Tube bending data

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jfc4120
Posts: 448
Joined: Sat Jul 02, 2022 11:16 pm

Tube bending data

Post by jfc4120 »

Code: Select all

OS: Windows 10 Version 2009
Word size of FreeCAD: 64-bit
Version: 0.20.2.29177 +426 (Git)
Build type: Release
Branch: (HEAD detached from 0.20.2)
Hash: 930dd9a76203a3260b1e6256c70c1c3cad8c5cb8
Python 3.8.10, Qt 5.15.2, Coin 4.0.1, Vtk 8.2.0, OCC 7.6.3
Locale: English/United States (en_US)
Installed mods: 
  * Curves 0.6.9
  * Help 1.0.3
Say a one inch tube with 3.5 inch radius.

Draw center lines and points.
tube1.png
tube1.png (19.75 KiB) Viewed 2163 times
A basic (the language) program I had since the 1990's converted to python generates bend data:
tube2.png
tube2.png (17.46 KiB) Viewed 2160 times
And to view if needed or desired:
tube3.png
tube3.png (21.09 KiB) Viewed 2163 times

I write to CSV and use Libreoffice Calc in case I need to do other calculation, add notes, etc.
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ThanklessLiving
Posts: 98
Joined: Sat May 30, 2020 1:49 pm

Re: Tube bending data

Post by ThanklessLiving »

Very nice! It's impressive how the sharp corners are radius'd into a smooth arc. Looks to be very useful for routing pipes in an existing assembly, and the simple segmented line is a good way to base the tube.

Could you post more info about how all this is done? Does the "length of bend" take into account a neutral factor (otherwise you can never obtain accurate dimensions in the finished part...)? Is it easily parametric?
jfc4120
Posts: 448
Joined: Sat Jul 02, 2022 11:16 pm

Re: Tube bending data

Post by jfc4120 »

@ThanklessLiving There are two centerline radiuses used, one for setback and the other is for the length of bend (the curve part) due to gain and loss.

They aren't sharp bends, even a 1.5 inch tube uses a 4 inch radius, but depending on material, a mandrel may be needed.

And yes it's very accurate, I have compared with tubes bend on Eaton Leonard tube bender automation, and all is within a very small amount, .01 , .02, etc.

I also have some springback charts, but it's not implemented in python.
Does the "length of bend" take into account a neutral factor
You always work off of a centerline, but depending on the material the centerline for length of bend can change, thus the entering of two different raduises. You also do test bends to calculate gain and loss in order to know the the radius to use for bend allowance.
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ThanklessLiving
Posts: 98
Joined: Sat May 30, 2020 1:49 pm

Re: Tube bending data

Post by ThanklessLiving »

jfc4120 wrote: Tue May 30, 2023 10:07 pm @ThanklessLiving There are two centerline radiuses used, one for setback and the other is for the length of bend (the curve part) due to gain and loss.

They aren't sharp bends, even a 1.5 inch tube uses a 4 inch radius, but depending on material, a mandrel may be needed.

And yes it's very accurate, I have compared with tubes bend on Eaton Leonard tube bender automation, and all is within a very small amount, .01 , .02, etc.

I also have some springback charts, but it's not implemented in python.
You always work off of a centerline, but depending on the material the centerline for length of bend can change, thus the entering of two different raduises. You also do test bends to calculate gain and loss in order to know the the radius to use for bend allowance.
I work in a similar way - I use test pieces to calculate a neutral factor using sheet metal formulas and use that to find the workpiece length. If everything is consistent and correct then the actual part will be pretty much dead on. For furniture +/- 1 mm is basically perfect so we can get away with measuring stuff with a miter gauge and a tape measure.

Though usually there are like 3 different batches of the same tube in the warehouse and they're all mixed up and unmarked and they all bend differently, if they even fit into the collet or over the mandrel lol

Also what's going on under the hood in freecad to make the wire into a tube?
jfc4120
Posts: 448
Joined: Sat Jul 02, 2022 11:16 pm

Re: Tube bending data

Post by jfc4120 »

@ThanklessLiving
Also what's going on under the hood in freecad to make the wire into a tube?
I just did a sweep. But the table is all that's needed to bend the tube.

Also after your question above, I posted this as well: viewtopic.php?t=78759
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