bend an object to an exact radius

Hello all
I have bent a cylinder to a parented curve object but cannot get it to an exact radius and angle.
Is there a way of doing this?
Thanks for any advice

Can you post the (part of) file here?

Thanks, I have attached the .blend.
Basically, I am modelling/animating a site intallation guide for a special bracket that fixes to some sockets which are in turn fixed to some cast in reinforcement bar. The rebar needs a 90 degree bend in it with an internal radius of 16mm.
The idea was to model the bend and then attach straight bits to each end of it.
Thanks, Matt.


RebarBend.blend (338 KB)

interesting model here

can you explain how you model this rebar which is kind of high precision modelling

also in blender i don’t remember any way to bend with a given radius of curvature
so as an alternative for this radius use a circle with the given radius and you can bend around this circle or you could try the simple modifier to bend it!

unless someone can write a small script to do this with high precison

mind you ounce you avhe some of the most used angle bend then you can copy theses
and it’s easier - but still ahve to do the first one


You could use the warp tool ‘Shift + w’

I think the best way would be as RickyBlender suggested and add a bezier curve circle. The radius of your rebar is 8mm so if you want an internal radius of 16mm you will need to make the radius of the circle 24mm. Use the transform properties in object mode, also change the handles to free. Break the circle (C key) remove 2 points to make a quadrant and extrude these straight out. Add this curve as the curve modifier to the rebar.

i would not recommend the warp tool in this case cause it creates too much distorsion

but for the example with curve modifier

it would be easier i think to understand if you load a sample file with this feature

in 2.5 is we do have unit like meter and yard
and i think may be it’s possible while entering it to specify the diam of the circle with proper units and dimensions!

have to try to test this in 2.5


Actually the warp tool gives exactly the same result as using a curve modifier.

In this file I’ve used your model and bent it 90° using a curve modifier and using the warp tool. As you can see, the two models are identical.

I have used the actual size of your model, and the radius is 32/(2pi) bu, which would make the inner radius 32/(2pi)-0.8 bu or about 4,293 bu. From here you can then scale the object to whatever size you need.


RebarBend (1).blend (553 KB)

(Sorry. Just saw it now)

Another way to get the curve:
Take a cube (or two joined planes). rotate one face to the proper angle in relation to the other.
Select the corner edge and use the Bevel Center script (with recursive)
Select the required edges at top and separate them.
In Edit Mode, run the “Edges to Curve” script on them.

Good luck, whichever way you take. :slight_smile:
(Seems odd that, as RickyBlender said, you can do a bit of precision modelling like the rebar and not do this :wink: Btw, I am curious too: How did you do that?)

how do you use the BU to size the circle
i can see N panel with diam = 10.186
mind you the circle diam should be function of the rebar diam not the size !
see pic

may be this rebar was done with an array then with some offset
can you explain how you did the first rebar model?

anybody did this in 2.5 ?

should be interesting with the new unit available !

but you have to remember that you can do precision with blender indirectly
cause blender is not really a CAD soft it’s more for artist then engineer! LOL

but there are always more then one way to do things in blender
you migth also be able to use the array with some offset too i guess
but might require some thinking about this modifier

happy blendering

Thanks very much for all this advice, I havent had a chance to go through it in Blender yet as I’ve been away all weekend but will go through it tonight.
Regarding how I modelled the rebar, I will explain. First of all though, somebody here at BA recommended the precision modelling guide by Robert Burke ( which has been invaluable.
Right, here goes and sorry if I’m telling you stuff you already know:-
I added a circle of the right size and created the top and bottom rectangle bits by extruding vertexes to the right location. I then used a weld script that places a vertex at the intersection of two edges (to connect the rectangle bits to the circle) and then deleted/W, Remove Doubles until I got the shape. Filled, then extruded a cylinder to 40 units.
Regarding the ridges, again I added a circle and rotated to 60 degrees using the transform properties window. Then 'control A, ‘scale and rotation to obdata’. Then I extruded 1.5 units (or 2, I cant remember) along X plane to give it that lopsided coin shape. Then I drew a line (by extruding a vertex from the top horizontally back on itself and the bottom vertically so that they meet in space and, again, using the weld script, placed a vertex where they meet. I removed the edges and created a top horizontal edge from the vertex in mid air to the furthest point of the geometry. (I havent explained that very well, sorry.) I then turned on edge length. This gave me the overall width (in the X plane) of the ridge geometry which in turn (using a calculator!) allowed me to work out what spacings the ridges need to be along a 40 unit length of rebar for uniformity if the 40 unit length of rebar and its ridges were copied and placed end to end. Hope that makes sense!
I will be trying to bend this rebar tonight and will post later.
Thanks again for all rthe advice! Cheers, Matt.

there might be another way to make this rebar
if you can make a unit lenght for this rebar then you could apply curve modifier and array to make follow it along a curve of whatever shape

i mean there is more than one way to do it in blender!

another thing here your saying that you did this Helix shape by hand ?

there is a script that can do that for you and also you culd also do that with the array and offset i think

and is there a small table showing the dimension for theses rebars?
are theses US or Euro style ?

keep up the good work

Thanks for sharing

I’m trying to bend the rebar by using a bezier circle quadrant but cannot get it to work, help!
So, I have created the bezier circle (to the correct radius) changed handles to free and removed two points but I am not left with a quarter circle as the remaining points are joined together as a loop. How do I get rid of the unwanted curve to leave me with the correctly radiussed curve?
Also, once I have done this, do I have to put the rebar geometry in a particular location before adding the modifier?
Thanks, Matt.

go to F9 and in edit mode change to poly type
you may have to also subdivide it ounce or twice to get enough points on the 90 degrees section

try it and see what it gives


Concerning the bezier circle quadrant, as I said in my post above you have to press the C-key when you are in edit mode and it will open the circle; then remove the end points.

Look guys, its worked a treat so I just wanted to say a big thanks to all.
I love Blender and I love the community, especially this website right here.
Cheers, Matt.

i forgot to mention also
in 2.5 there is a new feature for Unit measurement

you can select Meter or Yard Metric or English units or BU

but in 2.5 in any case 1 Bu = 1 mter now
but you also see in viewport if you are in meters of yard

so more interesting i guess to work on 2.5

happy 2.5