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problem with 3roll bender

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  • problem with 3roll bender

    picked up a used (vertical) 3roll bender.. the type that bend sections into long curves.

    powered by a 3ph/2hp motor through a huge gearbox. some of the gears inside were damaged, but it had some (seemingly) good dies for the price. 4sets of 3 dies for pipe ranging from 1/2" to about 1 1/2" and a 'flat set' for bending strap, channel, box, etc.

    got the thing rebuilt this past week, some fresh paint and new wiring and it seems to be running great on flat/square sections. rolled a 1.5" box section into a clean 4' circle.

    only i can't figure out whats up with the pipe dies. the pipes slip and don't get pulled through.

    maybe i'm not using it right.

    the dies are hardened and don't appear too worn (then again, i've never used one of these before). the flat set is knurled
    and works great. leaves some marks, but nothing serious. theres no way the pipe dies used to be knurled too, right? that'd be nuts.

    anyway, right now its basically useless for pipe (probably why i got the deal). and am trying to figure out how to fix it.

    anyone out there with experience using these things? is there a trick? what're the magic words?

  • #2
    I don't think you'll have any luck trying to bend pipe with a roll. Those dies are for round solid stock.


    • #3
      hey pete
      i've seem people using similar machines to form long curved handrails out of 2" stainless.

      whats would be the diff between a solid round and a pipe? (other than buckling if one goes too tight)



      • #4
        Post a picture. I got tool envy.

        I worked on a 3 roll bender using hydraulic motors, it never worked. Something about my design.

        A slip roll I have here, bending stainless sheet I can't get a cone out of it. Simple you crank one end down and leave the other loose.. It rolls a perfect round tube. It being mirrored stainless leads me to believe it is slipping in the rolls. I got so frustrated I put the last disaster around the yard water spickot and have not posted pictures of how I powered it. (*it was a hand crank one)

        The big tubing benders are worth some bucks. If you are not too deep in it you did really good.

        I'd love to automate one of them. Throw out a rolled loop to exact measurements, nobody else could copy your frames like that since the radius would be wrong.
        Post a picture please.


        • #5
          I have a big 3 roll bender like you describe- a CP 40 from eagle-
          And it works really well on pipe.
          In fact, its almost like they designed it to do that....

          The building block rolls and spacers for flat, square, and rectangular metals are available either knurled or plain. The knurled grip easier, but leave knurl marks. So most fab shops use the knurled kind, and sand off any obvious knurl marks.
          But some shops, doing high end ornamental work, or using em for aluminum, or bronze, use plain rolls. In fact, in Italy, they make em with delrin rolls, for rolling aluminum extrusions that are color anodized for things like window frames.
          With smooth rolls, you need a tighter grip, and often times it helps to have all 3 rolls driven, rather than just two.
          So the higher end, more expensive machines, have all 3 rolls driven with separate hydraulic motors- very expensive, but very nice. Like a Roundo, from sweden, which can easily run 15 to 20 grand, used, but will roll big stuff, very easily. They even have hydraulic up/down adjustment for roll tension. And a remote pendant with all the controls, that you can hold in your hand and walk around with.

          With your machine, there is no reason it wont roll pipe with smooth pipe dies- it was designed to do this, and it should. Are both your driven rolls really getting driven?
          Usually on the smaller ones, there is a chain drive connecting the two driven rolls. Maybe your gear is slipping on one of these, or a pin is broken. If only one roll is being driven, then it might be your problem.
          Is your adjustable roll tight enough? For smooth rolls, you need to tighten it down more than you would for knurled rolls.
          With smooth pipe rolls, you need to step up to your curve- you cant expect a radical radius to come with one rolling- you need to roll it, tighten, it and roll it again, especially on bigger pipe sizes.
          You can run 1/2" round solid right thru, but when I roll 2" schedule 40 stainless pipe, I need to creep up on my radius, running it thru a few times with successively tighter radii.


          • #6
            i can post pictures, but mine looks exactly like the CP20 on your link, except its bigger, and its already mounted on its own cast iron stand.

            since i've had it, i've rolled nothing but "big" stuff.. 2" square and up.. with no problem. like you said, i have to move up to my radius in small steps (there is a scale on the top roll that helps me get the same radius, though its not perfect).

            both bottom rolls are driven and everything seems to be working fine. on square, solids, heavy C channel, anything with flat sides it sucks right in.

            so far, it works like this:
            1.load the stock on the two driven rollers and bring the top roller down (theres a handcrank, no hydraulics).
            2 take the stock out, and give the top roll just a nudge (downwards)
            3. start the rollers and feed the stock in.

            since i'm cranking by hand, its impossible tigthten the radius while there is stock in there. have to take the stock out, give a nudge, then pull it through.

            works great.

            but on round stuff, even the smallest "nudge" keeps the stock from feeding. both bottom rollers roll, they just won't take -- it slips.

            if i load the pipe in first, its impossible to crank the top roll down. haven't tried a cheater bar, but i just might. the bender has a massive screw for lowering the top roll, but its got a square hole and uses a standard lathe chuck key. won't be getting a lot of power into that.

            i'll post detail shots of the pipe dies.

            sorry so long,