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  • #16
    Originally posted by cameron View Post
    That picture of the 20 ton hydraulic shop press is meant to be a joke, right?
    Surely it can produce 20 tons and even without failing, but with how much bending in the structure I don't know. Probably would fire like a shotgun when the thing you are pressing finally moves, as the spring load in the structure eases itself.
    Amount of experience is in direct proportion to the value of broken equipment.

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    • #17
      I am providing a guide that will ride the columns with the end of the piston ram to keep it centered. Any extension to the ram will also have a guide at the most convenient lowest point of it. The body of the jack should be concentric with the ram, but I'm not counting on that- instead I will use two identical guides to position the ram parallel to the columns both ways, then bed the base of the jack to the upper beam using pc-7 epoxy. That way the ram will always move parallel to the columns. I will also be providing some universal guides to which temporary fixtures can be mounted to hold whatever it needs to- first thing I'll need to do is center my roller assembly for the pressing of the bearings. This is what spurred me to suspend the belt sander project for the moment and actually get this press made.

      My movable beam will be made such that it will bolt through the column and become tight at any position I place it. What I'm up to at the moment, besides checking in here, is making a jig to ensure that the movable beam is oriented at a perfect right angle to the ram axis wherever it's placed along the columns. This is tedious work, but I will use this jig to place the beam for each position, then pilot hole the bolt locations at each point. When this is done I can drill out the columns and the holes in the beam for the support pins. With a ram extension of about 5 inches, I'll be placing the holes about 4 inches apart.

      I'm paying particular care to getting things square and true. Maybe a bit of OCD is creeping in here, but I do believe that a good degree of precision in the construction of this will pay off in easier pressing and fewer problems. I'm well aware of the dangers involved with things under pressure, but that's a good reminder for any and everyone.

      Now here's a point of interest (or maybe not) regarding the jack- pretty much any bottle jack- the fill level leaves room for fluid to change height in the body of the jack as the ram moves in and out. With the ram retracted, you fill to the level of the port and put the rubber stopper in. The air inside is at the same pressure as the outside air at this point. When you extend the ram, the internal air pressure must drop. Of course, the capability of the jack far overcomes this negative pressure, but I thought it worth noting that now the space above the fluid is at a reduced pressure. This should help suck the ram back in when the release valve is opened, an effect which is strongest initially and dwindles off as the ram retracts all the way. I wonder if anyone has noticed this effect?

      And as far as the particular jack in my case- yes it's a relative weakling, but I have another 6T jack in use on another type of press and I'm aware of what it can and can't do. I don't want to pay for a heavier duty jack at this time, but I can always upgrade with few if any mechanical changes needed to the press frame assembly.

      Last point- I see from scouring the web that I've asked about the threaded portion of the jack before- about 3 years ago when I built the last bender. I'd forgotten all about that. In that case I did saw off the threaded stub and screwed the remainder of it back down into the jack. Worked fine. I just did the same to this one, and I discovered there to be nearly 6 inches of depth inside the ram. I also found some acme rod of the same size and thread, so I'll be making my adapters using it. There is only about 3/4 inch of thread inside the ram, so to me asking that to sustain 12000 lbs is stretching it. I'll use it to secure the tooling, but not to take any of the pressure.
      I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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      • #18
        My dad built a press around 1944 using an upside down jack with a reservoir on top plumbed into the fill hole. Worked perfectly once all the air was bled out by laying the jack on its side. We used it mainly to press starter and generator shafts out of and into the armatures. Bushings and such were generally done in the vise.
        Don Young

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        • #19
          I dunno, i suppose even a 20t (apply doozer conversion factor which i now call it) harbourfreight or clarke over here is better than struggling with a bench vice or BFH, the jack part has a safety bypass doesn't it?
          Mark

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          • #20
            Safety bypass? I presume that's to limit the extension of the ram. I think my 12T has that.
            I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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            • #21
              Safety bypass?
              Probably an over pressure bypass valve like floor jacks have.
              Location: Long Island, N.Y.

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              • #22
                Originally posted by RichR View Post
                Probably an over pressure bypass valve like floor jacks have.
                All of the cheap Chinese jacks I've seen do not have an over pressure relief valve. They had to cut something to meet their price point.

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                • #23
                  I've been keeping an eye out for a pre-Chinese jack- even used they are most likely to be in better shape. People sometimes laugh when they see what I've brought home, but even graunchy-looking stuff cleans up nicely and is most often in better shape than this new junk.
                  I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                  • #24
                    Originally posted by darryl View Post

                    Now here's a point of interest (or maybe not) regarding the jack- pretty much any bottle jack- the fill level leaves room for fluid to change height in the body of the jack as the ram moves in and out. With the ram retracted, you fill to the level of the port and put the rubber stopper in. The air inside is at the same pressure as the outside air at this point. When you extend the ram, the internal air pressure must drop. Of course, the capability of the jack far overcomes this negative pressure, but I thought it worth noting that now the space above the fluid is at a reduced pressure. This should help suck the ram back in when the release valve is opened, an effect which is strongest initially and dwindles off as the ram retracts all the way. I wonder if anyone has noticed this effect?
                    It's noticeable only when you use the jack to apply force to something that doesn't spring back. When you release the valve, the ram retracts enough to give you a bit of clearance, though it's not much. It's more noticeable that when you push the ram all the way in, and don't shut the valve, the ram may rebound a bit, a half inch or more on some jacks, depending on the friction of the seals.

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