Thin walled tube.

[DuffyBB]

What is the definition of thin walled tube, is it wall thickness as a percentage of o/d?

Im looking into setting up to make an item(x2) for the company I work for with the possibility of 40/50 more over time if I can give them a better price per item than their current supplier.

They will require 90 degree bends in either 26.9x2.5 or 26.9x3mm S235 CHS meaning a tube bender. I have read a good few threads on here regarding benders but still not sure what my best option is.

I think a rotary bender would do it(looking at the JMR1000) without kinking but add in dies/formers and its a big outlay and a gamble if it goes pear shaped.

Other option is the hydraulic ones with a bottle jack type, but as far as I can ascertain they're prone to kinking thin walled tube but would obviously be the cheaper option.

So any advice as to whether the cheaper bender will bend the tube without kinking/need the JMR bender/other option would be appreciated(apart from fill with sand/water...cba with the hassle).

 

[Tigman]

The hydraulic , bottle jack type are pipe benders and are for bending gas barrel , thin wall tube will kink and or ripple !

 

[outofthefire]

Save your money and buy a bag of kiln dried silver sand, benders for thin wall tube are silly money.

 

[hotrodder]

Probably wrong but i don't think there's a simple definition for 'thin wall' when it comes to tube. 'Wall factor' is a common part of determining bend difficulty but it's only part of it and goes...

Tube OD divided by wall thickness = wall factor
CLR (centre line radius) divided by OD = degree of bend i.e. a 50mm OD tube bent on 125mm radius is a 2.5D bend
Wall factor divided by degree of bend = difficulty factor

As the wall factor number gets bigger and/or the degree of bend number gets smaller the difficulty factor goes up

All of the above is kinda a mute point for 26.9 dia tube with a 2.5 or 3mm wall... unless you want to bend it on a 1D radius it's not 'thin wall'

Hydraulic/bottle jack style are 'press' (or ram) benders and while the majority of them are designed with pipe kinking in mind (and thus have completely the wrong size formers for tube usually although 26.9 OD tube is very close to 3/4" pipe) they do exist for tubing. Many of the exhaust bending machines about are this style and will bend 2.5" OD 2mm wall tube albeit with some fairly severe 'necking' on the inside of the bend like the top example

After press benders there's compression bending which would produce clean results for the size of tube you're talking about. Plumbing and conduit benders like the old Hilmor/Record etc things work on this principle; static bend die that the tube is bent around by either a shaped roller or (better) a 'guide bar' which look like

As OD goes up and/or wall thickness goes down this style begin to neck the inside of the bend albeit nowhere near as severly as press benders. I recently used one of the old hilmors to do some of the gentle bends (20 - 30 degrees) for some Renalult Alpine coolant pipes which were 1.25" OD 1.5mm wall 6063-t6 aluminium. Would've used it for the 90 odd degree bends too if it weren't for the fact that they needed to be bent on a 2D CLR so i had to cut up a bunch of mandrel bends and weld 'em in as the Hilmor 1.25" die is 3.5 or maybe even 4D CLR

After compression bending comes rotary draw bending which supports the tube far better by clamping it to the bend die which rotates and the 'guide bar' becomes a pressure die which is dragged with the tube as it's fed into the bend die. This is the style of bender that's used for mandrel bending... mandrels and wiper dies added to further support the tube as bend difficulty increases past what rotary draw alone can handle, the mandrel prevents the outside of the bend from collapsing (and even helps stretch it) while the wiper die stops the inside of the bend from wrinkling as it enters the bend die

How tight a bend radius do you need and how clean do the bends need to be? If the answers are not important and some necking is acceptable respectively i'd begin by begging/borrowing/hiring a pipe kinker for a sample bend

 

[DuffyBB]

Cheers for the info guys. There is plenty of scope for the bend tightness and necking wont really be an issue either.