It’s easy enought to test so just do a quick test and you’ll know for sure.
Take a bit of tube, put it in a vise, suspend a weight to it and measure deflection.
Then pour foam into the tube, measure again and see if it changes.
My guess would be that it doesn’t worth the hassle, unless maybe if your tubes are made from paper thin metal.
As stated earlier, main downside will be cable management, basically you’ll have a hard time making any change to your machine later if it involves adding a wire into one of the tubes. Other than that I see no downside, just maybe lots of work for very little reward.
It’ll probably be cheaper and faster to get some thicker tubes in the first place.
Anyway, feel free to try, maybe it’ll surprize us, who knows!
This is exactly how I like to look at stuff like this.
Probably not, but try it!
I would expect (without having done the test, or seen any results from gear heads) that it would dampen vibrations, but that it wouldn’t affect the stiffness in the engineering sense. I would be surprised (and I would love to see it) if it deflected any less under load. But I wouldn’t be as surprised if you hit it with a hammer, that it would stop vibrating sooner.
FWIW, I have professional training as a software, electrical, and physics engineer, not mechanical. So I am an amateur when it comes to speculating this.
I was looking to see if there was a good reason not to, and what I got was reasons it wouldn’t work. I’m an empirical kind of guy with stuff like this. I get why it might and might not work, so what’s left is “try it and see.”
So my understanding is that the foam bonding to the steel is like thread. Each point of contact is a weak bond from one spot to another, but because they contact a lot of surface area, they serve to support the surrounding structure, like many stitches can support a lot of weight.
I also get that foam isn’t very strong compared to steel, and that a tube is already a very strong structure. Lots of reason to suspect that it will do no good… It’s all speculation until experimentation, and even then, there are a lot of variables, different kinds of foam, how well I can dispense the correct amount to fill the tube, how it bonds to the steel… The list goes on.
I will try to pull a rag through the tube to get the inside as clean as possible to reduce that variable.
In terms of damping vibration, that may also be of benefit, though I don’t know how I’d go about measuring it
What about printing alignment spacers for both ends and adding a second, smaller steel tube between the foam and outer tube? You keep the wiring channel open that way but the foam should stabilize the position of both tubes.
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
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.
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
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.
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.
