I mis-spoke, mild steel (low carbon content) does not heat treat well. Medium or high carbon steels are used for heat treating. That’s how they tool steel.
DOM tubing does not refer to a specific alloy, just the manufacturing method. But again, I don’t think it’s worth the trouble.
Heat treating causes all sorts of variance in the steel, if it starts straight and round it’s not likely to be so after heat treatment
I get what you’re saying. We need models to make progress, using theory until it breaks and then making new ones. Yeah, I’m doing an experiment and I’ll have about 20 bucks into it and no, I’m not betting either way. But I am willing to double down to the extent of ALSO trying a 0.75" inch rectangular wooden bar, which would give room to run wire through the head-supprt length of conduit. I’ll add that to the experiment. After all, if it doesn’t work, it can still be used in the build, after I cut it to length.
But lets never forget all thise noted scientist that stated in various publications that Goddard was a lunatic and rockets would never work in space because there’s nothing to push against. “I told Orville and I told Wilbur and now I’m telling you: that thing will never fly” is not really a good look, is it.
That’s a good point. You’d have to re-surface the tubes on lathe afterward to take out the run-out in the bearing surface.
It gets more and more complicated haha.
Regarding Goddard, Wright Bros, Yeager, and all those others pushing the understanding of fluid dynamics, they were working on the cutting edge of very complex systems. We’re just trying to keep a stick from bending.
If my bet at trillion-to-one wasn’t tempting enough, would you take quadrillion-to-one odds? 
I dunno know if you saw these two threads:
The idea was to allow people to use up to 1.25" tube. That’s about 2x the rigidity for 25% more weight. A lot less swearing involved than shoving a wood dowel slathered with epoxy into a metal tube. (I’ve been there, I hated it. It amazed me how a thin layer of epoxy maked for an impossibly tight fit!)
When the local unis shut down this spring I lost access to the 3D printers and so stuff on my end is stalled until they open back up. If you had an inclination to experiment with these larger diameter steel tubes, I’d be really happy to support it and draw up any new parts you might need. BTW, 1" EMT is also supported by this modular system, and it’s a lot easier and cheaper to come by than 1.25" tube stock.
A generous offer, as I know how much time and effort it would take.
Still, as you say, it’s just a conduit and a piece of wood. If all else fails, I’ll do a 2x2 foot build and I can leave the wood in. No epoxy, just a square bar and a dowel. Weight it down with the standard head, plus a RotoZip I have on hand (duplicating actual work load) and we’ll see what’s what. Should be plenty of load on a 4 foot conduit to show non-zero deflection. If nothing else, we’ll eliminate the simplest improvements as being worth the effort.
I’ll find a way to support the conduit while pounding wood through it, so as not to introduce bend. These things are pretty darn straight right out of the big box stores. I’ll taper the forward end a little, but it will be friction all the way down.
We’d all like bigger builds, but I may happy with a 2x2. This is just scenery along the path, probably.
Without glue, you won’t get composite movement. To visualize how much of a difference that makes, consider fiberglass before and after epoxying.
More predictions, Kenn.
It’s more important to be kind than to be right (in most cases).
If I may, it’s quite a different thing to claim that you don’t know the answer, and claiming that nobody knows since the experiment hasn’t been done. I think this is the point of contention.
So there are different viewpoints, some think it is settled because the theory is solid, others don’t believe the theory is of sufficient reliability. I happen to fall into the former camp but I don’t think we all need to agree on this.
As long as I’m not the one whose time is being wasted (according to my belief), I’m fine to let the experiment proceed.
How do you survive on the Internet?!? 
This is how you survive on the Internet.
I started this thread asking if anyone has tried it. Lots of response, but no one is saying they have indeed tried it.
