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. Cheers!
Hi, I can't say I've attempted to do super tight bends like the one you are describing but I have heard of people packing copper pipes with sand to stop it collapsing while they do tight bends and then simply flushing the tube out with plenty of water to remove any sand in there after tipping out as much as they can before flushing with water. I'm not sure if it'll work as well or at all with PETG tubing but I can't think of a reason off the top of my head why it wouldn't. Though you might get a few scratches on the inside of the tube from the sand grains. Perhaps fine grain salt? as it won't melt as you apply heat to the tube like sand but unlike sand when you flush with water it won't clump and stick but just dissolve away. Hope this helps!
Cheers dude I've had similar conversations around the interwebz and using a solid packing like sand or salt would mess up the inside of the tube as you bend it. One thing I've tried so far is freehand bending. The nitrile cord will bend more or less as tightly as I need it with some effort, but applying that effort around my bending guide (aluminium spacer) flattens the inside bend of the tube. Going freehand so far is a lot better, but gives a little bulging deformity on the inside bend as I'm trying to compress the acrylic a bit too far. I have some silicone fuel hose now which will bend tightly with little effort so I can avoid (hopefully) most of the flattening of the tube when using my aluminium spacer. Experimentation continues.
Ah I see, makes sense since when you head copper it just becomes malleable but doesn't loose too much structural strength compared to PETG which becomes much softer. I'm guessing the sand/salt grains end up actually sticking to the hot plastic on the side etc. Hopefully the fuel hose will work out, perhaps bending around those hard pipe bend forms you can get in kits would help? They would provide a surface for the PETG to bend around and thus help keep the forces across the tube more uniform that free handing it? At the very least it would stop that bulging deformity on the inside of the bend as the PETG would be pressed up against the bend form as thus have no space to bulge into. Something like this, the primochill rigid bender, perhaps would let you get tight radius bends?
I think that Primochill kit is discontinued and was, apparently, a piece of **** anyway. But yes, in an ideal world a bending mandrel would prevent the distortion problem as the soft acrylic will be held to shape. I'm a good chunk away from doing the tight bend for real so I'll look into getting something made up I think, probably 3D printed unless some of my friends have a lathe or similar.
Fair enough, not sure if 3D printing will be cheaper than lathing due to print times. Hope you have better luck than I do with trying to find affordable CNC time.
I have friends who do a lot of design and build work who may have access to stuff and things, plus there's a few maker spaces around here who could also help out. Plus I'm sure there's forum members who'd be able to assist too, we're supposed to be a community after all
If that's an offer of help then I'll gladly take it. Another forum member Nexxoo recommended some people to me but 2 of them can't do it as they don't have access to the correct tools or have the time right now and the other two haven't got back to me yet but one of them hasn't been active on the forums for a good while now ):
Cheers! Work is a bit slow right now because I need time and decent weather to chop up some MDF without scaring my rats and poisoning myself, but once the guide jig is built and I can true the case work up for a test fit things should start flowing much more rapidly.
I know you are referring to fabricating tools but have you considered fabricating the tubing? Couple options, first 3d print the tubing, probably would need to use an SLS or resin printer in order to get a water tight transparent tube. Alternatively, 3D print a mold and cast your own tube with the desired bends. Both options would be filled with potential issues to over come.
Casting the tube with the bend already in it? That's even more insane than brazing new ports into the radiator that's causing all the problems. I like it! I'll add this to the list of insane options and do some reading.
If we're going for insane(ly cool) ideas that are possible, how about using glass tubing and bending it. Apparently glass tube is happy to bend really tight. (Proof!)
That's still about a 2D CLR bend, mine needs to be 1.5D Current thought process is to make up a bending mandrel as close to the bend radius I need and use that. The idea is the softened tube will mold itself to the inside of a properly-shaped tool when it tries to bulge or flatten. May 3D print it, may lathe some Acetal. But to be honest I may have a tight-enough bend to to work with right now and just put up with slots in the back of the case rather than just holes. They'd be mostly hidden anyway.
