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How much force will this press take?

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  • How much force will this press take?

    I was wondering if someone could run some numbers on how many tons these plates will handle when used in a press. I already have the material on hand and would like to build a H frame press out of it. The pieces I have for the horizontals are 3/4" thick and 12" wide and they are long enough for a 36" opening on the press. The uprights are 3/4" thick and 6" wide and pretty sure 8' long.(I think I have enough of these to double up thickness if they are limiting). Pins and hydraulics will be sized accordingly to what the frame can handle.

    I see a lot of the presses are made with channel but there are some that are only made with flat plate.

  • #2
    Only my opinion,
    channel iron has strength without the weight.
    Definition: Boat, a hole in the water you throw money into!

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    • #3
      Plate takes tension without a problem, in proportion to area. Not so good with bending in the narrow dimension.

      Channel has bending resistance both ways, and tensile strength in proportion to area.

      Channel with a piece of plate on each side would probably take anything the channel would. Of course, it's all in the details, So it is impossible to say without the rest of the story. But a piece of plate 36 x 12 x 0.75 is pretty stiff against bending in the 12 dimension, IF you can keep it from buckling.

      A sheet of paper will hold up a brick if folded, but collapses immediately if flat.
      2730

      Keep eye on ball.
      Hashim Khan

      Everything not impossible is compulsory

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      • #4
        Originally posted by fastfire View Post
        Only my opinion,
        channel iron has strength without the weight.
        Problem is I have a pile of plate and not channel sitting around.

        Originally posted by J Tiers View Post
        But a piece of plate 36 x 12 x 0.75 is pretty stiff against bending in the 12 dimension, IF you can keep it from buckling.
        Which way will the plate want to buckle when using it for press operations?

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        • #5
          Originally posted by oxford View Post
          Problem is I have a pile of plate and not channel sitting around.



          Which way will the plate want to buckle when using it for press operations?
          Think of a yardstick on edge. load it with weight as it spans a gap.

          The top edge is in compression, which it can take so long as it is straight, and not loaded beyond its capability in area terms. BUT, if it EVER deviated from straight, due to some minor defect, the compression will work to "fold up" the edge and the thing can collapse.

          It has to do with the length to width ratio. The 36" vs 0.75" is a ratio of 48:1, which is getting towards marginal, although the depth works to stabilize it to some degree. You would want to brace it against the plate on the other side of the vertical piece, which widens the "effective beam", lowering the ratio and making it more stable.

          Plate is fine for the sides, if it will stand up OK under the work weight and handling, and has the area to resist the force, since they are in tension. Tension acts to straighten a strap. I would want to brace the sides just against general handling, though.

          Plate plus a welder can become anything you want......
          2730

          Keep eye on ball.
          Hashim Khan

          Everything not impossible is compulsory

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          • #6
            Originally posted by fastfire View Post
            Only my opinion,
            channel iron has strength without the weight.
            I've never liked channel for press frames, especially the uprights. There is very little support for the pins where they pass through and the holes will wallow out quickly with heavy use. Your 3/4" plates will give you roughly 3X the bearing surface that a similar sized channel will.

            With the material you have--four 3/4" x 6" uprights and four 3/4" x 12" horizontals--you can easily handle 50 tons across a 42" un-supported span. With more bracing you can probably go higher but 50 tons is a lot of press for a home shop. The nice thing about that setup is it will be very rigid with no flexing under load. A press that "springs" under load can be very dangerous...
            Keith
            __________________________
            Just one project too many--that's what finally got him...

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            • #7
              The uprights are under compression when supporting the weight of the press + work. The upright section between the horizontals will be under tension (transmitted from the ram by the horizontals).

              The horizontals will be under compression in use. Using I-beams (or boxing in the plate) for the horizontals will resist twisting as well as increasing the compressive strength.

              When dealing with plates, they are strong in the direction where the force is aligned with the widest part. If the part twists, and the force starts to be off center, the 12 inch thick part effectively becomes much thinner.

              Dan
              At the end of the project, there is a profound difference between spare parts and left over parts.

              Location: SF East Bay.

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              • #8
                oxford,

                Do a search on Dave Propst hydraulic press. He built a very unique design using the materials you have on hand. I did a quick google search but didn't find the article but will look again when I get home tonight and have more time. I think you'll like his design, at least the frame part anyway. Also, he has been mentioned on several forums including PM.

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                • #9
                  The pictures I saw of the Dave Propst press with a Google search shows he used channel for the horizontals. I may be looking at the wrong press though.

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                  • #10
                    Originally posted by danlb View Post
                    The uprights are under compression when supporting the weight of the press + work. The upright section between the horizontals will be under tension (transmitted from the ram by the horizontals).
                    the compression is insignificant in use, compared to the tension. It comes under the heading of "able to support itself plus work". Since that is presumably much less than 50 tons, welll?


                    Originally posted by danlb View Post
                    The horizontals will be under compression in use. Using I-beams (or boxing in the plate) for the horizontals will resist twisting as well as increasing the compressive strength.
                    Not strictly so..... it varies in different places.

