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what do you guys think on topic?

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  • what do you guys think on topic?

    I have often thought when using hollow suare-rectangular metal tubing for a project,would it help to incorporate a well fitting wooden plug of the exact internal dimension top to bottom and squeezed in under hammer or other pressure device. Surely this would add extra resistance to either horizontal bending or top down compressure-pressure in use. I HAVE HEARD OF COMPANIES FILLING THE BEAMS WITH A MIXTURE OF VARIOUS THINGS LIKE CONCRETE.i HAVE OFTEN WONDERED WHY METAL LIKE THIS DID NOT COME RADY FILLED WITH SOME FORM OF plastic substance to help with hollwo metal under stress-load what do you guys think and (sorry about typing ) Alistair
    Please excuse my typing as I have a form of parkinsons disease

  • #2
    I kinda think it would depend on what you need from the tube. The use of the tube. And how long the piece is. But yeah, sure. I think it would add some strength to the tube. Could use a heavier wall thickness too. JR
    My old yahoo group. Bridgeport Mill Group


    • #3
      Filling is usually to add mass to reduce vibration resonance, if you just want it stiffer you use a heavier wall as JR suggests, or an alloy steel tube as these will be the lightest solutions for a given increase in strength.

      - Nick
      If you benefit from the Dunning-Kruger Effect you may not even know it ;-)


      • #4
        Probably a moot idea on a number of fronts esp now with modern composites.

        I've heard of filling tubes with 'structural foam'. I know Bianchi cycles did it for a period.


        • #5
          filled with wood or plastic would make the welding interesting.

          Alistair, I don't know why you are always saying sorry for the typing, your typing is fine.


          • #6
            The idea is sound for sure. And on something like a bicycle with super thin wall tubes a dense but light foam fill would be a wondrous thing.

            But for "our" home projects I don't see the point. As a group we typically over engineer our material sizes almost universally. The only place I could see doing such a thing is for something along the line of an extension for a shop lift crane boom. Just about anything else in our shops is going to be just fine even with the lighter gauge wall tubing sizes. Let's put it this way. By the time the wall is thick enough for us ham fisted welders to not burn through frequently it's going to be more than thick enough to deal with any loads we might put into it. So expert welders good with 1/16" and thinner wall tubing might be wise to consider a filler for the tubing in SOME cases. Now I speak for only myself in this but I'm sure that a few other of you ham fisted "once in a blue moon" welders out there can identify with this....

            But using wood is an issue. For a good force fit the friction from inserting the wood is going to build up so fast that you'd need a serious tonnage press to push in any significant length of wood under enough pressure to provide enough of a difference to the bending of the tube. This isn't something where you'll gain anything worth while from a piece of soft wood which fits in with love taps from a big shop hammer. It would require a pretty serious compression fit for the wood to play any sort of valued role in this way. Even cutting the fillers to about 6" long with a roughly .005 to .010 interference fit so as to fit tightly enough to provide good wall support is going to result in a serious beating to push it along the tube. So all in all I'd say just use the next thicker wall option and call it a day.


            • #7
              When a friend of mine made a bar for tying cargo off in my van, he filled the center of the 2 by 2 metal square tubing with a square oak spindle. It really did make it flex a lot less. The oak dowel would have its own strength and then filling the metal tube would keep it from deforming as easily when least that what I think makes it stronger?
              Last edited by mikem; 12-09-2017, 04:51 PM.


              • #8
                Like mentioned it would make welding interesting. I would worry about rust personally. If the tube were completely sealed maybe not as much but if it has an open end for sure a moister trap.


                • #9
                  In the days of VHF TV and big antennas I went to buy a 'high winds' antenna. They looked exactly the same as the cheaper antennas so I said so to be told that the high winds ones had wooden dowels coated with expoxy and pushed into the antenna elements. We lived right by the ocean and that antenna lasted 30 years frequent gales and all.


                  • #10
                    I have modified Aluminum rectangle that was filled with the foam expanding insulation.
                    mark costello-Low speed steel


                    • #11
                      This in an interesting thought. Yes, some kind of fill would stiffen and strengthen any hollow member. Wood, plastic, concrete, any of them would improve the strength. The question in my engineering mind is benefit vs. cost.

