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