This wouldn't really be a woodworking question but I need to know for future reference. I'm doing a school project where my team and I are making a car out of cardboard, glue and two 3/4in x 40in dowels. So I would just like to know the strength of the dowels because they would most likely be used as the axles of the car (Where the wheels attach). Our "Driver" per se, weighs about 120 pounds so he's a skinny guy, but I just want to know if they have they strength to support his weight. The pressure would be mostly situated on the middle of the dowel so that is where my concern stems from. If anyone who knows what they're doing then that would be a big help because I know nothing of this. Thank you for your help!

  • 1
    Yeah, this is probably off-topic. But you should remember that engineering is a combination of research and analysis, and iterative experimentation. You should dream up some tests to see how your materials deform under static and dynamic loads. You probably need to come up with an idea of a safe margin as well. Like, don't design for 120lbs but rather some value above that.
    – jdv
    Dec 21 '18 at 15:40
  • A rough approximation via The Sagulator (using 40" length, 1.5" depth, 0.75" thickness, 120 lbs center load, floating, Oak, Southern Red) gives a 6" deflection. That agrees with my gut reaction that 3/4" dowel are way to skinny for supporting a 120 lbs person.
    – Eli Iser
    Dec 21 '18 at 16:23

The centre of the axle is the worst place a point load. The best place to apply it is just inside the 2 wheels. If the structure can't transfer the driver's weight out to those points, then build a truss unit that rests on top of the axle to help distribute the load without too much flex. You can also build a box beam or a triangle beam, much like a tower crane.
If the driver is the only major load, try to have the weight shared evenly by both axles.

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