It seems completely counterintuitive that a conduit reinforced with wood, either a round rod, a round rod with routed groove or a rod oriented corner up would NOT have more rigidity than an empty conduit. It would certainly not be LESS rigid. So the question here, since the original question seems to have answered, is now "Will reinforcing the conduit with wood enhance rigidity to the point that it’s worth the trouble? "
This should all be settled in a couple of weeks.
Fair enough. If you want to see how far your experiment deviates from theory, the stiffness (according to the top hits on Google) of steel is roughly 200 GPa (https://www.engineeringtoolbox.com/young-modulus-d_417.html) and the stiffness of wood is about 10 GPa give or take (https://amesweb.info/Materials/Youngs-Modulus-of-Wood.aspx), so about 20x stiffer.
According to my calculations, the stiffness of a 1" tube with 0.065" wall thickness is about 42% that of a solid steel bar. With a 20x basic difference in stiffness, at a bit less than half a solid bar, I would expect maybe a 8x to 10x difference in favor of a hollow steel tube compared to a solid wood bar. Maybe the theory is wrong or maybe my calculations are off, maybe by a lot. But that is what you are comparing against and that is the reason for the pushback.
I think you’re spot on with this statement. I’m not sure where we got turned around so that the opposite message was being heard.
Adding wood will absolutely increase rigidity, but the point I would like to make is that it’s not worth the effort. A seasoned and wise colleague would talk about “measurable but not noticeable” differences. Like removing a paperclip from a car before crash testing it: the car will indeed weigh less, but it won’t affect the results in any meaningful manner.
Your experiment will increase the rigidity by a few %. But a solid 1" steel rod would only be 2.3x more rigid than the 1"x0.65 tube (at the cost of 4x more weight), so there’s a very close ceiling on gains. Wood is about 15x less stiff (modulus) than steel, so that means a total gain of ~15% in stiffness. (And that’s only if you glue or otherwise fix the the two together so they move in composite motion.)
Only you can tell if that’s worth the effort. I think for most of us, moving to a 1.25" x .049" tube would be the bigger bang for the buck, since it weighs less, is 60% stiffer, and doesn’t require more construction effort than the smaller 1" tube.
However, if you needed 15% more rigidity and didn’t want any other modifications, then this might be your ticket. At that point, I’d suggest checking out which wood dowels have the right density vs. weight ratio, because you might find that bamboo is a really good option.
Yes… and no. The definition of composite movement is when the pieces move together without sliding. If you don’t fix them then they will slide at the shear interface, and there will be no force transfer. You’ll get double movement, but by definition you won’t get composite movement.
I do find it incongruous to reject the predictions about rigidity but accept the equally scientific predictions that the microcontroller will work to direct the cutting head, that the motor circuitry won’t blow up, that no one will get shocked to death by the mains because the system is properly insulated and grounded, that the computer/telephone being used to have this conversation isn’t corrupting the message, etc…
I don’t think we can pick and choose which scientific predictions we accept on the basis of convenience. If there’s a first-principles issue then let’s address that. Otherwise, what reason have we got to reject humanity’s expertise?
Goodness. We can’t pick and choose which predictions we accept? But we must. If we just accept scientific prediction, there would never be any reason for further experiment and no further scientific progress at all. The process of science would stop if we stop questioning our models.
Sorry. Not blindly accepting anything. I’m banging a dowel though EMT and doing some measurements. If you had done the experiment your prediction that it’s not going to enhance rigidity to a valuable extent would have more merit. You didn’t: it has merit, but it’s not convincing. Possibly because the amount of value is subjective. Good enough for me isn’t good enough for you or vice versa. I might like a 2% improvement. I might not.
l’ll have a better idea once I actually do science; experimentation rather than faith.
Feel free to drop this if you prefer: I won’t be converting to your religion.
OK guys, we need to be very careful here. Getting very close to the ad hominem arguments, and taking things too personally. Why doesn’t everyone take a break for the evening, and come back after a night’s rest and some time to chill. I’d hate to have to find someone with the ability to lock the thread…
Sure. Why not?