// Last edited on 2020-04-05 21:43:08 by jstolfi

#macro straight_tube( xlo, xhi, orad, th, eps )
  // A piece of straight tube.
  
  // {xlo,xhi} Min and max X of tube.
  // {orad}    Outer radius of tube.
  // {th}      Thickness of walls.
  // {eps}     Fudge radial displacement of walls.
  
  // The tube axis is the X axis.  The tube extends
  // in X from {xlo} to {xhi}.  The walls are
  // displaced inwards by {eps}.
  
  #local tau = 0.01*(xhi-xlo); // Displacement for ends of borer.
  
  #local obj = 
     difference{
       cylinder{ < xlo, 0, 0 >, < xhi, 0, 0 >, orad - eps }
       cylinder{ < xlo-tau, 0, 0 >, < xhi+tau, 0, 0 >, orad - th + eps }
     }

  obj

#end