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  #1  
Old 01-03-2021, 07:20 PM
Sbgunderson Sbgunderson is offline
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Default Bending 3” Steel Tubing

Hello all,

I am working on the design for a ladder frame chassis, similar to the one found on a 550 Spyder. I am planning on a 3” diameter tube with a .063 wall thickness for the two main rails. What would you use to make bends in this? The bends aren’t severe, maybe 15-25*. Thanks in advance.

Spencer
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  #2  
Old 01-04-2021, 12:55 AM
Mr fixit Mr fixit is offline
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Hi Spencer,

This is going to require a pipe bending machine in my opinion. there are two routes I would consider.
1. go to the local muffler shop and pay to have them bend it for you to a template that you provide with the angles that you need.

2. find a electrical contractor or friend in the field that has a large shop that does commercial industrial work, they should have a EMT bender that is hydraulic that might fit the pipe size OD and can bend it for you.

The 3rd way would be to build your own dies and bender, or heat the pipe to bend it to the die you make. Now the die would not have to be metal for a single bend, any good wood buck would possibly do it, but I'm unclear about the metal integrity after heating, which could be a problem with a car frame.

On second thought do not heat, forget the last idea.

Good luck, and let us know what you work out.

TX
Mr fixit
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  #3  
Old 01-04-2021, 01:33 AM
Overkill Overkill is offline
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Default Tubing benders

Most tubing bender brands top out at 2". There are some that go a bit bigger, but I'm not aware of 3". I wonder if the Hossfeld would go that large? Wrought iron guys and fence builders use them.

It would be important to know the radii of the bend, more than the degrees.

The actual size of 3" EMT electrical conduit is 3.5" with a 0.072" wall thickness. The radius for electrical is 13" - to get a visual, go to Home Depot and look at the pre formed pieces. So the EMT bender may be able to pull it off, as the 3" tube may deform.

Muffler shops have units that bend stuff that large, but their machines typically crush the inner surface.

Trick Tools sells a couple benders that will go that large. Wonder if they have a customer in your area they can direct you to?
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Last edited by Overkill; 01-04-2021 at 01:39 AM.
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Old 01-04-2021, 07:33 AM
Marc Bourget Marc Bourget is offline
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I'm jumping to a bit of a conclusion, but, as I see it the problem with bending larger diameter tubing, with "saddle style" inner mandrels, is the collapse of the inner portion due to the pressure concentrated by the bending anvil.


Ron Covell demonstrated bending (IIRC) 2" 4130 at a Santa Cruz Metalmeet.


He packed the portion to be bent with sand over a plywood form. No "production setup" but should be good for the small number of bends you contemplate.


FWIW
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Old 01-04-2021, 12:49 PM
Overkill Overkill is offline
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Default Packing with sand

Just make sure the sand has been dried in an oven. You weld caps over both ends, after it's packed tightly. Having a form that supports the sides so they don't bulge out, is also recommended.

I've used the technique, but with and without heat for smaller diameter tubes and odd radii. As it's a closed vessel, all the safety precautions must be followed.
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Old 01-04-2021, 01:20 PM
crystallographic crystallographic is offline
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Quote:

Hello all,

I am working on the design for a ladder frame chassis, similar to the one found on a 550 Spyder. I am planning on a 3” diameter tube with a .063 wall thickness for the two main rails. What would you use to make bends in this? The bends aren’t severe, maybe 15-25*. Thanks in advance.

Spencer


Hi Spencer,
Have you called any of the guys doing the 550 rebuilds to see if they can spare you some parts?
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Old 01-04-2021, 01:51 PM
Essexmetal Essexmetal is offline
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I will add something when using the sand packed method.



On one of the end caps weld at least a 1/2" nut and use a bolt that will press against the packed sand with a disc / or cup if you can turn one. This gives you some preload on the sand. Don't over do it with the preload, you want counter pressure not forming pressure.


As noted very dry sand. Patients and a soft red heating. If you can clamp one tail, be able to heat it and get the form dropped into place look for a way to attach a come-along to the moving end so you can keep a little pulling force to gauge against your heating. To keep it controlled do in 1" bands. Concentrate on the outside (that will stretch) and the inside (that will compress). The top and bottom of the bend or neutral axis will not need as much heat. Too much heat is always worse than not enough.
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  #8  
Old 01-04-2021, 10:56 PM
Sbgunderson Sbgunderson is offline
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Thanks for all the useful information guys. Such a wealth of knowledge here. I think I will ask around at the local muffler shops once I get a detailed plan.

Bending with sand inside the tube sounds like a good option but this I going to be a one off project. So setting all the tooling might not make as much sense for me.

Thanks for the help,
Spencer
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Old 01-05-2021, 01:47 AM
Marc Bourget Marc Bourget is offline
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Besides the heat source(s) Mr. Covell bent his tubes over a built-up plywood pattern.


The suggestion, above, to use top/bottom heat, would appear to solve the only difficulty experienced by Mr. Covell as it took considerable time to reach bending heat.
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Old 01-05-2021, 03:08 AM
skintkarter skintkarter is offline
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Spencer, I'm tighter than a duck's bottom under-water (ex Yorkshire and now living in New Zealand) but whilst the methods outlined by the previous posters will undoubtedly work (particularly I understand the sand bending) there is quite a bit of time to be invested in the setup, former etc...

It may well be worth scouring your local area for a tube bending firm who does jobbing work or short productions runs. A muffler shop is unlikely to give you the absence of necking that you require.

I've had some small items bent locally before and if you are prepared to wait for them to have a run of your diameter of tubing (and thus the setup) it may not be that expensive. You may be lucky enough to have somebody locally with a CNC bender.

Worth looking around before you commit to DIY and several attempts to get it bang on.
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