it, then overbending to correct springback. An AMS feature, not a description of AFS's folder.

Video: Pathfinder Automatic Springback Compensation Feature by AMS Controls, on YouTube. AFS checked its description against this lesson.

Glossary

$INSUNITS
A DXF header variable that Autodesk describes as the default drawing units for AutoCAD DesignCenter blocks, stored as a code: 0 Unitless, 1 Inches, 2 Feet, 4 Millimeters, 5 Centimeters, 6 Meters, among others. AFS's CAD reader reports it as the drawing unit, so confirm it against a known dimension.
Model space and paper space
In a DXF, model space holds the drawn geometry and paper space holds sheet layouts; group code 67 set to 1 marks an entity in paper space.
Definition point
A point stored with a DXF dimension that lies on the geometry being measured; a linear dimension has two, in group codes 13 and 14.
Included angle
The angle between the two legs of a bend: 180 degrees is flat, 90 a right angle. FlashDraft labels bends with this angle, signed for direction.
Bend angle
How far the metal is turned from flat; for a sharp bend it equals 180 degrees minus the included angle. AMS Controls documents its folder feature angle this way.
Handedness
Which way a fold turns. A bend's sign only means something together with its coordinate frame: coordinates moved between a y-down and a y-up frame without negating y come out mirrored, with every bend sign reversed.