[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]

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]

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]

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]

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]

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).

[Northboy]

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.

The foam was only going to act as an adhesive as there would only be .015 all around the dowel, my concern was getting it completely covered and keeping the dowel more or less centred. The more I think about it the more I like the idea of fibreglass resin because it would be fairly easy to just paint it on the whole dowel and put in a little extra and cap one end and shove it in

Regardless I won't get a chance to even think about it until at least Saturday. Great to see people kicking around ideas though!

Northboy

[ger21]

Epoxy resin is much stronger than fiberglass(polyester), and would give you a much better bond.

[jsheerin]

To nit pick, fiberglass is glass fibers in a resin matrix. The resin matrix can be epoxy or polyester. Either is stronger when the fiberglass is in them. And raw fiberglass is not very strong except in tension without the resin matrix holding it in place.

[joecnc2006]

Don't mess with the pipes, you will not get very far trying to reinforce them from within, Just add a support to the outside at intervals, your skate bearings ride on the inside so you will not have any interference on the outside.

[USMCPOP]

Don't mess with the pipes, you will not get very far trying to reinforce them from within, Just add a support to the outside at intervals, your skate bearings ride on the inside so you will not have any interference on the outside.

I second this.

[Northboy]

Don't mess with the pipes, you will not get very far trying to reinforce them from within, Just add a support to the outside at intervals, your skate bearings ride on the inside so you will not have any interference on the outside.

You are probably correct, I had pretty much planned to make supports regardless of whetehr I try thisor not, probably three per side.

Northboy

[radcliffe]

Originally Posted by joecnc2006
Don't mess with the pipes, you will not get very far trying to reinforce them from within, Just add a support to the outside at intervals, your skate bearings ride on the inside so you will not have any interference on the outside.

I go along with joe, I exspermented with Dap Anchor Fast, anchoring cement filling .375 3/4" thin wall square tubes from Home Depot. This did reduce soom of the flex, but not enough I scraped the project.

Harold

[FandZ]

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).

I hear you but when the pipe bends it'll have to push the water out and away from the point it wants to bend at. Since water can't compress, all that force will be directed to the walls of the pipe. For it to bend, it would seem to me the pipe itself will have to expand some, which would be at a high PSI point. Bend it too much and the pipe will burst.

I know in an extreme case, it'll take much more force to bend a pipe in two if it is full of water and capped at both ends than a pipe with air in the center. I don't know for cnc use if it may offer any additional strength, though, as the amount it would bend could be absorbed in a flattening of the pipe that'll extend from the center of the bend point. But if it gives it 20 more pounds of resistance for a minor bend then I'd think that could be worth it.