Tuesday, January 13, 2015

3D Printing: E-Bike Frame Joint

I'm using these joints to build the PVC frame of the E-Bike. They'll most likely be solid urethane resin casts for a couple of reasons.

The primary reason being that these joints take about 4-5 hours to print with a 50% infill.  An OOMOO 30 silicon mold would require roughly 6 hours to cure, but each Smoothcast 320 resin part has a demold time of only 10 minutes.

I need about 16 of these.

Another reason is that the cast joints would be solid and therefore stronger.  ABS has stronger material properties than Smoothcast 320, but the nature of the FDM (FFF) process makes the part prone to delamination under stress.

Here's a quick comparison between the two materials:

  • Smoothcast 320:  (datasheet)
    • Tensil strength: 3,000 psi
    • Compression strength: 3,650 psi
  • ABS: (datasheet)
    • Tensil strength: 5,532 max psi (based on Makerbot filament)
    • Compression strength: 7100 max psi (based on Makerbot filament)
As you can guess from the pictures below, I now split tricky parts in half when printing.  They're merged either with ABS glue, super glue, or JB Kwik Weld.

I used to split the parts directly in Solidworks, but for 2015, I'm trying to ween off commercial software and rely on open source tools wherever I can.  

This part was:
The toolchain becomes much longer when going the open source route.  However, with the exception of the 3D printer itself, everything is free and available for Windows, OSX, and Linux.  More to come!


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