formula for tube bending

[luke]

I want to know if there is a formula for determining what the fininshed length of a piece of metal tubing will be once I have put two bends in it. I am trying to make a roll-cage for a Mini and need to be able to accuratley determine the length of tube required so that the finished product will fit! [sig][/sig]

 

[DonLeffingwellPE]

I would take a length of tubing long enough to make the part, start bending at one end, and then finish by cutting off the excess at the other end. Tehn I would measure what I cut off. Since I know what I started with, I would have an exact answer. Otherwise:

S = r*theta
s = Arc Length
r = bend radius
theta = angle in radians (2*pi radians = 360°)

Use the above to calculate the curved sections. [sig][/sig]

 

[MSerry]

Use this formula:

Tube Length=Length of straight parts measured along the longitudinal axis of the tube + Mean Radius of the bend which is determined along the longitudinal axis of the tube *angle of the bend

 

[FLisa]

This is from a website I found on tube bending while looking for something else. Unfortunately I didn't note the URL, but I did print it. Here is their formula.

Measure or calculate the length you need along the centerline of the pipe as if you had sharp angles. Bends will "add" length according to the following (they only included 90 and 45 degree bends)
For 90 degrees:
2R-(Pi*R)/2 or 0.429R where R is the radius of the bender used.

For 45 degrees:
.8284R-(Pi*R)/4 or 0.043R where R is the radius of the bender.

Subtract your "gains" from the first length measured or calculated to get the length of pipe you need. I haven't tried this but I hope it helps.