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This is a section of the ball chain from my roller blind. It seems to be a length of braided polymer cord with little thermoplastic spheres moulded around it. ball chain

It's one continuous loop and I cannot for the life of me find a join. I know connectors exist that clip around two of the balls, but this doesn't have one. I also know you can connect metal ball chains seamlessly by deforming one of the balls, but I can't see that working here.

A knot in the cord would be bigger than the balls. You could maybe bond the cord thermally and mould a new sphere to hide the join but I can't imagine the installer would go to that amount of trouble. Unless they just come that way out of the factory.

I need to make it shorter, and I know I could just get a connector but I have perfectionist issues regarding making things worse.

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    what is your specific question?
    – jsotola
    Feb 23 at 4:05
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    Look up continuous loop on YouTube, there are people who do this at home with various techniques using braided rope. But not with the plastic balls. For a perfect finish these are factory made. Your solution is to buy one of the desired length and just replace it.
    – jay613
    Feb 23 at 6:08
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    For the record, it is entirely possible to splice cordage like this in-line without anything that looks like a knot. A properly tied long splice is only a few percent thicker than the cordage it’s tied in, looks nothing like what most people think of as a ‘knot’, and will run smoothly though pulleys and other mechanisms as long as they are large enough to accommodate the additional width. That said, I think it’s far more likely that the cordage is thermoplastic (probably an aliphatic polyamide like nylon) and is just fused under one of the balls (it’s much more economical that way). Feb 23 at 14:47
  • I can do a short splice. But the balls are less than 2mm apart. Not sure I can do one quite that short. :)
    – Spike
    Feb 24 at 6:36

4 Answers 4

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Cut two of the balls in half, heat up the cut sides and fuse them together.

(probably you want a slight excess (over half) as there will be some ooze when you're smushing them together)

Alternatively join the line by fusing the ends together and then cover the join with epoxy formed into a ball - perhaps make a mould from silicone.

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  • I'd be very surprised if that could be made strong enough, and heating balls will inevitably char them. Feb 23 at 19:10
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    This is the method. It 100% works and will not "char" them unless you're using a flame, which is way too hot. The right method is to use a soldering iron (with a tip you don't care about gunking up) set for somewhere around 250-300 °C. Touch the split halves to opposite sides of the iron tip, then quickly move them together. Welding plastic like this is, for practical purposes, no weaker than how it originally came from the factory. Folks with 3D printers do this kind of thing to assemble parts all the time, and it works with a broad range of plastics (basically, any thermoplastic). Feb 24 at 2:30
  • That is absolutely bonkers. I love it. One of the balls actually has a large plastic cover over it. Jams the rolling mechanism to limit the travel. Would also strengthen joined ball. My soldering iron has a flat wide tip for exactly this purpose. Will report when it's done.
    – Spike
    Feb 24 at 6:34
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    "One of the balls has a cover"... that's probably the existing join. Feb 24 at 8:28
  • The good thing is you want to make the cord shorter so the removed balls provide plenty of material for practice.
    – jay613
    Feb 24 at 9:25
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The pull cord is fused into a loop of that length at the factory. It's most likely done with heat, since plastic likes to melt, ooze, and form a single solid when heated. The pre-fuzed loop is installed at the factory over the gear in the head rail during the assembly process.

In order to install a shorter cord, you'd need to carefully disassemble the side of the head rail where the pull cord is (there may be springs and/or other little parts that will do their best to escape and run off to wherever it is that small parts go to die), then remove the too long cord and replace it with a Goldilocks-style "just right" pull cord, then reassemble.

You could, of course, attempt to cut and refuze the pull cord yourself. I'd suggest putting a small piece of tape on a ball when the blinds are all the way closed one way, then pull the cord to adjust the blinds to all the way closed the other way and see where that ball ends up. The goal is to find a ball that does not actually go through the gear mechanism if at all possible. Keep trying different balls until you find one that doesn't.

Once you've found this one, you know where to start your disassembly of the existing pull cord. Cut the cord or ball and attempt to reassemble. Both Solar Mike and Jasen have provided good suggestions on how to do that. By working at a point where the cord doesn't go through the mechanism, you'll minimize the risk of a "not quite right" fix jamming in the mechanism because it's too big.

If you find that doesn't work, or that it doesn't hold as hoped, you'll have to go with the replacement method.

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You could open out the weave of the two ends, remove half the strands of the two ends and weave then the two ends together.

Once joined like that the joint is very strong - I have done it for tow ropes...

Only suggested removing half the strands to keep the overall diameter the same.

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    Otherwise known as a splice. The problem with that is going to be that any realistic splice will be longer than the pitch of the balls... I think it would be necessary to find a way of moulding one or more balls over the join: epoxy heavily loaded with titanium dioxide or similar. Feb 23 at 19:08
  • @MarkMorganLloyd Couldn't you take one of the balls from the removed section, carefully split it in half and super-glue it over splice?
    – JimmyJames
    Feb 23 at 20:18
  • @JimmyJames I'd be very surprised if something like that could be split (without either distortion or shattering) or cut (with a razor saw), it might however be possible to take two balls and sand each to half-thickness... subject to having suitable work-holding fixtures. And even then it would be complicated by the intimacy with which the balls are bonded (by moulding or casting) onto the original cord which looks like kernmantle. This would be a thoroughly unpleasant and fiddly job, and the best solution by far would be to get a premade assembly from an appropriate supplier. Feb 23 at 20:34
  • @MarkMorganLloyd Agreed on all points. I just like to think through how to do such things and I am sometimes stupid enough to do them.
    – JimmyJames
    Feb 23 at 21:30
  • @JimmyJames "Thee and me both" :-) Feb 23 at 21:34
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Other answers here are good, but the spectacularly lazy one is this:

Take up the slack in a loop (where it doesn’t want to run through pulleys in either direction) and zip tie the loop, top and bottom.

Have an adult beverage.

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