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About hydraulic presses.......or at least one of them...

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  • About hydraulic presses.......or at least one of them...

    A while back there was a short discussion of presses, with discussions of pin sizes and qty, etc.

    How about this for holding the top crossmember..... that takes the entire force of the press?

    it's on one at work....

    2730

    Keep eye on ball.
    Hashim Khan

    Everything not impossible is compulsory

  • #2
    Well, the bolts are in double shear so that is a good thing. I would prefer the unthreaded portion to extend completely through the channel and frame with the shank washered up to the threads to clamp the assembly. The thread interuption creates a stress riser at the root of the thread that is in the area of shear.
    Joe

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    • #3
      If you have a machinist hand book you can look up the shear strength of bolts and pins.

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      • #4
        Wouldn't it be the entire force of the press √∑ 4 ? I figure there are two bolts shown for one side... surely there are two bolts also on the other side.

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        • #5
          Not being smart enough to calculate "good enough", I would have made the bolt unthreaded part extend through the members, as Joe Rogers said. I would also install spacers so the bolt tension could cause friction between the members to take more of the load. It just doesn't look right to me.
          Don Young

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          • #6
            Top plate bolts

            Originally posted by Don Young
            Not being smart enough to calculate "good enough", I would have made the bolt unthreaded part extend through the members, as Joe Rogers said. I would also install spacers so the bolt tension could cause friction between the members to take more of the load. It just doesn't look right to me.
            Mine originally was like the photos , I took all four long bolts out and replaced them with 8 grade 8.8 shorter bolts as I also didnt trust the threads being in a high stress area.
            The diameter was increased from 5/8 to 3/4 as well.
            Michael

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            • #7
              Yeah... the shear, exactly HALF of the total load, is on the threads..... since all 4 bolts* are the same.

              Things are often much stronger than you think.... until they aren't, and these appear to be chinese "grade 5" bolts.....

              To be fair, I am not at all sure that this would give way first, but I just didn't like it that ALL the bolts were like that.

              Again being fair, the net per "shear point" is total load /8, since there are two ends to each of 4 bolts. I think this is a 15 or 20 ton press, but carrying loads on threads is just "not done" in any critical situation in my book.

              And if I am pumping the lever on this, I have just defined it to be a "critical situation"....

              * I guess these are "screws" since I bet they don't conform to the threading and dimension limits for "bolts" per a recent definition of a "bolt".
              2730

              Keep eye on ball.
              Hashim Khan

              Everything not impossible is compulsory

              Comment


              • #8
                Since the top crossmember is a welded assembly with two deep channels, it's not going to flex enough to get much clamping on the joints with the vertical member, even with spacers on the bolts.

                I'd rather see four bolts just long enough to have the unthreaded portion extend through the joint. That'll ensure you get some frictional support from the clamping in addition to the shear of the bolts.
                Any products mentioned in my posts have been endorsed by their manufacturer.

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                • #9
                  The correct way would be -tubes welded in each hole in the frame & shoulder bolts so the thread only takes a clamping force.

                  But it's cheap, Chinese & Mellow yellow, what did you expect
                  John

                  I used to be indecisive. Now I'm not so sure , but I'm not a complete idiot - some bits are still missing

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                  • #10
                    Mr. Tiers, Those are bolts because they get a nut on the end and not screwed into threads in the frame itself.

                    All that is based on what Mr. Bullis quoted from the bible.
                    Location: The Black Forest in Germany

                    How to become a millionaire: Start out with 10 million and take up machining as a hobby!

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                    • #11
                      Originally posted by jugs

                      But it's cheap, Chinese & Mellow yellow, what did you expect
                      Well, I don't expect much...... other than it should exert force reasonably similar to its rating, and that it should not fly apart if I use it to press something......

                      So far I can say that my expectations have been substantially met.

                      I didn't buy it.
                      2730

                      Keep eye on ball.
                      Hashim Khan

                      Everything not impossible is compulsory

                      Comment


                      • #12
                        The bolts definitely need to be longer.

                        Using my remote lcd optical micrometer, it looks like the bottom holes are bigger than the top ones, especially the one on the bottom right.

                        If you had the time, it would be interesting to put a level on the top of the press and then 'crank her up' and see if there is any movement. My guess is the right side will lift.

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                        • #13
                          I'd be inclined to replace the two long bolts with 4 short Grade 8 bolts. This would give positive clamping without the need for spacers.

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                          • #14
                            Most of the over the counter hydraulic presses are a bolt together effort not because of it being a superior way to assemble the press, but because it is a convenient way to put it a box.
                            Shipment and storage while in stock makes disassembly a requirement.

                            If you have concerns about the compromises inherent to this process then by all means wire wheel the paint off and lay down some good hot passes with a welder. Takes the worry factor out of the equation. Leave the bolts in an make sure it's square.
                            You will of course need a bigger box to put it in, but then I've never seen anybody put one back in the box after assembly.
                            Home, down in the valley behind the Red Angus
                            Bad Decisions Make Good Stories‚Äč

                            Location: British Columbia

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                            • #15
                              Originally posted by rancherbill
                              If you had the time, it would be interesting to put a level on the top of the press and then 'crank her up' and see if there is any movement. My guess is the right side will lift.
                              Probably don't even need a level -- how much does it move as it approaches it's rated force?

                              Like others have said, replacing the cheap bolts with grade 8's with a longer shoulder would be cheap insurance, and probably reduce the frame movement too, since quality bolts are much closer to the nominal major diameter...
                              "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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