Bend Formulas?

sirhk100

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Hey all, What formula are you using to get the distance of a bend? I mean, what formula tells me how long of tube I need to cut if I say want 10" straight, then a 75degree bend w/4" radius, then 10" straight, then a 40degree bend w/4" radius, then 10" straight. How do I figure out what length tube to start with? I don't think the formula I've been using is correct... Does that make sense what I'm asking for or did I just jabber on about nothing and confuse you?

Khris



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Brian Mapes

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Makes sense. I have always wondered how to get the correct lengths also when you have a bend.

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KitRacer

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try this i made it, if you have any questions just ask

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Brian Mapes

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What do you mean by tube height, diagonal inside and diagonal outside. tubing used is what is taken up by the bend? right.

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sirhk100

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I too am kinda confused about the chart... Wouldn't the tubing used differ depending on what radius die you're bending with? If so, what radius was that chart made with? Did you use a formula on each degree to build that chart or was that measured?

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KitRacer

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okay, sorry i didn't have time to clear that up
i built this for a 6.5 radius die with 1.5 tubing, both of which matters

tubing used is the amount of tubing consumed in the bend from the beginning to the end
diagonal inside is the distance from each start of the bend on the inside (a straight line)
diagonal outside is the distance from each start of the bend on the outside (a straight line)

i found the second two lengths to be very handy when building tight fitting roll cages and what not

if you have any special requests for radius or tubing size or a different length, post them and i can modify it to fit you

all of the numbers are derived from simple algebra, if you get into the formulas i used, you could probably modify it yourself

if all else fails, there is a program called bend-tech, it does all the math for you, just draw the part and add dimensions, and it will show you where to mark your tubing and how much to bend and how much to use. i think it goes for $395, and a trial version is included with the JD squared benders. good luck trying to find the serial number or the full version on the net, i have tried for a long time, but if you do let me know

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sirhk100

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Okay, all makes sense now... Is it a pita to make a couple of those charts for me? If not, any chance of making three of them? All 1.5" tubing but with different radius. 4.5", 4", and 2.5"? If you could I would be in great debt to you cause you would make my job WAY easier!!!!

Khris

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1992f150

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Here is how I do it, it involves math. Basicly think of the tube bend as part of an entire circle (360 degrees) and then figure out what fraction of 360 the bend is, gotta use that geometry formula to figure it out: radius x 2= diameter & diameter of circle = circumference x Pi

Let me use your example: "if I say want 10" straight, then a 75degree bend w/4" radius, then 10" straight, then a 40degree bend w/4" radius, then 10" straight"

first get rid of the straight parts to make it simpler, add this on at the end (30" of straight) figure out each bend at a time.

Radius is 4, 4 x 2 = 8 (diameter) 8 x Pi (or 3.14) = 25.12 inches. This is how much tubing it would take to make an entire circle, but you only have a fraction of 360 degrees so
25.12 x ( 75/360) = 5.233 inches for the first bend
repeat for second bend
4 x 2 = 8 x 3.14 = 25.12 x 40/360 = 2.791 inches

2.791 + 5.233 +30 = 38.042 inches of tubing.

It seems like alot of work, but once you figure out the 25.12 for your die, you just plug in x/360 and multiply for every different bend using that die.

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Kritter

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"diameter of circle = circumference x Pi"

You mean Circumference = Pi*diameter

Kris
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1992f150

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oops sorry, the calculations should be right though.

one more thing remember when your marking the tube for where to bend you have to factor in how much it will slip in the die before the bend starts.
 

sirhk100

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'92F150, thanks for the info... Makes sense to me!!! Kritter, I just played with that program and it's pretty cool. I used it to figure out a Dual Shock hoop for a '03 Chevy 2500HD that we're working on here. Gave me all the info I needed. I'm gonna go play somemore and see what oprions are available on it and maybe see if I can talk the owner into buying it...

I'm needing this for mass production. In my example above, do you really need to worry about the material stretching or can I take that figure, cut 200 tubes to length, stick them in the CNC bender and go to town? How much does the material stretch? How can I figure that out? It obviously depends on wall thickness, alloy, dia., etc... I've looked through the machinest handbook and can't find info. I'm gonna look in some of my manufacturing text books tonight... Any leads on where to find this out?

Khris

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KitRacer

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alright, i revised the program, now you can enter the bend radius and tubing size, i don't know how to reduce the fractions though, does anybody??? i like this better than bend-tech, cause i don't have a computer near the shop, i can print this out for each die that i have go at it, give me some more suggestions, and i will revise it

oh yeah, the last program had an error in the formula, so i changed that

tubing height is best described if you where to hold one end of the tubing vertical, it would be the vertical measurement form the beginning of the lower bend to straight across from the upper bend, it comes in very useful when making the second bend in the front of a truck rollcage.

if you need a further example, i have a picture describing it all, but i can only save it as .DXF, so if you can read that ill send you an explanation, until then, happy bending

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curt

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Damn thats sweet, and to think of all that tube I wasted just because of a simple lack of education....Could you upload the dxf also just so we have a visual reference as well? Thanks, Curt

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KitRacer

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okay here it is, i got it to work in .JPG. Does anybody have a serial for Bend-Tech or know how to reduce fractions in Excel, I think Ramsey knows Excel pretty well????

Heres the Formulas I use

Tubing Used In Bend = (Bend Radius)*(PI / 180)*(angle)
Height Of Tubing = (Bend Radius + Tubing Size)*(SIN angle)
Distance Inside= (Bend Radius*2)*(SIN (angle / 2))
Diagonal Outside = ((Bend Radius + Tubing Size)*2)*(SIN (angle / 2))

is there any other measurements needed??

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Kritter

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right click on the cell and click format and then you can change the number to look like whatever you want...let me know if you need any help with Excel...I am pretty experienced with it.

Kris
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sirhk100

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Oh man you guys kick ass!!!!! Thanks a ton... My guy down on the floor is gonna love me... Right now they just start with some long tubing, make the bends, then measure the length. Kinda rude for a mass production. We're learning as we go though and things are definately improving around here!!!

Khris

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Brian Mapes

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They do that at RCD?

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Billy_the_Kid

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Isn't there still some amount of stretch in the pipe? Or does the inner bend compress to offset the stretch? And what about spring back?

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TimHayosh

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To simplify:
Bend radius X degree of bend X 6.28 / 360 = amount of tube used in bend.

this is the formula the Pro-Tools gives with their bender. It worked perfectly for me.
(6.28 = 2Pi)

Happy motoring, Tim
 
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