how to measure force?

use a spring force testor.

very cheap.

Hello proto-typer

You will need to be more specific.

What is the intended included angle you intend to bend that tubing?

Do you have a "former" to prevent the tubing collapse?

1. Easy and cheap is fill the tubing with DRY sand, hammer a wooden tapered bung into each end, ensuring the sand fills the space between the bungs.
2. Carefully heat the tubing EVENLY with a wide-nozzled propane torch - do NOT overheat the tubing.
3. While the tubing is heated, bend it around a circular metal former - it should go quite easily, and the sides should not collapse.
4. When completed, remove from heat and former.
5. Remove the wooden bungs.
6. If the tubing is to be heat-treated do it now.

I and others have used the above method successfully on steel, brass, copper, and other tubing, with good success, but you will need to experiment if the sand-filled method is new to you.

Advise your progress, or lack thereof, with

Kind Regards....

If you want to bend you need a bending moment and not only a force so that what determines the force is the radius the tube will have to be bend.

Depending on the quantities you may use one of other technologies as suggested in other comments but of course the most productive will be a cold bending if the material will support it.

"...What determines the force is the radius the tube will have to be bend." HUH?

Force in this application is determined by how much is required to exceed the yield strength of the material. Say like exceeding the materials' modulus of elasticity is a good start

What is required to provide the radius would be the die/pin or object you roll the tube around and a rotational travel length to provide the appropriate angle of bend.

Yes, it's possible to do it cheaply, if what you want to know lends itself to it.

Can you be more specific about what you mean when you say, "how much pressure it takes to bend a piece of tubing . . ." ?

For example, if one has a tube 20 feet long, and one anchors one end and places a fulcrum one foot from that end, and then one hangs a weight on the free end, the tube will bend. It may not buckle, but it will bend. If you want to make a 90 degree bend in the tube without buckling it, then refer to Sparkstation's (who also said to be more specific) reply.

ok i will try to explain what i am trying to do,

I want to make a "ring roller". you know, it has three round dies in a pyramyd pattern and the top middle die will go up and down, the other two dies will be the powerd dies. they will get some sort of low speed high torq Hydraulic motors that will push the piece of tubing though the set of three dies at a low low speed, the top middle die travels verticly when it pushes on the piece of tubing it will creat an arced piece of tubeing.

the two lower dies will be approximatly 18" appart from each other and the diam. of each die is 6".

ok i was trying to calculate the amount of force/pressure that will benessecary to put the top middle die into effect and the amount of pressure that will be nessecary to rotate the two other dies, making the tube travel back and forth through the dies turning the piece of tube into a radiused or arced material. the more pressure from the top middle die the more of an arc or tighter the radius..

i am sure alot of people already know all about this but i want to be very clear.

The finished diameter is a factor also. If you intend to roll the tubing back and forth to displace metal, then chrome-moly 1/4" thick wall will require a lot of umpfh. How much I don't know -- I'm not familiar enough with such processes to tell you how to determine how much force will be required to roll a ring. And, I've seen rings rolled for bar tables, for example, which had wrinkles on the inside, but who cares? It's just a bar table.

In addition to filling with sand, which is one methd I've used myself to prevent crimping, I've also seen a process using hydraulic fluid under high pressure to prevent crimping. In that case, the tubing was not something as tough as chrome moly (it was mild steel), and the tubing was rolled continuously around a drum and cut into 360 degree sections and realigned and welded. I don't have a clue what the motor HP was.

Would you happen to know of anyone/company doing this now?

I know someone in the machining and fabrication industry who may know, and I also know someone in the tubing manufacturing industry who may also know, but I think they will need to know the chrome-moly alloy and the bend radius.

sorry! the post above was me.....thought i was logged in

Hello again, proto-typer

You do not give your location or Country, which you may easily do in your Profile.

Commercial Pipe Bending Machines are made in many Countries, and the easiest way should you intend to make your own, would be to hire a suitable pipe-bending machine from a local hire company, and carefully take note of dimensions, hydraulic pressures and other useful measurements.

This would only be useful, should you intend to manufacture multiple bends of various pipes, over a long period of time.

Advise your progress, or lack of it, with

Kind Regards....

First you need to understand what pressure is. Pressure is a mathmatical representation of the 2 physical attributes that are what you realistically need to know. It is not one of the actual physical attributes.

You need to determine the force required to bend the tube. This can be done by finding the modulus of elasticity for 4130 chromoly and calculating the required force to exceed it, then adding in a buffer for variation. Next determine the shape of the bend desired in order to select the size of the hardened pin that you will be rolling the tube around. With the selection of the pin, calculate the surface area that the tube will be engaging into.

With these calculations, you can determine the pressure setting from the simple formula of P=F/A.

Alright thats is essentialy what i wanted to know!!! Now how can i find such data? the modulus of elasticity for 4130 chromoly??

once i find this i will try to work out the rest!!

i will keep everyone posted on it too!!

And doing a google search is too difficult?

1st result.

http://my.fit.edu/rev/images/PDR.doc

ok the modulus of elasticity for 4130 chromoly, it seems there alot of these for 4130. i found this site and there alot of types of4130. http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=M4130r

and once i know the modulus of elasticity for 4130, can help me with the calculating the required force?

thanks alot

that link was not realy that informative. i will keep looking though