making telescoping tubing

 Telescoping (nesting, sliding fit) tubing is handy for many structural projects, and for light-duty designs, COTS tubing may be purchased which is ready to go.

 But when one needs a heavy wall thickness, it is much harder to find nesting tubing. 

The solution is to make your own, and it's not terribly hard.  I am assuming square tubes.

• place two pieces of angle steel outside/around your inside tube

• insert two short pieces of .023 MIG wire between the angle stock and each face of the inside tube
  (this creates the necessary gap for sliding the two pieces - don't use a pop can gage, it's too thin)
   You need the wire spacers at both ends of your piston, so this can be fidly.  The judicious use of
   clear plastic tape to hold wires in place won't hurt.

• aggressively tack-weld the angle steel pieces to each other

• remove inside tube and finish welding angles together

 This completely avoids having to remove the $%^&!@ weld bead inside factory tube.  👀

See YouTube if you have any questions. :P