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Flexible bending cord options for tight acrylic bends

Hi all

I've started experimenting with some hardline bending for my current project because I have some really tight bends to pull off in order for most of the loop to work. I'm using 12mm OD acrylic tube and I'm looking ideally at a mere 16mm bend radius in some places. So far it looks theoretically possible to do if I have a flexible enough bending cord. PETG may give more bendability in the tube itself, but that's redundant if the cord itself won't flex.

I grabbed some 9.5mm OD nitrile o-ring cord from fleabay and it doesn't bend that tightly, and if the cord won't bend as I need it then of course the tube won't either.

What other options are there? Would something hollow like fuel line do the trick? I've read a few times that hardliners moved away from hollow tube because it would collapse and knacker a bend. Silicone tubing? I'm going to try out filling a tube with mineral oil and bending that way later tonight.

Suggestions welcome, because yay or nay on getting the required small bends will greatly affect the project.


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I've heard that Primochills tubing can be bent tighter than most but not sure on the way of inserts. I just use a fitting for extremely tight spots.


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Hollow tubing does work, but you'll want to make sure the walls are still thick enough that it doesn't collapse too much, like you mentioned.  I know some things like copper and brass are bent with sand packed in them, or ice, but that wouldn't really work with acrylic/PETG since you have to heat it up first, and I'd fear sand would scratch it up.  

I also usually go with angled fittings and elbows when it comes to really tight bend requirements.  Or re-route the loop to avoid them when I can.

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Cheers folks.

It's all just thought process really because I'm trying to avoid cutting slits into the case walls and new floor to accommodate large (i.e. normal) sized bends. I knew things were going to be tight in some places, but since I'm truing up the new case internals soon some of the bends need looking at now.

My issue with just using fittings is twofold, both valid and petty :tongue: I personally don't like the look of a bazillion elbow joints for hardline loops when you can bend the stuff (glass is a different matter), and the Bitspower/Barrow 90 degree compression adapters look totally different to the EK fittings I'm using so the mismatch will make my teeth grind lol

EK have released a new 2F 90 degree adapter, so at least the nickel will match, but I don't have the space to use those with a pair of HDCs either. Changing the routing I don't think is viable either, but it's worth a look I guess.

I've sacked off the idea of replicating some copper pipe tricks because I'm an idiot to even think of them lol but I did try to freehand bend the tube last night with mixed success; I can get the bend itself down almost tightly enough, but the tube is flaring out a bit in the process. Fuel hose may help with that as it shouldn't require as much force to get it bending as required, so we'll see.

I've also had the crazy idea of threading the tubes themselves and screwing into the EK 2F adapters directly. Putting a 1mm cross section o-ring inside the adapter thread would give me 4.5mm left to screw into and make a seal through compression, similar to how the HDC fittings work. That, of course, raises many questions in its own right: can 12mm OD tube carry enough of a thread to be structurally stable, can I screw the tube in to create enough pressure against the o-ring to seal without breaking the tube, and will the whole thing actually remain stable when in use.

I do like to make life hard for myself, don't I?!?

To be honest I'll just end up working out a realistically small enough bend that will work and adjust the case holes accordingly.

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Threading the standard tubing: Probably not.  You can thread it, but standard tubing ends up VERY thin once you do.  When I was experimenting with that, 1/2x1/4 worked fine, but the threads made the tubing rather weak when I used 1/2x3/8.  12mmx10mm tubing will provide a little more wall thickness, but is .4mm enough to make it that much better?  The thicker walled tubing I used was also much better for making a seal with an o-ring as well.  

Threading the inside of larger tubing works well though, just a lot of work:


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