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Shear strength of bolts, check me on this.....

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  • Shear strength of bolts, check me on this.....

    My Perkins horn type punch press has a height adjustable table. I need to know the rated tonnage of this punch press.

    The table has four 5/8" grade 8 bolts holding it in position. While setting up the press the bolts were mistakenly not tightened leaving the table with some looseness. The press was stroked with the table loose shearing off all four bolts in their threaded area. Googling tells me the shear strength of the bolts are 30kn each in the threaded area. Converting to pounds force equals 3.35 tons, times 4 equals 13.4 tons.

    So, is it fair to assume the tonnage of this press is at least 13 tons?


  • #2
    Assuming the bolts all sheered at once, I'd say there's a good chance.

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    • #3
      Originally posted by kendall View Post
      Assuming the bolts all sheered at once, I'd say there's a good chance.
      There's only maybe .030" play in the table when the bolts are loose so they all sheared very close to the same time. What is a little puzzling is why the bolts don't shear when tightened up with the same die set mounted as when they sheared.

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      • #4
        Originally posted by DR View Post

        There's only maybe .030" play in the table when the bolts are loose so they all sheared very close to the same time. What is a little puzzling is why the bolts don't shear when tightened up with the same die set mounted as when they sheared.
        I don't have the time to check the number right now, but I can answer the second.

        Except in specially designed shear bolts, meant to fail, bolts should never be loaded in shear. Instead, the tremendous tensile force they can create holds items together via friction. In a bolted joint say on a beam, zero percent of the load should be handled by the bolt in shear. This is why it is important to torque bolts in such a load case to their specified value.
        21" Royersford Excelsior CamelBack Drillpress Restoration
        1943 Sidney 16x54 Lathe Restoration

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        • #5
          Be easier to look up the press specs. Model 200b, 22s, 2a, 20c, ??

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          • #6
            They wouldn't have broken if they had been done up properly. 8.8 bolts are medium strength, the 10.9 and 12.9 are stronger.

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            • #7
              What TMB said.........

              Also, if they were loose, the failure was probably some combo loading in between shear and tensile. Plus, odds are they failed in some zipper type failure, not all exactly at once. Nothing was really forcing them to fail at once, so they didn't.

              2730

              Keep eye on ball.
              Hashim Khan

              Everything not impossible is compulsory

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              • #8
                Originally posted by old mart View Post
                They wouldn't have broken if they had been done up properly. 8.8 bolts are medium strength, the 10.9 and 12.9 are stronger.
                You're talking 'metric'. A US grade 8 is stronger than a metric 10.9, closer to the 12.9. In any case, as you and others mentioned, the clamping force is critical to proper support for the press.
                Southwest Utah

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                • #9
                  Sorry, I misread the original post, I take it the USA and Japan use the same number system on their bolts.

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                  • #10
                    Originally posted by reggie_obe View Post
                    Be easier to look up the press specs. Model 200b, 22s, 2a, 20c, ??
                    You're absolutely right, if I knew the model number, that is.

                    Perkins appears to be long gone. All the searches I've done for pictures of Perkin's presses show a different style than mine. The ones I find have the typical arrangement with the flywheel on the right side, On mine the flywheel is on the back with the crankshaft pointing at the operator. I have found a small bench Perkin's with my style, that bears no tonnage relationship to mine.

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                    • #11
                      Originally posted by DR View Post

                      You're absolutely right, if I knew the model number, that is.

                      Perkins appears to be long gone. All the searches I've done for pictures of Perkin's presses show a different style than mine. The ones I find have the typical arrangement with the flywheel on the right side, On mine the flywheel is on the back with the crankshaft pointing at the operator. I have found a small bench Perkin's with my style, that bears no tonnage relationship to mine.
                      Fair enough.
                      Perkins Machine, Warren, Mass.?
                      Indulge me with a photo or two please? Maybe with something in the images for scale.
                      Last edited by reggie_obe; 09-07-2021, 10:45 PM.

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                      • #12
                        Originally posted by The Metal Butcher View Post

                        I don't have the time to check the number right now, but I can answer the second.

                        Except in specially designed shear bolts, meant to fail, bolts should never be loaded in shear. Instead, the tremendous tensile force they can create holds items together via friction. In a bolted joint say on a beam, zero percent of the load should be handled by the bolt in shear. This is why it is important to torque bolts in such a load case to their specified value.
                        This!!!

                        Proper torque will assure the bolts will not be subjected to shear loads in this application.

                        There is a tremendous amount of clamp load applied by the leverage the threads on fasteners provide using only a relatively small amount of torque input to a fastener.
                        5/8" grade 8 bolts, whether coarse or fine thread will exert in excess of 20,000-23,000 lbs. of clamp load each depending on thread count!
                        Makes a huge difference compared to the shear only value.

                        I'll include a link to a clamp load chart for various grades and sizes of fasteners as a reference.

                        https://sabreindustrial.com/content/...ad%20Chart.pdf
                        Home, down in the valley behind the Red Angus
                        Bad Decisions Make Good Stories​

                        Location: British Columbia

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                        • #13
                          DR I’ve got some FKE 200+ which are 50,000 tensile strength stronger than Grade 8 if my info is correct,there Socket Head Cap Screws that I could send you if my stock has your required length.Also have similar in metric there labeled 14.99.

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                          • #14
                            Originally posted by Willy View Post

                            This!!!

                            Proper torque will assure the bolts will not be subjected to shear loads in this application.

                            There is a tremendous amount of clamp load applied by the leverage the threads on fasteners provide using only a relatively small amount of torque input to a fastener.
                            5/8" grade 8 bolts, whether coarse or fine thread will exert in excess of 20,000-23,000 lbs. of clamp load each depending on thread count!
                            Makes a huge difference compared to the shear only value.

                            I'll include a link to a clamp load chart for various grades and sizes of fasteners as a reference.

                            https://sabreindustrial.com/content/...ad%20Chart.pdf
                            Yet if you factor in the joint friction coefficient you'll find out that ultimately the bolts hold more in shear than just clamping.
                            Location: Helsinki, Finland, Europe

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                            • #15
                              Originally posted by DR View Post
                              You're absolutely right, if I knew the model number, that is.

                              Perkins appears to be long gone. All the searches I've done for pictures of Perkin's presses show a different style than mine. The ones I find have the typical arrangement with the flywheel on the right side, On mine the flywheel is on the back with the crankshaft pointing at the operator. I have found a small bench Perkin's with my style, that bears no tonnage relationship to mine.
                              Does yours look like this?
                              https://www.youtube.com/watch?v=OWFq...ssetsMachinery
                              SE MI, USA

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