On Wed, 5 Sep 2018 12:10:57 -0400, "Jim Wilkins"
wrote:

wrote in message
...
On Tuesday, September 4, 2018 at 11:08:33 PM UTC-4, Jim Wilkins
wrote:
"pyotr filipivich" wrote in message
...

Lifting Unit raises I-beam up by [bottle jack | screw jack | cam
|
"other"] powered by [electric | steam | pneumatics | Hydraulics |
magic].

My Lifting Units are tripods of pipe or tubing that support chain
hoists. The legs are joined at the top by a simple yet clever
flexible
arrangement of bolts and chains I devised 20 years ago that leaves
the
legs free to move around and divides the load between both sides of
each leg, I think, in a manner that lets K=1 in the column
equation.
Likewise the pipes rest on actual balls or their near equivalents
to
keep the axis of thrust centered within the tube.
https://en.wi "kipedia.org/wiki/Euler%27s_critical_load

If I could prove the design's weight bearing capacity I'd reveal
it,
but I can't so you hereby know that a very simple folding pipe
tripod
is possible. All parts are common consumer hardware though they
aren't
necessarily used as intended. The load rating can be determined
with
on-line column calculators. I proof test them with a load cell when
pulling stumps, which won't drop if anything fails. So far only one
5000 lb load cell has failed, and two legs and bottom ends were
retired for their battered conditions.

They move loads horizontally by walking the legs forward while the
load is lowered, then raising it enough to slide. It's slow but
requires only relatively level ground solid enough to support the
leg
baseplates.

I would enjoy seeing your lifting tripods. I made something
similar, but the top was three sockets made of pipe welded to a
plate. Worked well enoug to lift a small horizontal mill off a
trailer.

Dan

They aren't too different from the original that a neighbor used to
pull engines. There was chain wound around the top and rather
haphazardly attached to through bolts. IIRC he tossed another chain
over it to hang the chain hoist. I liked that it folded parallel to
carry and the legs could be repositioned independently if they sank
in.

Or, by moving one leg at a time, you could "walk" a load across the
yard so long as you kept the load from swinging.