This thread is to start discussion on College Custom Plastic Parts.
I have some ideas drawn in sketchup, but I’d have to redraw them in Inventor or Solidwork, etc, before submitting to a CNC shop I’m talking to.
Because CNC requires CAD drawings, I’m posting this in the CAD forum.
Here are some example problems, current workarounds if any, and why custom plastic would be nice. Note that using unique custom plastic can also make your design harder to copy, yet still be an inspiration.
- flat bearing blocks are not thick enough, and have protruding nuts/screws, so spacers are needed to keep rotating parts from hitting the nuts.
- use 1/2" Forstner bit to grind down nut pockets, and polish off square protrusions, use this block as stacked with normal one to make integrated spacer bearing block.
- thicker bearing block with nut pockets, or even 8-32 tapped holes, acts like integrated spacer; Lower parts count, easier assembly (no need to thread spacers)
- 4" omniwheels have a wider tread than axle, and often need spacers on the axle stack, which is a pain to maintain. Even above integrated spacer bearing blocks don’t work well, because tire is too think to install between them.
- move the ground down second stacked bearing block to the wheel, one on each side, makes the axle thicker than tread so it fits nicely, use 3/4" hex beams to join the screws from each side. May require a little grinding of the wheel spokes to get hex bars to fit nicely.
Custom plastic to the rescue:
- Similar to above. For lowest parts count, make two types, one with threaded plastic hex-beam eqv, so only two screws are needed from other side. For lowest plastic type count, make hex beams meet in middle and use one screw from each side.
- Hex axle hole cutout for using Hex beams as “high strength axles”
- square axle hole cutout, to reinforce wheel square axle hole
- design as sprocket spacer, No nut pockets, thickness correct to push sprocket out past tire edges. sprocket can be bolted directly to spacer+wheel rather than sending torque through skinny axles.
Hard to use Vex pillow blocks with 1/2" diameter spacers as rollers, since roller will both touch the ground, plus not stick out past pillow block bearing.
Workaround: mount on washers or standoffs, Grind down top.
Custom plastic would be less work, could contain two pillows with roller trapped between them for lower parts count.
Any college teams using custom plastic now? Anyone want to collaborate, if I can get a deal or sponsorship from some CNC place? They might be willing to help out the future generation of procurement engineers.