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Minimum diameter for hard tube bends...

bjcsoln

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Apr 19, 2013
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So, this is a bit of a tough one to fully articulate / answer but with regards to hard tubing, specifically PETG @ 14 or 16mm OD - as I am planning my next build, I am wondering how tight I can bend these tubes. I noticed that there are a plethora of bending kits out there that have pre-formed slots for bends (so you get them accurate) but they are not very tight.

I my current build (Blue Max), I used fittings to accomplish the turns, although with the unforeseen downside of the extra weight causing my runs to sag. So for this new build, I will go back to using bends but I am kind;'ve thinking I will want some of them tighter then these stock template bending kits that you can buy.

Has anyone had any experience / issues with really tight bends using these tubes? Is it one of those cases where, if during the bending, if its going to crack (cause you went to tight) it will crack / deform during the bending, but if it survives and hardens then you should be fine?
 

Izerous

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Feb 7, 2019
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Edmonton
I did some weird triple bends and tighter 90 bends. If it is heated properly it won't crack but on my tightest bends I was getting wrinkling on the inside edge of the tube.
 

clshades

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What you need to be concerned about is the wall thickness after the bend. The outside of the bend will be thinnest. If you want to be sure do a bend and then cut it in half at the apex to check it.

Of you can find a thicker walled pipe it will handle tighter bends.
 

bjcsoln

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Thanks - clshades, the point about the wall thickness is probably the critical one - the tighter the bend the thinner the outer edge needs to stretch, combined with the inner edge having to do something will all the extra material, in this case possibly wrinkle. Guess I will see how this turns out, and if I still have the option to go to glass for some of these runs. I really do like how the glass tubing worked out on my current build, but they were all straight runs so easy to produce.
 

clshades

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Thanks - clshades, the point about the wall thickness is probably the critical one - the tighter the bend the thinner the outer edge needs to stretch, combined with the inner edge having to do something will all the extra material, in this case possibly wrinkle. Guess I will see how this turns out, and if I still have the option to go to glass for some of these runs. I really do like how the glass tubing worked out on my current build, but they were all straight runs so easy to produce.
You can bend glass too and then add to the outer edge after but you'd need some knowledge about blowing glass, and an expensive kiln.
 

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