                      If you have a specific application, like the TV antenna mentioned above, then it could very well be a good idea. They seem to have gotten around the "how do you do it" question with using epoxy around a loose fitting wood filler. Probably the biggest plus of doing this would be to help prevent the hollow tubes from bending: when a tube bends, it usually crushes at that point and the wood fill would resist that.

                      However, on a more general basis, when we need a stronger member, we usually just step up in size, one way or another. I was amazed when I first saw thick wall tubing. Up until then all I had seen was pipe or fence post or other things like that and they all had relatively thin walls. When I first saw tubing that had walls that were one inch and more thick I was amazed. This is one way of increasing the strength of hollow members, just make the walls thicker. Such tubing is a compromise of strength vs. weight. Oh, and cost is in there somewhere. A piece of thick wall tubing will have more strength than a piece of solid that is made with the same amount of material, with the same cross sectional area. Such thick wall tubing is used to construct things like tall towers where not only cost and strength come into play but also wind resistance. The thick wall tubing is probably specifically made for each level on such a tower. Different levels may look the same on the outside but have different wall thicknesses as needed where they are placed.

                      As for selling it ready made, I can see several factors and most of them rest on cost. The fill material needs to be economical for the intended use. Wood springs to mind but the real cost would be in assembling it into the tubing. Pressure would work but would the fit be tight enough to really prevent a bend/crease from starting. That would require intimate contact preferably with some initial outward pressure. The epoxy idea is a good one but that could be labor intensive.

                      What about plastic? We used to call plastic things cheap. But plastic is not really that cheap. Most plastic parts are made with thin walls. Cross sections that resemble I, U, or T beams are used to save plastic and cost. If you fill a piece of tube completely with plastic, it may more than double the cost. Heck, it could easily go 4X or more. I suspect adding a thicker wall with more metal would be a lot more cost effective in most circumstances.

                      Concrete? Easy to apply and it would be in intimate contact with the tube. And it would undoubtedly add more strength. The cost would be OK. But oh the weight.

                      I suspect that the reason why you do not see any tubing like this sold as a generic item is because it is not a good mixture of qualities, including cost, for general purpose use. It takes a special use and a filling scheme that is designed to work well for that particular purpose. For general use, tubing with a thicker wall would be the engineer's choice.

                      I found some hits with a search for "filled tubing".

                      Concrete fill article"


                      I did not see anything on metal tubing filled with anything other than concrete. Perhaps someone with better Google-foo can do a better search.
                      Paul A.

                      Make it fit.
                      You can't win and there is a penalty for trying!


                      • #12
                        No first off I slipped up. I do it often when typing and jumped from small to large type ie caps, some people so I believe think this is shouting so might take it on the nose. so anyway Thanks friends for the replies. I was thinking of two projects which are currently in my mind a shop made press hydraulic. I can actually buy a cheapy here in the uk for around £54 pounds inc delivery . It just smacks of flimsy, so maybe since I bought recently two more expensive long hydraulic pumps with handles,I thought it might be nice to design and make my own. Well after all, I am a hobbiest, and should really try more of this shop made stuff. I see it all as fun and a challenge .So when you get to be like me ,old shuffler LOL , then a challenge is just the thing to get your cognitive resources back onto heated up mode or in from the cold..l Love you people here all of you, god bless Alistair
                        Please excuse my typing as I have a form of parkinsons disease


                        • #13
                          I agree whole heartedly with the idea of designing and making it yourself.

                          I've been telling my wife for years that I absolutely refuse to go to the store and purchase something for $10 when I can make it myself for $50.


                          • #14
                            Wow that an overall saving Frank when you consider autojuice costs around 25 bucks each way educate all women into realizing a happy man is relative to a happy home no-ifs-arr-butts-a-rbout-ett. Your pal big Al
                            Please excuse my typing as I have a form of parkinsons disease


                            • #15
                              Tube in tube so there's a space between them, fill the space between the tubes with a structural foam.
                              Seems like it would work by turning every point between outer and inner 'skins' into a 'truss' like boat decks, foam core paper and cardboard.