Bend Table value - Correlation to drawing flat pattern bend extents

[CadManagerMoffatNZ]

Hi All

i'm looking for some technical (Autodesk back office) type advice on a issue / non issue problem that has been brought to my attention.

Please see the attached image file.

You can see that for our 0.8mm material we have a bend table value of 1.48mm for a 90° bend.

However when the flat pattern (with bend extents shown) is fully dimensioned (for use by a subcontractor) the distance between flats is shown as 2.10mm.

The actual part in question develops correctly and when folded hits the desired finish size of 20.8 x 20.8.

Can anyone provide some information on the 2.1mm dimension.

From my calculation it looks like the neutral axis (k-factor) length from the bend table 0.44.

FYI inner bend arc-length is 1.61mm and outer face arc length is 2.12mm (see attached image)

Like i said i don't necessarily think its right or wrong probably more just confusing for our users how were expecting to see the 1.48mm value.

So if anyone can shed some light on this for me so i can pass it on that would be appreciated.

[johnsonshiue]

Hi Daren,

There should be a logical reason explaining the behavior. Please share an example sheet metal ipt file. Forum experts can help take a look and understand the behavior better.

Many thanks!

[CadManagerMoffatNZ]

Johnson

here is a simple section that illustrates the non-error.

Like i said its not wrong in respect of the final part being folded correctly and to specification its how and where the bend extents are generated in relation to the bend table values.

Thanks

[johnsonshiue · Accepted solution]

Hi Daren,

I took a quick look. This is about the confusion of how the Bend Allowance was calculated. In your case (the images you attached), the bend zone height is 20.8 mm - 19.0 mm = 1.8 mm. It is the same on the other side, so the sum of both sides is 3.6 mm. Then, it needs to subtract the Bend Allowance. From the table, it comes to 1.48 mm. So the resultant bend zone is 2.12 mm, which is in sync with the drawing.

The same calculation can be done for the sheet metal part you attached. The result should be the same. The back K-factor is only in action when the Bend Table is incomplete or Inventor cannot find the appropriate Bend Allowance based on the given thickness and bend radius. I am not seeing a bug here.

Many thanks!

[CadManagerMoffatNZ]

Hi Johnson

Yes i never thought it as a bug more of a WTF moment by one of the design team here and i was at a loss to explain where the exact value came from.

Its hard to tell someone its right but wrong without being able to give some substance to that argument.

Thanks to your explanation i now can.

regards