On Thu, 19 May 2011 09:08:16 -0400, "Ed Huntress"
wrote:


"john B." wrote in message
.. .
On Wed, 18 May 2011 19:09:01 -0500, Ignoramus15557
wrote:

Guys... I am not talking to anyone specifically right now... I sense a
little bit of B/S on this topic.

Right now, I have a crane that lifts 500 lbs, mounted on a 1x1 foot
plate, with angle iron underneath the bed holding it in [place with
thru bolts. While it is slightly shaky, it works just fine.

With this Ramco crane, I am going to have a crane that would lift
about twice more weight -- 1k lbs -- supported by a 3x4 foot
plate. That is 12 times more area than the 1x1 foot plate! Even if it
is not evenly distributed across the plate, it is still a hell of a
lot more support and weight distribution than a 1x1 foot plate.

I think that I will be just fine with it without fabricating any funky
adapters and bolting them to the frame.

i
I don't know the weight of your 5,000 lb. capacity crane or your
plate, but assuming that your plate is 3/4" and the crane weighs 500
lbs then you have a maximum weight of components plus load of 5,868
lbs. divided by 1728"2 = ~3.4 psi.

I just measured the area of one foot and weighed myself. If I stand on
one foot in the back of your pickup I will exert a force of ~5.36 psi.

I haven't followed this and I may have missed this point, but I would think
that the issue here is not transferring the load evenly to the area of the
plate, but rather the effect of the lever arm, with the weight loaded some
distance from the center of the vertical column. That's what I'm picturing
as the "crane," anyway.

And if that's the case, then the specific load on the edges of the plate can
be many, many times the force of lifting the load.


There were all kinds of arguments going on. Mash the sheetmetal, etc.

But you are correct, the limits to crane operation are usually tipping
moments, not actual maximum lifting capacity as that is usually
specified with the boom at 89 degrees.