See accompanying photos

gantry01.jpg
gantry02.jpg
gantry03.jpg

The crane is designed to lift 1000 lbs. It can be easily erected by one
man (a six foot stepladder comes in handy in the erection process).  It
comes apart for ease of storage and can be transported on a car-top carrier.   

It is constructed of 2 x 4 x 3/16 rectangular tubing.  The uprights are
2 1/2 in. O.D. thick wall pipe.  The pieces of tubing on the feet and
on the cross beam are 2 1/2 in I.D. and are kind of a loose fit.  It is
eight feet high and spans eight feet.

Obviously, by using heavier parts, one can lift heavier loads.
I also have built a 4000 lb gantry that differs from this one as follows:

1.  It has heavier 5" steel casters and heavier rollers on the traveler.
2.  The cross member is a truss made from a 2 x 2 x 1/4 square tube on
    the top and a 1 1/2 x 1 1/2 x 1/8 square tube on the bottom.  The
    tubes are 10 inches apart and are braced by 10 1 x 1 x 1/8 tubes 
    set at a 60 degree angle distributed across the 9 ft. span.
3.  The legs are A-shaped, 6 ft wide at the bottom and 11 ft. tall.
4.  Diagonal braces run from a cross member on the A-shaped legs to the
    truss.  They are about 3 ft. long and attach to the truss about 
    1 ft. from each end.

gantry01.jpg shows the "feet" of the crane.  They easily rotate so that
the crane is assembled on the ground, then are turned 90 degrees after
it is stood up.

gantry02.jpg shows the traveler and the ends of the cross beam.  The only
thing not obvious in the picture is that the ends of the top pieces have
rings welded in them to keep the cross piece from sliding down the sides.
While, at first glance, it might seem nice to have them adjustable, having
them slip under load would not be good.

gantry03.jpg shows the crane lifting the back end of my pickup off of the
ground and getting a good "shake test."  It proved to be surprisingly 
rigid and no measurable (with a tape measure) deflection occurred under
this load.