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  • Trying to lift a machine, need to know material strength.

    Discussion in 'Help, info & forum announcements' started by JoBrCoGB, Oct 6, 2020.

    1. JoBrCoGB

      JoBrCoGB Member

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      Hello,

      Thanks for your time, it's greatly appreciated.

      First, I'm no engineer! I've just played with mechanical things for several years, mainly repairs following workshop repair manuals.

      I need to move a cast iron machine that weighs approximately 700 lbs. It has a hollow cast(sand)-iron column with two 22mm lifting holes opposite one another. I plan to insert a 22mm round bar into the holes to safely lift the unit using collars with set screws to stop a lifting sling (1 ton capacity) from sliding off the bar. I also planed on using collars to keep the bar centered in the machine. My concerns are bending which would load up the collars, potentially causing them to slide off and cause the machine to drop, I also don't want to have the bar permanently fixed in the machine or the casting to be damaged due to potential bending.

      I'm looking at a 22mm diameter 304 coldworked Rockwell B80 stainless steel bar that's 1 foot long to do the job. It's a bit expensive for my budget, but I'll buy it if necessary. Of course the main concern is that what ever material I use that it doesn't bend under the weight. I thought about using standard threaded rod that can be bought at any big box hardware store, that's just under 22mm, but I'm afraid they might be too soft and may bend, also worried about threads not making enough contact with the cast iron holes which are not perfectly cylindrical (slightly tapered or irregular). The squarish column is 7.25" wide and the holes bearing surface (depth) is approx .450". I would be lifting at the ends of the 1 foot rod due to thinner, potentially more fragile, protrusions above the hoisting holes. So the distance between the beginning of the two fulcrums (bearing surfaces) is approx 6.35" which ends .450" later and the bar extends beyond them on each side by about 2.375".

      I have no idea how to do the math, and don't know where I can find material strengths either tensile, shear, etc to plug into the equations necessary to find my answers. So any information that can help me would be greatly appreciated. I'm not sure if I've provided all you may need to know, so just ask if you want to help.

      Again thanks for your time!

      Joe
       
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    3. Jim Haaser

      Jim Haaser Member

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      Can you just put the sling through the two holes and lift away?
       
    4. JoBrCoGB

      JoBrCoGB Member

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      Thanks for your response!

      No, the sling is far too large to fit through the 22mm holes. Even if it would fit, I'd be worried that it might be cut on the cast iron, it's a polyester sling.

      I'm probably over thinking the problem. It's just that the machine is the most expensive tool I've ever bought, and it's new so I really want to make sure I don't break it before using it. It's still attached to the shipping pallet, It was delivered on the 21st of Sept, so you can see that I'm taking my time, with each new consideration on how to proceed safely.

      Thanks though, again appreciate you taking your time.

      P.S. I think I may have put this thread in the wrong forum, but I didn't want to interfere with the back and forth between the engineers. Since the only thing I've engineered was solutions to basic problems.

      Joe
       
    5. s.weinberg

      s.weinberg Well-Known Member EngineeringClicks Expert

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      22mm is a lot. I doubt you'll have much problem with bending, so long as you're not lifting too far from the center of the bar.

      Why stainless? Regular ol' steel is stronger, harder and cheaper.

      EDIT: Did a quick back of napkin calculation (it could be way off, I haven't done simple bending by hand in forever. I also made a couple of conservative approximations).

      Got 454 MPa maximum bending stress - which could actually be a problem. To be safe, maybe go with a high strength steel, like 4340, or even tool steel if you have some handy
       
      Last edited: Oct 9, 2020
    6. Dana

      Dana Well-Known Member

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      I only get 13 ksi or 90MPa, M= 350*2.375 right where the bar exits the tube.

      But yeah, no point in using stainless; any grade of steel will be fine for that. Even if you used readily available 3/4" bar, it would only be 23ksi, still fine. So lift away.

      You could also buy a long 3/4" bolt and nut, then you don't need the collars. McMaster has grade 8 (high strength) 3/4" bolts in 13 and 14" length, though even the low strength bolts that are half the price are still rated to 60ksi.
       
    7. s.weinberg

      s.weinberg Well-Known Member EngineeringClicks Expert

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      Sounds more reliable. I just used a point load in middle of the bar, and supports at the ends - which was super conservative. Just to make sure it was completely safe.
      Likely ridiculously conservative, as you've indicated.

      I was 'surprised' as I'd expect 22mm to be able to hold way more easily - and it looks like my inclination was correct.
       
    8. Jim Haaser

      Jim Haaser Member

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    9. Jim Haaser

      Jim Haaser Member

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      Why are the lifting straps so large? A 1 inch wide tie down strap is rated at 500 lbs. You one strap through each of the 2 holes, put a piece of plastic or leather to prevent cutting at the sharp edges and lift 2000 lbs..
       
    10. JoBrCoGB

      JoBrCoGB Member

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      Thanks! Yeah I understand leverage, I gave the distances in my original post. I only need a 1 foot bar and it'll have 2 fulcrums as the body is hollow. Each fulcrum is about 6.35" apart and are .450" wide and I'll be lifting about 2.375" from the fulcrums on both sides.

      Actually I thought that SS would be less apt to bend, while I know that high carbon steel would be harder, the harder it gets the more crystalline the grain structure, at a certain point it tends to shatter rather than bend.

      I was looking at McMaster Carr's rods, both SS and high carbon steels. I'm probably going to go with the high carbon instead of the 304SS. It's cheaper and less likely to bend and I don't think I'll shock it such that It'll shatter.

      So thanks, multiple heads are better than one, and I'm happy you decided to help.

      Have a good one!

      Joe
       
    11. JoBrCoGB

      JoBrCoGB Member

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      Thanks!

      Yeah I've settled on McMaster Carr, I've already bought a few of their products and happy with them so far.

      I'll be going with the higher carbon steel, and I'll probably go with the threaded rods, nuts and flat washers, using two nuts together as jam nuts, it'll just be an easier process, without the need to manufacture collars.

      Originally I was worried about the threads digging into the iron sandcastings. This machine is Chinese manufactured, and has been said to contain voids. I'll just take it slow, keeping a close eye on the contact points. I'm using a 2 ton engine hoist to lift which means very slow lifting.

      Thanks much for your time, it's really appreciated. Getting multiple inputs about things I've considered gels confidence.

      Have a good one!
       

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