Flexible bending cord options for tight acrylic bends

LePhuronn · 15 Mar 2017 at 22:02

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 in places 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?

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

Cheers!

niro750 · 16 Mar 2017 at 08:00

Pipe fitters use sand and water to stop bends collapsing. Problem with water is plugging your ends and the water transferring heat from the joint quickly and warming up the rest of the tube. I'd be giving that a bash for kicks anyway. Make a former and try to get enough heat in the tube just to get it round. Water won't compress so the joint would stretch slightly. Nothing ventured nothing gained. Sand would never work as it would ingrain into the pipe once heated.

Your idea of o-ring nitrile cord would have been my first try as well as I've used that and have access to it. Shame it doesn't work

LePhuronn · 16 Mar 2017 at 08:24

Cheers niro

I might be able to train the nitrile cord a little to improve its flexibility, but it takes a firm hand to bend it tightly, by which time I've flat-spotted the inside of the tube.

I did see some rubber bungs on fleabay a while back when I was considering dyeing the tube, so it might be worth trying the water-filled approach. Silicone fuel line is cheap enough so I'll grab a length of that as well.

Still, back to Photoshop and draw up some new bends to see how big a radius I can realistically get away with.

orbitalwalsh · 16 Mar 2017 at 08:46

niro750 said:
Pipe fitters use sand and water to stop bends collapsing. Problem with water is plugging your ends and the water transferring heat from the joint quickly and warming up the rest of the tube. I'd be giving that a bash for kicks anyway. Make a former and try to get enough heat in the tube just to get it round. Water won't compress so the joint would stretch slightly. Nothing ventured nothing gained. Sand would never work as it would ingrain into the pipe once heated.

Your idea of o-ring nitrile cord would have been my first try as well as I've used that and have access to it. Shame it doesn't work

could mineral oil be used instead of water? as the stuff used for Ghetto Submerged PCs? should be able to take a lot more heat then water and contain it better

LePhuronn · 16 Mar 2017 at 09:11

orbitalwalsh said:
could mineral oil be used instead of water? as the stuff used for Ghetto Submerged PCs? should be able to take a lot more heat then water and contain it better

I was thinking this on the bike ride into work. I have a bunch of foam and silicon ear plugs and some Ikea mineral oil so I'll see if I can seal up some tube and expose to heat.

Never bent an acrylic tube in my life, and here I am going down unconventional routes to get unconventional bend radii for my very first attempt! Madness, I tell you

Smffy · 16 Mar 2017 at 09:39

Aquarium filter line like a fuel line, the hollow inside will let it bend far tighter - the last thing you want is th insert forcing a sort of flare in the hard tube.

niro750 · 16 Mar 2017 at 12:34

Smffy said:
Aquarium filter line like a fuel line, the hollow inside will let it bend far tighter - the last thing you want is th insert forcing a sort of flare in the hard tube.

Not a bad shout. I used to have silicone tuning for the rc cars I raced. It's readily available and may do the trick.

niro750 · 16 Mar 2017 at 12:37

LePhuronn said:
I was thinking this on the bike ride into work. I have a bunch of foam and silicon ear plugs and some Ikea mineral oil so I'll see if I can seal up some tube and expose to heat.

Never bent an acrylic tube in my life, and here I am going down unconventional routes to get unconventional bend radii for my very first attempt! Madness, I tell you

At the end of the day it's just bending tube and it's quite cheap so you have plenty of scope for messing about trying things. I have bought the thermaltake pacific light fittings for my first water cooled build and it means I cannot use any elbows at all so I've just had to buy extra tubing in case of any waste on the multiple compound bends and twists

LePhuronn · 16 Mar 2017 at 13:10

Smffy said:
Aquarium filter line like a fuel line, the hollow inside will let it bend far tighter...

Yeah, this is what I'm thinking. I recall early in the hardline days people were using hose such as this but things moved to solid core after a while.

I've just grabbed some cheap silicone hose and will give it a shot too.

LePhuronn · 16 Mar 2017 at 13:12

niro750 said:
At the end of the day it's just bending tube and it's quite cheap so you have plenty of scope for messing about trying things.

I grabbed 5m of Shakmods tube for £20 delivered as a starting point, but can get about double that for the price from engineering plastics companies online. I'll also give some PETG a go once I'm more confident I can get bend radii down closer to where I need as that's more forgiving to work with.

niro750 · 17 Mar 2017 at 06:23

LePhuronn said:
I grabbed 5m of Shakmods tube for £20 delivered as a starting point, but can get about double that for the price from engineering plastics companies online. I'll also give some PETG a go once I'm more confident I can get bend radii down closer to where I need as that's more forgiving to work with.

It's ridiculously forgiving. I've never bent plastic tube before and was able to re heat and reset joints etc...