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Author Topic: Advantages of symmetrical Leverage for tubing roller?  (Read 3206 times)

Offline CliffordK

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I recently purchased a tubing roller for bending some pipe. 

It is an interesting.very simple machine.  One can get a pretty smooth curve, as large, or presumably as small as one wishes without collapsing the pipe or tube by rolling it through properly sized dies.



The dies are arranged in a triangle, with the bottom two dies fixed, essentially exerting an upward force, F.  The middle die is screwed or pressed downward, essentially exerting a downward force 2F (the sum of the two upward forces), ignoring the weight of the pipe and apparatus, and the non vertical force components.

One typically bends the pipe in small increments rolling it through the dies, and I believe that most of the bending is occurring at or near the middle roller which would receive double the force of the side rollers.

I've been having a horrible time with my roller, that I've been chewing through bearings in the middle roller like crazy.  I suppose I've been cranking it down pretty hard.  I'm going to try bushings instead of bearings to see if those will last better, or perhaps a different brand of bearings.

One person suggested that I could improve the leverage by widening the rollers.  I'm skeptical.

Deflection, of course, would be greater, so it would take more cranks on the screw to generate the same downward force, or bending angle.  But, it seems to me that it would take the exact same force to generate, say a 0.1 bend.

What do you think?

It would seem to me that the only advantage of the wider rollers then would be perhaps alignment of the work, with the disadvantage that the bend would start farther from the end.


 

Offline damocles

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Re: Advantages of symmetrical Leverage for tubing roller?
« Reply #1 on: 03/11/2012 13:20:35 »
Clifford a few comments from someone who is academic and not at all practical in these matters:

(1) While the geometry is "symmetrical" the operation presumably is not, in that if the "rollers" are to do any "rolling" there must be one direction or the other that they move in. Or is it really just that they are strainers with rounded surfaces?

(2) There is an issue with the plasticity or brittleness (and toughness and shear strength) of the metal or polymer involved. (Can you bend HDPE or PVC pipes with this device?). Generally speaking it seems intuitive that warmer would be better than colder, and that slower would be better than faster. Could the device do an intractable metal with a series of tiny bends rather than trying to get it in a single pass?

(3) It also seems intuitive to me that narrow would be better than wide, because the latter leaves the work freer to "do its own thing", and would tend to exaggerate irregularities and imperfections in the materials along the arc.
 

Offline SeanB

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Re: Advantages of symmetrical Leverage for tubing roller?
« Reply #2 on: 03/11/2012 18:27:13 »
If using ball bearings I would suggest either spherical ball or roller bearings, as they have a greater radial load capacity. Use a molybdenum loaded grease as well to provide extra protection to the race surfaces. If the bearings are cheap poor quality ones a better made unit will improve life.

Using a plain bush will just be added friction, and will not have the load capacity unless you make the bushing out of phosphor bronze and use an EP additive in the lubricant for it.
 

Offline Phractality

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Re: Advantages of symmetrical Leverage for tubing roller?
« Reply #3 on: 03/11/2012 18:33:03 »
Perhaps you can find answers in some of these videos.
 

Offline CliffordK

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Re: Advantages of symmetrical Leverage for tubing roller?
« Reply #4 on: 03/11/2012 21:54:05 »
Ok,
A few comments.

One does the pipe bending with the tubing roller as multi-pass, back and forth. 

The "bender" setup linked by Phractality uses a die, and more or less creates a fixed radius bend.  The tubing roller gives an arbitrary radius bend.  While it can be used on a small section of pipe, one can also make the bend over a long section.  I'm putting a gentle radius onto 15 foot long, 2 inch diameter, 0.128" wall pipe.

This is the tubing roller that I have...  now with a few mods.



Steel will hold the shape you give it.  If you bend PVC cold, it will spring back to the original shape.  If bent hot, then it will retain the shape you give it. 

Anyway, I'm bending steel, but the PVC example may still be relevant.  I presume there is a certain bending force one must exert to actually bend the steel, rather than just flex it a bit.  So, if I say exerted 100 lbs downward force on the pipe, I might be able to roll it back and forth all day, and not get any permanent bend.

Heat might be good, but it would take a lot of heat to do the 15' pipes, and I would risk burning off the zinc coating.

As far as the bearings, the tubing roller I have comes stock with 20mm x 42mm x 12mm spherical ball roller bearings.  I think what may be happening is that the downward force I need to bend the pipe is enough to crush the balls.  I don't think it is heat as much as a force problem.  Perhaps a different brand of bearings would be better.  A cylindrical roller, or pin needle bearing might have better weight distribution, but I've had troubles finding them of the appropriate size.  My thought is that the bronze bushing may take the weight better.  Perhaps not last forever, but as long as I get more than 5 minutes out of the bushing, I'll be happy.

As Damocles mentioned, there are some additional asymmetrical forces including the torque generated by the rolling.  In this case, the middle roller is the one that is powered.  Originally by hand, now by a small motor that actually generates other torque issues.

So, the two lower rollers are essentially idler rollers...  The top roller where I'm blowing out the bearings not only has the downward force, but also the cross torque pushing the pipe through the system.
 

Offline CliffordK

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Re: Advantages of symmetrical Leverage for tubing roller?
« Reply #5 on: 03/11/2012 21:59:15 »
I suppose, the question was what the advantages would be of moving the rollers outward?

I can buy a "kit" to weld onto the roller to widen the rollers, or probably make it myself.


http://www.swagoffroad.com/Harbor-Freight-Tubing-Roller-Dies_p_51.html

But, logically it doesn't seem as if it will do what I want.
 

The Naked Scientists Forum

Re: Advantages of symmetrical Leverage for tubing roller?
« Reply #5 on: 03/11/2012 21:59:15 »

 

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