V0.19: Tube Bender Tool Design using Assembly4

[ppemawm]

This is a model of a tube bender designed by C. Horace Clarke (1956). Drawings can be found in the Model Engineer magazine dated 22 March 1956, pp.470-473.

The model was created with the Assembly4/PartDesign workbench using a top-down, in-context approach referencing a master sketch of all the articulating components. All parts including ISO fasteners were created in one file and then assembled and animated with the Assembly4 workbench.

The Assembly4 workbench provides a convenient means to assemble Parts using Links and local coordinate systems (LCS) from separate Part files or from Parts in the same file, the latter which nicely facilitates a top-down design work process. A simple master sketch is used as the assembly solver for any combination of variables.

Several screenshots are as follows with a few comments on the design process:

The tube bender model consists of fixed and translating or rotating parts grouped in separate folders for tree organization. All bodies were created from sketches that referenced shapebinders of the top level master sketch.

The tube bender can accommodate bend angles 0-180 deg as well as different tube sizes and bend radii. It is important during modelling to be able to check the operation of the tool over the full range of the variables.

Picture1.jpg (88.37 KiB) Viewed 2768 times

This is the master sketch used to dimension and locate all of the translating/rotating parts and to constrain them for proper operation as shown in the image. The master sketch serves as an efficient assembly solver for any combination of the defined variables.

The master sketch was created at an arbitrary bend angle, tube size, and bend radii. Each body starts with a shapebinder of this master sketch. The body sketches use External References to locate and generate body features. A copy of the master sketch is also located in the Assembly Model for the Animator.

Note that several of the dimensions include expressions related to the Assembly4 > Variables defined to allow different bend angles, bend radii, and tube outer diameters as shown in the Property panel. The table of variables can take the place of a spreadsheet including intermediate calculations using Expressions. It is also a good way to collect and document all of the variables used in the various sketches in one convenient location.

Picture2.jpg (85.7 KiB) Viewed 2768 times

These are all of the moving Parts assembled with Assembly4. Several of the parts must be able to translate linearly for different bend radii and tube diameters as well as rotate for a given bend angle.

The vise subassembly that grips the tube must also be able to translate on its base to accommodate the tube and bend radii variables.

Picture3.jpg (77.92 KiB) Viewed 2768 times

This image shows the LCS's that were added to assemble the parts and the fasteners. Most of the Part LCS's are directly linked to the Model > LCS0 since they are already in their proper location when created in-context.

Fasteners LCS's were added with the Assembly4 > Create LCS attached to a hole tool.

Picture4.jpg (77.7 KiB) Viewed 2768 times

The model can be easily animated with the Assembly4 > Animator over the full range of the variable bend angle as shown above. The same can be done for the tube size and bend radii to verify proper operation of the tool.

tube_bender_short3.gif (933.25 KiB) Viewed 2768 times

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The Assembly4 workbench has become my go to workbench when working on articulating assemblies or those in which key dimensions must change parametrically for given design variables. IMHO it is a serious no-frills essential tool for top-down design and in-context modelling.

EDIT: The Assembly4 > Add Variables tool is especially valuable and quite useful for any model, an example as shown in:
https://forum.freecadweb.org/viewtopic. ... 40#p363215

OS: Windows 10 (10.0)
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.19311 (Git)
Build type: Release
Branch: master
Hash: 120b69c74f7dac8c4fa6dbc0a7e10674bde9216c
Python version: 3.6.8
Qt version: 5.12.1
Coin version: 4.0.0a
OCC version: 7.3.0
Locale: English/United States (en_US)

[vocx]

The Assembly4 workbench has become my go to workbench when working on articulating assemblies or those in which key dimensions must change parametrically for given design variables.

Awesome.

I know it's boring, but with every model that you create can you provide a description of your computer, file size, modelling time (days, hours, minutes?!), and problems that you encountered, if any? I think it's nice to give new users an idea of what is already possible with FreeCAD without using a very expensive system. I presume you don't use a supercomputer to make these models.

And in the topic of articulating assemblies, I just thought about this: can you model a mechanism with a chain or a rope (pulleys)? The specific thing I'm thinking about right now is a garage door. I just fixed mine so I thought, it'd be nice to model this in FreeCAD so next time I disassemble my door, I know how to put it all back together without taking days and days of testing. I have a door that folds horizontally, so not up and down, but sideways, like an accordion.

[funkysod]

Awesome project! Thanks for sharing it!

[ppemawm]

can you provide a description of your computer, file size, modelling time (days, hours, minutes?!), and problems that you encountered, if any?

Thank you for your comments.

I am using a mid-range Toshiba Satellite laptop with Intel I7 2.50 GHz chip and 16 Gb RAM in touchpad mode, no external mouse.
File size is 792 Kb.

I work on these kinds of small projects, several at a time, for 2-3 hours/day to stay current with the software development. This particular project probably took me about 10 hours including research.

The biggest problem I have encountered is making sure that sketch constraints are not ambiguous as the sketch is animated over its full range of variables. My recommendation is to check each body over its range of its variability as its built. It gets easier and more sure as you gain experience.

A problem for me with Assembly4 when using it for top-down design is the difficulty keeping track of all the seemingly redundant Part and Body origins, and LCS's especially when created in context and then used in the Model assembly. I am still experimenting with this.

And in the topic of articulating assemblies, I just thought about this: can you model a mechanism with a chain or a rope (pulleys)?

Hmmm...I'll have to think about that one, but probably not with a simple master sketch. But, I am sure @zolko could figure it out!

[Zolko]

And in the topic of articulating assemblies, I just thought about this: can you model a mechanism with a chain or a rope (pulleys)?

Hmmm...I'll have to think about that one, but probably not with a simple master sketch. But, I am sure @zolko could figure it out!

I think it's actually easy: the Variables object can store variables, and their value can either be set manually, but can also be calculated by its ExpressionEngine. For a chain, you'd define the angle of the driving pulley Angle_drive, you'd define the gear ratio Ratio, and the angle of the driven pulley would be Angle_driven = Angle_drive * Ratio. And you attach the LCS for the 2 pulleys with their respective angles.