Spline between / across front and top planes

Hello all. Can anyone help me understand how to create a spline from the centre of the lower flange, (sitting above the top plane in this image), and the centre of any of the upper flanges (on the front plane). Ultimately, I’d like to sweep the circular flange opening along the spline.

Really appreciate your time!

To do it with a spline you can target that top face, draw your lines on that plane and then tip it up and rotate it into position with the move tool (moving the pivot point before you do).

Or you can cheat like me and use a body instead :slight_smile:


Hello Shaun. Thanks so much for you help. Great suggestions! I’ve just spent a couple of hours tying to apply it, but I’m not yet getting the results I’d like. I should say that the design I’m trying to create is an exhaust manifold, where the pipe and gas flow from 4 exhaust ports sweeps / flows smoothly to the single exhaust down pipe represented by the 5th flange…something like the image below.

Any further suggestions always appreciated.

This is the method I would likely use. How to model a pair of handlebars? - #3 by Oregonerd

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Always more than one way to skin a cat so here was my technique for this :slight_smile:

I used the Add Construction Plane feature across 3 points to bridge the gap between splines on different planes. You’ll notice I put a little hook onto the top of some of them. I found that adding this ensured the point where it intersected the construction plane became clear.

I’m sure there’s more ways to do this but this was my first thought. I guess you could mess around further and add curves to the splines.

Here’s the video (I had to shorten it so you’re only seeing me do the last one):


As someone who’s built quite a few exhaust systems, you’re probably better off starting with a base point model. ie. Tubing OD, ID, bend radius. Then piecing them together like you would with various cuts at angles.

If you’re not worried about manufacturing @Oregonerd tutorial on handlebars is a good start. A search for 3d splines will bring up other workarounds to get the desired effect.


Here is a possible way, with splines on two orthogonal planes to define 3D edge to sweep.
A few hints:

  • you need to add the external fillets at the pipes junctions before the shell command, in order to get smooth edges inside the pipes
  • the order of the fillets 01 and 02 is important, as well not including tangent edges for fillet 02. I started with a small radius for fillet 02 because otherwise it fails before disabling tangent edges
  • I applied a 0.99 scaling factor to the center pipe to get a better looking result at the junction of the 4 pipes

Hope it helps.

Exhaust.shapr (2.1 MB)



Hey APDesignMachine

I will watch the handlebar tutorial as soon as I get a chance, and really appreciate your input on the starting point. Many thanks!

Hey PEC…you really did that in Shapr3d…amazing!!! I’ve still got a lot to learn for sure. I did wonder what kind of result I might end up with, but seeing what you’ve produced has made me really enthusiastic about Shapr3d again. Love it!

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Wow! Thanks so much Shaun. Really generous of you to take that amount of time. I can’t wait to try this out. And so pleased that Shapr3d can handle this kind of task. Please forgive me if I don’t come back to you for a week as I’m traveling a lot, and I’m a slow learner :smile:

Hello PEC, well, I just had my first Sunday morning off from work for a while and followed your amazing example for the exhaust manifold. I’ve spent about 6 hours now, and although underneath, in terms of sketches and planes etc, it’s nowhere near as clean as yours, I managed to produce this. So I just wanted to say thanks again. I really appreciate how you helped!


Hi @Wick

thank you for sharing and showing us the result. You did great! Looks really clean and neat!

It’s always nice to see that you did it your way, and I’m more than happy if I could help you at the beginning.