Increase rigidity cheaply, street racer trick?

I hadn’t seen that…looks good. I might have to try it.

Wait what? I’ve been through that thread twice and I don’t remember that picture!

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Well then that’s at least one of those ideas that someone DID test.

I wanted to buy .100 wall tube, but the only stuff that comes that thick is specialty that the company that I work for (Reliable Tube) does not stock. It’s really expensive. So, I got the .065 wall tube after all. That’s also the smallest that we sell, so I can’t get anything (at work) like 3/4" and run it inside. This would also be a lot of extra mass to move, not ideal.

I am hoping for measureable gains for under $10. Something that produces real world results for very little cost, and hopefully very little extra moving mass. Anyway, I’ll have results in a week or so

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Hi guys. What happened with the test? did it improve?

Well, I did some testing, and made a lot of mess. :slight_smile:

I have 2 lengths of tube, about 36" one was cleaned out on the inside and filled with expanding foam. Closed cell foam was used.

I clamped the ends to a bench and hung a 5 gal pail on the end of it with water. I got a little more than 1mm of deflection based on a 3’ level from the unfilled tube. No discernable deflection on the filled tube. Then I broke the clamp on my bench trying to see what it would take to get measureable deflection on that 36" tube, and haven’t repaired it. I only had about 5" of tube clamped down, and there’s a lot of torque on it with a 5 gal pail hanging off of the end of the tube already.

I still have a write-up planned, but it’s got to wait until I can get some help taking pictures and recording measurements. This means I need 2 things. I need warmer weather so that I can touch the steel without getting frostbite, and I need this Covid thing to settle down so that I can have help come over.

That there is an improvement, I am sure. Is it “worth it” I have my doubts. The foam takes a very long time to cure in the tube, and it makes a mess. One interesting thing is that the sound that striking the tube makes is seriously altered. The pitch is lowered dramatically, and the duration of the ringing sound is shortened. A change in resonance could be a good thing if there are problems that can be traced that way, but it might simply be a change, rather than an improvement.

Mostly though I just don’t have any hard numbers.

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Did you use 2-component foam? The 1 component uses moisture from the air to cure. There is very little of that in a tube.

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Just poking through some of the threads as I procrastinate other work and found this. If someone doesn’t get to it before me, there’s a pretty good chance I’ll try an empirical experiment with this once summer comes. I figure I can set up a jig to pull on the center of a tube with a chain hoist, a 250lb force gauge, and a dial indicator to get deflection. Basically a crappy 3-point flexural test, to get the bending modulus of elasticity.

Of course I’d be very happy if someone gets to it before me, because it sounds rather annoying. I do want to know if spray foam would actually make a real, measureable difference.

@SupraGuy when you filled your tube with foam, how did you go about it? Just keep spraying until it seemed full, leaving the ends open, then chop the cured excess off the ends? I feel like I want to clamp caps on the ends while it’s curing to keep it under pressure, like expanding gorilla glue.

I got a length of 1/4" clear PVC water hose, and pushed that over the foam can nozzle. That let me place the foam in a bead through the length of the tube. The stuff I got said that it did not need air to cure, but still took much longer than I thought it should. Maybe because it was really cold, too.

I would not recommend pressure. You want the foam to expand, rather than be a solid plastic in the steel in order to maxmimize its ability to provide cross-tube bracing. (Plus I’ve seen frame rail welds crack from the pressure of the expanding foam, and I would absolutely not want to distort the tube.) I cleaned the oil (used to prevent corrosion) from inside the steel and ran a thin bead, which expanded to fill the tube entirely.

The PVC hose made an awful mess though, since the foam inside it kept wanting to expand, too

So I can say that there is less deflection, but again, no hard numbers

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Howdy everybody, I’d like to start off by saying how much I appreciate all the awesome people testing out new methods and posting their results. I’m new to the world of CNC, but I’m a pretty proficient woodworker and have a decent bit of EE experience, so I settled on building a foldable Lowrider2 on machine casters sometime early last December. [current plans if your interested]

I’ve collected/fabricated most of the mechanical assemblies and fine_more fiddly bits including the main board, wiring, steppers and stuff, but I’ve been torn on deciding how the spindle is going to work out (seems to be a common problem). I’d really like to gat a “cheap” ER20 water-cooled spindle mostly for the lower noise levels, standardized collect system, software controll for CSS machining, low end torque for driving wider cutters (not really the speed), and increased duty cycle/bearing life.

My issue (similar to many others) is that I need some way to support this large spindle. I’ve seen videos and forum posts of people going to extreme lengths to get more load capacity out of their machines but most of them seem to kinda defeat the purpose of having a low cost CNC (the low cost).

My proposed “rigidification” procedure is as follows:

Using some available means (like a 4x36 belt sander) clearance fit a piece of ~1/8" flat-bar into the frame rails such that it is oriented like a little vertical wall inside the tube. This bar can be then glued in place using JB-weld or epoxy mixed with sand to increase intermaterial friction. Permanent wires could be run to bulkhead connectors/penetrators or caps, on either side. The cavity is then filled with two component closed cell foam [foam like this] to reduce noise and higher frequency vibrations.

As a result of using flat-bar It’s probably easier to find a “more exotic” steel that could be heat treated like 1080. The tube now has similar properties to if it were solid but just in one axis, with much less weight and more vibration damping.

Thank you for coming to my TED talk about making your flaccid tubes more rigid. I hope that isn’t too much for ths thread.

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Thanks for your input. It really sounds interesting!
By the way: I would like to have your woodworking skills :slight_smile:

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Well thank you, I’m certainly not the most efficient, but I’ve got lots of extra time working from home. I like your username.

Has anyone tried aluminum? Not sure what pouring molten aluminum into conduit would do to the conduit, but my cupcake pans that i pour ingots in seem to hold up well.
So far im liking the concentric emt. Especially since i have the 3/4 and the parts coming already… just gotta grab some 1/2.

It’ll shrink away from the tube.

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