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Shop press build

@ShawnR I designed a hydraulic press for a friend in the early 80s, and yield strength is a small part of the design process. Predictable deformation at the maximum load is also a factor.

For a 10 ton 36" span Hydraulic press I specified a table beam made out of 2 pcs of 6" X 1/2" solid bar, with spacers welded to prevent local deformation under load. This was the lightest that would work, and it still will deform more than he specified under 10 ton load. My vague recollection was that at 10 tons with 36" pin spacing, it would deform about ,060 under 10 tons. to get to his .030 desired deflection, we would have needed a 9" depth and more webs welded in place.

thr problem with deflection is that 'bumping' you hear when the object suddenly moves, and that movement reduces the pressure as the table is acting like a big flat spring.

So over-design the table by several times the material and double the depth if you want a press that is both easy to use and works well. This is why industrial presses have a hand winch to raisle and lower the table...
 
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I have twin 5" C that is about 3/8 with the middle of C reinforced with some scrap square segments of 1/8 wall tubing throughout its length. Span is 36" and both Cs are held in the middle with some 1/2" cut C sections (6 spacers in 3 pairs). At 10t load it flexes.
 
Tom Kitta said:
I have twin 5" C that is about 3/8 with the middle of C reinforced with some scrap square segments of 1/8 wall tubing throughout its length. Span is 36" and both Cs are held in the middle with some 1/2" cut C sections (6 spacers in 3 pairs). At 10t load it flexes.
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It doesn't matter how strong you make it, it will always flex. It's just a matter of how much.

So it's good to have an idea of just how much is too much. That's why I liked @Dabbler 's approach with max deflection specified.

Anyone who doesn't believe that should mount an indicator on some heavy steel bar or plate or tube and then put a small load on it.
 
I like where this thread. is going...... I just posted a shop project but it is becoming a good learning thread! But leading to many more questions.....:)

@Tom Kitta would you post a photo of your table?

@Dabbler Thanks! Good point. I think with my table (embarrassingly inadequate I think...), it would not take much load till I could detect deflection. I might try that tomorrow using a dial indicator. Unfortunately, no way to measure the force. I am sure there is but not in my shop.

The press width has been mentioned several times, and, of course, is a huge factor in strength. My table is 23" inside so about 25" pin to pin.

It would be really interesting to be able to monitor the press pressure. I might watch for a deal on components to make it into a system whereby I can install a pressure gauge. My neighbour offered me an automotive frame straightening system similar to the ones posted earlier but it is only 2 ton. At the time, I had a 12 ton jack planned as my pressure source. But now considering all of the numbers kicking around, I may have to rethink that. Very unlikely I will ever need a 12 ton press but you never know what project will appear. I just grabbed 12 tons out of the air when thinking I would build a press. :rolleyes:

Today, when I first started pressing the hobart bearing off, I was using some small angle 1.5 x 1.5 x < 0.125 as the bearing support (probably old bed frame...lol) . I felt like I had barely moved the jack handle and the angles were bending already. I just wanted to see how snug the bearing was. So next time I put .375" material as the bearing backers. I did not look for but neither noted any deflection when the bearing actually started moving. I guess my point is that unfortunately, with the bottle jacks, you really don't know how much force you are putting on the components. Probably the first flawed step towards an accident....

Thanks all.
Cheers,
 
Susquatch said:
Boy, she is beautiful!

At a safety factor of 1.0 (reasonable for something like that in a shop environment where bending out of shape in not a big issue), a 36" span, and plain steel tubing, your tubing will take about 1250 pounds each or 2500 pounds total (evenly distributed) before permanently deforming. That looks like a 6 ton cylinder so best to be very careful. Your top section looks MUCH stronger than the business end. The column load on the posts is mostly tensile so they should be fine. Prolly MUCH stronger than the top or bottom section.

That jumps to 8000 pounds total if you weld another 1x2 above or below (not beside) the existing ones.
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Going back to this post...but given the posts made since this one.

