# Keep a fixed distance between two bevelled surfaces

I'm not sure to use the correct words. Anyway, here what I did:

1. created a bezier curve
2. duplicated it
3. bevelled the original one with the round option (but I should work even with an object)
4. created a curve to be used as bevel object for the second one

Now I have this situation:

At the end, the inner object will be "subtracted" from the outer one, in order to make a "trench" inside.

My goal is to define a constant distance between the surface of the outer object and the surface of the inner one, along all the path.

I tried with either scaling or offsetting the bevel object but it does not keep the distance along the path. Ideally, I would define this distance in mm. I understand it depends on the two curves and the shape of the bevels. I'm not sure if it is even possible...

• You got lots of answers in just an hour, lol, but the simplest way to get what you want is not to use two curve objects, but to use a single curve object with a solidify modifier. Jul 9 at 15:26
• @Nathan feel free to add your answer if you want to!
– Mark
Jul 9 at 15:30

If your bevel curve-object is 2D, you can make it with holes, simply by including more splines:

Yo may have to Edit Mode > Header Menu > Segments > Switch Direction on the perimeter of the hole, to get inner face's normals to point in the right direction .. ( 'Face Orientation' overlay shown, above)

• Great idea! But I'd prefer to keep them separated since changing the outer shape would affect the inner one too...
– Mark
Jul 9 at 15:50

If i understand correctly what it is you're trying to do, I would do it in a different way.

You want to make some sort of tunnel where the inner walls are evenly distanced from the outer wall.

You can create one part of the tunnel, a thin loop of faces for example. The shape of the outer + inner tunnel. Then i'd create a curve object, starting from a circle or other. And add an array and curve modifier on the tunnel part you modeled. Adjusting accordingly.

Is this what you mean? Do you need more info on what I mean exactly? let me know!

good luck! :D

• Yes, exactly! The only downside I see in you approach (but perhaps I'm wrong) is it modelled ad hoc. Since the outer shape can be modified a bit (i.e. make it bigger or smaller at some points) I would be nice a simple way to create again the tunnel without designing it manually from scratch!
– Mark
Jul 9 at 15:04
• Anyway I'm going to play with your hints!
– Mark
Jul 9 at 15:04
• You'd like to have some variation in shape on the outer part? thats understandable. I'd apply the array and curve modifiers after I have the desired shape and then use 'proportional editing' with 'connected only' selected to drag some parts out. Jul 9 at 15:08

Here are some pictures illustrating what I mean :)

• The 'deform axis' ofcourse depends on your own scene and objects. Play around with it until it looks good! Jul 9 at 15:15
• Thanks! Very interesting! I'll give it a try
– Mark
Jul 9 at 15:18

Playing around with the great hints of user Ward D, I find a simpler method that can be easily followed again if the outer shape changes:

1. edit the outer shape
2. select an edge loop on the inside surface
3. CTRL+D to duplicate, ESC to leave it there and P to separate
4. then convert it to a curve
5. now I can bevel it with an object and define a distance from the surface changing the offset value

The upper left corner is wrong of course, but this is just a dummy example.