                    The plate is acting as a "beam". There is compression against the pins or bolts. There is shear through the "beams" amounting to the entire force applied. There is lengthwise compression on the beam where the force is applied, and tension on the opposite side. there is local compression against the load.


                    Originally posted by danlb View Post
                    When dealing with plates, they are strong in the direction where the force is aligned with the widest part. If the part twists, and the force starts to be off center, the 12 inch thick part effectively becomes much thinner.

                    Dan
                    Which is essentially what several have said. This bit is pretty accurate, although rather than saying it effectively becomes thinner, it may be more accurate to say the compression is transformed into a bending force.
                    2730

                    Keep eye on ball.
                    Hashim Khan

                    Everything not impossible is compulsory

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                    • #11
                      So assuming I made a fabricated C channel out of the plates, how wide should the pieces be to make the "C". It would still be the 3/4" thick material. Would there be a better way of resisting the twist? The horizontal plates will be tied together but only in one place on each side near the verticals. I would like to keep the centers open as I plan on having the ram being able to move to either side. I do have the material to make those tie in pieces the full 12" tall.

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                      • #12
                        I think you would be OK if you just space the plates on the side rails, and then block between them near the middle, leaving the actual middle open. Use a couple chunks of plate as a set-on platen to lay over them.

                        Most any steel is good for 30,000 psi, and de-rated by half is 15,000 psi. A piece of 30 lb plate has a lot of square inches...... and you will have two of them. the two straps of 6" x 3/4" will be 9 square inches, so 270,000 lb yield @ 30,000 psi. That's kinda close for 100 tons, but fine for 50 tons even with some imbalance. If you only want a 25 ton press, it's the rock of Gibraltar as far as the straps, even with reasonable sized holes removed.

                        Worry more about the pins and their attachments. 2 or 4 pins in double shear, figure the square inches at 15,000 psi.
                        2730

                        Keep eye on ball.
                        Hashim Khan

                        Everything not impossible is compulsory

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                        • #13
                          Originally posted by J Tiers View Post

                          Which is essentially what several have said.
                          Yep. I said it first, the only problem is that I read the post, started typing, fixed breakfast, washed the dishes and added a few lines. Then I had to help my wife with the christmas wrapping. By the time I hit the "post quick reply" button, there were several similar posts.

                          But thanks for taking the time to critique each point in detail. Not sue it was really necessary since the points had already been covered in other posts.

                          Dan
                          At the end of the project, there is a profound difference between spare parts and left over parts.

                          Location: SF East Bay.

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                          • #14
                            How much of a gap do you want between the horizontals? Using 3/4 inch plate for the columns gives you 3/4 inch between the horizontal plates if you fit it all up snugly. I'm thinking the limitations for pressure are going to be more related to the pins you use than the thickness of the material, unless you skimp on the widths for the columns and horizontals.

                            With a 3/4 inch thickness, the area where the pins contact in the columns will be equivalent to using square tubing with a wall thickness of 3/8. If that isn't enough for the pressures you want, you can always add some thickness to the columns where the holes are to be placed. Adding a 3/8 thick plate to each side of the columns doubles the area where the pin can be in contact, and also increases the spacing between the horizontal members to 1-1/2 inches- adding a 3/4 thick plate to either side of the columns increases that spacing to 2-1/4 inches- much more useful in my opinion. The added plates don't have to be much wider than the pins you plan on using- I'd say make them about 2-1/2 times as wide as the pins would be. If your columns are 6 inches wide and the pins 1-1/2 inches diameter, and the added plates are about 3 to 4 inches wide- I'd say you would have some serious tonnage capability. As I see it, the limitations would be in how you assemble and brace the horizontals- the platen and the beam holding the press cylinder.
                            I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                            • #15
                              I'd have suggested not using just the thickness, but you could. And then there would be less connections between the crossrails and the columns.... they would go direct. I saw the sides as being at right angles to the crossrails. Two columns per side would allow a reasonable space between the crossrails, which I would figure needs to be 3 or 4 inches.

                              With 4 of them (4 just to avoid welding or bolting) the rails would be crazy strong, and the pins would have lots to bear against. And he'd get the wider space between the crossrails.

                              But man would that thing be heavy! Strong, but heavy. Did I mention how HEAVY that would be?

                              3 feet of double 30 lb plate 12" wide would be 180 lb x 2, so 360 for each cross rail, plus 8 x 30 lb for the uprights.... sounds like it would be north of 1000 lb all told, and strong as the dickens. For most purposes, you wouldn't need any bracing..... but you need something to hold the crosspieces together, so.......

                              And you need something across to hold the uprights apart.... maybe 1200 lb+ all told.

                              You could back down to some 3/8" plate... swap some of the heavy stuff......
                              Last edited by J Tiers; 12-20-2015, 07:42 PM.
                              2730

                              Keep eye on ball.
                              Hashim Khan

                              Everything not impossible is compulsory

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