My table is about 25" between pins. What does the do to the numbers versus your quote based on 36" span? Welding on another 1x2 will be what I do tomorrow. So with a narrower table and the extra material, will the table meet a 12 thousand spec? and then...what is permanently deforming? Is say 0.001 considered a permanent deformity with regards to this discussion or is there a factor somewhere ie 1 % of the vertical (so in this case at 2" height, a 1 % deformity would be 0.020" ... am I on the right track?

As to "evenly distributed", since the load is supported equidistant either side of centre, is this classed as evenly distributed? So if I was to move the object supports further out towards the pins, then the better for the table, although now I have longer supports....

Yea, whole bunch more questions coming....:eek:
 
YYCHM said:
Instrument it with strain gauges, that will keep you busy all winter:p
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I have actually been toying with this....sounds like a good little Arduino project! I will go look for transducers.

Thanks! Well, maybe not....;)
 
Some short answers for you @ShawnR .

No, pinned at both ends and loaded in the center is not a distributed load. It is more like a point load, but not quite. It depends mostly on how the load is spread out under the part you are loading in the press. The pins at the ends do simplify the math a bit but not a lot. This is one of the reasons that I am not fond of those internet sites that simplify all this stuff excessively.

At 25 inches, your press is quite a bit stronger than at 36. It can handle "roughly" 4000 pounds before it will start to deform permanently. With two additional 1x2 tubes, that increases to roughly 13000 pounds. Roughly is the operative word here. Small defects, Welding, material variations, corrosion, exact dimensions, thickness variations, material composition etc etc etc can all affect the numbers. I've just made a crap load of assumptions to get you close. Measuring before and after will tell you how close I got! I would not be surprised to be out 30% or more. That's what a safety factor is all about. The higher the safety factor, the less chance there is of permanent deformation and buckling. Safety factors of 2 or higher are common for things like your press.

An Arduino is not necessary for this job but might be fun anyway.
 
I don't know a good way to measure Hydraulic pressure in a jack. But @Dabbler has a great idea that can be used effectively with a regular cylinder. If you know the area of the cylinder bore, you can get force very easily by multiplying the oil pressure in psi by the area in square inches. It will be plenty close enough for your needs.

Also remember that you are after one of two possible numbers. The force it takes to reach a given deflection or the force it takes to deform the press permanently. Everything else is just a bunch of numbers. Everything bends under a force. It's not if it will bend, it's how much will it bend.
 
Here is a very short analogy to help you understand steel.

Imagine a rubber ball. If you stick your finger into it, it will deform. The harder you press, the more it will deform. When you remove your finger it will return to its previous shape. But if you press hard enough, the ball will get deformed permanently and will not return to its original shape. Steel is like extremely strong rubber. The stronger the force, the more it bends or dents. But you can only go so far before it will not return to its original shape.

This is a gross simplification just to help visualize what happens. Rubber and steel are different in many other ways. But hopefully the visual helps.
 
Scratch that rubber example. Here is a WAY better one. We are all used to small coil springs - like say the ones in a ball point pen. They are made of steel. You can compress them or stretch them. The harder you push or pull the more they deform. But you can only go so far before they stretch permanently. A spring is just a long steel bar. Usually a special steel, but still steel.
 
A-typical-stress-strain-curve-for-polymer-film-undergoing-tensile-strain-testing.png
 
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Brent H said:
@Susquatch - I didn't mean to cause you any undo stress. I realize though, that your elastic personality would allow you to bounce back without any undo - elongation - I mean you are tall enough and would not want to yield to being stretched to the breaking point.
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Very well done my friend! Very well done indeed!
 
YYCHM said:
The fact that @ShawnR knows what a strain gauge is, would indicate he knows all this stuff already:rolleyes:
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It's funny what we know and don't know sometimes. I sometimes find the forum a bit awkward. Nobody wants to offend anyone else, but none of us knows what we don't know. Heck, sometimes we don't know what we do know!

I try hard to figure out what our knowledge overlaps are so we can communicate more easily and completely, but I fail more often than I succeed.

In the end, it feels good to help and be helped even if the edges are all a bit ragged.
 
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