Improve rigidity for standard EMT you know.... wood. A 3\4" dowel, sanded if necessary, would for. Rout a groove for wires if necessary. If no one has tried it, I'm your huckleberry

At the lengths the tubes are, I don’t think they will have a measurable deflection by themselves.

I know how you feel. I was fighting tooth and nail for 7 years to get into design after I graduated. Finally a startup took a chance on me, and it all fell into place from there.

Manufacturing engineer is really interesting too, I’ve been getting more and more interested in that side of things, which is what led me to this site…

What if you 3D printed a structural frame that fit perfectly inside the tube? You could print it in whatever size sections your printer could handle and then glue/screw each one together to match the length of your conduit. Just glue it in there and you should be good to go.

We’ve had this conversation (several times). Different versions of stuff to put inside the tubes to make them more rigid. The conclusion I always end up with is:

  • I definitely don’t want to impede someone trying something, even if I think it won’t work. If you’re willing to do the test, and it brings you joy, go nuts.
  • The strength of tubing is in its skin the rigidity comes from the outside, not the middle.
  • Steel is much more rigid than 3D prints, or concrete, or epoxy.
  • A good balanced machine has enough rigidity in the tubing to not need any more. With more weight, more rigidity in the tubes, you’ll need to upgrade other parts.

I feel like I need to mention that. I don’t want to discourage progress, but nothing has compared with the ease and performance of just a 1" tube. If we really needed more rigidity in the tubes, 1.25" tubing would be much better, but it isn’t worth the extra space, and components that would need to be upgraded to use the increase in rigidity.

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Wasn’t an alternative to EMT and Stainless mentioned by Ryan a while back. I think one of the issues was maintenance associated with rust/needing to be oiled or cleaned regularly. The low cost as well as the properties were all excellent though. Could be a worthwhile effort for someone willing to try it out.

Now, if I could just find that darn thread with the exact type of tubing…

Well, couldn’t find the thread but here is a link for those interested in reading more “Science” as it applies to tube selection.

Likewise I don’t want to discourage anyone from experimenting and learning something, and it’s a fine line if (I think) someone is going to waste their time. It costs me nothing for someone else to waste their time but it still hurts.

Sometimes a good alternative is to steer toward trying the simple thing first. Like try estimating the relative stiffness of metal tube and wood dowel separately when it’s outside the tube. If the wood is 5x more flexible by itself then you learn something without all the hassle.

Actually, it’s not any bother at this point. I’m just going to collect the pieces and take some measurements. No big deal. My original question was whether anyone had tried a dowel inside the EMT. There’s been a lot of theorizing, but it looks like the answer is that no, no one has. So I will and I’ll get back to you.

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Best way to add rigidity would be to weld a piece of flat bar to the bottom on edge. If you could figure out a way to braze a bar inside the tube that would work as well. Has to be welded the entire length to work properly though.

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Not sure the technical term, but they were talking about gas pipe.

Usually for that they use a carbon fiber or fiberglass epoxy overwrap.

Not that.

There was another thread talking about using ‘black pipe’ I’ve always called it gas pipe:

Ah, gas pipe is heavy. It’s also a funky diameter.

Easy to attach flat bar to the bottom. If one possesses a welder. What I’ve got is a mallet to force wood through the EMT. But, yeah, I’m assuming that flat bar would work.

I mean, you can do it, but it won’t add noticeable stiffness. I don’t mean to be smug about it, but it does strike a dissonant chord to reject the the well understood science. Cross-sectional stiffness is not loosey-goosey (although material characterization is somewhat). I have personal experience with novel fiberglass/wood/concretecomposites and it’s really cool stuff so I encourage you to follow through on your experiments because you’ll learn things. I also encourage you to be careful in your scientific method and observations.

What you’re looking for is to see how putting a dowel rod inside will improve crushing strength, as well as tensile and compressive strength. Because of the improved crushing resistance, it also resists buckling failure better. However, it will marginally improve bending stiffness because 1) wood is nowhere near as stiff as steel, and 2) the dowel’s moment of inertia is inferior to the tube’s.

BTW, one of the interesting things about combining starkly different stiffness materials like this is that it can cause premature failure. It won’t in your case, but in high-performance aircraft and multihull sailboats the designers have to be very careful in their mixing of fiberglass and carbon fiber. If you have a CF and FG cloth expoxied together, the CF’s high modulus of elasticity means it transfers very little load to the FG. This means that the resulting composite piece is less than the sum of its parts.

Gosh! Just AWFULLY sorry to strike a dissonant chord. To be honest, though, when I hear that the"science is settled", I think people are using a different concept of science as one can see from various “medical model” failures. And meteorological scandals. Science is never settled. I simple asked if anyone had tried this. Apparently, you haven’t but you feel the need to defend your models. If you’re correct, an experiment will only confirm your theory . So relax. Have a beer.

What do you have to report if it works out it will be a great.cheap addition

It’s a shame we can’t heat treating the galvanized conduit, since it would produce toxic fumes. Mild steel heat treats real nicely, and would increase stiffness A LOT. You can add an annealing stage to prevent brittleness. And it would add no weight to your machine. But I think stripping the coating, heat treating, and re-coating are beyond the realm of the usual DIY-er haha.

How much would it cost to heat treat 20 foot of 1 inch Dom tube? Less than 20 foot of stainless and would it be stiffer?

TimW: waiting for payday when I do supply run. Results early next month.

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