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What's a good vibration dampener?

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  • What's a good vibration dampener?

    I'm putting the final touches on a combination planishing hammer and english wheel frame. The frame is made from square and rectangular tubing. The problem is that it "rings like a bell".

    Before I button up the frame, I want to fill it with something. Maybe sand? Lead shot is out. That's toooooooo heavy. The space to be filled will be about .6 cubic feet (1024 cubic inches).

    I need something that won't explode or burn when I weld up the caps.

  • #2
    How about oil sorb/kitty litter? Should work well, and be lighter then sand. If you do use sand, make sure it is dry. I was thinking about “Great Stuff" but I don't know if it is flammable after it dries. I have some I can test if you like.

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    • #3
      Sand,kitty litter,how bout steel shot?
      I just need one more tool,just one!

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      • #4
        Yea, I've tried that "foam in a can" stuff on another project. It didn't work. It cures with too much air in it. It needs to be very dense.

        The kitty litter idea might be worth a try. I'll try that tomorrow on a small piece mock up. I wonder if concrete would work?

        Edit:
        Hummmmmm. I was just thinking. Kitty litter would have to packed in tight. Otherwise, there would be lots of air pockets around fairly light material. That may not work.

        Steel shot? Seems like that would add a "ringer" to the bell. (And about 250lbs.)

        I'll try a test with sand and concrete.

        [This message has been edited by CCWKen (edited 05-05-2004).]

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        • #5
          CCWKen --

          No first-hand experience with sand fillings myself, but a former coworker claimed that oil-dampened coarse sand works well to damp the ringing of a hollow-member weldment. The same guy was not satisfied with concrete filling; he said that the concrete didn't bond to the steel well enough and pulled away while curing.

          I don't know what, if any, surface preparation he did before pouring in the concrete, but concrete does bond to clean steel so I suspect that he may well have cut some corners on the cleaning.

          Even with good cleaning, though, it might be worthwhile to consider using one of the slightly-expansive concrete materials such as "anchoring cement" or "machine grout".

          John

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          • #6
            First you need hydraulic cement, it expands on curing.

            To dampen something you need friction and dead mass, nothing light and fluffy. Varying the stiffness will change the natural frequency of the structure, the stiffer the higher the frequency.

            How about some pictures to see what your weldment looks like?

            ------------------
            Neil Peters
            Neil Peters

            When on the hunt, a broken part is better than no part at all.

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            • #7
              Neil - I wish I had a digital camera.
              I've been taking film pictures of the build but finishing the roll and waiting on the pictures is a PITA.

              The main structure looks like a capital "I". The vertical beam is 4x4x3/16" and 39" long. The top and bottom bars are 2x3x3/16" and 60" long, centered on the vertical. The 4x4 was notched at the top and bottom so that the horizontals would fit full length "through" the vertical and flush on top and bottom.

              On the top horizontal, I have a spead "M" shape bridge. This is made from 1x1/4 flat. The center of the M is centered over the vertical. The lower horizontal bridge is constructed the same way in a spread "W" form. There's a vertical stringer from the apex of the M and W legs to the horizontals.

              The plan is to also add gussets on the inside corners. The form is VERY stiff and has a high pitched ring if struck.

              There will be other parts added for the hammer and e-wheel mechanics but the main shape is all that will be filled. There will be a dampener under the hammer anvil too.

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              • #8
                Got the mail. Thanks Joel.

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                • #9
                  I am not sure about the acoustics involved in an enclosed tube, but sound insulation relies on the decay of energy by repeated impacts. I wouldn’t think that the air pockets would necessarily be bad. You could try it loose or lightly tamped, and then pack it to see if there is a significant difference.

                  I am surprised that the concrete didn’t work better. Concrete shrinks when it is cured, so I am unsure that a spotless tube would change things very much. Anchoring cement might just be the answer. It sure would be easy to work with, just pour it in. It’s not particularly cheap though. Floor leveling compound is similar, but IIRC, it shrinks as well. Concrete without any water wouldn’t shrink, but your getting back to mostly sand. Any powder might work, like plaster, gypsum, or even flour? I wonder how well foam pipe insulation would work (melting aside), maybe neatly zip tie it on the outside?
                  I guess you sparked my curiosity, I hope you’ll post your results.

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                  • #10
                    Don't use Cement or grout. Among other things, you'd have to leave the ends uncapped for several weeks in a warm, dry shop for most of the moisture to migrate out.

                    Sand is fine. You want something somewhat loose (IE, it can shift a bit to absorb the vibration motion) and reasonably dense.

                    Don't use beach sand due to the salt. Commercial landscaping sand is fine, just be sure it's dry before sealing it up. If you're not sure, spread the sand out on tarps or Visqueen on the floor of your garage for a night or two, then collect it up and dump it right in.

                    Doc.
                    Doc's Machine. (Probably not what you expect.)

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                    • #11
                      Use gravel, old chain, or junk nuts and bolts but don't fill the spaces up. Dense is better. The media has to have freedom to jostle and rattle. Several trays of loose stuff in a single layer is far more effective than a loose pack.

                      You only need damping at the ends of an "C" shaped structure. This catches the first and third order of resonance and the feet in contact with the floor will deal with the second and fourth. Generally there's so much intrinic damping there's little problem with third and higher orders unless there's direct excitement.

                      Don't use oil or grease thinking the viscous damping will help. It's effect is mostly as a coupling medium unless fluid shear han be evoked somehow. There's too much chance for a leak unless the sturcture is seal welded.

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                      • #12
                        I'd do hydraulic cement, as per NAMPeters.


                        ----------
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                        • #13
                          I would go with the sand first, if it dosen't work you can remove it and try something else, not so with concrete. With cat litter I think that over time vibrations would break it down into dust, it is just lumps of clay. Anything liquid or semi-liquid would just be messy to remove if it didn't work.


                          ------------------
                          Paul G.
                          Paul G.

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                          • #14
                            You might experiment with oil based modeling clay. It stays pliable for decades and should dampen pretty well, won't rattle either. It won't leak but I wouldn't get it too close to the welding bits. Weld one end, make up a bunch of clay balls and drop them in.
                            Free software for calculating bolt circles and similar: Click Here

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                            • #15
                              Ear plugs?
                              All of the gear, no idea...

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