5 ms·

The chains are pretty neat! Any idea on backlash?

• foobarian 10y ago
  Author made a comment in the last video; the weight of the cutter keeps the motors under constant tension one way, so there is no play caused by changing direction.
  • lostapathy 10y ago
    Mostly true but not quite. The forces on the chains are actually higher when the chains are "shorter" and the router is higher up. The farther from vertical the chains are, the more horizontal tension there is on top of the vertical component. The same basic principle shows up in rigging - http://www.fdlake.com/rig-slng.html http://www.fdlake.com/rig-slng.html - the illustration where the straps are at 90 degrees is rated higher than 45 degrees.
    • grogenaut 10y ago
      Also there is slack in any gear/chain train when switching directions as they never fit perfectly. Same with gears. Even tiny amounts will throw you past .4 mm quickly
      • prashnts 10y ago
        I think by keeping the object to be cut out in the centre, having small (relatively) size would experience lower slack, hence reduced deviation from the said accuracy.
      • lostapathy 10y ago
        Actually that kind of backlash isn't a problem in a machine built like this. The tension of the chain against the sprocket is always pulling in the same direction around the sprocket. Even when the sprocket reverses direction, the chain is pulling the same way and staying tight to the same side of the teeth it was on.
        • grogenaut 10y ago
          That would be correct until you figure in momentum as long as you stay under that threshold your hypothesis holds, if you get the device moving or swaying it won't. Of course this can be compensated for in software. So Point taken.
• analog31 10y ago
  His explanation is pretty good that the weights always pull the chain in one direction, which eliminates most of the backlash. I think he mentions that the remaining backlash is taken out in software. There could be some error due to rotation of the entire router as it encounters friction, but it should be manageable, and whatever error remains is basically how accurate you can get.
  • Already__Taken 10y ago
    In the video where he explains that rotation, to me it doesn't look like the chains come down mounted in the same axis as the router bit to form a V, just a little higher. I just wondered if that by its nature is imparting a moment on the router. I wonder if you could mount the router on a bearing, have each chain attach to a free side of the bearing so each side can rotate around the router. Then just figure some way to lock the routers torque that isn't the x/y control mechanism. Perhaps 1 chain pulling directly down.