"Bob La Londe" wrote in message
news
"Bob La Londe" wrote in message news
"Jim Wilkins" wrote in message news
"Richard Smith" wrote in message
...
Bob La Londe writes:
https://www.youtube.com/watch?time_c...&v=f2xlAWytx9g
I know some folks may not be a fan, but I noticed he made his main
uprights out of 1/4" steel plate welded up into a box.
I just made a deal on a small quantity of 4x8x1/4 A36 plate for
about
half local metal yard retail. I'm going to use one piece as the
top
for my welding table until I run across a good deal on something
thicker. I decided to buy some extra just because the price was
good
enough to be worth sitting on it for a while.
I've been want a little better hydraulic press for a while. I
have
pulled my 12 ton partially apart. I can still use it, but only
above
the torn metal. LOL. My 20 ton now has a bow on the top beam.
That's what happens when you try to press a prop hub out in the
wrong
direction.
Anyway, I was wondering if 1/4 plate really was adequate for the
uprights on something like that. I have no need to make one as
tall
as stretch built his in the video. I won't have a joint in the
pieces
like he does, and I wasn't planning on going 50 ton. I've got a
pretty beefy 30 ton cylinder and power unit off of a log splitter
I
was thinking about using for the hydraulic part. My 20 ton has
been
adequate for anything I needed to press except for the fact that I
managed to bend it. I've also got some heavier stock for things
like
the top and table.
Ok, tell me how stupid the idea of using 1/4 plate and making my
own
upright tube is.
The frame "uprights" of a press (hydraulic press) are in pure
tension.
Very rare engineering loading case. Abnormally easy to treat.
Opposite of instability - the load "assists" pulling them straight.
Load bearing in this very special case is totally simply to
calculate
on-paper:
multiply the cross-sectional-area (width*thickness)
by the
yield stress divided a safety-factor (say 5?)
and there you have it.
Typical other cases:
In a beam you have to consider buckling instability, etc.
Likewise a column (it looks the same as a "tie" but is in
compression).
The engineering design is much more complex and you have to work
out
which effect comes to the fore in most limiting the load-bearing
capacity.
Hope this is helpful comment...
Regards,
Rich S
What he wrote is true only if the connections to the horizontal
members that withstand the pressing force are somewhat free to
rotate
at their ends as they deflect, ie they are bolted along the
centerline
of the uprights instead of being welded.
A bolted or pinned joint with some give leaves the tension evenly
distributed across the uprights, while a solid welded joint
concentrates the stress on the inner corner as the top crosspiece
flexes upward.. Look closely at the design of commercial presses.
-jsw
***************
Thanks. Being a boat fan (welded and molded) I am somewhat familiar
with
the stresses at what we call hard points. I have experienced
various
degrees of failure at hard points from broken welds in aluminum to
stress
fractures in gel coat even in name brand commercial products. Its
good to
think about this in a different application. I'd note that I've
also seem
failures on two hydraulic presses. Neither was instant or
catastrophic.
Both were Harbor Freight presses. The column on a 12 ton literally
pulled
apart with a 12 ton jack, and the top beam bent on a 20 ton using a
20 ton
jack. They are both still moderately useable. I had certainly
intended to
study their modes of failure as I approach the new build.
****************
Hmmmmm.... looks like if I use 1" pins and holes closely sized I'd
get some minor hole deformation at high tonnage the first time I
used a particular set of holes, but be below the yield strength on
those holes afterwards (full engagement of pins after first
deformation.) If I used larger pins the upto under 50% of the
column width my strength just goes up. As to the column itself I'd
be an order of magnitude below what a 30 ton ram could dish out.
After that it's a matter or making sure the table and top beam are
good for the stresses involved. I have time to think about this
though. Its not tomorrows project. I'm still finishing up my
welding table.
https://www.egr.msu.edu/~harichan/cl...e405/chap5.pdf
You can increase the bearing strength of the column holes by welding
on doubler plates.
I have a similar bolt strength problem to solve for the splice
plate(s) joining 8' channels into the the 16' track of a gantry
hoist.
-jsw