Measuring bends

T

tommyr

Guest
What are your guys' methods for taking measurements so the bends end up in the right spot?
 

generis

Maybe take up knitting.
man, it's trial and error for me. I have no real solution for it. I've tried to use the center of the arc, the start, the end, everything, but there always seems to be some variations after it is done.
 

Wrencher

Moderator
alot of times when i am bending a peice of tube and i want it to match one from the other side. I will leave it a little long put in the bend and then cut end off. this way i can hold the two that i want identical together and cut them both to the same length. A bit of a waste of material but makes it easier to make matching peices.
 

LRTd5

Supporting Member
I use the "ROBBE Robivor" ...
for me the ideal bender for small diameters (brass) tubes...

ROBBERobivor_zpsc1e511a4.jpg



I try to have the same start point and leave it a little bit longer, cut it later....
...and also lot of trial and error .... but the more I do,the better the result ....
 

evilozz

New member
yea ive been tring to figure this out myself forever, like a dog chasing his tail around and around and around .....
 
B

bananaclip

Guest
alot of times when i am bending a peice of tube and i want it to match one from the other side. I will leave it a little long put in the bend and then cut end off. this way i can hold the two that i want identical together and cut them both to the same length. A bit of a waste of material but makes it easier to make matching peices.

x2 this is my method.
 

Kokuzu

V.I.P. Member
Each metal shows a bid of flex when bend. Meaning, if you bend a rod 90degr, it will flex back some degrees. This is the elastic behavior of metals and you find that this flex is a bid bigger for steel than for alloy.

Same time you need to bend around a slightly smaller diameter / radius than the desired one due to flex resulting in small increase of diameter after you release the pressure again.

Your bending gets more exact, if one end of the rod is fixed inside a bending tool, and if the rod is constantly kept under axial pulling force. This force ensures the rod will not create a smaller radius 'on top' of the bending role. You can induce this force with pliers pulling the rod towards yourself during bending.

The recommended radius and required opening angle of the radius to achieve the desired geometry can be calculated considering the specific material properties, e.g. the flexibility of the material. (E-modulus etc...)

But that only makes sense, if your bending process is repeatable - at least you need a bending tool which really locks the material and is rather rigid during bending.

What is a nice approach to reduce wasting material is the calculation of the length before bending, or the developed length. This is the required length of the material consideing the thickness and all straight and radius sections.

Here is the fomula to calculate one radius section. Do the calculation for all bend sections and then add (if any) length of the straight sections. This length is the mimimum length you have to cut the material for the bending job.

Take alook here for the formula for Band Allowance:
http://en.wikipedia.org/wiki/Bending_(metalworking)#Roll_bending


Ok, most likely until you have calculated all of the above, you might have bend some rods with some pretty good results.

As most often my reply seems a bid over-engineered I guess:idea:
 

FRIZZLEFRY

New member
If you have never realy bent any tube, looking up some how to's on 1:1 tube bending will help you out. Exact same methods apply to our small stuff.

For the best repeatable and accurate bending, using some type of bending tool will get you the best no guess results. Using a tool you have a known bend radius and start of bend point. Those things never change. Knowing those two things you can bang out pairs of identical parts with a pencil sketch and either adding or subtracting the bend radius from the point you want your tube to land.

I built a simple rotary draw bender for .250 material and set up a profile for it in my tube bending software. Yeah yeah I know lazy ha ha, but entering four or five measurements into a template and the software telling where each start of bend is and how many degrees is cool.

I have bent more stuff without software than with,but with it its really fast to get good parts.


 
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