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

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  • #16
    Originally posted by MattiJ View Post

    Yet if you factor in the joint friction coefficient you'll find out that ultimately the bolts hold more in shear than just clamping.
    The coefficient of friction being largely the great unknown quantity in an assembly much like this, a well engineered or designed product will allow for the variables inherent in such an assembly and with a large safety factor.
    The bolted assembly's surface finish may be etched, painted, or as supplied by the manufacturer and will play a large part in it's success or failure, as does proper torque and thus clamp load.
    As demonstrated by the OP, fortunately without much drama, clamp load is a very vital key, since shear strength was simply not enough.
    Home, down in the valley behind the Red Angus
    Bad Decisions Make Good Stories​

    Location: British Columbia

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    • #17
      Originally posted by Tundra Twin Track View Post
      DR I’ve got some FKE 200+ which are 50,000 tensile strength stronger than Grade 8. . .
      That's something a lot of guys don't realize: The spec for SHCS is much higher than for hex-head bolts, even grade 8. BUT, when you buy chinese, you have no idea whether or not that spec is actually met. Also, since tensile strength is always published and easily found, too many people figure that shear strength will be similar. It is NOT. At best, shear strength comes in around 60-65% of rated tensile.

      Southwest Utah

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      • #18
        If you're looking to find out what tonnage your press can actually produce, you could look up how to press a bearing ball into a known material and measure the width of the dimple produced. This is dangerous as the ball can shatter, but it's a poor mans way of gauging the force. As for the bolts, being loose they allowed a bending moment to occur, and of course the weak spot would be at the first narrowest part of the bolt- where the threads start. You'd be lucky to have 40% of the tensile strength under that condition.
        I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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        • #19
          Originally posted by chipmaker4130 View Post

          That's something a lot of guys don't realize: The spec for SHCS is much higher than for hex-head bolts, even grade 8. BUT, when you buy chinese, you have no idea whether or not that spec is actually met. Also, since tensile strength is always published and easily found, too many people figure that shear strength will be similar. It is NOT. At best, shear strength comes in around 60-65% of rated tensile.
          Not sure but I think these FKE should be decent as I wouldn’t think Barnes would purchase junk. Click image for larger version

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          • #20
            Yes, that description seems like good stuff. If a good company is willing to put their name on it, that's always a plus. The real trouble often accompanies un-branded/no-name products.
            Southwest Utah

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            • #21
              Originally posted by DrMike View Post
              Yes, it's exactly like that in configuration, same flywheel and crank shaft orientation. But mine is a floor model with a single casting from top to bottom that probably weighs 5 times what that bench model weighs, Years ago I had a small Perkins like the one shown, 3 ton capacity.

              I read in old literature the crank journal diameter was used as a good indicator of press tonnage. Sounded like a good way, the problem was another of my punch presses with capacity marked in the casting violated that method. I've had 4 or 5 punch presses over the years and Perkins seems to be the only one that doesn't specify tonnage on the casting.

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