A reprise.....how to build a gantry for a chain falls....

["Gerald Brazil" <gerrybraz@voyager.net>]

Thanks to everybody who gave me a lot of good suggestions.
 
I rejected the idea of wood because I wasn't confident that I would be
able to build it well enough. I then explored making one out of steel.
When I visited the place where I buy steel, I learned that you can't get
a nice slip fit in square tube because of the weld seam on the inside.
If you get an inner tube that will slide, it is a sloppy fit. 
 
So, the bottom line? The Harbor Freight's gantry doesn't look like such
a bad deal after all, considering that you get all of the parts
delivered to your door already painted and they pay the shipping.