Crazy pipe stiffening idea- Input wanted

[Northboy]

A friend who is a good overall fabricator and often has good ideas came up with this one when I told him how much I found my my 1 inch pipe was deflecting when I made the (had to be done) mistake of putting on a dial indicator.

He suggested putting a hardwood dowel inside the pipe and epoxying it, then went further and suggested expanding foam.

I see no problem with the idea it sure is cheap enough, and have even bought the dowels and foam.

There is .030 clearance around the dowel (with my particular dowel and pipe). I think it is crazy enough it just might work, and might even reduce some resonance in the pipe (or increase it, as this is just arse talk till it is tried)

As I said, I have the stuff, but have not tried it yet. Any input here guys?

Check out the picture if you miss what I am rambling about.


Northboy

[DareBee]

Sure it will help.
I think the foam is too flexible, but is better than nothing.
Epoxy would be a much better choice.
Packing it with some good grade Sa-Crete works good.

[Northboy]

Originally Posted by DareBee Sure it will help. I think the foam is too flexible, but is better than nothing. Epoxy would be a much better choice. Packing it with some good grade Sa-Crete works good.

I had thought of epoxy,and also was considering fibreglass resin. It seemed if the foam could have enough force to ruin windows and doors it might expand and hold the whole thing solid, but you are probably right, it would still be too soft.

In any case if I do this this weekend, I will do some sort of before and after tests with a measured weight and dial and post the results.

[ger21]

I don't think the foam would do much of anything, but the dowel and epoxy should make it stiffer, but you need to make sure you get a lot of epoxy in there. One way would be to cap the end, then poor in the epoxy, then slide the dowel in, forcing the excess epoxy out the top. A bit messy, though.

[jsheerin]

No, it's probably not worth it. The strength in a beam (or pipe) comes from having load bearing structures far away from each other. Iow, an I-beam that is very tall or a pipe that is a large diameter. Removing material from the center of the tube or from the sides of a solid rectangle to make the I-beam only increase deflection by a small percent.

Now if you add in that you are thinking about putting materials with a much lower modulus of elasticity in the middle of your pipes (as compared to steel), it's even less worth it.

The best ways to get lower deflection are to use bigger diameter pipes, space multiple pipes apart and connect them together (like an I beam), or support the bottom of your pipe (in effect making an I-beam-like structure with something besides pipe for the other side of the beam).

[Northboy]

Originally Posted by ger21 I don't think the foam would do much of anything, but the dowel and epoxy should make it stiffer, but you need to make sure you get a lot of epoxy in there. One way would be to cap the end, then poor in the epoxy, then slide the dowel in, forcing the excess epoxy out the top. A bit messy, though.

Really messy as I was going to try it without taking apart the machine.....

With only .030 clearance it might be a big ugly mess when I am done. Regardless of what I try, I am going to mask the hell out of everything

Northboy

[greybeard]

What happens if you put a steel rod down the centre of the pipe, threaded ends, then use nuts to tension the rod ?
You can tell I'm not an engineer, otherwise I wouldn't have to ask
The pipe is then under compression, and stiffer than if you filled it with foam ?
John

[Northboy]

Originally Posted by jsheerin No, it's probably not worth it. The strength in a beam (or pipe) comes from having load bearing structures far away from each other. Iow, an I-beam that is very tall or a pipe that is a large diameter. Removing material from the center of the tube or from the sides of a solid rectangle to make the I-beam only increase deflection by a small percent. Now if you add in that you are thinking about putting materials with a much lower modulus of elasticity in the middle of your pipes (as compared to steel), it's even less worth it. The best ways to get lower deflection are to use bigger diameter pipes, space multiple pipes apart and connect them together (like an I beam), or support the bottom of your pipe (in effect making an I-beam-like structure with something besides pipe for the other side of the beam).

Thanks jsheerin

This is the kind of thinking and bench racing I was hoping for.
Regardless of whether I try something like this or not, I am almost positively going to make some supports anyway.

Northboy

[Northboy]

Originally Posted by greybeard What happens if you put a steel rod down the centre of the pipe, threaded ends, then use nuts to tension the rod ? You can tell I'm not an engineer, otherwise I wouldn't have to ask The pipe is then under compression, and stiffer than if you filled it with foam ? John

I am also far from an engineer.(Though I curse them regularly in my day job...)
You have another idea that I also have no idea about. Certainly sounds reasonable.

Northboy

[greybeard]

2nd thoughts -you need to keep the rod central, (just intuition) so perhaps fill the space between the rod and the pipe with foam.
Any load on the pipe trying to bend it will try to put more tension in the rod. Perhaps the rod needs to be high tensile steel, whatever that means .
John

[FandZ]

Ya know, since water does not compress, I've wondered if you filled a pipe with water and capped it at both ends, in a way that there wouldn't be any trapped air, if it would make it stiffer.

On the topic though, if you do try the expendable foam, don't get the Homedepot stuff. Get the stuff drifters use to strengthen their car chases. You want structural foam and a high density foam at that. Around 12 to 15 lbs per square foot. They usually come in two parts and you mix them and pour. Marine supply shops should have some good stuff too. A high density foam can increase a cars body stiffness by up to 300%, meaning a lot less body roll. So I know it could do something with the pipes.

[jsheerin]

Originally Posted by FandZ Ya know, since water does not compress, I've wondered if you filled a pipe with water and capped it at both ends, in a way that there wouldn't be any trapped air, if it would make it stiffer.

The water can still move within the pipe - the molecules can move around - so the water can still 'flex', meaning the pipe can still flex. And then it would probably rust from the inside out over time (assuming the pipe is some kind of steel).